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ASPECTS OF THE ECOLOGY OF GARLIC MGSTABD, ALLIARIA PETIOLATA (BIEB) CAVARA AND GRANDE, IN OHIO
DISSERTATION
Presented in Partial Fulfillment of the Requirements for
the Degree Doctor of Philosophy in the Graduate School
of The Ohio State University
By
Daniel Raymond Scott
The Ohio State University 2000
Dissertation Committee; Approved by Dr. Emilie E. Regnier, Adviser
Dr. John Cardina Adviser O Dr. Miller MacDonald Horticulture and Crop Science Graduate Program Dr. Allison Snow UMi Number 9994936
UMI'
UMI Microform 9994936 Copyright 2001 by Bell & Howell Information and Learning Company. All rights reserved. This microform edition Is protected against unauthorized copying under Title 17, United States Code.
Bell & Howell Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor. Ml 48106-1346 Copyright by Daniel Raymond Scott 2000 ABSTRACT
Garlic mustard, Alliaria petiolata (Bleb) Cavara and Grande, seed dormancy, competition effects, and spatial distribution and spread were studied in Ohio woods. Buried seed experiments lasting 3 yrs were begun in 1996 and 1997 to examine dormancy aspects of garlic mustard. Seeds were surface covered and buried 10 cm deep in fiberglass mesh packets. Average germination of shallow seeds was 61% the first season (1997) with a cumulative germination of 94% after 3 years. Among the deeply buried seeds, the cumulative germination was 16% after 3 years. No germination in the field was observed prior to February or after April of each season. Seeds were 100% viable at harvest and maintained 99% viability during the study. A competition experiment was begun in 1997. Garlic mustard seeds were planted into meter square plots of woodland herbs in the fall of 1997 at densities ranging from 0 to 6400 seeds m“^ at two locations. Census of forest herbs taken during the experiment was used to calculate the Population Relative Growth Rate (PRGR) for each native species. Impatiens capensis PRGR at the highest density of garlic mustard was significantly reduced compared to the control at the Wooster site. There was no effect on other species. A mapping study was initiated in 1998 and continued through 2000 to quantify the spread of nascent foci in established woods. Plots were selected at three sites based on remoteness of small populations of garlic mustard rosettes. The area occupied by seedlings in 1999 ii was on average 53% to 170% greater than 1998 at the three sites. The area occupied by rosettes in 2000 increased by an average of 161% over the first season (1998) at Wooster. The number of rosettes in 2000 was an average of 301% higher than the number of rosettes in 1998 at Wooster and 588% greater at S. Charleston. Approximately 30% of 1999 seedlings survived to flower in 2000. Elimination of these nascent foci should be the primary goal for controlling garlic mustard.
I l l Dedicated to my Grandmother Dorothy M. Scott 1909-1998
Her love and belief in me was always a constant And her faith was as solid as a rock.
XV ACKNOWLEDGMENTS
I wish to express my deepest appreciation to my
advisor. Dr. Emilie E. Regnier for her valuable
assistance, encouragement, and patience during the course
of this study and the writing of this dissertation. I
also want to thank the members of my committee: Drs. John
Cardina, Miller MacDonald, and Allison Snow for their
time and advice during this important moment in my life.
I must give a large thank-you and a tip-of-the-hat
to my fellow graduate students and the staff of the
Department of Horticulture and Crop Science, especially '
Andy Evans and Jerron Schmoll, for their help and
friendship.
To my good friends Bill and Kathy Ardla who were always there with prayers and support and to Dave and
Debbie Poole who never lost faith in my ability to complete this task, I can only say thank you.
Jacob and Jarrod, thank you for your patience and willingness to help around the house while Dad was totally "out of it". I love you guys.
To my Mom who helped me harvest and take notes, and accompanied me on my walks to discover the impact of this invasive, I can say that you have a share in this
endeavor. And to my Dad I say thank you for doing all the
things with the cars and lawn mower and other stuff I couldn't do.
Finally, and most importantly, to my loving wife
Kathy, I thank you for your longsuffering patience and support. Your confidence in me never wavered and your prayers sustained me, and I will always love you for that. May God be with us always.
VI VITA
December 20,1951 ...... Bom - Springfield, Ohio
1987 BA- Biology/Math Wittenberg University
1992...... MS - Agronomy Ohio State Um'versity,
1992 - 1995...... Adjunct Instructor Clark State Community College, Springfield, OH
1996 - Present...... Graduate Research Assoc. Ohio State University
PUBUCATIONS
Research Publication
Wieboid, W.J., R.E. Buehler, and D.R. Scott 1990. Repeatable writing assignments to enhance student writing. JAgjroruEduc. 19:51-54.
StMartin, SiC., D.R. Scott, A.F. Schmitthenner and B.A. McBlaiit !994. Relationslup between tolerance to phytophthora rot and soybean yield. Plant Breeding 113:331-334.
FIELDS OF STUDY
Nfojor Field: Horticulture and Crop Science Studies in Weed Ecology. Dr. E.E. Regnier
vxi TABLE OF CONTENTS
Page
Abstract ...... ii
Dedication...... iv
Acknowledgments...... v
Vita ...... vii
List o f Tables ...... x
List of Figures ...... xi
Chapters;
1. Introduction and literature review ...... 1
2. Seed dormancy in garlic mustard. Abstract ...... 29 Introduction ...... 31 Materials and MeUiods...... 35 Results and Discussion ...... 40 Literature Cited ...... 68
3. Competition of gprlic mustard with forest ephemerals. Abstract ...... 71 Introduction ...... 72 Materials and Methods ...... 77 Results and Discussion ...... 81 Literature Cited ...... 99
vxxx 4. The spread of garlic mustard Grom nascent foci. Abstract ...... 101 Introduction ...... 103 Materials and Methods ...... 108 Results and Discussion ...... 110 Literature Cited ...... 126
Summary ...... 128
Appendix A - Seed survival Grom pulled garlic mustard plants ...... 138
Appendix B - Dispersion of Alliaria petiolata seeds...... 140
Appendix C - Species seen ...... 142
Appendix D - Regression graphs ...... 143
List of References...... 168
XX UST OF TABLES
Table Page
1.1 Characteristics of Alliaria petiolata flowering stalks observed in October, 1999 in Clark County, Ohio...... 27
2.1 ANO VA table for percent of seeds recovered that were nondormant, for percent of seeds recovered that germinated naturally in seed packets, for the percent of intact seeds that germinated naturally and for those that germinated in the growth chamber, and for the percent of dormant seed that exhibited physiological dormancy at Clark County, Ohio...... 50
2.2 ANO VA table for percent of seeds recovered that were nondormant, for percent of seeds recovered that germinated naturally in seed packets, for the percent of intact seeds that germinated naturally and for those that germinated in the growth chamber, and for the percent of dormant seed that exhibited physiological dormancty at Wooster, Ohio...... 51
2.3 Seasonal ANO VA table for Clark County for percent of seeds recovered that germinated naturally in seed packets, for the percent o f dormant seed that exhibited physiological dormancy, and for the percent of tested seed that displayed physical dormancy only...... 50
3.1 values of total number of siliques and siliques per plant with characteristics of A. petiolata at Wooster ancl S. Charleston...... 84
4.1 Results of a three- year stucty of isolated populations of Alliaria petiolata at three locations...... 116 USTOFnOURES
Figure Page
1.1 County distribution in Ohio of A. petiolata since 1900 (from Ohio State University herbarium records and personal observations) ...... 28
2.1 Nondormant garlic mustard seeds buried in lots of 170 seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a Maple-Beech regrowth woods in Clark County...... 52
2.2 Natural germination of garlic mustard seeds buried in lots of 170 seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a Maple-Beech regrowth woods in Clark County...... 53
2.3 Cumulative natural germination of garlic mustard seeds buried in lots of 170 seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a Maple-Beech regrowth woods in Clark County...... 54
2.4 Physical & physiological dormancy of garlic mustard seeds over time as affected by depth of seed burial. Seeds were buried in lots of 170 seeds per fiberglass mesh packet at surface covered & 10 cm depths in a Maple-Beech regrowth woods in Clark County & packets were retrieved monthly. 55
2.5 Germination of garlic mustard seeds buried in lots of 170 seeds per fiberglass mesh packet at the surface covered depth in soil in a Maple-Beech regrowth woods in Clark County. Comparison is between those seeds that germinated in the growth chamber without scarification at 15/6°C on a 12/12 hr cycle & those seeds that germinated in the field & were recovered as seedlings... 56
2.6 Natural germination of garlic mustard seeds buried in lots of ICO seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a second-generation Oak-Hickory woods at the OARDC Badger Farm near Wooster, Ohio...... 57
XX 2.7 Cumulative natural genmnation of garlic mustard seeds buried in lots of 100 seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a second-generation 0^-Hickory woods at the OARDC Badger Farm near Wooster, Ohio...... 58
2.8 Physical and physiological dormancy of garlic mustard seeds over time as affected by depth of seed burial. Seeds were buried in lots of 100 seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a second-generation Oak-Hickory woods at the OARDC Badger Farm near Wooster, Ohio and packets were retrieved monthly...... 59
2.9 Germination of garlic mustard seeds buried in lots of 100 seeds per fiberglass mesh packet at the surface covered depth in soil in a second-generation Oak- Hickory woods at the OARDC Badger Farm near Wooster, Ohio. Comparison is between those seeds that germinated in the growth chamber without scarification at 15/6‘*C on a 12/12 hr <^cle and those se eds that germinated in the field and were recovered as seedlings...... 60
2.10 Percentage of recovered buried (10 cm) intact seeds from the Clark County and Wooster, Ohio sites that germinated in the growth chamber without scarification...... 61
2.11 Germination of garlic mustard seeds following scarification and maintained in a growth chamber at 15/6‘*C on a 12/12 hr cycle for seeds buried over a 3- year interval at 10 cm in a Maple-Beech regrowth woods in Clark County and a second-generation Oak-Hickory woods at the OARDC Badger Farm near Wooster, Ohio...... 62
2.12 Relationship of cumulative germination per season to cumulative number of days with maximum soil temperatures above and minimum soil temperatures below 1®C for two locations (Clark County and Wooster, Ohio). 63
2.13 Percentile of recovered seed at surface covered depth at Clark County. Classification is based on when recovered seeds germinated...... 64
2.14 Percentage of recovered buried (10 cm) seed at Wooster, Ohio. Classification is based on when recovered seeds germinated...... 65
2.15 Percentage of recovered buried (10 cm) seed at Clark County. Classification is based on when recovered seeds germinated...... 66
XXX 3.1 Average Population Relative Growth Rate (PRGR) over (bur replications from 1998 to 1999 of two forest ephemerals at Wooster, Ohio at varying densities o f Alliaria petiolata...... 88
3.2 Average Population Relative Growth Rate (PRGR) over four replications from 1998 to 1999 o f two forest ephemerals at S. Charleston at varying densities o f Alliaria petiolata...... 89
3.3 Alliaria petiolata hei^t per plant per plot versus A. petiolata density per plot at Wooster, Ohio...... 91
3.4 Alliaria petiolata height per plant per plot versus A. petiolata density per plot at S. Charleston...... 91
3.5 Total number o f Alliaria petiolata siliques per plot versus A. petiolata density per plot (A) and versus total A. petiolata dry weight per plot (B) at Wooster, Ohio...... 92
3.6 Total number of Alliaria petiolata siliques per plot versus A. petiolata density per plot (A) and versus total A. petiolata dry weight per plot (B) at S. Charleston...... 93
3.7 Total number of Alliaria petiolata siliques per plant versus A. petiolata plant height (cm) at Wooster...... 95
3.8 Total number of Alliaria petiolata siliques per plant versus A. petiolata plant height (cm) at S. Charleston...... 96
3.9 Average number of Alliaria petiolata siliques per plant versus A . p etio la ta average height per plant per plot...... 97
3.10 Average number o îAlliaria petiolata siliqu% per plant versus density of A. p etio la tain m^ plots at two locations...... 98
4.1 Spatial distribution maps of Wooster plot #l from 1998 to 2000 using a gray scale...... 117
4.2 Spatial distribution maps of Wooster plots 2,3, and 4 from 1998 to 2000 using a gray scale...... 118
4.3 Spatial distribution maps of Buck Creek Park plots 1 and 3 from 1998 to 2000 using a gray scale...... 119
xiii 4.4 Spatial distribution maps of Buck Creek Park plot #2 and Western plot from 1998 to 2000 using a gray scale...... 120
4.5 1999 seedlings (log 10 values) vs. 1998 rosettes (log 10) per 10 m^ for all locations...... 121
4.6 Relationship between 2000 rosettes (log 10 values) and 1998 rosettes (log 10 value) per 10 m^ at Wooster and W estern...... 122
4.7 Relationship between 2000 rosette area (m^) and 1998 area at Wooster... 123
4.8 Relationship between 2000 rosette area (m‘) and 1998 rosette area at all locations...... 124
4.9 Relationship between 1998 seedling area (m^) and 1998 rosette area at all locations...... 125
5.1 Representation of the fate of one generation of Alliaria petiolata seed over four years...... 135
5.2 Representation of the fate of one generation of Alliaria petiolata seed at one location with seed inputs in alternate years...... 136
5.3 Representation of the fate of one generation of Alliaria petiolata seed o f a mature population at one location with seed inputs every year...... 137
XIV CHAPTER 1
INTRODUCTION AND LITERATURE REVIEW
Garlic mustard, Alliaria petiolata (Bleb) Cavara and
Grande, is native to Europe, being found at 68®N southwards although it is less common in the extreme south Tutin et al., 1964). It was first recorded in
North America in 1868 on Long Island, NY and by 1991 was found in 28 Midwest and northeast states and two adjacent
Canadian provinces (Nuzzo, 1993b). It has also been reported in Portland, Oregon (Ornduff, 1959; Gleason,
1963). Garlic mustard was first reported in Ohio on
Kelley's Island in Sandusky county in 1899 (Moseley,
1899). Its range has rapidly increased in the last 15 years, and is now found in at least 62 of the 88 counties in the state.
Garlic mustard is a biennial that flowers in its second growing season and spreads by seed (Cavers et al.,
1979). It is an excellent source of Vitamin A and
Vitamin C (Zennie & Ogzewalla, 1977) and can be used as a salad green or on sandwiches (Fernald et al, 1958). In addition, it has medicinal properties (Grieve, 1959), and helps prevent erosion (Cavers et al., 1979).
Unfortunately, garlic mustard taints cow's milk and
anecdotal evidence suggests that garlic mustard replaces
spring ephemerals in the understory of woods,
particularly in areas where it has greater than 50% cover
(Yost et al., 1991; Cavers et al., 1979; Grieve, 1959).
The species is also a host for certain mosaic viruses
that attack several cultivated vegetables (Al-Shehbaz,
1988).
Garlic mustard grows best in damp shaded soil
(Gleason, 1963), and is commonly found in partial or full
shade at the edges of deciduous woods and in hedgerows
(Nuzzo, 1993a; Byers & Quinn, 1987; Trimbur, 1973).
Generally its presence is associated with anthropogenic
disturbances such as trails (including deer trails),
roads, and railroads (Nuzzo, 1993a).
The typical lifecycle of garlic mustard in Ohio
begins with seedling emergence during the first warm period in late February or early March. Growth is rapid
as plants add 3 to 5 basal leaves before canopy cover by
the trees reduces the sunlight. Little vegetative growth
occurs during the summer, but growth resumes in the fall
(Cavers et al., 1979, reported that 4 new leaves were added in November in Ontario, Canada). Plants overwinter as rosettes and in the spring of their second year
2 initiate inflorescences. First flowers appear at the end
of April with flowering peak by mid-May. Flowering
usually ceases by the first week in June.
Siliques are present by mid-May and seeds ripen
until shedding begins in late June. Only 5 to 9% of the
seeds produced in a given stand emerge to form rosettes
and of these seedlings only 2 to 4% survive to flower
(Cavers et al., 1979). The greatest mortality (over 50%)
occurs in May at the seedling stage followed by a slow
steady rate of mortality through summer, fall, and
winter. Most seedlings perish from drought since there
appears to be no predation at the rosette stage (Byers
and Quinn, 1987). All first year plants that survive the
winter flower in the spring and then die..
Garlic mustard is adaptable to a wide range of
irradiance conditions. Anderson and Dhillion (1991)
measured photosynthetic rates and stomatal conductance
for plants grown under four irradiance levels in a growth
chamber from 125 to 1,125 uE/m^/s, and from plants grown
in partial shade and under a forest canopy. They found
that plants had maximum photosynthetic rates under
irradiance levels similar to those under which they were grown and that no plants had maximum photosynthetic rates under full sunlight conditions (1,791 uE/mf/s). In its native environment in Europe, garlic mustard is the host plant of the monophagous weevil Ceutorhynchus contrictus Marsh, which feeds on the leaves, flowers, and pods of garlic mustard in the spring. The female lays eggs in the young pods and the developing larvae inside feed on the seeds (Nielsen, et al., 1989).
Control of garlic mustard in North America is difficult. Mown plants send up new flowering shoots from the root crown that produce viable seed (Cavers, et al.,
1979), and trampled plants exhibit regrowth of flowering shoots from leaf axils. Therefore, the only effective mechanical control is physical removal, including roots, of flowering plants before they set seed. The pulled garlic mustard shoots should then be placed in garbage bags to stimulate rapid degradation. Other researchers
(V. Nuzzo, personal communication) and myself have noted that pulled garlic mustard plants show an ability to produce seed if the root is sufficiently intact to absorb moisture or if the pod is developed enough to mature on the ground.
