Silvicultural Treatment Effects on Oak Seed Production And

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SILVICULTURAL TREATMENT EFFECTS ON OAK SEED PRODUCTION AND

ACORN WEEVIL DIVERSITY IN SOUTHEASTERN OHIO

A thesis presented to

the faculty of

the College of Arts and Sciences of Ohio University

In partial fulfillment

of requirements for the degree

Master of Science

Jeffrey A. Lombardo

March 2007

This thesis entitled

SILVICULTURAL TREATMENT EFFECTS ON OAK SEED PRODUCTION AND

ACORN WEEVIL DIVERSITY IN SOUTHEASTERN OHIO

JEFFREY A. LOMBARDO

has been approved for

the Department of Environmental and Plant Biology

and the College of Arts and Sciences by

Brian C. McCarthy

Professor of Environmental and Plant Biology

Benjamin M. Ogles

Dean, College of Arts and Sciences

Abstract

LOMBARDO, JEFFREY A., M.S., March 2007, Environmental and Plant Biology

SILVICULTURAL TREATMENT EFFECTS ON OAK SEED PRODUCTION AND

ACORN WEEVIL DIVERSITY IN SOUTHEASTERN OHIO (63 pp.)

Director of Thesis: Brain C. McCarthy

Oak regeneration failure in the hardwood forests of eastern North America has been well documented. Fire and thinning (fire surrogate) treatments are being studied as

possible management tools to promote oak regeneration. We examined oak seed

production and acorn weevil (Coleoptera: Curculionidae) diversity from two forests in

southeastern Ohio under different silvicultural treatments. Seeds were collected for five

seasons from 2001-2005. Overall, stand level treatments only resulted in a slight increase

in acorn production in the burn and thin & burn stands (as expected) relative to the

control; however, this response was species specific. Masting was not attributable to the

treatments. Insect data showed an increase in weevil activity in areas with the greatest acorn production. Stand level treatments did not have a significant impact on weevil

abundance patterns. Our data suggest that factors influencing the masting cycle (e.g.,

climate) account for a much greater proportion of the variability in seed production than

do stand level criteria.

Approved:

Brian C. McCarthy

Professor of Environmental and Plant Biology

Acknowledgements

I would like to thank my advisor Dr. Brian McCarthy, as well as my committee

members, Dr. Kim Brown, Dr. Harvey Ballard and Dr. Kelly Johnson, for their encouragement, advice and assistance in completing this work. Funding for this work was

provided by the USDA Forest Service and the Ohio University Graduate Student Senate.

I would also like to thank the rest of the faculty, staff and students of the Department of

Environmental and Plant Biology at Ohio University. Special thanks to Matt Albrecht,

Ryan McEwing, John Graham, Rochelle Jacques, Kurt Hartman, Jie Yang, Chris Havran,

Jyh-Min Chiang, Sarah Stewart, and Krysta Hougen…thanks for all your help.

Of course, none of this would have been possible without the support of all of my

friends and family back home, THANK YOU! 5

Table of Contents

Page

Abstract...... 3

Acknowledgements...... 4

List of Tables ...... 6

List of Figures...... 7

Chapter 1: The Effects of Silvicultural Treatments on Oak Seed Production ...... 8 Introduction...... 8 Methods...... 11 Species Characteristics...... 11 Study Site...... 12 Sampling Design...... 14 Statistical Analysis...... 15 Results...... 16 Discussion...... 20 Conclusion ...... 26

Chapter 2: Curculionid Weevil Diversity in Two Experimental Oak Forests in Southeastern Ohio...... 39 Introduction...... 39 Methods...... 41 Study Site...... 41 Sampling Design...... 42 Statistical Analysis...... 43 Results...... 44 Discussion...... 45

Literature Cited ...... 55 6

List of Tables

Table 1-1. Repeated measures analysis of variance outlining the effects of species, treatment and year on acorn production by black oak and chestnut oak in two southeastern Ohio forests...... 34

Table 1-2. Repeated measures analysis of variance of silvicultural treatment effect on acorn production in two species of oaks over five years of study...... 35

Table 2-2. Simpson’s Diversity Index values for individual treatments as well as total site diversity for the Zaleski State Forest and REMA experimental forests in Vinton county, southeastern Ohio. Values are reported as a reciprocal (1/Ds). There was no significant difference in diversity between treatments (ANOVA, P = 0.6986)...... 53

Table 2-3. Analysis of variance for silvicultural treatment effects on occurrence of two genera of acorn weevils in two managed oak forests in southeastern Ohio...... 54 7

List of Figures

Figure 1-1. Acorn production for two species of oaks under four different silvicultural treatments at two experimental forest sites in southeastern Ohio. A) Black oak at Zaleski B) Chestnut oak at Zaleski C) Black oak at REMA and D) Chestnut oak at REMA...... 28

Figure 1-2. Seed production for individual chestnut oak trees at the Zaleski and REMA study sites combined. (A) control, (B) thin, (C) thin and burn and (D) burn...... 29

Figure 1-3. Seed production for individual black oak trees at the Zaleski and REMA study sites combined. (A) control, (B) thin, (C) thin and burn and (D) burn...... 30

Figure 1-4. Regression plot of number of acorns per 0.5 m2 seed trap area by m2 basal area of each individual tree of (A) chestnut oak and (B) black oak trees at the Zaleski State Forest in Southeastern Ohio from 2001-2005...... 31

Figure 1-5. Mean weight of sound chestnut oak seeds from trees exposed to four different silvicultural treatments. Seeds were collected from the REMA and Zaleski field sites in October of the 2005 mast season. n = number of seeds. Bars with the same letter are not significantly different at P = 0.05. Contrasts indicate treatment effect is not significantly different from the control (P = 0.49)...... 32

Figure 1-6. Number of sound and unsound (with acorn weevil larvae) acorns for two species of oaks across five years of study. Data from two 0.25m2 seed fall traps per tree; 72 trees of each species from two experimental forests in southeastern Ohio...... 33

Figure 2-1. Species abundance plot indicating rank order abundance of individual species vs. the log of percent abundance for twenty six species of Curculionid weevils from two experimental forests in southeastern Ohio...... 49

Figure 2-2. Change in occurrence of 26 species of Curculionid weevils through time at two experimental forests in southeastern Ohio. A) including C. castaneus B) excluding C. castaneus...... 50

Figure 2-3. Number of weevils in the genus Curculio and Conotrachelus captured in each of the four silvicultural treatment areas at the Zaleski and REMA experimental forests in southeastern Ohio...... 51

Chapter 1: The Effects of Silvicultural Treatments on Oak

Seed Production

Introduction

Oak species (Quercus L.) often occur as a dominant component of the tree canopy in the hardwood forests of the eastern and central United States. Witness tree data from early land surveys demonstrate the prevalence of oak in eastern forests prior to European settlement (Abrams and Ruffner 1995), and paleoecological studies show this trend dating back as far as 9,000 ybp (Delcourt et al. 1998). Oak dominance in the eastern forests was enhanced during the 19th century due to disturbance from logging and post- logging fires; however, over the last two decades researchers have observed a failure in the natural regeneration of the dominant oak species (McCarthy et al. 1987, Crow 1988,

Lorimer 1992, Goebel and Hix 1996, Abrams 1998, McDonald 2003, Van Lear 2004).

This lack of regeneration is evident by a replacement of oaks in the understory with more mesophytic, fire-intolerant species, namely red maple (Acer rubrum L.), tulip poplar

(Liriodendron tulipifera L.) and sassafras (Sassafras albidum (Nutt.) Nees). These competing species inhibit oak regeneration by suppressing the growth of seedlings and preventing their advancement to larger size classes. Strict policies of fire suppression beginning in the early 20th century likely facilitated the occurrence of these mesic, fire- intolerant saplings in oak dominated landscapes. 9

A number of key characteristics contribute to the difficulty in maintaining natural oak regeneration. Among these are a high percentage of seed predation, and highly variable seed production (masting).

Three major insect acorn pests are prevalent in the southeastern Ohio area: the acorn moth (Lepidoptera: Oleuthreutidae), the gall wasp (Hymenoptera: Cynipidea) and the acorn weevil (Coleoptera: Curculionidae). Of these, the weevil is the most problematic. Weevils have been reported to destroy > 90 % of acorns in eastern hardwood forests (Gibson 1972, 1982, Riccardi et al. 2004). Adult acorn weevils deposit an egg in developing acorns and the larvae feed from within the pericarp, resulting in seeds which are either unable to germinate or produce seedlings of low vigor (Lombardo and McCarthy, unpublished).