Nuzzo (1994) reported that a summer application of
Basagran (bentazon) at 0.5 lb/acre reduced the cover of garlic mustard rosettes by an average of 94%. This is comparable to a dormant season application of 3% glyphosate solution which reduced garlic mustard cover by
4 glyphosate solution which reduced garlic mustard cover by
91 to 100% (Nuzzo, 1991).
Although prescribed fire and/or herbicide applications will control garlic mustard during its dormant season (Nuzzo, 1991), the seed bank may allow quick reinfestation. Because a single self-compatible plant is sufficient to populate a site (Babonjo et al.,
1990), annual monitoring for and immediate removal of garlic mustard is required to prevent establishment or repopulating of individual natural areas (Nuzzo, et al.,
1991). This will succeed if the infestation is small or the area to be covered is manageable. Large areas of heavy infestation are not compatible with these techniques due to limited manpower and resources. Aerial applications would not be feasible except in areas of high density with no desirable native species and applications would have to be applied during late fall after tree leaf drop or before leaf canopy formation in the spring. Although garlic mustard occurs most often in partial or full shade, it can also grow in full sun giving it potential to become an agricultural weed. It has been found in Ohio in both soybeans and wheat
(personal observation). Seed dozmaaey
Vleeshouwers, et al. (1995) defined dormancy as a
strictly temperature controlled characteristic that
determines the range of conditions in which a seed is
able to germinate. Those seeds considered nondormant will
germinate if their microenvironment falls within the
range required for that seed to germinate. Those seeds
considered dormant will not germinate due to the
physiological factors of the seed regardless of the microenvironment. These dormant seed may have physical
(exogenous) dormancy or physiological (endogenous) dormancy (Baskin and Baskin, 1998). Seeds with physical dormancy have some type of structural characteristic (ex: seed coat) that prevents germination. Seeds with physiological dormancy have a characteristic of the embryo that prevents germination (ex: incorrect ratio of promoters and inhibitors)(Baskin and Baskin, 1998). Some species have seeds that are both physically and physiologically dormant (Barton, 1934; Baskin and Baskin,
1992; Baskin and Baskin, 1998). Freshly shed seed that are dormant have primary dormancy. If primary dormancy has been relieved but suitable conditions for germination did not exist, then the seed may develop secondary dormancy. This dormancy may be relieved and re-induced during successive seasons (Vleeshouwers, et al., 1995).
Alliaria petlolata is a strict biennial that produces a large seed drop in its second year {Cavers, et al., 1979). The seeds have a strong innate dormancy
(Cavers, et al., 1979; Lhotska, 1975) which is partly attributed to a thick, more or less impervious seed coat
(Klykken, 1937), and to an embryonic physiological dormancy (Lhotska, 1975) even though the embryo is well developed and differentiated at maturity (Klykken, 1937;
Murley, 1951; Lhotska, 1975). Cavers et a l . (1979) attempted more than 70 treatments to break dormancy, but the only ones that were successful involved scarification and gibberellins (6A3).
Baskin and Baskin (1992) sowed garlic mustard seeds on June 26, 1986 and observed that 70% germinated in
1987, 4% germinated in 1988, <1% germinated in 1989, and
3% germinated in 1990. All of these seeds germinated in
February and March. They also found that the peak of natural germination in Kentucky occurred when mean daily max/min temperatures were 8 and -1.0°C respectively.
Roberts and Boddrell (1983) observed up to 55% germination the first spring, between 24% and 1.4% the second spring, and less that 1% the third, fourth, and fifth springs. In this study in England, germination occurred from January to March (Roberts & Boddrell,
1983). In Czechoslovakia, Lhotska (1975) sowed garlic mustard seed in August and October and found germination values of 72% to 76% the following March to April.
The earliest attempts at germination of garlic mustard in the laboratory produced no germination
(Klykken, 1937). In 1975, Lhotska obtained 42% to 100% germination by constant cold stratification at 3® to 6®C on saturated sea sand. Germination began between 60 and
90 days after the seeds were placed in the refrigerator.
The majority of seeds germinated from 75 to 100 days after the initiation of the cold treatment. Cavers et al. (1979) used the same procedures on garlic mustard seed from Ontario but saw no germination. They concluded that Ontario seed needed longer periods of stratification than did seeds from Czechoslovakia.
In 1988, Byers reported 80% germination on blotter paper at 4®C for 100 days (Byers, 1988). Baskin and
Baskin (1992) placed seeds collected in 1987 on soil in constant 1° or 5°C for 22 weeks (154 days) and obtained
94% to 99% germination. Germination began after 91 days and ceased by 126 days. Meekins and McCarthy (1999) also obtained germination after seeds were stratified at 4®C for 105 days on moist filter paper.
8 MacKenzie (1995) placed harvested seeds in pots,
cooled them for 8 weeks at 4.5°C, and then cold
stratified the seeds at -10**C for 1 to 5 weeks in
November. The pots were then located in a natural
setting until the following spring. Those exposed to
four weeks of cold had the highest germination value of
68%. Control pots were maintained at a constant 4.5°C
during the cold stratification, and had germination
values of only 1%.
Lhotska (1975) buried seed for varying intervals and
obtained 2 to 54% germination at the time of retrieval.
The remaining seed grown in the laboratory (under
unreported conditions) resulted in 10 to 44% additional
germination. Baskin and Baskin (1992) buried seeds in
July, exhumed them periodically until February, and
germinated the seeds under various conditions. They
found that optimum temperature for germination of
nondormant seeds in a laboratory growth chamber was
15/6°C at a 12/12hr thermoperiod. Germination was highest
in constant darkness compared to a 14-hour photoperiod.
An additional result reported by Baskin and Baskin
(1992) involved a comparison of fluctuating temperature
stratification versus constant temperature. Seeds were overwintered in an unheatea greenhouse in 1984-85 and
1985-86. They received 1269 and 1452 hours,
9 respectively, of temperatures ranging from 0.5° to 10°C.
Germination of these seeds was higher (66-70%) than those exposed to constant 1° or 5°C for 16 weeks (2688 hrs)
(46-60%). They concluded that garlic mustard, like a few other species (Flemion, 1933), after-ripens better at fluctuating low temperatures than at constant low temperatures (Baskin and Baskin, 1988; 1D92).
Naturally occurring garlic mustard seeds are thus after-ripened in the winter, germinate in late winter or early spring, establish themselves before canopy closure, set seed their second year, and produce a short-lived seedbank for subsequent years. Baskin and Baskin (1992) found that seedlings that emerged the second year after dispersal did not survive in competition with second year rosettes. This agreed with their observations that plants located in many sites flower only in alternate years. This has not been my personal observation, however. I have observed seedlings and rosettes in close proximity and have observed flowering plants in the same location every year, implying that many seedlings survive in competition with rosettes.
The Baskin and Baskin (1992) study left unanswered some important questions. First, they collected soil samples from garlic mustard sites after germination but before seed dispersal to determine if there was a
10 persistent seed bank. These samples were 6 dm^ in area
and 6 cm deep. They were lifted intact and fitted into
flats and kept in an unheated greenhouse for two years.
While this method seems effective in determining a seed
bank, it does not address the question of how many seeds
were in the samples and how viable they were. Second,
the study did not address the fate of ungerminated seed: were the seeds eaten, dormant, or diseased? Third, the
research was conducted in an unheated greenhouse instead of a natural leaf covered site in a forest. Fourth,
Baskin and Baskin did not address the effect of soil depth on germination or dormancy. My study placed seed 0 and 10 cm deep and monitored germination over 3 years.
Finally, their research may lead to the incorrect conclusion that since their seeds failed to germinate in the first spring, they did not afterripen during the previous winter. If this were true, then no seeds harvested after natural germination would germinate on petri dishes placed in a germination chamber. Our results showed that there were a few seeds (<1%) that germinated by placing them in a growth chamber without scarification.
The study by Roberts and Boddrell (1983) in Great
Britain also involved seeds sown in soil in buried earthenware containers. To test for viability of
11 ungerminated seeds, the top 10 cm of soil was removed
after the 5 year study, and transferred to another
container where it was stirred periodically for two years
to secure germination of remaining seeds. Again, no
determination was made as to the fate and viability of
non-germinated seeds. Their conclusion: few seeds
survive longer than 2 years- My study refutes their
conclusion.
Ohio provides a unique geographic location to study
garlic mustard. Cavers, et al. (1979) reported that
seeds shed in the summer do not germinate until the second spring (18 months later) in Ontario, Canada. This may be due to inadequate freeze/thaw cycles suggesting garlic mustard in that cold climate requires 2 winters to afterripen. This correlates well with Baskin and Baskin
(1992) results showing poor germination when seeds are kept at a constant cold temperature of < 4®C for 16 weeks. However it contrasts with Byers (1988) and Meekins and McCarthy (1999) who obtained germination on filter paper at 4®C for 100 days and 105 days respectively.
Competition with woodland qphemerala
Richard N. Mack (1985) defined invasion as an incursion of organisms into a new area. These organisms are often called aliens or exotics and they are assumed
12 to be detrimental to the natives. Invasive species
(invaders) that have reportedly reduced populations of
native species are Puerarla lobata (kudzu), Lonicera
maackii (amur honeysuckle), Rosa multiflora (multiflora
rose), Elaeagnus umbellata (autumn olive), and Lythrum
salicaria (purple loosestrife) (Stuckey, 1980; Williams,
1994; Luken and Thieret, 1996). Sometimes these
invasions result in the establishment of permanent
populations. Such activity is termed naturalization and
the species are referred to as being naturalized. In
terms of succession, all invaders are colonists but not
all colonists are invaders. Most botanists consider
invaders as unwanted and therefore categorize them as
"weeds".
Geneticists have used invaders to examine founder
effects, genetic drift and introgressive hybridization
(Mack, 1985). However, few field experiments have been
done to determine the effect of invaders on native
populations. Generally, research of this type has been
restricted to islands.
The study of plant invasions allows the precise assessment of:
a. factors affecting the spread of aliens,
b. competition between alien and native species, c. extinctions.
1 3 a) Spread of aliens: The rate of invasion has been estimated by plotting the first sighting (compiled from herbarium records) vs. time. However, this only predicts gross features of invasion, not an estimate of area occupied or the rate of expansion. Some have tried to model the rate of spread of plants. They consider spread spatially as similar to a ripple in a lake caused by the throwing of a rock. The ripple spreads out in all directions uniformly from the point of entry, the focus, until it meets an object or another ripple. If the focus is duplicated elsewhere, then the ripples cover a large area much quicker. This idea leads to many questions:
What is the rate of spread? What is the potential range of spread? Are there limiting or enhancing factors to the spread? Are there pathways of spread or is it random? When and why does the spread depart from a wave phenomenon? To address those points in any population you must look at the factors affecting the rate of spread: 1) the number and location of points of entry
(foci); 2) the suitability of the adjacent habitat for colonization; 3) the corridors and barriers between suitable habitats; and 4) the initial size of the invasive population. To address these factors, the species life history characteristics must be quantified
(Mack, 1985)
14 The usual pattern for invasion of exotic plants
parallels that of diseases: a slow initial spread, a
phase of rapid expansion, and then a slowing to a stable
population. The spread and expansion phases are often
referred to as a classic J curve and are a description of
logistics growth. If the spread comes from only one
focus, then the initial lag time is long. If, however,
there are many nascent foci (foci that are far apart),
then the lag time is shortened because more area can be
covered before the population ranges join (Moody and
Mack, 1988; Mack, 1985). This helps explain why the
control of aliens is ineffective: unless you obtain total
eradication, the remnant populations become the foci for
reinvasion. In fact, the reinvasion will proceed faster
than an initial invasion of one or two foci (Mack, 1985).
An important factor in the spread of an invader is
anthropological disturbance. Foci can be established
hundreds of miles apart due to human intervention. (See
Fig 1.1 - map of garlic mustard in Ohio pre-1940.) Even
with a forest invader like garlic mustard surrounded by
tilled fields, small foci of garlic mustard pop up in
adjacent woods due to seed adhesion to deer hooves and
human footwear. It is also possible that birds and small mammals may act as carriers of seeds.
15 b) Competition : Anecdotal evidence of the decline of native populations due to competition with aliens abounds, but little experimental evidence exists. In fact, because most evidence is circumstantial, there is controversy in population biology as to how much interspecific competition exists in nature (see Schoener
1982, Connell 1983)- Strong (1983) has stated that to assume that interspecific competition is the overwhelming factor in the coexistence of plant species in general is to ignore the primary forces of autecology (individual x environment interaction) on plant populations. Grime
(1977) has suggested that only in relatively productive, undisturbed vegetation should competitive forces prevail over autecological ones. The removal of leaf litter in late fall to prepare plots for garlic mustard seeding would be considered an autecological disturbance and may have an effect on competitive forces.
Schoener (1982) has proposed six main propositions regarding interspecific competition:
1) Species very similar in the resources they use
cannot coexist for very long: one will
competitively exclude the other.
2) Species that do coexist in nature have sufficient
differences in ecological niche and/or in use
of resources.
16 3) Interspecific competition is an evolutionary
force selecting for adaptations that result in
species difference in resource use. In fact a
difficulty in measuring competition is that
selection in either competitor may cause the
two populations to no longer interact (Thompson
1982).
4) Competitive pressures determine geographic
distributions of species. (Overlooked in the
course of repeated reference to the role of
disturbance in enhancing invasion has been the
displacement of native colonizers, i.e.,
populations that would have increased with
increasing disturbance. For example, Festuca
microstachys, Festuca octaflora, and Bromus
Carinatus were presettlement colonizers on the
steppes of western North America. Today,
however, aliens Poa pratensis, Bromus tectorum,
and Salsola kali predominate (Mack, 1981).
Field and greenhouse experiments indicate that
in the case of Bromus tectorum it usurps
resources from the natives (Mack, 1985).)
5) Species may interfere with each others growth by
many means including the production of
allelochemicals and the depletion of resources.
17 Allelopathy may play a role in garlic
mustard’s competitive abilities not only with
other species (Kelley and Anderson, 1990) but
also with itself. McCarthy (1997) observed
that seedling establishment was greater in
experimental plots where garlic mustard was
periodically removed than in control plots
where garlic mustard rosettes were established.
However, an assessment of the allelopathic
potential of garlic mustard on radish, hairy
vetch, lettuce, and winter rye proved negative
(McCarthy and Hanson, 1998).
6) Experiments performed in species with substantial
overlap in use of resources should detect
interspecific competition. A study by McCarthy
(1997) showed that the removal of garlic
mustard from experimental plots resulted in
release and proliferation of forest herbs,
especially those species with a persistent seed
bank (annuals), species with fast vegetative
growth rates (vines), and species with high
dispersability by wind or animal vectors (tree
seeds). The effects on slow-growing spring
perennial herbs was mixed with an increase in
mean relative cover of 7 to 8% the first year
18 after removal but no difference from the
initial year in mean relative cover two years
after removal.
Therefore, garlic mustard introduced into a forest understory should depress the native herb population directly or should affect individuals by way of decreased vegetative growth or reduced seed production that will ultimately depress its population. This depression will only affect those species that fill a similar niche or those that compete directly with garlic mustard for resources during rapid growth stages (i.e. early spring when rosettes are forming from seedlings).
Even in plant communities where interspecific competition has been shown to be important many other factors (i.e., nonlinear interaction and spatial interdispersions) can undermine simple models of community behavior. Niche models do not account for sparseness. Some plant species are always locally rare, and we cannot assume it is because of poor competitive abilities. Their summed competitive effect on other species in the community is probably very small, even though individuals may compete quite well in their microenvironment (Strong 1983). This is especially true in the forest understory where a few individuals persist
19 over the whole area but do not concentrate in
monocultures (i.e., Arisaema triphyllum, jack-in-the-
pulpit; Jeffersonia diphyllar twinleaf; Sanguinaria
canadensisf bloodroot; Orchis spectabilis, showy orchis)
as opposed to species that exist in patches (Podophyllum
peltatum, mayapple; Smilacina racemosa, false Solomon's
Seal) or are moderately or heavily sprinkled throughout
the understory (Impatiens capensisr jewelweed; Dentaria
laciniata, cutleaf toothwort; Claytonia virginica, spring
beauty).
Competition in a forest understory is also affected
by the seasonal growth cycles of the competing species.
Three different growth cycle categories can be observed
among herbaceous herbs in a forest understory (from
Kawano, 1985): 1) shade-intolerant species in which
flowering and new vegetative growth occurs before tree
canopy formation (Claytonia virginica and other spring ephemerals); 2) semi-shade species which come up with
spring ephemerals but wait until after canopy formation before flowering (Sanicula marilandica, black snakeroot;
Circaea quadrisculata, enchanter's nightshade); and
3) shade-tolerant species that come up after canopy formation and flower before leaf drop (Eupatorium rugosum, white snakeroot). Garlic mustard has a combination of growth cycles with semi-shade
20 characteristics the first year when rosettes form after
canopy formation, and shade-intolerant characteristics
the second year when bolting to flower occurs before
canopy closure. It follows that garlic mustard would
compete with shade-intolerant and semi-shade species more
than with shade-tolerant species.
c) Extinction: Mack (1985) states that to his knowledge
there is no irrefutable evidence of plant extinction
caused by the spread of alien invaders. He also states
that there are not enough demonstrable examples of
native-alien interaction to predict the likelihood of
extinction through competition as opposed to predation.