High year-to-year variability in seed production, commonly known as masting, also influences regeneration. Masting has been documented in a number of oak as well as other plant species (Janzen 1978, Norton and Kelly 1988, McCarthy and Quinn 1989,

Sork et al. 1993). Ultimately, masting may confer a selective advantage in reproductive fitness by way of economies of scale. This hypothesis states that pollination efficiency, predator satiation, and seed dispersal increase with variable seed production (Kelly

1994). In the absence of such advantages, mast seeding would reduce reproductive fitness due to increased density dependent mortality and reduced seedling growth. In order to maintain the selective benefit of mast seeding however, synchrony of individuals, and to some extent populations, must be maintained. Proximate causes of masting are hypothesized to be a physiological response to the environment dictated by accumulation 10 and allocation of resources (Norton and Kelly 1988, Isagi et al.1997, Satake and Iwasa

2002, Iwasa and Satake 2004).

Numerous studies of oak masting in natural settings have been conducted, and most focus mainly on the patterns of synchrony among individuals and populations

(Koenig et al. 1994, Greenberg 2000, Abrahamson and Layne 2003, Liebhold et al 2004).

Studies addressing the effects of stand level manipulation on oak seed production were generally conducted in homogeneous environments (Healy et al. 1999, Abrahamson and

Layne 2002, Guariguata and Saenz 2002, Bellocq et al. 2005) not typical of the

Appalachian region. In southeastern Ohio, the topography is typically heterogeneous with highly variable microsite conditions. In managed forests this heterogeneity may increase due to soil compaction from heavy equipment, fragmentation from logging road construction, and canopy gaps from silvicultural applications. A clear understanding of how stand level treatments might affect seed production in a heterogeneous environment would benefit forest managers attempting to maintain present oak overstory composition in the forests of southeastern Ohio.

Typically, regeneration from seed occurs following fire, and a number of studies have focused on the use of prescribed fire to amplify the natural regeneration of oaks.

Most of these studies also incorporate some form of fire surrogate (i.e., thinning) to enhance the efficacy of the method (Brose 1999, Lanham 2002, Franklin et al. 2003). The purpose of this study is to determine the effects of prescribed fire and thinning, both alone and in conjunction, on oak seed production and predation in two managed, heterogeneous oak forests of southeastern Ohio. Specifically we wish to address the following questions: 1) Do silvicultural treatments affect seed production, mast cycle 11 occurrence, and synchrony of individual oak trees? 2) What, if any effects do treatments have on the percentage of sound, aborted or weevil depredated acorns? 3) What benefit might these treatment effects present in the effort to regenerate oak forests in the eastern and central hardwoods region?

Methods

Species Characteristics

The present day distribution of oaks spans from Nova Scotia to southern

Florida and west to the Pacific coast, with the exception of the rocky mountain region of

Idaho, Montana and western Wyoming (McWilliams et al. 2002). When a regular cycle

of disturbance is maintained, oaks may sustain dominance, even in mesic areas. This is

most apparent in areas where fire return intervals are short, since the thick bark and

vigorous resprouting ability of the dominant eastern oak species make them well suited to

re-establishment after fire.

The majority of oak species in the Central Hardwoods Region reaches maturity

and begins producing seeds at around 20 years of age. Oak acorns are an import food

source for many vertebrate and invertebrate animals, and the role of oaks as a keystone

species has far-reaching ecological consequences (Ostfeld et al. 1996). The two species

of oak trees used in this study were chestnut oak (Quercus prinus L.) and black oak (Q.

velutina Lam.). The characteristically high root:shoot ratio and drought tolerance of these

oak species allow them to dominate on xeric ridge tops. On more mesic areas they

generally co-occur with shade tolerant species, and in the absence of disturbance they 12 may be succeeded by those trees. Pistillate flower buds initiate in the late summer.

Development stops during the winter and resumes in late March. Fully developed flowers are small and inconspicuous, appearing approximately 5 – 10 days after emergence of the male catkins in early May (Sharp and Sprague 1967).

Staminate inflorescence buds begin to differentiate in late spring and early summer in the white oaks (Cecich 1992). Catkins begin to appear prior to vegetative bud break in the spring, from approximately late April to early May, and emergence is dictated by warm air temperature. Generally the red oaks respond to this cue earlier than the white oaks which require about 10 days with minimum temperature above 50°F. The inflorescence buds are located at the tips of the previous year’s shoots and clusters of 3 –

10 catkins per shoot tip are common.

Temperature and relative humidity have a strong influence on the time of pollen dissemination in oaks. Sharp and Chisman (1961) found that anther dehiscence in the white oak group required relative humidity at or below 45 % for a period of up to 3 days, and Romashov (1957) showed an increase in pollen shedding with rising air temperature.