In fact, most extinctions involve the invading alien.
One such example is the cheatgrass introduction into the western United States. Nine other exotics have been
introduced into this area yet none display the distribution and abundance of cheatgrass (Mack 1981) due to winter hardiness. Nilsen and Muller (1980) observed that Schinus terebinthifolius is unable to naturalize southern California because of the shrubs slow germination before the end of seasonal rains even though it readily invades areas of Florida and Hawaii.
Mack (1985) concludes that the diversity of plant invaders and frequency of their movements provide a
21 multitude of experimental scenarios. If rate of extinction is dictated by the ratio of birth rates to death rates (along with the impact of repeated immigration) then varying population size, life history characteristics, and competitors effects on extinction should be examined.
Many researchers have implied that garlic mustard crowds out the spring ephemerals in the understory of open woods (Cavers, et al, 1979; Yost, et al, 1991;
Baskin and Baskin, 1992; Nuzzo, 1993a; MacKenzie, 1995) but there has been only one natural study to verify this.
Nuzzo (1992) found that the cover of Dentaria laciniata declined to an average of 31% when associated with garlic mustard as compared to 79% cover when not associated with garlic mustard. Those plants associated with garlic mustard were described as being yellow, stunted, and had failed to flower. No negative impact was detected on
Phlox divaricata (phlox) or on Asarvm canadense (wild ginger). The study involved the census of recently established populations of garlic mustard versus populations where there was no garlic mustard.
Meekins and McCarthy (1999) used a multiple deWit replacement design for a greenhouse study to test for competition between garlic mustard rosettes and three target species: Acer negvndo L., box elder; Quercus
22 prinus L., rock chestnut oak; and Impatiens capensis
Meerb., orange touch-me-not, or jewelweed. Garlic mustard was a superior competitor with Q. prinus with the total dry wt. yield of Q. prinus being 34.8% lower in mixture with garlic mustard than in monoculture. The yield of garlic mustard was 21.6% higher in mixture with
Q. prinus than in monoculture. In the cases of the other two species, the yield of garlic mustard was 17% to 36% lower in mixtures than in monoculture. The yield of I. capensis was 11.7% higher in mixture and the yield of A, negundo was 37% higher in mixture than the yields in monoculture of these two species.
Mapping the Spread of Garlic Mustard
Information on the spatial distribution of weeds in crop fields can aid in predicting yields and managing weeds (Cardina, et al., 1997) as well as to model the changing population of weeds within a field (Ballare, et al., 1987). In order to understand the spatial distribution of a metapopulation (the population over an entire field or forest), sampling over large spaces requires kriging to produce unbiased estimates of values at locations that were not sampled (Cardina, et al.,
1997). However, in a forest situation, trees and streams and other geophysical features act as barriers to the
23 spread and distribution of the species. The metapopulation then becomes a series of patches that may
or may not join together. The dynamics within these patches may be a better predictor of the dynamics within the metapopulation than trying to determine the dynamics of the whole population (Hastings and Wolin, 1989).
Moody and Mack (1988) have observed that control of these small patches, or nascent foci, can reduce the overall spread of the population. Indeed, the spread of the Striça asiatica, witchweed in the Carolines has been held in check by the diligence of eradication of small, isolated foci while slowly working at the perimeter of the main population (Eplee, 1981).
The process of invasion can be divided into arrival, establishment, and spread. With garlic mustard, arrival comes with immigration of seed into the patch.
Establishment means that the patch is firmly established which for garlic mustard would mean an alternate year flush of seedlings followed by a year of few seedlings until the seed pool in the low years builds up. Because it is a biennial, spread in garlic mustard does not become discernable until the population has firmly established a pattern of consistent recovery. When the dynamics of expansion and contraction at the edge of the population no longer overlap the focus point, a pool will
24 develop from which spread can occur without the threat of
extinction. Models constructed to estimate the spread of
invasives from that pool tend to be exponential, although
linear approximations can give reasonable representations
(Williamson and Brown, 1986) .
Researchers have used life-tables to quantify life
cycle stages and thereby either demonstrate or project
the growth or decline of a population (Werner, 1975;
Werner and Caswell, 1977; Hubbell and Werner, 1979;
Leverich and Levin, 1979; Silvertown, et al., 1993).
While this has been done with biennials on a limited
scale, the main focus of these studies has been the size
(or stage of growth) vs. age aspect of these facultative biennials (Kelly, 1985; Klemow and Raynal, 1985; Cochran and Ellner, 1992), that may also be called monocarpic or
semelparous perennials (Silvertown, 1984). I did not find any life tables published for strict biennials and no
life table has been published for garlic mustard.
Byers and Quinn (1987) tested garlic mustard across a range of habitats to compare drier, more open habitats with the more common open woods habitat. They found survivorship was not significantly different among the populations and that the highest mortality occurred in the drier months. They also found significant differences in germination among families and among habitats with the
25 floodplain population exhibiting the highest germination.
If garlic mustard is to become an agricultural weed, it will have to survive these drier, more open habitats.
Alliaria petiolata has the plasticity to survive and flower in many situations. The following observations demonstrate this elasticity. Table 1.1 shows data from late developing flowering stalks that arose from lateral buds along the length of old flowering stalks that had shed seed in July. The first plant had >50 old siliques of approximately 5cm length with approximately 16 seeds per pod based on septum indentations. The second and third plants had been mowed, but appeared to have had inflorescences and pods, the stems being robust. The plants were located on the west side of a decaying leaf/brush pile that has been in existence since 1990.
The site was in full sun from at least noon until sunset.
The new stalks appeared in mid-October. No seed were produced. Under the right circumstances and given enough time, garlic mustard may eventually exhibit some perennial lifecycle characteristics.
2 6 Plant stalk # Mew # New # of # Open # of # # Brnch Leaves Size Inflor Flowrs Pods size 67 1 3 Table 1.1 Characteristics of Alliaria petiolata flowering stalks observed in October, 1999 in Clark County, Ohio. This study sought to further the understanding of the seed biology, competitive ecology and spread of garlic mustard. Specifically, the research objectives were: 1) To determine the effects of burial depth on dormancy, germination, and longevity of garlic mustard seeds; 2) To quantify the competitive effects of garlic mustard in relation to woodland herbs; 3) To quantify the external expansion and internal increases in density of remote patches of garlic mustard. 27 Pre 1940 (4 counties) 1940-1959 (13) 1960-1979 ■ (24) 1980-Present (62) Fig 1.1 County distribution in Ohio of A. petiolata since 1900 (from Ohio State University herbarium records and personal observations) 28 CHAPTER 2 SEED DORMANCY IN GARLIC MUSTARD ABSTEIACT Garlic mustard is an exotic weed of the forest understory that is competing with native spring ephemerals. Buried seed experiments lasting 3 yrs were begun in 1996 and 1997 to examine dormancy aspects of garlic mustard. Seeds were surface covered and buried 10 cm deep in fiberglass mesh packets. Average germination of shallow seeds was 61% the first season (1997) with a cumulative germination of 94% after 3 years. Among the deeply buried seeds, the average germination was 11.5% the first season with a cumulative germination of 16% after 3 years. No germination in the field was observed prior to February of each season or after April. The majority of seedlings were found in March and April. The majority of dormant seeds were physiologically dormant the first two seasons when they comprised 87 to 96% of the total number of dormant seed. By the third season, they comprised only 66% of the dormant seed regardless of depth. Seeds were 100% viable at harvest and maintained 99% viability 2 9 during the study for both experiments. The pattern for naturally germinating garlic mustard seeds progressed from physiological dormancy through physical dormancy to non-dormant to germination. A fraction of the seeds remained non-dormant or only physical dormant throughout the summer and fall months, giving the species variation in dormancy status that may allow garlic mustard to adjust to changing environmental conditions. 30 INTRODUCTION Garlic mustard, Alliaria petiolata (Bleb) Cavara and Grande, is an exotic weed of the forest understory that is competing with native spring ephemerals (Nuzzo, 1992). It occurs most often in partial or full shade, but can also grow in full sun giving it potential to become an agricultural weed. Garlic mustard has been found in Ohio in both soybeans and wheat (personal observation). It is a strict biennial that produces a large seed drop in its second year (Cavers, et al., 1979). Garlic mustard seeds have a strong innate dormancy (Cavers, et al., 1979; Lhotska, 1975) which is partly attributed to a thick, more or less impervious seed coat (Klykken, 1937), and to an embryonic physiological dormancy (Lhotska, 1975) even though the embryo is well developed and differentiated at maturity (Klykken, 1937; Murley, 1951; Lhotska, 1975). Cavers et al. (1979) attempted more than 70 treatments to break dormancy, but the only ones that were successful involved scarification and gibberellins (GAa) . Previous studies (Lhotska, 1975; Roberts and Boddrell, 1983; Baskin and Baskin, 1992) have shown that 55-7 6% of garlic mustard seeds germinates in the first spring after sowing (January to April). Baskin and Baskin 31 (1992) found the peak of natural germination in Kentucky occurred when mean daily max/min temperatures were 8 and -1.0®C respectively during late winter. They also found that optimum temperature for germination of nondormant seeds in a growth chamber was 15/6®C at a 12/12hr thermoperiod. Germination was highest in constant darkness compared to a 14-hour photoperiod. An additional result reported by Baskin and Baskin (1992) involved a comparison of fluctuating temperature stratification versus constant temperature. Seeds were overwintered in an unheated greenhouse in 1984-85 and 1985-86. They received 1269 and 1452 hours, respectively, of temperatures ranging from 0.5® to 10®C. Germination of these seeds was higher (66-7 0%) than those exposed to constant 1® or 5°C for 16 weeks (2688 hrs) (46-60%). They concluded that garlic mustard, like some other species (Flemion, 1933), after-ripens better at fluctuating low temperatures than at constant low temperatures (Baskin and Baskin, 1988; 1992). Cavers at al. (1979) reported that seeds shed in the summer in Ontario, Canada, do not germinate until 18 months after seed dispersal. Reports by other researchers showed that the majority of seeds germinate in the first spring after seeds are shed (Roberts and 32 Boddrell, 1983; Baskin and Baskin, 1992; Anderson et al., 1996). Naturally occurring garlic mustard seeds are thus after-ripened in the winter, germinate in late winter or early spring, establish themselves before tree canopy closure, set seed their second year, and produce a short lived seedbank for subsequent years (Cavers et al., 1979; Roberts and Boddrell, 1983; Byers, 1988; Baskin and Baskin, 1992). An understanding of the temporal patterns of garlic mustard seeds in a seedbank is important for predicting the extent of infestation in a natural setting. Previous studies of garlic mustard dormancy and seedbank potential did not account for ungerminated seed (Baskin and Baskin, 1992; Roberts and Boddrell, 1983). In addition, the effects of seed burial was unknown even though seeds can be buried through rodent activity, insect activity, and physical incorporation by animals and humans. The objectives of this study were to determine how long seeds remained viable in the soil, the fate of ungerminated seeds, the time needed to deplete the seed bank, and the effect of burial on dormancy, viability, and seed fate. Therefore, to determine the effects of burial depth on dormancy, germination, and 33 longevity of garlic mustard seed a buried seed dormancy experiment was conducted based on methods used by Cardina and Sparrow, 1997. 34 METHODS AND MATERIALS A three-year buried seed experiment was conducted from 1996-1999 in Clark County. Ohio to examine dormancy aspects of garlic mustard. The experiment was repeated from 1997-2000 in Wayne County, near Wooster. OH. C l a r k C o u n t y Site\ Seeds were collected from the Ohio State University Waterman Farm in Columbus on July 20. 1996. Seeds were sieved to provide a more uniform seed population and stored in a mesh bag in a ventilated garage until packets were prepared. Packets made of permeable fiberglass mesh measuring 6 cm square were filled with approximately 170 seeds. The seeds were measured volumetrically by means of a small test tube with a line on it at the level of 170 seeds. Periodically a measured amount was counted to confirm this approximation. The experiment was conducted in a young regrowth Maple-Beech woods (the soil was a fine- loamy. mixed, mesic Typic Hapludalfs). Experimental design was a Randomized Complete Split-Block with depth and months as main plot factors and three replications. Burial depths were surface covered (shallow) and 10 cm. (deep). The plots 1.5m by 5m and were raked to bare soil. The resulting leaf litter and debris was used to 35 cover the surface placed packets which were buried on August 12, 1996. Packets were retrieved on approximately the 15th of each month for three years. Seeds that had germinated in the packets were removed and counted. These were evident as seedlings or as empty seed coats. The testas were intact but split open longitudinally and were all that remained in the packets following the death and decay of the seedlings. These were counted as germinated seeds. A standard germination test was conducted on the remaining non-germinated seeds at 15/6“C on a 12 hr cycle (Baskin and Baskin. 1992) for 10 days on two layers of filter paper moistened with 7 ml deionized water in 9 cm diameter petri dishes. Germinated seeds as determined by protrusion of the radicle were removed and counted. Seeds not germinated following this procedure were nicked on the side opposite the embryonic axis (rounded side) (Murley. 1951) and replaced in the germination chamber for an additional 10 days. Only one cotyledon was slightly injured during the nicking procedure and the embryo was not damaged. Those seeds that did not germinate after nicking were placed in 5 ml of 0.2 % tétrazolium (TZ) to determine their viability. Beginning in January 1998. half of the nicked dormant seeds were placed on filter paper with 7 ml 10* M GAj to test whether 36 the dormant seeds would germinate. Those that did not germinate after 24 days were placed in TZ as above to test for viability. Site: Garlic mustard seeds were collected from the Ohio State University Waterman Farm in Columbus on July 31. 1997 and stored as before. Lots of 100 seeds were counted and placed in permeable fiberglass mesh packets and buried as described previously on August 14. 1997 in a second-generation Oak-Hickory woods located at the OÂKDC Badger Farm near Wooster. Ohio. The soil was a fine-loamy, mixed, mesic Aquic Fragiudalfs. Protocol for retrieval and testing was the same as described previously. A germination test was conducted before burial on four lots of 50 seeds using the lab protocols previously described. Temperature at each site was recorded from temperature probes located at surface covered and 1 0 cm deep. Where missing, temperatures were estimated from local weather station air and soil data using regression techniques. Daily minimum and maximum temperatures were determined and cumulative days with maximum temperatures above and minimum temperatures below 1°C were plotted against cumulative germination values for each depth. Seeds were classified based on germination tests as nondormant. physically dormant, physiologically dormant, 37 or nonviable. Nondormant seeds included those that germinated in the field and those that germinated in the growth chamber without scarification. Seeds that did not germinate naturally in this experiment, but did germinate when placed in the growth chamber, are classed as nondormant because their microenvironment in the seed packet was less than that required for germination. This was in agreement with Vleeshouwers. et al. (1995) who defined dormancy as a strictly temperature controlled characteristic that determines the range of conditions in which a seed is able to germinate. Seeds that germinated after nicking were classified as having a physical dormancy only, while those that failed to germinate after nicking but were viable were classified as possessing physiological dormancy. Physical dormancy may also have been part of the overall dormancy of this latter group (Cavers et al.. 1979). All data were expressed as percentages of seeds recovered. The average percent germination was determined for each category in each treatment at each depth and plotted over time on a monthly basis. Linear regression analysis was then used and the slopes of the regression lines were subjected to a t-test (Zar. 1996). A split-block ANOYA was used to analyze all data with depth and months as main-plot factors and an F-test 38 was used to test for differences. Additionally, monthly germination values were averaged over germination seasons and the averages analyzed in the same manner (split- block) with depth and seasons as the main-plot factors. A germination season was defined as that period between February of one year and January of the following year, the time when one season of testas would be found. Finally, total germination was combined over all reps for each season at each depth and total percent germination calculated. Seasonal germination values were thus determined by subtracting the previous season's germination values from the total. 39 RESULTS AND DISCUSSION The winter of 1997-98 was very mild compared to the other winters in this study. This was especially true at the Wooster site where there were only 70 days with minimum soil temperatures below 1"C compared to an average of >140 days during the other winter seasons. The percentage of seeds recovered that were live was over 99.3% for the Clark County site and over 99.8% for the Wooster site regardless of depth. Over 97.5% of the physiologically dormant Clark County seeds placed in GA, germinated within 24 days regardless of depth of planting. Nearly 85% of the physiologically dormant Wooster seeds germinated when placed in GÀ 3 . Seedlings were only found in the packets during the months of February. March, and April. In most cases testas were split longitudinally and were still distinguishable by the end of the three years. Although seeds were measured volumetrically for the Clark County experiment, a recovery rate of over 99.5% of the Wooster seeds, which were counted to ensure 100 seeds per packet, lends confidence to the assumption that almost all seeds were recovered at the Clark County site. The actual recovery rate at Wooster was much higher but six packets were found that contained only 95 seeds, a 40 difference attributed to counting error rather than loss of seeds during the experiment, because seeds were counted in lots of five. There were differences for depth, month, and depth by month interactions (Table 2.1). Month effects can be attributed to the germination periods each season. Month by depth interaction can be attributed to differences in the effect of depth on germination at different times of the year. A linear regression analysis was conducted on the means from February 1997 to August 1999 at Clark and from February 1998 to July 2000 at Wooster to determine if the slopes were different. The difference between the slopes of the regression lines for each depth was subjected to a t-test and this confirmed the difference (data not shown). The ANOVA for the Wooster data (Table 2.2) was similar to Clark County data including the t- test of slopes. Table 2.3 lists the seasonal ANOVA's for Clark County. Depth effects were only significant for % natural germination. Seasonal effects were significant for the percent of dormant seed that were physiologically dormant due to the increase in seeds that were physically dormant only (Fig. 2.4). Season by depth interaction was attributed to a difference in magnitude of increase between the two depths (see previous discussion). 41 The percentage of recovered shallow seed at Clark classified as non-dormant was over 95% by the spring of 1999 (Fig 2.1) with the range being 47.8% to 98.1% over the three seasons of the experiment (Feb 1997 - Aug 1999). Variation month to month during a season can be attributed to variability in the seed population and in the microsite in which the packet lay (Vleeshouwers et al.. 1995). Of those seeds considered non-dormant, the vast majority (90.4%) germinated in the field (Fig. 2.2). Cumulative natural germination among the shallow seeds rose from an average of 60.9% the first season to 94.2% the third season (Fig. 2.3). This was higher than the average germination in the deeply buried seed, which rose from 11.5% to 16% by the third season. At Wooster, the percentage of recovered seed that germinated naturally among the shallow seeds at Wooster ranged from 10.5% to 91% (Fig. 2.6). Among the deeply buried seeds the highest percentage was 1 0 .7% in the third season (February 2000). Cumulative natural germination in the deeply buried seed averaged 5.5% by the third season. Among the shallow seeds the average percent natural germination rose from 18.4% the first season to 72.3% the third season (Fig. 2.7). Seeds with physiological dormancy comprised the majority (87 to 96.4% at Clark) of the total number of 42 dormant seed the first two seasons (Fig. 2.4). By the third season, however, seeds with physiological dormancy comprised 6 6 % of the dormant seed recovered, regardless of depth. There was a difference between seasons 2 and 3 of 21% (LSD.os = 11.75%) in the portion of dormant seeds with physiological dormancy, averaged over depths. At Wooster, no decline was found as seeds with physiological dormancy comprised 80 to 94% of the total number of dormant seed over the three seasons (1998-2000). Of the shallow seeds that germinated each year, those that germinated in the growth chamber did so mainly in January and February (Figs 2.5 & 2 9). No seeds germinated in the growth chamber at Wooster during January and February 2000 (Fig 2.9). This can be attributed to the small quantity of shallow seeds tested. From February to July 2000, 10 of the 17 recovered packets had less than 30 intact seeds in them with 3 packets having no intact seeds remaining. Seedlings were mainly found in the packets from February to April, with the majority found in March and April. At Clark, a few seedlings were found in January ( 8 in 1998. 2 in 1999) and at Wooster. 4 seedlings were found in one packet in January 1998 and 1 was found in January 1999. The highest average percentage of seedlings found each season was 66.5. 60.1 and 94.1% of 43 remaining intact seeds at Clark (Fig. 2.5). The third season was higher than the other two seasons (LSD ^ = 20.3%). The number of remaining intact seeds in the second and third year was estimated by subtracting the average number of germinated seeds from the previous seasons from the total number of intact seeds and empty testas recovered. The highest average percentage of seedlings found at Wooster was 58.6% of remaining seeds in March of the second season (1999) (Fig 2.9). Discussion: Baskin and Baskin (1992) found that optimum day/night temperature for germination of non-dormant seeds was 15/6“C. The average high temperature for late April in Ohio is greater than 16“C. and the average high/low temperatures for May are 22/8.5“C. Since seedlings were not found in packets after April, a secondary dormancy may have been induced due to the increasing temperatures of late April and May (Vleeshouwers et al.. 1995; Bouwmeester and Karssen, 1992). However, not all seeds display this secondary dormancy. A small fraction remain non-dormant especially at the 10 cm depth (Fig. 2.10). where seeds retrieved during all warm season months at Clark County had at least one seed that germinated in the growth chamber 44 prior to nicking. The same also held at Wooster the majority of the time (Fig 2.10). This may be attributed to variation of dormancy intensity in the population (Evans et al.. 1996). Germination of non-nicked surface covered seeds occurred only in the first season at Clark. There was no germination of seeds during the warm months of the second and third seasons at either location. When cumulative germination was plotted against cumulative number of days with maximum soil temperatures above and minimum soil temperatures below I“C. a strong relationship was seen (Bf=0.9046. Fig. 2.12). Baskin and Baskin (1992) stated that garlic mustard achieved maximum germination in response to fluctuating temperatures. This may explain differences among years in the amount of natural germination observed (Figs 2.5 and 2.9). However, a second mechanism, an accumulation of cold units, could account for the slow decrease in seeds that are physiologically dormant (Fig. 2.4) among the deeply buried seed (Fig 2.16). It could also account for the increase in nondormant seeds that germinate in the growth chamber and for the duration during which nondormant seeds are found at Clark (Fig. 2.10). This also agrees with those researchers that observed germination of garlic mustard seeds exposed to constant cold (1-5“C) temperatures for long (90-125d.) periods of time (Byers 45 1988; Baskin and Baskin. 1992; Meekins and McCarthy. 1999) . Of those seeds that acquire a secondary dormancy, a fraction has only physical dormancy (Fig. 2.11). A possible reason they remain only physically dormant may be an accumulation of CO, levels in the surrounding soil air. Using seeds of Trifolium suJbt&rraneum. Ballard (1958) showed that germination percentages increased when imbibed physiologically dormant seeds were exposed to higher concentrations of 00%. Assuming CO% levels are higher in the soil than in the air above the soil (Egley. 1986). buried seed could overcome physiological dormancy more rapidly than seeds at the surface (Baskin and Baskin. 1998). Since garlic mustard has both physiological and physical dormancy, higher CO; levels may shift buried seed from a physiologically dormant state to only physically dormant. Over time, this shift would result in higher germination of seeds after nicking. Fig. 2.11 shows that among buried seed at Clark County, the percentage of those dormant seed that were considered physically dormant only rose from an average of 4.4% the first season to an average of 32.5% the last season. The surface covered seeds were also not exposed to the air. A layer of decomposing leaves and forest 46 material would have maintained higher levels of C0% than the surface air (Egley and Duke. 1985). Therefore, the percentage of surface covered seeds that were only physically dormant could also have increased (Figs 2.4 and 2.8). There was no difference between surface covered and deeply buried seeds in this regard. Seeds of garlic mustard require imbibition and cold stratification to break physiological dormancy (Baskin and Baskin. 1992). This is similar to other species that have both physical and physiological dormancy (Barton. 1934; Quick and Quick. 1961; Heit. 1967; Garner and Lewis. 1980; Baskin and Baskin. 1998). Cold temperatures also are needed for loss of physical dormancy in some species (Baskin and Baskin. 1998). Physiological dormancy decreased and penetrability of the testa increased during cold stratification of Cercis canadensis (Eastern redbud). another species with both physical and physiological dormancy (Geneve. 1991). Since fluctuating temperatures may enhance the breakdown of physical dormancy (Baskin and Baskin. 1992; Heit. 1967). a fraction of garlic mustard seeds may quickly lose physical dormancy by January allowing germination under ideal temperature conditions (Fig. 2.5). As temperatures rose, suitable conditions for germination no longer were present and physical and physiological dormancy were both 47 reacquired (Vleeshouwers et al., 1995) in most but not all seeds (Fig. 2.11). Secondary dormancy is relieved by a second period of chilling (Staniforth and Cavers, 1979). This cycle continues until the seedbank is depleted at the surface covered depth (Fig. 2.13). For deeply planted seeds (10 cm), three years depleted the seedbank by only 15-25% (Figures 2.14 and 2.15) The normal progression in dormancy states for naturally germinating garlic mustard seeds appears to progress from physiologically dormant to physically dormant only to non-dormant to germination. Those seed that do not germinate reacquire secondary dormancy, with a fraction of the seeds remaining non-dormant or physically dormant, giving the species variability to adjust to a changing environment. In some seeds, the progression may begin with a period of physical dormancy and then an acquiring of primary physiological dormancy while on the plant. A previous experiment (Appendix A) showed that, among newly formed seed. 9.7% of viable seed harvested May 17*^ were non-dormant. 48% had only physical dormancy and 42% were physiologically (plus physically) dormant. As the date of harvest was delayed, the percentage of seed with physical dormancy only decreased while the percentage of 48 seeds with physiological (plus physical) dormancy increased, so that by June 7 nearly all seeds had physiological dormancy and failed to germinate after nicking. Since garlic mustard has a shortlived seedbank under shallow burial conditions (Fig 2.13). natural resource managers would make best use of their limited resources by concentrating on preserving areas with few garlic mustard plants. Those areas would require removal of garlic mustard plants for only four years with periodic spot checks to get those plants that may have germinated from buried seed. 49 Clark County Deoth Month Deoth Z Month % Nondormant Hf it ititit ititit % Natural germination it * ititit ititit % Natural germination of intact * icicic ititit seeds % Growth chamber germination of ititit ititit intact seeds n.s. % of dormant seed that has it ititit ititit physiological dormancy Table 2.1 ANOVA table for percent of seeds recovered that were nondormant. for percent of seeds recovered that germinated naturally in seed packets, for the percent of intact seeds that germinated naturally and for those that germinated in a growth chamber, and for the percent of dormant seed that exhibited physiological dormancy. Seeds were buried in lots of 170 seeds per fiberglass mesh packets at surfaced covered and 10 cm deep in a Maple- Beech regrowth woods in Clark County. Ohio. Clark County Deoth Season Deoth X Season Z Natural germination ** •** n.s. % of dormant seed that has ««• «•» physiological dormancy n.s. % of tested seed that had *** ** physical dormancy only n.s. Table 2.3 Seasonal ANOVA table for Clark County for percent of seeds recovered that germinated naturally in seed packets, for the percent of dormant seed that exhibited physiological dormancy, and for the percent of tested seed that displayed physical dormancy only. 50 Wooster Depth Hbnth Depth Z Month % Non—Dormant * Nr NfNf NT Nr Nr Nr % Natural gemination ** NrWNr Nr Nr Nr % Natural gemination of intact * Nr Nr Nr Nr Nr Nr seeds % Growth chamber gemination of Nr Nr Nr Nr Nr intact seeds n.s. % of dormant seed that has Nr Nr Nr Nr Nr physiological dormancy Table 2.2 ANOVA table for percent of seeds recovered that were nondormant. for percent of seeds recovered that germinated naturally in seed packets, for the percent of intact seeds that germinated naturally and for those that germinated in a growth chamber, and for the percent of dormant seed that exhibited physiological dormancy. Seeds were buried in lots of 1 0 0 seeds per fiberglass mesh packets at surfaced covered and 1 0 cm deep in a second- generation Oak-Hickory woods at the OARDC Badger Farm near Wooster. Ohio. 51 Shallow en W illlllll iunitui Fig 2,1 Nondormant garlic mustard seeds buried in lots of 170 seeds per fiberglass mesh packet at surface covered and 1 0 cm depths in soil in a Maple-Beech regrowth woods in Clark County. Means are the average of 3 replications (packets) and are expressed as a percentage of the total seeds recovered from the packets each month. Vertical bars represent the standard error. LSD 05 between depths = 24.1. m NatGrm Shallow NatGrm Deep VI w {IIIISiitHtlilüSünHHÜIÜHiHî3 § 5 Q c» OB » 0» S rig 2.2 Natural germination of garlic mustard seeds buried in lots of 170 seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a Maple- Beech regrowth woods in Clark County. Means are the average of 3 replications (packets) and are expressed as a percentage of the total seeds recovered from the packets each month. Vertical bars represent the standard error. L S D 05 between depths = 23.8. P Nat Deep □ Nat Shallow Ü1 Season Fig 2,3 Cumulative natural germination of garlic mustard seeds buried in lots of 170 seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a Maple-Beech regrowth woods in Clark County, Data for each season was averaged over the months, February of the year labeled to January of the following year. The 1999 season average was from February through August, LSD os between depths = 10,6, LSD.os between seasons =11,7. ■ k in in I Physical Deep B Physical Shallow ^ B Physiological Deep □ Physiological Shallow Fig 2,4 Physical and physiological dormancy of garlic mustard seeds over time as affected by depth of seed burial. Seeds were buried in lots of 170 seeds per fiberglass mesh packet at surface covered and 10 cm depths in soil in a Maple-Beech regrowth woods in Clark County and packets were retrieved monthly. Means are the averages of the monthly values within each year and are expressed as a percentage of the total dormant seeds recovered. LSD.os between depths = 10,3, LSD.os between seasons = 1 1 .8 , GrChmbr NatGerm U1 Fig 2.5 Germination of garlic mustard seeds buried in lots of 170 seeds per fiberglass mesh packet at the surface covered depth in soil in a Maple-Beech regrowth woods in Clark County, Means are the average of 3 replications (packets) and are expressed as a percentage of the total intact seeds recovered from the packets each month, Comparison is between those seeds that germinated in the growth chamber without scarification at 15/6®C on a 12/12 hr cycle and those seeds that germinated in the in the field and were recovered as seedlings. Vertical bars represent the standard error. LSD.os between months for growth chamber germinated seeds = 10.8. LSD.os between months for naturally germinating seeds = 20.3. •nir-Shallow -♦-D eep | Ln HfUifUEIfllill Fig 2.6 Natural germination of garlic mustard seeds buried in lots of 100 seeds per fiberglass mesh packet at surface covered and 1 0 cm depths in soil in a second- generation Oak-Hickory woods at the OARDC Badger Farm near Wooster, Ohio. Means are the average of 3 replications (packets) and are expressed as a percentage of the total seeds recovered from the packets each month. Vertical bars represent the standard error. LSD,, between depths = 18.1. go 80 ■ D eep 1 70 □Shallow 72.31 60 50 53.87 40 30 œ 2 0 18.4Q 5.47 10 0.82 2.03 0 1998 1999 2000 Season J Cumulative natural germination of garlic mustard seeds buried in lots of 1 0 0 seeds per fiberglass mesh packet at surface covered and 1 0 cm depths in soil in a second-generation Oak-Hickory woods at the OARDC Badger Farm near Wooster. Data lor each season was averaged over the months, February of the year labeled to August^ ° following year. The 1999 season average was from February through 100 p 90 - 80 - 1 70 t 60 r t 1 50 1# 1 40 1 g 30 tn 20 - VD 10 % 0 ■ 1997 m 0 Physical Deep ■ Physical Shallow ■ Physiological Deep m Physiological Shallow FiQ 2,8 Physical and physiological dormancy of garlic mustard seeds over time as affected by depth of seed burial. Seeds were buried in lots of 100 seeds per fiberglass mesh packet at surface covered and 1 0 cm depths in soil in a second- generation Oak-Hickory woods at the OARDC Badger Farm near Wooster and packets were retrieved monthly. Means are the averages of the monthly values within each year and are expressed as a percentage of the total dormant seeds recovered i GrChamber NatGerm o 40 m M ONDJFMAMJJASONDJFMAMJJASONDJFMAMJJA Fig 2.10 Percentage of recovered buried (10cm) intact seeds from ttie Clark County and Wooster sites that germinated in the growth chamber without scarification. Monthly percentages are averaged over three replications for the two sites. # " Wooster o> NJ SONDJFMAMJJASONOJFMAMJJASONOJFMAMJJA Fig 2.11 Germination of garlic mustard seeds following scarification and maintained in a growth chamber at 15/6°C on a 12/12 hr cycle for seeds buried over a 3-year interval at 10 cm in a Maple-Beech regrowth woods in Clark County and a second-generation Oak-Hickory woods at the OARDC Badger Farm near Wooster, Monthly percentages are averaged over three replications. 100 • C 90 70 I # w 1 40 o> w 1 0 0 SO 100 ISO 200 250 days Fig 2,12 Relationship of cumulative germination per season to cumulative number of days with maximum soil temperatures above and minimum soil temperatures below 1°C for two locations (Clark County and Wooster). Those data points labeled S are of surface covered seeds and are for soil temperatures at that depth. The unlabeled data points are of buried (1 0 cm) seed and are for soil temperatures at that depth. 100% □Non-Germinable □Natural germination 60% □ Growth Chamber gemiinateci ■Physically dormant ■ Physiologically dormant 60% 40% o> A 20% 8 8 Fig 2.13 Percentage of recovered seed at surface covered depth at Clark County. Classification is based on when recovered seeds germinated. Monthly percentages are averaged over three replications. 100% 80% 60% □Non>Germinable 40% □Natural germination o> en B Growth Chamber germinated 20% B Physically dormant B Physiologically dormant Fig 2.14 Percentage of recovered buried (10cm) seed at Wooster. Classification is based on when recovered seeds germinated. Monthly percentages are averaged over three replications. 100% 80% 1 60% □Non-Germlnable e 40% t P Natural germination » S s ? ? f N !5 è 8 S 8 ^ Fig 2,15 Percentage of recovered buried (10cm) seed at Clark County. Classification is based on when recovered seeds germinated. Monthly percentages are averaged over three replications. 40 y = 0.5342x-3.3057 = 0.9085 O 1 0 • ~ — 0 5 10 16 20 25 30 35 40 days Fig 2,16 Relationship of cumulative germination of buried (10cm) seed per season to cumulative number of days with minimum soil temperatures below 1 C for two locations Clark County and Wooster). REFERENCES Anderson, R.C., S.S. Dhillion, and T.M. Kelley. 1996. Aspects of the ecology of an invasive plant, garlic mustard (Alliaria petiolata] in central Illinois. Restor. Ecol. 4 (2):181-191. Ballard, L.A.T. 1958. Studies of dormancy in the seeds of subterranean clover {Trifolium subterraneum L.). Aust. J. Biol. Sci. 11:246-260. Barton, L.V. 1934. Dormancy in Tilia seeds. Contrib. Boyce Thompson Inst. 6:69-89. Baskin, C.C. and J.M.Baskin. 1988. Germination ecophysiology of herbaceous plant species in a temperate region. Amer.J.Bot. 75 (2):286-305. Baskin, C.C. and J.M.Baskin. 1998. Seeds. Ecology, biogeography, and evolution of dormancy and germination. Academic Press. San Diego. Baskin, J.M. and C.C.Baskin. 1992. Seed germination biology of the weedy biennial Alliaria petiolata. Nat. Areas J. 12(4):191-197. Bouwmeester, H.J. and C.M. Karssen. 1992. The dual role of temperature in the regulation of the seasonal changes in dormancy and germination of seeds of Polygonum persicaria L. Oecologia 90:88-94 Byers, D. 1988. Life history variation of Alliaria petiolata in a range of habitats in New Jersey. M.S. thesis. Rutgers University. Cardina, J. and D.H. Sparrow. 1997. Temporal changes in velvetleaf {Abutilon theophrasti) seed dormancy. Weed Sci. 45{l):61-66. Cavers, P.B., M.I.Heagy and R.F.Kokron. 1979. The biology of Canadian weeds. 35. Alliaria petiolata (M. Bieb.) Cavara and Grande. Can.J.PI.Sci. 59:217-229. Egley, G.H. 1986. Stimulation of weed seed germination in soil. Rev. Weed Sci. 2:67-89. 68 Egley, G.H and S.O. Duke. 1985. Physiology of weed seed dormancy and germination. In S.O.Duke (ed.) Weed physiology. Vol. 1, Reproduction and ecophysiology. CRC Press. Boca Raton, FI. pp 27-64. Evans, A.S., R.J. Mitchell, and R.J. Cabin. 1996. Morphological side effects of using gibberellic acid to induce germination: Consequences for the study of seed dormancy. Am. J. Hot. 83:543-49. Flemion, F. 1933. Physiological and chemical studies of afterripening in Rhodotypos kerrioides seeds. Contributions of the Boyce Thompson Inst. 5:143-159. Garner, J.L. and A.J. Lewis. 1980. An evaluation of techniques used for germinating goldenrain tree seeds. Am. Nurseryman 151(8):12, 36. Geneve, R.L. 1991. Seed dormancy in eastern redbud iCercis canadensis). J.Am.Soc.Hort.Sci. 116:85-88. Heit, C.E. 1967. Propagation from seed. Part 7: Germinating six hardseeded groups. Am. Nurseryman 125(12):10-45. EQyyken, Odd. 1937. Anatomie und Entwicklungsgeschichte des Samens von Alliaria officinalis Andrz. Nytt.Mag.Nat.Skadenz. 77:201-215. Lhotska, M. 1975. Notes on the ecology of germination of Alliaria petiolata. Folia Geobot. Phytotax. (Praha). 10:179-183. Meekins, J.F. and B.C.McCarthy. 1999. Competitive ability of Alliaria petiolata (garlic mustard, Brassicaceae), an invasive, nonindigenous forest herb. Int. J. Plant Sci 160(4):743-752. Murley, M.R. 1951. Seeds of the Cruciferae of Northeastern North America. Amer. Mid. Nat. 46:1-81. Nuzzo, V.A. 1992. Experimental control of garlic mustard [Alliaria petiolata (Bieb) Cavara & Grande] in northern Illinois using fire, herbicide, and cutting. Nat. Areas J. 11(3):158-167. Quick, C.R. and A.S. Quick. 1961. Germination of Ceanothus seeds. Madrono 16:23-30. 69 Roberts, H.A. and J.E.Boddrell. 1983. Seed survival and periodicity of seedling emergence in eight species of Cruciferae. Ann.Appl.Biol. 103:301-304. Staniforth, R.J. and P.B. Cavers. 1979. Field and laboratory germination responses of achenes of Polygonum lapathifolium, P. pensylvanicum and P. persicaria, Can.J.Bot. 57:877-85. Vleeshouwers, L.M., H.J.Bouwmeester, and C.M.Karssen. 1995. Redefining seed dormancy: an attempt to integrate physiology and ecology. J. Ecol. 83:1031- 1037. Zar, J.H. 1996. Biostatistical analysis. Prentice-Hall, Upper Saddle River, NJ pp 353-357. 70 CHAPTER 3 COMPETITION OF GARLIC MUSTARD WITH FOREST EPHEMERALS ABSTRACT Garlic mustard {Alliaria petiolata Bieb., Brassicaceae) is an exotic weed of the forest understory that is competing with native spring ephemerals. A. petiolata was planted into meter square plots of woodland herbs in the fall of 1997 at densities ranging from 0 to 6400 seeds m‘^ at two locations. Census of forest herbs taken during the experiment was used to calculate the Population Relative Growth Rate (PRGR) for each species. All plots were harvested in July 1999 and dry weights recorded. Impatiens capensis PRGR at the highest density of A. petiolata was significantly reduced compared to the control (-0.424 vs 0.375) at the Wooster site. There was no effect on other species. A. petiolata siliques per plant were positively correlated with plant height and A. petiolata siliques per plot were positively correlated with density per plot. 71 INTRODUCTION Garlic mustard. Alliaria petiolata (Bieb) Cavara and Grande, is an exotic weed of the forest understory that is competing with native spring ephemerals (Nuzzo. 1992). It is a strict biennial that develops a basal rosette its first year and then bolts to a flowering stalk which produces a large seed drop in its second year (Cavers, et al.. 1979). Many researchers have suggested that A. petiolata crowds out the spring ephemerals in the understory of open woods (Cavers, et al., 1979; Yost, et al., 1991; Baskin and Baskin, 1992; Nuzzo, 1993a; MacKenzie, 1995) . Nuzzo (1992) found that the cover of Dentaria laciniata (cutleaf toothwort) declined to an average of 31% when associated with A. petiolata as compared to 79% cover when not associated with A. petiolata. Those plants associated with A. petiolata were yellow, stunted, and had failed to flower. No negative impact was detected on Phlox divaricata (phlox) or Asarum canadense (wild ginger). The study involved the census of recently established populations of A. petiolata versus understory areas where there was no A. petiolata. 72 Garlic mustard introduced into a forest understory may depress the native herb population directly or affect individuals by way of decreased vegetative growth or reduced seed production that will ultimately depress its population. This depression will only affect those species that fill a similar niche or those that compete directly with garlic mustard for resources during rapid growth stages. The most rapid growth phase in garlic mustard is in early spring when rosettes are forming from seedlings. Competition in a forest understory is also affected by the seasonal growth cycles of the competing species. Three different growth cycle categories can be observed among herbaceous herbs in a forest understory (Kawano, 1985): 1) shade-intolerant species in which flowering and new vegetative growth occurs before tree canopy formation [Claytonla virginica (spring beauty) and other spring ephemerals]; 2 ) semi-shade species which come up with spring ephemerals but wait until after canopy formation before flowering ISanicala marilandlca (sanicles), Circaea qaadrisculata ^enchanter's nightshade)]; 3) shade-tolerant species which come up after canopy formation and flower before leaf drop [Eupatorlum rugosum (white snaJceroot) ] . A. petiolata has a combination of growth cycles with semi-shade 73 characteristics the first year when rosettes form after canopy formation, and shade-intolerant characteristics the second year when bolting to flower occurs before canopy closure. It follows that A. petiolata would compete with shade-intolerant and semi-shade species more than with shade-tolerant species. Meekins and McCarthy (1999) used a multiple deWit replacement design for a greenhouse study to test for competition between A. petiolata rosettes and three target species: Acer negundo L. (box elder), Quercus prinus L. (rock chestnut oak) and Impatiens capensis Meerb. (orange touch-me-not, or jewelweed). A. petiolata was a superior competitor with Quercus prinus with the total dry weight yield of Q. prinus being 34.8% lower in mixture with A. petiolata than in monoculture. The yield of A. petiolata was 21.6% higher in mixture with Q. prinus than in monoculture. In the cases of the other two species, the yield of A. petiolata was 17% to 36% lower in mixtures than in monoculture. The yield of I. capensis was 11.7% higher in mixture and the yield of A. negundo was 37% higher in mixture than the yields in monoculture of these two species. Anecdotal evidence of the decline of native populations due to competition with aliens abounds, but little experimental evidence exists (Schoener 1982, 74 Connell 1983). Experiments performed in species with substantial overlap in use of resources should show interspecific competition. Invasive species that have reportedly reduced populations of native species are Pueraria lobata (kudzu), Lonicera maackii (amur honeysuckle), Rosa multiflora (multiflora rose), Elaeagnus umbellata (autumn olive), and Lythrum salicaria (purple loosestrife) (Stuckey, 1980; Williams, 1994; Luken and Thieret, 1996). A study by McCarthy (1997) showed that the removal of A. petiolata from experimental plots resulted in release and proliferation of forest herbs, especially those species with a persistent seedbank (annuals), species with fast vegetative growth rates (vines), and species with high dispersability by wind or animal vectors (tree seeds). The effects on slow-growing spring perennial herbs was mixed with an increase in mean relative cover of 7 to 8 % the first year after removal but no difference from the initial year in mean relative cover two years after removal. Currently the only evidence of competition between A. petiolata and other species has not involved an introduction of A. petiolata into a native population where no A. petiolata existed. Therefore, a planting 75 experiment was undertaken which involved introducing A. petiolata seeds into an established native population to determine interspecific competition. 76 METHODS AND MATERIALS A competition experiment was conducted from 1997 to 1999 to determine the effect of Alliaria petiolata density on native herbaceous plants at two locations. The first site was the Ohio Agriculture Research and Development Center (OARDC) Badger Farm near Wooster with a fine-loamy, mixed, mesic Aquic Fragiudalfs soil in a second-generation Oak-Hickory section of woods free of A. petiolata infestation. The second site was the OARDC Farm near S. Charleston with a fine, mixed, mesic Aerie Ochraqualfs soil in a young regrowth Maple-Beech woods. A. petiolata seeds were harvested in July of 1997 from a private woods in Clark County, Ohio. The seeds were scattered by use of a 0 . 6 meter high, one-meter square planting bench. Seeds were planted at 7 densities (0, 200, 400, 800, 1600, 3200, and 6400 seeds m“^) over meter square plots of established woodland herbs, particularly Impatiens capensis (jewelweed), Dentaria laciniata (cutleaf toothwort), and Claytonia virginica (spring beauty). There were four replications at Wooster and three at S. Charleston. The experimental design was a Randomized Complete Block with the densities of native populations used as the criteria for the blocking of replicates. Through thinning densities of 0, 2, 4, 8 , 77 16, 32, and 64 garlic mustard rosettes were established by November of the following year (1998) at the Wooster site. Similar densities were established at the Western site, however the density of 64 rosettes m"^ plots was not established due to a lack of sites with suitable native populations. The highest density used in this experiment (64 garlic mustard rosettes m'^} was based on observations in the field, and calculations based on percent cover. The plants in each plot were identified and counted weekly during April, fortnightly during May and June, and monthly thereafter until October beginning April 1997 and ending September 1999. The native population was enumerated by counting each shoot as one plant. A. petiolata was counted in 1998 as seedlings and basal rosettes, and in the spring of 1999 as adult flowering plants. Shoots that were flowering were also noted. In July 1999, entire plots were harvested and dry weights determined for A. petiolata adult shoots, A. petiolata rosettes (from seeds that germinated in late winter 1999), and summer ephemerals. Plants were placed in paper bags and dried in an oven at 57°C for 1 week. Prior to drying, height and number of siliques were recorded for each A. petiolata adult shoot. 78 Census of forest herbs taken during the experiment were used to calculate the Population Relative Growth Rate (PRGR) for each species (Harper, 1977). The PRGR = In (l+ngg) - Ind+ngs) where nx% = the number of plants counted in the year (xx) shown. A negative PRGR indicated a decline in the population. The PRGR for each species selected was plotted against garlic mustard dry weight and garlic mustard densities including: a) fall rosettes before thinning in September 1998; b) fall rosettes after thinning in November 1998; and c) flowering adults harvested in July 1999. A Pearson correlation was conducted to determine (per plot) the correlation between the initial native plant density and the final native plant density. A paired t-test was then conducted on the correlation matrix (all pairs of within-plot data) to determine significance (i.e. if the covariate affected final density). If significant, then an analysis of covariance (Gomez and Gomez, 1984) was conducted. An F-test for homogeneity of variances was conducted to determine whether the variances of the populations before and after the introduction of the A. petiolata were equal. The test was conducted for Claytonia virginica (spring beauty), spring plants (those plants that flower in April and May), Impatiens capsensis (jewelweed), and 79 summer plants (those plants that emerge and flower later than spring plants) at Wooster. The same categories of plants for S. Charleston were used for analysis. Sanicula marilandica (black snakeroot) was analyzed separately because of its prevalence at the S. Charleston site. Due to its absence, J. capensis was not analyzed at S. Charleston. Regression techniques were used to determine the relationship of A. petiolata height per plant, siliques per plant, and siliques per plot with A. petiolata dry weight per plot. 80 RESULTS Wooster: A paired t-test showed that there was a difference (p=0.049) between the total number of spring plants of 1998 and 1999. However, an analysis of covariance (Gomez and Gomez, 1984) showed no difference among the treatment means. The paired t-test also showed a difference (p=0.0016) between the number of Impatiens capensis (jewelweed) plants in 1998 and 1999. An analysis of covariance showed a significant difference between the mean for the control (179.3) and the mean for the highest density plots (6 6 .8 ) (LSD.o5=72.8). There were no significant differences between the other treatment means. The analysis revealed no differences between 1998 and 1999 for Claytonia virginica (spring beauty) or for summer plants at Wooster. The average PRGR for Claytonia virginica showed a decline in five of the eight treatments (Fig 3.1). The average PRGR for Impatiens capensis showed a decline only in the highest density plots (Fig 3.1). Results were mixed for all other species categories. S. Charlestoni Claytonia virginica (spring beauty) was the only species that had a significant difference (p=0.00045) between the number of plants of 1998 and 1999. However, an analysis of covariance showed no 81 difference between treatment means. There were no differences between 1998 and 1999 for spring plants, summer plants, or Sanicula marilandica (black snakeroot). The average PRGR for C. virginica declined in all six treatments with the 400 seeds m*^ treatment showing the largest decline of -1.2 (Fig 3.2). The plots with highest density (3200 m ‘^) had a decline in average PRGR for Sanicula marilandica (-0.3). All other treatments had PRGRs above or near zero (Fig 3.2). Results were mixed for other species categories. Regression analysis showed no relationship between species PRGR and garlic mustard dry weight nor garlic mustard densities of fall rosettes or adult plants at either location (see Appendix D). A. petiolata density did not affect A. petiolata height (Fig 3.3 and 3.4) nor dry weight per plant at either location (data not shown). The density of forest ephemerals did not affect A. petiolata height per plant nor dry weight per plot at either location (data not shown). Regression analysis (Table 3.1) indicated that as A. petiolata dry weight per plot increased there was also an increase in total number of A. petiolata siliques per plot at both Wooster (r^ = .97, p < .001) and S. Charleston (r^ = .96, p < .001) (Fig 3.5b and 3.6b). 82 There was also an increase in total number of siliques per plot as the density per plot of A. petiolata increased (Wooster: r^ = .19, p < .001; S. Charleston: r^ = .81, p < .001) (Fig 3.5a and 3.6a). As A. petiolata plant height increased there was a corresponding increase in the number of siliques per plant (Figures 3.7 and 3.8) at both Wooster (r^ = .82, p < .001) and S. Charleston (r^ = .85, p < .001). This also applied on a per plot basis where an increase in A. petiolata average height per plant per plot corresponded with an increase in the number of siliques per plant (Fig 3.9) at both Wooster (r^ = .89, p < .001) and S. Charleston (r^ = .8 6 , p < .001). In summary, as the density and height of A. petiolata plants increased, the number of siliques per plot also increased. Harper (1977) stated that fruits per plant decline with increasing density. This was not seen in this experiment with the highest density plot (91 plants m“^) having an average of seven siliques per plant, an average higher than the majority of lower density plots (Fig 3.10). If intraspecific competition among garlic mustard plants was occurring, it was not shown in the characteristics measured in this experiment. 83 Wooster Western Total number of siliques per plot with: r~ = r^ = Total garlic mustard dry weight / plot 0.9732 0.9583 Garlic mustard density / plot 0.7934 0.8116 Number of siliques per plant with: Garlic mustard plant height 0.8230 0.8526 Garlic mustard height per plant / plot 0.8858 0.8614 Table 3.1 R values of total number of siliques and siliques per plant with characteristics of A. petiolata at Wooster and S. Charleston. Discussion: Intraspecific competition between A. petiolata and forest ephemerals was not proven in this experiment. Only one category of species showed a significant difference between the control and the highest density of A. petiolata : Impatiens capensis (jewelweed). Computation of average PRGR for J. capensis at Wooster showed an increase in population for all 84 treatments up to 3200 seeds and a decline at only the highest density level (6400 seeds m"^. Fig 3.1). This is in agreement with the results obtained by Meekins and McCarthy (1999) who reported an increase in vigor and survival of J. capensis in association with increasing densities of garlic mustard. Similar to J. capensis, Sanicula marilandica had a negative PRGR in only two of the plots (Fig 3.2). However, the decline was not statistically significant. Although the average PRGR for C. virginica had negative values at higher densities of A. petiolata at both S. Charleston and Wooster, the analysis of covariance showed no significant differences between the higher densities and the controls. At both sites the control plots on average showed a decline in C. virginica populations, an indication that environmental factors had caused an overall decline in C. virginica populations at these locations. Although care was taken to choose plots that were uniform in native plant densities, the act of choosing those plots was only one moment in time in an otherwise dynamic varying of species density over the growing season. Analysis of covariance decreased some of that experimental variability (Gomez and Gomez, 1984) but could not compensate for the changes in the forest 85 understory plots as different species grew and died during the growing season. Trimbur (1973) reported seed production of up to 38,000 seeds m"^ at high garlic mustard densities in Ohio woods. This resulted in approximately 20,000 seedlings m"^ with a seedling mortality of 41% by late spring (Trimbur, 1973). In northern Illinois rosette densities in the spring ranged from 4 to 102 m'^ and the number of adult plants reached a high of over 4500 plants m"^ (Nuzzo, 1993b). The density range for spring rosettes in this study (2-91 m“^) approximated the natural observations of Nuzzo (1993b). However, these densities were not high enough to affect ephemeral populations for the 2 year span of this study. A four-year controlled experiment that allowed reseeding and subsequent thinning of fall rosettes to targeted densities would more effectively demonstrate whether any interspecific competition between garlic mustard and native ephemerals was occurring. Also, densities of higher magnitude of A. petiolata should be used. Richard N. Mack (1985) defined invasion as an incursion of organisms into a new area. These organisms are referred to as aliens or exotics and they are assumed to be detrimental to the native species. Sometimes these invasions result in the species becoming naturalized. 86 A, petiolata has the potential to become naturalized. It competes well with native ephemerals to the possible detriment of some species (C. virginica, Dentaria laciniata) (Nuzzo, 1992). However, this study did not show conclusively that A. petiolata significantly impacted those species. The effects after two years were not evaluated and therefore further study is required. This study showed the difficulties in conducting controlled studies in a natural ecosystem. However, it may also indicate that these ecosystems were stable enough to withstand a temporary influx of garlic mustard. Natural resource managers may thus have a 'window' of time to get rid of garlic mustard before native species are affected. Further research may help determine how long that window remains open. 87 E: ::: 00 00 BCl9ytonl9 ^iglnfca Bfmpatlsns capwnsis ' 1.2 100 200 400 BOO 1600 3200 6400 # A petfo/ata seeds planted Fig 3,1. Average Population Relative Growth Rate (PRGR) over four replications from 1998 to 1999 of two forest ephemerals at Wooster at varying densities of Alliaria petiolata. Differences were not significant. Il nm Ü D, '0 .4 ■ m I 00 VO a Claytonia \riiglnlca ■ Sanicula miÿandka 400 800 1800 3200 # A. pel/o/a(« seeds planted Fig 3.2, Average Population Relative Growth Rate (PRGR) over four replications from 1998 to 1999 of two forest ephemerals at S. Charleston at varying densities of Alliaria petiolata. Differences were not significant. r!- NOTE TO USERS Page(s) not included in the original manuscript and are unavailable from the author or university. The manuscript was microfilmed as received. 90 This reproduction is the best copy available. u m t Ifc M ; £ Fig 3.3. Alliaria petiolata height per plant per plot versus A. petiolata density per plot at Wooster. Height is averaged of four replications. 15 20 25 40 gaiNe muslaftf daiHlty pw plat Fig 3.4. Alliaria petiolata height per plant per plot versus A. petiolata density per plot at S. Charleston. Height is averaged of three replications. 91 i-.- L-’ 700 y«4.9412x-4.4S72 600 1 ^ » 0.7934 400 S ^ S 200 100 20 40 SO 60 70 90 100 garlic tnustanl density p er ptot B 600 700 600 E 500 I 400 = 300 y = 11.073X +18.022 200 f^ = 0.9732 too 0 10 20 30 40 SO 7060 garlic mustard dry waigM / plot (g) Fig 3.5. Total number of Alliaria petiolata siliques per plot versus A. petiolata density per plot (A) and versus total A. petiolata dry weight per plot (B) at Wooster. 92 t e - : 140 120 100 BO y »3.577)t^ 5.8623 80 I f =0.8116 40 2 0 gailie mustard ifensitjr par plot 140 120 10O 60 y>23.5Sx>2.9988 I f =09583 gutic mustard dry wslglit/ piot(g) Fig 3.6. Total number of Alliaria petiolata siliques per plot versus A, petiolata density per plot (A) and versus total A. petiolata dry weight per plot (B) at South Charleston. 93 NOTE TO USERS Page(s) not included in the original manuscript and are unavailable from the author or university. The manuscript was microfilmed as received. 94 This reproduction is the best copy available. UMT R*» 0.8227 u> tn 30 plant heiglit (cm) Fig 3.7. Total number of Alliaria petiolata siliques per plant versus A. petiolata plant height (cm) at Wooster. s ♦ ♦ VP m ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ • ♦ ♦♦♦ ♦ • • 10 15 20 25 30 35 40 45 plant height (cm) Fig 3.8, Total number of Alliaria petiolata siliques per plant versus A, petiolata plant height (cm) at S. Charleston. 12 10 ♦W estern A W ooster I 8 I 6 I VO 4 2 0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 heiBlit/plant/plot(cm) Fig 3.9. Average number of Alliaria petiolata siliques per plant versus A. petiolata average height per plant per plot. Averages are for three replications at S.Charleston and four replications at Wooster. 12.0 10.0 I 8.0 I 6.0 \ 4.0 ID 00 2.0 0.0 —r— I ' ■ — —f I 10 20 30 40 60 60 70 80 90 100 A. petiolata density per plot Fig 3.10. Average number of siliques per plant versus density of Alliaria petiolata in plots at two locations. REFERENCES Baskin, J.M. and C.C.Baskin. 1992. Seed germination biology of the weedy biennial Alliaria petiolata. Nat. Areas J. 12(4):191-197. Cavers, P.B., M.I.Heagy and R.F.Kokron. 1979. The biology of Canadian weeds. 35. Alliaria petiolata (M. Bieb.) Cavara and Grande. Can.J.Pl.Sci. 59:217-229. Connell, J.H. 1983. On the prevalence and relative importance of interspecific competition: evidence from field experiments. Am. Nat. 122:661-696. Gomez, K.A. and A.A. Gomez. 1984. Statistical procedures for agricultural research, 2*“^ edition. John Wiley & Sons. N.Y. Harper, John L. 1977. Population biology of plants. Academic Press. London. Kawano, S. 1985. Life history characteristics of temperate woodland plants in Japan. In J. White (ed.) The population structure of vegetation. Dr.W.Junk Publishers. Dordrecht. pp515-549. Luken, J.O. and J.W. Thieret. 1996. Amur honeysuckle, its fall from grace. BioScience 46:18-24. McCarthy, B.C. 1997. Response of a forest understory community to experimental removal of an invasive nonindigenous plant (Alliaria petiolata, Brassicaceae). In J.O.Luken and J.W.Thieret (eds) Assessment and management of plant invasions. Springer-Verlag. New York. pp. 117-130. Mack, R.N. 1985. Invading plants: their potential contribution to population biology. In J. White, ed.. Studies on plant demography: a festschrift for John L. Harper. Academic Press. London, pp. 127-142. MacKenzie, S.J.B. 1995. Response of garlic mustard {Alliaria petiolata (M.Bieb) Cavara and Grande) and first year plants to cold, heat, and drought. M.S. thesis. Wright State University. 48p. 99 Meekins, J.F. and B.C.McCarthy. 1999. Competitive ability of Alliaria petiolata (garlic mustard, Brassicaceae), an invasive, nonindigenous forest herb. Int. J. Plant Sci 160(4):743-752. Moody, M.E. and R.N. Mack. 1988. Controlling the spread of plant invasions: the importance of nascent foci. J. Appl. Ecol. 25:1009-1021. Nuzzo, V.A. 1992. Garlic mustard (Alliaria petiolata [Bieb] Cavara and Grande) rate of spread and potential impact on groundlayer species. Report to the Illinois Dept, of Conservation. Native Landscapes. 17p. — . 1993a. Distribution and spread of the invasive biennial Alliaria petiolata (garlic mustard) in North America. In B.L. McKnight, ed. Biological pollution: control and impact of invasive exotic species. Indiana Acad. Sci., Indianapolis, pp. 137- 145. ------. 1993b. Natural mortality of garlic mustard (Alliaria petiolata Bieb. Cavara and Grande) rosettes. Nat.Areas J. 13:132-133. Schoener, T.W. 1982. The controversy over interspecific competition. Am. Scientist 70:586-595. Stuckey, R.L. 1980. Distributional history of Lythrum salicaria (purple loosestrife) in North America. Bartonia 47:3-20. Trimbur, T.J. 1973. An ecological life history of Alliaria officinalis, a deciduous forest "weed". M.S. Thesis. The Ohio State University. 56 pp. Williams, T. 1994. Invasion of the aliens. Audubon 96(5):24-32. Yost, S.E., S.Antenen and G.Hartvigsen. 1991. The vegetation of the Wave Hill natural area, Bronx, NY. Bull.Torrey Bot.Club 118:312-325. 100 CHAPTER 4 THE SPREAD OF GARLIC MUSTARD FROM NASCENT FOCI ABSTRACT Garlic mustard is an exotic weed of the forest understory that is competing with native spring ephemerals. It spreads rapidly through a site from low-density nascent foci that eventually merge to form a high-density population with a large front. A study was initiated in 1998 and continued through 2000 to quantify the spread of nascent foci in established wood lots. Plots were selected at three sites based on remoteness of small populations of garlic mustard rosettes. Grids were established on each plot as 0.5 meter square blocks. The area occupied by seedlings in 1999 was on average 53% to 170% greater than 1998 at the three sites. The area occupied by rosettes in 2 0 0 0 increased by an average of 161% over the first season (1998) at Wooster. The density of each plot increased by an average of 8.3% at Wooster. The number of rosettes in 2000 was an average of 301% higher than the number of rosettes in 1998 at 101 Wooster and 588% greater at Western. Rosette numbers declined by an average of 43% and the area occupied by rosettes declined by an average of 18% at Buck Creek State Park. This was attributed to lower rainfall. Approximately 30% of 1999 seedlings survived to flower in 2000. Elimination of these nascent foci should be the primary goal for controlling garlic mustard. 102 INTRODUCTION Garlic mustard, Alliaria petiolata (Bieb) Cavara and Grande, is an exotic weed of the forest understory that is competing with native spring ephemerals (Nuzzo, 1992). It occurs most often in partial or full shade, but can also grow in full sun giving it potential to become an agricultural weed. Garlic mustard has been found in Ohio in both soybeans and wheat. It is a strict biennial that produces a large seed drop in its second year (Cavers, et al., 1979). Information on the spatial distribution of weeds in crop fields can aid in predicting yields and managing weeds (Cardina, et al., 1997) as well as to aiouel the changing population of weeds within a field (Ballare, et al., 1987). In order to understand the spatial distribution of a metapopulation (the population over an entire field or forest), sampling over large spaces requires kriging to produce unbiased estimates of values at locations that were not sampled (Cardina, et al., 1997). However, in a forest situation, trees and streams and other geophysical features act as barriers to the spread and distribution of the species. The metapopulation then becomes a series of patches that may or may not join together. The dynamics within these 103 patches may be a better predictor of the dynamics within the metapopulation than the dynamics of the whole population (Hastings and Wolin, 1989). Moody and Mack (1988) observed that control of these small patches, or nascent foci, can reduce the overall spread of the population. The spread of Striga asiatica (witchweed) in the Carolines has been held in check by the diligent eradication of small, isolated foci while slowly working at the perimeter of the main population (Eplee, 1981). The typical lifecycle of garlic mustard in Ohio begins with seedling emergence during the first warm period in late February or early March. Growth is rapid as plants add 3 to 5 basal leaves before canopy cover by the trees reduces the sunlight. Little vegetative growth occurs during the summer, but growth resumes in the fall (Cavers et al., 1979, reported that 4 new leaves were added in November in Ontario, Canada). Plants overwinter as rosettes and in the spring of their second year initiate inflorescences. First flowers appear at the end of April with flowering peak by mid-May. Flowering usually ceases by the first week in June. Siliques are present by mid-May and seeds ripen until shedding begins in late June. Only 5 to 9% of the seeds produced in a given stand emerge to form rosettes 1 0 4 and of these seedlings only 2 to 4% survive to flower (Cavers et al., 1979). The greatest mortality (over 50%) occurs in May at the seedling stage followed by a slow steady rate of mortality through summer, fall, and winter. Most seedlings perish from drought since there appears to be no predation at the rosette stage (Byers and Quinn, 1987). All first year plants that survive the winter flower in the spring and then die. Ohio provides a unique geographic location to study garlic mustard. Cavers, et al.(1979) reported that seeds shed in the summer do not germinate until the second spring (18 months later) in Ontario, Canada. Baskin and Baskin (1992) found that seedlings germinated the first spring and second springs after dispersal but did not survive in competition with second year rosettes, leading to alternate year flowering at many Kentucky sites. Ohio sites have first and second year germination, but also have flowering every year at many sites. The steps in alien invasion are 1) immigration, when seeds initially infest an area; 2 ) a time when births are greater than deaths; 3) a period when range restrictions and higher densities allow deaths to equal births; and 4) emigration to new ranges in order to continue expansion (Mack, 1985). The process of invasion can be divided into arrival (step 1), establishment (steps 2 and 3), and 105 spread (step 4). With garlic mustard, arrival comes with immigration of seed into the patch. Establishment means that the patch is firmly established which for A. petxolata would mean an alternate year flush of seedlings followed by a year of few seedlings until the seed pool in the low years builds up. Because it is a biennial, spread in A, peticlata does not become discernable until the population has firmly established a pattern of consistent recovery. When the dynamics of expansion and contraction at the edge of the population no longer overlap the focus point, a pool will develop from which spread can occur without the threat of extinction (Williamson and Brown, 1986). In Illinois, Nuzzo (1992) found that coverage of established A. petxolata populations doubles every 4 years on average when given adequate room for expansion. Nuzzo (1992) measured the advancing fronts of large populations in seven northern Illinois woods and found the greatest increases on sites with large-scale (flooding, windstorms) disturbances (241% to 1000% increases). Mack (1985) proposed that a single focus with a large front spreads slower than several nascent foci with smaller fronts. A possible invasion strategy for A. petxolata is that it initially spreads rapidly through a 106 site at low density and then establishes higher density populations (Nuzzo, 1993a). A study was undertaken in 1998 to 1) quantify the external expansion of remote patches of A. petiolata, and 2 ) quantify increases in the internal density of those patches. 1 0 7 METHODS AND MATERIALS To quantify the spread of small isolated populations of garlic mustard, a study was initiated in 1998 in woods at three different locations in Ohio: Buck Creek State Park near Springfield, the OARDC Badger Farm in Wooster, and the OARDC Western Branch in Clark County. The Buck Creek site and the Wooster site are both second- generation Oak-Hickory forests. The Western site is a young regrowth Maple/Beech forest. Three plots were established at the Buck Creek and Wooster sites. Only one plot was established at the Western site. Plots were selected based on rosette populations in March of 1998. Criteria for selection of plots were isolation, general size of the area occupied, and hardiness of the rosette population with isolation being the main criteria. Plots selected were at least 100 ft. distant from another population of garlic mustard and occupied an area less than 10 m^. Rosettes in the area were judged hardy if they had more than three rosette leaves larger than 3 cm in diameter. Grids of 0.5 meter square were established using a form made of PVC pipe which was 0.5 meter in length on each side and plot stakes and flags. Since remote populations tend to establish at the base of trees, the 108 grids were started at the base of the largest tree in the plot. Spatial distribution maps were created on an X,Y coordinate plane using the center point of each square. Census of garlic mustard adults and seedlings per square were taken May and June of 1998 and 1999 and in March and April of 2000. Additionally, percent ground cover of garlic mustard seedlings and adults and all plants in each square was recorded in May of 1998 and 1999. In the fall of 1999 a census of garlic mustard rosettes was taken and percent cover of garlic mustard per square determined by approximation. Spatial distribution maps of each year were created for both garlic mustard adults and seedlings. Densities were highlighted using a gray scale with highest densities at 80% gray and lowest densities at 1 0 % gray. Blocks fully occupied by trees were blackened. Rosettes per block, seedlings per block, percent survival, and percent increases were calculated. Regression analysis was performed to determine the effect of 1998 rosettes on 1999 seedlings and 2000 rosettes. Regression analysis was also used to plot 2000 rosette area against 1998 rosette area. 109 RESULTS AND DISCUSSION Claytonia virginlcsr Dentaria laciniata, Galium aparine, Osmorhiza longistylisr Podophyllum pel ta turn, Partheoncissus quinquefolia, and Rhus radicans characterized the understory herbaceous species at the Wooster and Buck Creek sites. In addition at Wooster were found Circaea quadrisculatar Hydrophyllum virginianum, and Impatiens capensis. The Western site was characterized by later ephemerals and perennials such as C. quadrisculatar Eupatorium rugosum, Geum canadense, O. longistyliSr P. quinquefolia^ Polemonium reptansr R. radicansr Sanicula marilandicBr and Tovara virginiana. In addition Cardamine bulbosar Cardamine douglassiir and C. virginica were seen in the spring {Appendix C). The natural progression of garlic mustard during the 3 years of this experiment was: 1) rosettes which bolted to flowering in the spring of 1998, 2) seedlings in the spring of 1999, and 3) flowering rosettes once again in the spring of 2000. The converse progression was also occurring with seedlings in 1998, rosettes in 1999, and seedlings again in 2000. Seedlings in the lag year of 2 0 0 0 were not shown because data for that year was still being processed. The existence of a converse progression is in contrast to the results reported by Baskin and 110 Baskin (1992) who found that seedlings that emerged the second year after dispersal did not survive in competition with second year rosettes. They observed that garlic mustard populations flower only in alternate years at many Kentucky sites. In this study, rosettes were seen in the same block in 1999 as in 1998, regardless of the density of rosettes in 1998, but not at the same levels. However, the plots were selected based on number of rosettes present in the spring of 1998. For this reason, and because the seedling population was low in 1998, the results discussed will center on the first progression: rosettes, seedlings, rosettes. Both progressions are shown in Fig. 4.1. The converse progression for all other sites is not shown because the seedling and rosette populations were very small and did not affect the leading edge of the populations being studied. Wooster plot #1 had the greatest number of initial rosettes (452) and the greatest number of seedlings counted (3909) during the experiment (Table 4.1) . It also had the largest area with 9.2 in 1998 and 19.5 m^ in 2000. Overall, Wooster plots averaged 9.39 rosettes per 0.5 meter square block in 1998 and 10.24 rosettes per block in 2000 (data not shown). The number of rosettes per plot increased by an average of 164% and represented 111 an average increase of 161% in total area occupied from 1998 to 2000. The area covered by seedlings in 1999 increased by an average of 170% over the rosette area of 1998. Summer drought and winter kill reduced that area by an average of 7% by the spring of 2000 at the three Wooster plots. Buck Creek plot #3 had the largest number of rosettes in 1998 (34) and 2000 (24) but plot #2 had the largest number of seedlings in 1999 (1,499) (Table 4.1). The area covered by rosettes was fairly equal over the three plots in 1998 but showed an average decrease of 18% by the year 2000, and parallels the decrease of 43% in the number of rosettes between 1998 and 2000. This was in spite of an increase in area from 1998 rosettes to 1999 seedlings of 10.5 m^ per plot (148%). It again reflects the drought of 1999 as only 1.7% of the seedlings on average survived as rosettes to the following spring at the Buck Creek site. This contrasts with the Wooster site where 26.9% of the seedlings survived to rosettes in 2000. The difference between the two sites may be attributed to summer rain at Wooster. There was one plot at the Western branch of the OARDC and it displayed an increase of 53% in area and 588% in the number of rosettes between 1998 and 2000 (Table 4.1). The number of seedlings per rosettes was greatest at Buck 112 Creek (average of 36.5), and the average number of seedlings per block was greatest at Wooster (40.3) (data not shown). Wooster plot #4 was unique among all plots in that it consisted of only one rosette and one seedling near a tree in 1998. The rosette had 8 flowering stalks in 1998 and produced 244 seedlings in 1999 of which 91 survived to flower in 2000 (Table 4.1). The area occupied by garlic mustard in this plot rose from 0.25 m^ to 3.6 m^ in three years, a 1340% increase (Fig. 4.2). The #2 plot at Wooster showed an increase in the number of rosettes per block in 33 of the 35 blocks. However, the two blocks with the highest density of 1998 rosettes showed a decrease. The same was true for the ft3 plot at Wooster where 8 of 9 blocks showed an increase but the highest density 1998 block showed a decrease in the number of rosettes (Fig. 4.2). There was a decrease in 11 of the 6 8 blocks at the #1 plot at Wooster. Ten of those blocks had initial 1998 densities greater than 15 rosettes per block (Fig. 4.1). Rosette densities greater than 15 resulted in high seedling densities the following spring, which caused increased intraspecific competition leading to a decrease in the number of rosettes the following year (data not shown). This pattern was seen at all Wooster plots. 1 13 A moderate slope characterized the Buck Creek site. The resulting maps show a trend for higher seedling densities downslope of the previous year's rosettes (Fig. 4.3). The summer drought of 1998 caused a large seedling kill and a subsequent average decline of 43% in the number of rosettes in 2000 (Table 4.1). Since the three Buck Creek plots were of similar size and density, the Buck Creek data was averaged and considered one plot in relation to the other plots for purposes of regression. A linear relationship (r^ = 0.68, p = 0.04) resulted from regressing 1998 seedlings (log 10 values) on 1998 rosettes (log 10) (Fig 4.5). Plotting 2000 rosettes against 1998 rosettes resulted in a linear relationship (r^ = 0.70, p = 0.08) (Fig 4.6). When comparing rosette area (m^) of 2000 with 1998, a strong linear relationship was seen at Wooster (r^ = 0..98, p = 0.0009) (Fig 4.7). When the Western site and Buck Creek sites were included, the relationship was very weak (r^ = 0.59, p = 0.08 (Fig 4.8). Since the Buck Creek site was experienced a drought in the summer and fall of 1999, the seedling area of 1999 was a better indicator of area expansion. There was a strong linear relationship between 1999 seedling area and 1998 rosette area (r^ 0.91, p = 0.02) with all but Western doubling in size from 1998 to 1999 (Fig 4.9). Thus, doubling of the 114 area of nascent foci occurs every two years instead of every four years as reported for larger population foci (Nuzzo, 1992). In summary, nascent foci can experience great increases in both the number of rosettes arising from the previous cycle (up to 1 1 2 rosettes from 1 single rosette) and in the area occupied (from a 2 to 4-fold increase). In addition, unless drought induced mortality is high, rosettes per square meter increase until garlic mustard begins to compete with itself at an environmental capacity determined by water and nutrient availability and crowding. Higher rosette densities lead to increased numbers of seedlings and further expansion of the population. Barring any barriers (i.e., streams, downed trees), the nascent foci can expand linearly until they meet and form a large population that appears as a mass on the forest floor. Natural resource managers would make best use of limited resources by concentrating on preserving areas with few garlic mustard plants. Suppression of these nascent foci that can expand on all sides very rapidly is a higher priority than trying to hold back a single, wide front from a large population (Eplee, 1981; Moody and Mack, 1988). 1 15 rosette increase 1898 1999 2000 % Area (m*) area % increase 1998->2000 Wooster rosettes sdlnos rosettes survival 1998 1999 2000>98 .>'99 '99 *>'00number area #1 452 3909 923 23.6% 9,2 19,8 19,5 115% -2% 104% 112% #2 66 923 338 36,6% 3 9,6 8,9 220% -7% 412% 197% #3 8 93 39 41.9% 1,2 3,3 3.3 175% 0% 388% 175% #4 1 244 91 37,3% 0.25 3,6 3,6 1340% 0% 9000% 1340% ave; 132 1292 348 34,9% 3,4 9.1 8,8 170% -2% 301% 161% Western " - # 1 ■ 24 473 165 34,9% 1 4,3 6.6 6.6 53% 0% 588% 53% 1 M H Buck Cree ( #1 30 965 20 2,1% 8,2 18,7 6,5 126% -71% -33% -33% #2 31 1499 10 0,7% 7,6 20.6 2,6 171% .87% -68% ■66% #3 34 989 24 2,4% 5,5 13,5 7,9 145% -41% -29% 44% ave: 32 1151 18 1,7% 7,1 17,6 5,3 148% -66% ■43% -18% Table 4,1, Results of a three-year study of isolated populations of Alliaria petiolata at three locations. WOOSTER n SITE 1998 Rosettes 1998Î 1 2 2 5 2 1 S 1 4 r 3 ® 2 3 5 8 3 1 2 3 2 1898Seedhgs 1999 Rosettes 1 2 2 4 1 4 3 2 1 2 2000 Rosettes Rosettes tree 4 0 * 3 0 - 3 9 200 - 299 2 0 - 2 9 100-199 1 0-19 4 0 - 9 9 1 - 9 Fig 4.1. Spatial distribution maps of Wooster plot #1 from 1998 to 2000 using a gray scale. 117 W008TERB2 1868Roset(0s leWSwdkig» ZOOORowttes i B'.: • B WOOSTER «3 1098Ros»ttes ISSBSeeilnos 2000 Rosettes Rt»ettes 8 7 1 9 8 18 1 9 9 1 8 2 30.38 1 4 8 2 2 4 20.28 H 9 $ 8 10.18 00 WOOSTER #4 18BB Rosettes 1888 SeeiMngs 2000 Rosettes 75.88 50.74 20.48 Fig 4.2. Spatial distribution maps of Wooster plots 2, 3, and 4 from 1998 to 2000 using a gray scale. , BUCK CREEK STATE PARK » 1 199B Rosettes 1889Seedings W 10 2000 Rosettes 0 « 10 8 * 10 10 10 1 8 1 4 14 1 1 ■ a 14 10 0 0 10 10 0 4 U> BUCK CREEK STATE PARK « 3 Slope Rosettes 1090 Rosettes 1999 See dings 2000 Rosettes 10 10 11 4 30.38 » 1 10 0 10 20-29 3 S 10 0 10-18 : K 9 1 9 8 : 9 1 1 10 14 SeedHnos 1 3 18 17 10 3 8 60-79 40-59 20-39 Fig 4,3. Spatial distribution maps of Buck Creek Park plots l and 3 from i s s a ' to 2000 using a gray scale, S t BUCK CREEK STATE PARK # 2 1898 Rosettm 1999 Seedmgs 2000 Rosettes a « t 1 11 19 10 11 1» I » 9 2 1 8 9 1 2 :8 slope ■a- 1 .'a: 1 1 tsj O Rosettes WESTERN BRANCH OARDC # 1 30-39 20-29 1988 Rosettes IsgeSeetUngs 2000 Rosettes 10-19 Seedlings 1 8 8 1 19 IP 18 9 60-79 40-59 20-39 F.iq 4,4, Spatial distribution maps of Buck Creek Park plot #2 and Western from 1998 to 2000 using a gray scale. ^Wooster il 3.5 Buck Cteefc Ave A Wooster 12 ^Western H y =0.6244%+ 2.0531 N) R* = 0.6831 M 0 0.5 1 1.5 2 2.6 3 1998 rosettes (loglO) per 10 sq.m. Fig 4.5. 1999 seedlings (log 10 values) vs. 1998 rosettes (log 10) per 10 sq.m. for all locations. R* = 0.68, p = 0.04. 3 . 6 1 Wooster eI T* W ooster#, I 2.5 o* 9 Western M N) g NJ (M W ooster# y = 0.443SX + 1.6528 1.5 R* = 0.7001 0 0.5 1 1.5 2 2.5 3 1998 rosettes (loglO) per 10 sq.ro. Fig 4.6. Relationship between 2000 rosettes (log 10 value) and 1998 rosettes (log 10 value) per 10 sq.m. at Wooster and Western. R' = 0.70. p = 0.08. ' 1 ■ I"" 21.0 18.0 15.0 i I 12.0 y =1.8836x + 2.4655 Ig 9.0 R*«= 0.9817 NI NiH» 6.0 W 3.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 1998 rosette area (m ) Fig 4.7, Relationship between 2000 rosette area (mM and 1998 rosette area at Wooster (r* = 0.98. p = 0.009). 21.0 Wooster #1 1 1 8 . 0 y s 1.3456X + 2.2544 15.0 R* = 0.5867 I I I H Western N> 6.0 4k m Buck Creek Wooster #4 Wooster *3 0.0 0.0 1.0 2.0 3 . 0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 1998 rosette area (m') Fig 4.8. Relationship between 2000 rosette area (mf) and 1998 rosette area at all locations. R* = 0.59, p = 0.08. 21.0 1 8 , 0 Buck Creek 1 5 . 0 S I 12.0 f y = 1.9606X +1.098 1 «° R* = 0 . 9 0 8 4 M NJ I H Western CJ» 6.0 Wooster #4 3.0 Wooster #3 0.0 0.0 1.0 2.0 3 . 0 4 , 0 5 . 0 6.0 7 . 08.0 9 . 0 10.0 1998 rosette airea (m^) Fig 4.9, Relationship between 1998 seedling area (mf) and 1998 rosette area at all locations. R' = 0.91, p = 0.02). REFERENCES Ballare, C.L., A.L.Scopel, C.M.Ghersa, and R.A.Sanchez. 1987. The population ecology of Datura ferox in soybean crops. A simulation approach incorporating seed dispersal. Agric. Ecosyst. Environ. 19:177-188. Baskin, J.M. and C.C.Baskin. 1992. Seed germination biology of the weedy biennial Alliaria petiolata. Nat. Areas J. 12(4):191-197. Byers, D.L. and J.A.Quinn. 1987. The effect of habitat variation in Alliaria petiolata on life history characteristics. Amer. J. Bot. 74:647. (Abstract). Cardina, J., G.A.Johnson, and D.H.Sparrow. 1997. The nature and consequence of weed spatial distribution. W.Sci. 45:364-373 Cavers, P.B., M.I.Heagy and R.F.Kokron. 1979. The biology of Canadian weeds. 35. Alliaria petiolata (M. Bieb.) Cavara and Grande. Can.J.Pl.Sci. 59:217-229. Eplee, R.E. 1981. Striga's status as a plant parasite in the United States. Plant Dis. 65:951-954. Mack, R.N. 1985. Invading plants: their potential contribution to population biology. In J. White, ed.. Studies on plant demography: a festschrift for John L. Harper. Academic Press. London, pp. 127-142. Moody, M.E. and R.N. Mack. 1988. Controlling the spread of plant invasions: the importance of nascent foci. J. Appl. Ecol. 25:1009-1021.Moseley, E.L. 1899. Sandusky flora. Ohio State Academy of Science, special papers No.l. p 92. Nuzzo, V.A. 1992. Garlic mustard {Alliaria petiolata [Bieb] Cavara and Grande) rate of spread and potential impact on groundlayer species. Report to the Illinois Dept, of Conservation. Native Landscapes. 17p. — . 1993a. Distribution and spread of the invasive biennial Alliaria petiolata (garlic mustard) in North America. In B.L. McKhight, ed. Biological pollution: control and impact of invasive exotic species. Indiana Acad. Sci., Indianapolis, pp. 137- 145. 126 ------. 1993b. Current and historic distribution of garlic mustard {Alliaria petiolata) in Illinois. Mich. Bot. 32:23-33. Trimbur, T.J. 1973. An ecological life history of Alliaria officinalis^ a deciduous forest "weed". M.S. Thesis. The Ohio State University. 56 pp. Williamson, M.H. and K.C.Brown. The analysis and modeling of British invasions. Phil. Trans. R. Soc. Lond. B 314:505-522. 127 SUMMARY The typical lifecycle of Alliaria petiolata in Ohio begins with seedling emergence during the first warm period in late February or early March. Growth is rapid as plants add 3 to 5 basal leaves before tree canopy cover reduces the sunlight. Little vegetative growth occurs during the summer, but growth resumes in the fall. Plants overwinter as rosettes and in the spring of their second year initiate inflorescences. First flowers appear at the end of April with flowering peak by mid- May. Flowering usually ceases by the first week in June. Siliques are present by mid-May and seeds ripen until shedding begins in late June. As seeds mature, they appear to move through stages of non-dormancy, physical dormancy, and then into physiological dormancy (see Appendix I). All seeds are physiologically dormant by June and remain dormant until December. A period of freeze and thaw appears to be necessary to move the seeds from physiological dormancy to physical dormancy to non-dormant, although constant cold temperatures for 3-6 months will also lead to 128 germination (Baskin and Baskin, 1992, Meekins and McCarthy, 1999). By January, seeds are non-dormant but cold temperatures prevent germination. This was reflected in the peaks observed in seeds that germinated in the growth chamber prior to nicking (Fig 2.5). When warmer temperatures arrive in February, germination begins and continues into early March (again see Fig 2.5). By April seeds that have not germinated have moved from physical dormancy to physiological dormancy (secondary dormancy) (Fig 2.4) although a small percentage remain only physically dormant (Fig 2.11). A few seeds remain non- dormant but do not germinate due to a lack of ideal conditions (Fig 2.10). The cycle then repeats itself the following winter and spring. By the third spring nearly all shallowly buried seeds have germinated (94%, Fig 2.3). A logical conclusion would be that any remaining seeds will have germinated by the fourth spring, although this study did not go that far. The above theoretical discussion of one generation of seed is represented in figure 5.1. From the results of this study it is likely that a cohort of seed that remained near the soil surface would be depleted by the fourth spring after dispersal. However, the same would not be true of seed that has become buried due to the 129 actions of insects, rodents, and physical disturbances to the soil surface. With viability over 95% and seeds with physiological dormancy of over 50%, a seedbank could exist for a longer period than 4 years (Fig 2.14 and 2.15). An interesting facet of the seedbank study was the increasing percentage of seed that were only physically dormant among the deeply buried seed (Fig 2.4). When the percentages were based on the total number of dormant seeds, the portion that was physically dormant was the same at both depths. Deeply buried seed appear to be following the same progression as the surface covered seed but at a much slower pace due to limited germination of buried seed (caused by a lack of temperature fluctuation?). If freeze-thaw cycles enhance the germinability of A. petiolata (Baskin and Baskin, 1992), then the deeply buried seed may not be receiving such enhancement. Data (not shown) from soil recorders indicate that by December 15 soil temperatures fluctuate little from a constant cold temperature. Since A. petiolata will germinate under constant cold temperatures, then an accumulation of cold units may slowly break down physiological dormancy in natural situations. This would account for the increase in seeds with only physical dormancy. A longer term buried seed experiment may address this question. 130 Fig 5.2 shows a shallow seedbank that is refreshed with new seed from adult plants of the same cohort as the original seed. Because of the biennial lifecycle of A. petiolata^ new seed is initially only added in alternate years. Thus the seedbank would drop to nearly 15% before new seed would increase the dormant portion to nearly 99% of all seed. As the population matures, additional inputs of fresh seed would be added in the years of few adult plants, and eventually a continuous cycle of seed inputs would occur (Fig 5.3). Since it requires four years to fully deplete the seedbank (Fig 5.1) a mature population would require removal of all A. petiolata plants in the population for four continuous years to effectively control that population. Additional removals would have to occur in the next two years to remove any plants coming from deeply buried seed that had reached the soil surface due to disturbance. Natural resource managers would make best use of their limited resources by concentrating on preserving areas with few A. petiolata plants. Suppression of these nascent foci must be of prime concern in order to control this invasive. Since cutting or pulling is the preferred method of control of small populations (Nuzzo, 1991), the timing of control is important. Plants pulled as early as May 10^ and left on the ground can produce viable seed 131 (Appendix A). Therefore resource managers should remove all pulled plants to a disposal site or place them in trash bags for disposal. The usual pattern for invasion of exotic plants parallels that of diseases; a slow initial spread, a phase of rapid expansion, and then a slowing to a stable population. The spread and expansion phases usually exhibit logistics growth, which is described as a J curve. If the spread comes from only one focus, then the initial lag time is shortened because more area can be covered before the population ranges join (Moody and Mack, 1988; Mack, 1985). This helps explain why the control of aliens is ineffective: unless total eradication is achieved, the remnant populations become the foci for reinvasion. In fact, the reinvasion will proceed faster than an initial invasion of one or two foci (Mack, 1985) because more than two foci now exist. The mapping study demonstrates how quickly a small population can increase in area and density. One well- placed plant in a sunny location with adequate moisture at the base of a tree through a process called stemflow (Crozier and Boerner, 1984) increased its range by 1340% and increased its density by 9000% in just one generation (Table 4.1). Even a large nascent focus of 452 rosettes covering 9.2 m^ doubled its range and density in one 132 generation (Table 4.1). This can potentially have devastating effects on slow growing spring ephemerals that regenerate from tubers and corms [Claytonia virginica and Dentaria laminate) by crowding them out. The area of dispersal of garlic mustard contributes to its rapid increase in density at a site. An average of 60% of seeds fell within the elliptical cone formed by the branches and 96% of seeds fell within the shadow of the cone created by the height of the first branch (Appendix B). Since wind dispersal is nearly non-existent due to the weight of the seed (Cavers et al., 1979) garlic mustard seedlings come up in close proximity to the mother shoot. In those situations where garlic mustard plants fall over, 8 8 % of the seed fall within the height of the first branch and the top of the plant (Appendix B). While this concentrates seedlings around the fallen skeleton, at an average height of 1.2 to 1.5 m (4 to 5 ft) (Cavers et al., 1979), the range of garlic mustard can also increase. Although this study did not show that A. petiolata has detrimental effects on native populations, it did show that higher densities can adversely affect both seed reproducing species (Impatiens capensis) and rhizomatous perennial species (Sanicula marilandica) (Fig 3.1 and 3.2). Therefore, control of A. petiolata is essential in 133 order to preserve species diversity in our native forests. Finally, A. petiolata is highly plastic. It will tolerate sunny locations and has been described as a nitrophile (Passarge (1976) as cited in Cavers et al., 1979). It does well in high nitrogen areas exhibiting large, dark green, robust rosettes in such environments. Its potential as an agricultural weed is suppressed by its biennial lifecycle and the lateness of its flowering shoots. However, in a no-till environment with delayed or incomplete control, A. petiolata could become a problem. It has been observed creeping out into a soybean field from the edge of a woods and in a bare spot of a wheat field at least 250 yards from the nearest woods (personal observation). Its adherence to hooves and boots allow it to reach uninfested areas. And as was shown earlier, one plant can quickly become a small population. 134 □Germinated Non-Dormant ■ Physically dormant D Physiologically dormant c8 w cn months Fig 5.1. Representation of the fate of one generation of Alliaria petiolata seed over four years. 100% 6 0 % 60% B î 4 0 % w cr» □Germinated 20% B Non-Dormant ■Physically dormant o%l E Physiologically dormant B L , — ,— ,— ,— ,— ,— .— . . . Illillllllllllllllll month» Fig 5.2. Representation of the fate of Alliaria petiolata seed at one location with seed inputs In alternate years. 100% 8 0 % g 6 0 % c 4 0 % w 20% □Germinated ■Non-Dormant ■Physically dormant ■Physiologically dormant illlll Months - cycle year Fig 5,3. Representation of the fate of Alliaria petiolata seed of a mature population at one location with seed inputs every year. APPENDIX A SEED SURVIVAL FROM PULLED GARLIC MUSTARD PLANTS Pulled garlic mustard plants show an ability to produce seed if the root is sufficiently intact to absorb moisture or if the pod is developed enough to mature on the ground. To test for this ability, 10 flowering plants were harvested from a sunny location for 8 weeks beginning May 10*\ 1999. The plants were pulled with roots intact and placed on secured brown wrapping paper on the ground in a shaded site until desiccation. The seeds were then collected and tested for germinability by using protocols described in Chapter 2 with 1Q‘^M GAa and for viability by using lOT^M TZ at room temperature for 24 hrs. Only 5 seeds were recovered from plants harvested on May 10^. All were viable and physiologically dormant. Of the 59 seeds recovered from plants harvested May 17^, 31 were viable (53%), 3 were non-dormant (germinated prior to nicking), and 15 (48%) were only physically dormant. Of the 691 seeds harvested May 24**, 6 8 % of the tested seeds were viable, and 22.5% of those were physically dormant. Of the seeds harvested 138 on May 31“^, 99% were viable and only 16.5% were physically dormant. Of the seeds harvested in June, 99 to 1 0 0 % were viable and all were physiologically dormant. Ave of 10 plants # seeds #non- dormancy % germ #% Date ht (cm) #pods total tested dormnt physical physiol in GA3 viable viable 10-May 84 5.3 5 5 0 0 5 0 5 100% 17-May 94 16.0 59 59 3 16 13 57% 31 53% 24-May 92 31.1 691 200 0 45 90 71% 135 68% 31-May 122 52.2 2036 200 0 33 165 96% 198 99% 7-Jun 112 65.3 8958 200 0 0 194 61% 194 97% 14-Jun 120 58.4 9000 200 0 1 198 49% 199 100% 21-Jun 128 75.3 10424 200 0 0 200 72% 200 100% 28-Jun 122 70.3 9340 200 0 0 200 86% 200 100% 139 APPENDIX B DISPERSION OF ALLIARIA PETIOLATA SEEDS A study was conducted in 1999 in which harvested Alliaria petiolata plants were tested for seed dispersal. Seven mature plants were carefully harvested by cutting the stalk near ground level. Each plant was measured for overall height and height from the base to the first branch. The widest diameter of the plant was noted as was the perpendicular diameter. Using the diameters and the height of the vegetative portion of the plant, an elliptical cone was plotted. Using trigonometric principles, the elliptical shadow of the cone was also plotted. The plant was then placed in the center of the drawn ellipse on a poster board and flicked with a finger 10 times causing seed drop to occur. After seed drop, the plant was shaken vigorously in a paper sack and the remaining seed collected and counted. An average of 39 +/- 9% of seeds dropped during flicking. An average of 60 +/- 8 % of the seeds fell within the elliptical cone formed by the branches. An average of 96 +/- 2% of the seeds fell within the shadow of the cone created by the height of the first branch. 140 A second study was conducted in 1999 in which harvested A. petiolata plants were allowed to fall and the dispersal of the oeeds recorded. In this study seven mature A. petiolata plants were harvested as before and heights and diameters were recorded as above. A center line was drawn as were longitudinal lines every 5“ on either side. Arcs were then constructed at 15 cm distances from the end point. The plant was placed on the end point and forcibly pushed onto the center line to mimic wind or disturbance. The plants were then shaken into a paper bag as above and seeds were retrieved and counted. An average of 45 +/- 5% of seeds fell upon hitting the surface. An average of 8 8 +/- 2% of seeds fell between the height of the first branch and the top of the plant. Nearly all seeds (98%) fell within 30 cm of the upper tip of the plant and 30“ either side of the fall line. The farthest recorded distance from the fall line was 43“ i &ét^âJCét 1 1 1 /i--= 141 APPENDIX C SPECIES SEEN Listed are herbaceous species observed in woods at either Buck Creek State Park (1). OÀRDC Badger Farm in Wooster (2), or Western Branch O A R D C (3). Scientific Name Common Name Anemonella thalictroides Rue anemone(2) Àrisaema triphyllum Jack-in-the-pulpit ( 2) Cardamine bulbosa Spring cress(3) Cardamine douglassii Purple cress(3) Circaea quadrisculata Enchanter * s nightshade(2.3) Claytonia virginica Spring beauty(1.2.3) I^ntaria Jaciniata Cutleaf toothwort(l.2) Eupa tori urn rugosum White snakeroot(3) G a l i u m a p a r i n e Cleavers(1.2.3) Geum canad&nse White avens(3) HydrophylJum virginianum Virginia waterleaf(2) Impatiens capensis Jewelweed(2) Lamium purpureum Red deadnettle(3) Osmorhiza longistylis Aniseroot(l.3) Partheoncissus quinquefolia Virginia creeper(1.2.3) Podophyllum peltatum Mayapple(1.2) Polemonium rep tans Jacob's ladder(3) Polygons tum biflorum True Solomon's seal(2) Panunculus arborti vus SmaIlflower crow foot(3) Shus radicans Poison ivy(1.2.3) Sanicula marilandica Black snakeroot(3) Smilacina racemosa False Solomon's seal(2) Tovara virginiana Virginia knotweed(2.3) Viola s p p . Violet(2.3) 142 APPENDIX D REGRESSION GRAPHS Following are regression graphs of native plants PRGR with garlic mustard dry weight and garlic mustard densities at two locations: Wooster OARDC Ely farm and Western OARDC at S. Charleston. Densities used were 1998 fall rosettes before thinning. 1998 fall rosettes after thinning, and harvested adult plants. The after thinning densities were not used for Western data because rosette populations were not thinned due to low numbers. 143 Spring plants PRGR based on # garlic mustard plants at Western •Fall rosettes t A e ▲Harvested adults 1 1 1 * : " H* 20 26 # GM plants Spring plants PRGR based on total garlic mustard dry weight in July 1999 at Western 0 . 5 o> s -0.6 0 1 2 3 4 5 6 7 8 GM dry weight (shoot * seed) (g) Spring plants PRGR based on # garlic mustard rosettes In Sept 1998 before thinning at Wooster 1.5 R* a 0.0674 0.5 § e M 0.0 a\ T*I L -1.0 -1.5 50 100 150 200 250 300 350 # GM rosettes before thinning Spring plants PRGR based on # garlic mustard rosettes in Nov 1998 after thinning at Wooster 0.5 e % 0.0 T- ■0.5 -1.0 -1.5 4- 0 20 40 60 100 120 14080 # GM rosettes after thinning Spring plants PRGR basset on # garlic musfaitl plants harvested at Wooster R‘ = 0.0825 8 •f» CO I 40 SO 60 # GM plants harvested Spring plants PRGR based on total garlic mustard dry weight In July 1999 at Wooster 1.6 0.5 9 VO 0.0 -0.5 0 10 20 30 4050 60 70 60 G M dry wieght (shoot + seed) (g) Jewelweed PRGR based on # garlic mustard rosettes in Sept 1998 before thinning at Wooster 2.0 1.5 ▲ ► ♦ ♦ R' = 0.158 1.0 A. ♦ ♦ ê 05 r H* Ü 1 O 1 ♦ ♦ ♦ g 00 A . . 2 -0.5 -1.0 ♦ 50 100 150 200 250 300 350 # GM rosettes before thinning m m Jewelweed PRGR based on # garlic mustard rosettes in Nov 1998 after thinning at Wooster 2.0 1,5 0.5 t-* Ü 1 5 0.0 £ -0.5 R-* = 0.0721 -1.0 -1.5 0 20 40 60 80 100 120 140 # GM rosettes after thinning i , ! Jit' Jewelweed PRGR based on # garlic mustard plants harvested at Wooster 2.0 1.0 g 0.5 M Ü 1 N) I g 00 g -0,5 -1.0 0 10 20 30 40 SO 60 70 80 90 100 # GM plants harvested Jewelweed PRGR based on total garlic mustard dry weight in July 1999 at Wooster 2.0 I t* e 0 , 5 M U 1 W IT" S »o E - 0 . 5 = 0 . 0 0 4 7 -1.0 - 1 . 5 0 10 20 3 0 4 0 5 0 60 70 80 GM dry wieght (shoot * seed) (g) Summer plants PRGR based on # garlic mustard rosettes in Sept 1998 before thinning at Wooster 1.0 0.5 sV s M Ul 0,0 4k Îf f -0.5 ■ 1.0 0 50 100 150 200 250 300 350 # GM rosettes trefore thinning Summer plants PRGR based on # garlic mustard rosettes in Nov 1998 after thinning at Wooster 1.5 r 2 « 0.0097 I 0.5 e in i 0.0 in y -0.5 ^ -1.0 J 0 20 40 60 80 100 120 140 # GM rosette» after thinning i: Summer plants PRGR based on # garlic mustard plants harvested at Wooster 1.5 ♦ ♦ 1.0 ♦ ♦ ♦ R* = 0.001 0.6 ♦ ♦ 9 r ♦ in m K ♦ I ♦ ♦ -0.5 ♦ ♦ -1.0 o ♦ -1.5 10 20 30 40 50 60 70 80 90 100 # GM plants harvested I'-: Summer plants PRGR based on total garlic mustard dry weight in July 1999 at Wooster 1.6 ♦ ♦ ♦ 1.0 ♦ r 2 = 0.0038 0 . 5 ♦ ______a L i t H U 1 & 0.0 r * ♦ f ♦ ' 0.6 ♦ ♦ ' 1.0 (► ♦ --7 - 0 10 20 30 40 50 60 70 8 GM dry wieght (shoot * seed ) (g) Spring beauty PRGR based on # garlic mustard rosettes in Sept 1998 before thinning at Wooster 0.0 e * en 0.5 œ I; •2.0 0 100 150 200 25050 300 350 # GM rosettes tiefore thinning Spring beauty PRGR based on # garlic mustard rosettes in Nov 1998 after thinning at Wooster 1.0 0 . 0 6 3 3 0 . 5 I C" 8 -0.5 Ü 1 i lO -1.6 -2.0 • -2.5 0 20 40 60 80 100 120 140 # GM rosettes after thinning Spring beauty PRGR based on # garlic mustard plants harvested at Wooster 1 . 5 0 . 5 y = -0.0112x-0.0825 r2 = 0.1159 I o» 8 o> i • 0 . 5 o I .1,0 • 1 . 5 •2.0 •2.6 0 10 20 30 4 0 5 0 6 0 70 80 90 100 # GM plants harvested Spring beauty PRGR based on total garlic mustard dry weight in July 1999 at Wooster 1.0 0.5 0.0356 0.0 9 Ch I -1.5 -2.0 -2.5 0 10 20 30 40 50 60 70 80 GM dry wieght (shoot * seed) (g) Black snakeroot PRGR based on # garlic mustard plants at Western •Fall rosettes ▲Harvested adults 1 H g to 2 f 20 #GM plants Black snakeroot PRGR based on total garlic mustard dry weight In July 1999 at Western 0.8 0,6 0.4 o>s H 0.2 w A -0.4 -0.6 -0.8 0 1 2 3 4 5 6 7 8 GM dry weight (shoot + seed) (g) II-’!'- Summer plants PRGR based on # garlic mustard plants at Western A • 1 • A • • A # 0 . 5 A # • A ■ e 1 T*I I e H S A ■0.6 m •Fall rosettes A Harvested adults >1 ■L.— — -r ' — — 1 ■ 1 1 " — . — If. n 1 . 10 15 20 25 30 35 40 #6M plants J Summer plants PRGR based on total garlic mustard dry weight In July 1999 at Western T*§ H a m in S I 3 4 6 GM dry weight (shoot + seed) (g) spring beauty PRGR based on # garlic mustard plants at Western •Fall rosettes ▲Harvested adults A A e # H ▲ e •7" -r "T 10 16 20 30 35 40 #GM plants Spring beauty PRGR based on total garlic mustard dry weight in July 1999 at Western 0.6 9 R* = 0.0732 Î -0.5 •X- -1.5 0 1 2 3 4 5 6 7 8 GM dry weight (shoot + seed) (g) REFERENCES Al-Shehbaz, I.A. 1988. 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