Periods of prolonged wet weather and high humidity can inhibit pollen dispersal (Sharp and Chisman 1961, Wolgast 1977).

Study Site

The two study sites for this experiment were located at the Zaleski State Forest

(39°35′5″N; 82°37′0″W) and the Raccoon Ecological Management Area (REMA)

(39°20′0″N; 82°39′0″W), both in Vinton County in southeastern OH. Both sites are located on the unglaciated Alleghany Plateau and consist of mature second growth forest initiated in the mid – late 19th century. The topography of the area is highly dissected 13 with steep xeric ridges dominated mainly by white oak (Quercus alba L.), chestnut oak, black oak, and hickory (Carya Nutt.). The valleys are more mesic and also include red oak (Q. rubra), sugar and red maple (Acer saccharum Marshall, A. rubrum L.), black cherry (Prunus serotina L.) and tulip poplar (Liriodendron tulipifera L.) among others.

Overall, the region is classified as mixed mesophytic forest by Braun (1950), though canopy tree basal area consists of approximately 85 percent oak at both study sites (2000; data on file USDA Forest Service NE research Station, Delaware, OH). Soils are acidic and well drained, composed mostly of Gilpin series silt loams from the Pennsylvanian sandstone, siltstone and shale (Boerner et al. 2003). The climate in this area is classified as humid continental with a mean yearly temperature of 11.6 ºC and mean annual rainfall of 97.84 cm (NOAA 2005). The warmest month is July with a mean temperature of 23.9

ºC and the coldest is January with a mean temperature of 2.1 ºC.

The study sites for this research were used in cooperation with the Ohio Hills branch of the USDA Forest Service’s, National Fire and Fire Surrogate (FFS) study. The goal of the Ohio Hills FFS project is to determine the effects of silvicultural treatments on a diverse topic of environmental and vegetation features (e.g., vegetation structure, soil nutrients, fuels dynamics, etc.) as they relate to oak regeneration in the southeastern

Ohio area (Yaussy 2001). Each of the two study sites were divided into four 20 hectare

(ha) treatment areas consisting of: (1) Control, (2) Thin only, (3) Thinning followed by prescribed fire and (4) Prescribed fire only. Thinning was completed in the fall and winter of 2000-2001 as a shelterwood thin with a resulting basal area reduction of 30%.

Trees were removed from both the canopy and mid-story, with maple and other mesic species preferentially selected for removal. Prescribed burning was conducted in the 14 spring of 2001 and again in spring 2005. Prescribed burns were low intensity consuming mostly leaf litter and 1 – h fuels. Flame lengths averaged less than 2 m in height and spread rate did not exceed 11 meters per minute (Iverson et al. 2004). All thinning and prescribed burning treatments were conducted by the USDA Forest Service.

Sampling Design

At the Zaleski and REMA study sites, nine 20 × 50 m plots were established within each of the four 20 ha treatment areas. Adjacent to each plot, one mast tree each of black oak and chestnut oak was selected for study. Beneath each mast tree, two 0.25 m² seed traps were placed 1.5 m aboveground, resulting in 36 traps per treatment area for each of the two study sites (288 traps total). As opposed to ground collecting, this method eliminates bias in favor of weevil infested acorns by excluding vertebrate seed predators that may preferentially consume un-infested seeds. Seed collections were completed each season from 2001 to 2005. The seed traps were set up each year in July and collections occurred mid-month beginning in August and continuing every four weeks until the final collection in December. Seeds collected were brought back to the lab and identified to species to ensure only the target species was used in the study. Seed size and condition

(sound, aborted, weevil infested, other) were recorded. Sound seeds are those which are fully developed and free from insect or other damage. Aborted seeds are shed early, prior to becoming fully developed. Weevil infested seeds are those containing larvae of acorn weevils, or evidence of their having been in the seed (feeding damage, exit holes, frass, etc.). Other refers to seeds which have been partially consumed by squirrels, mice, or other vertebrates, as well as those destroyed by fungi. 15

Statistical Analysis

Seed production data were analyzed with a randomized block, repeated measures analysis of variance (ANOVA) using the PROC MIXED statement in the SAS software package (SAS Institute 2001). “Tree species” (black and chestnut oak), “treatment”

(control, thin, thin and prescribed burn, prescribed burn) and “year” were fixed effects, and “site” (Zaleski and REMA) was a random effect. The number of seeds produced was the dependent variable. Tests of normality and equal variance assumptions were completed using the D’Agostino Omnibus test (D’Agostino et al. 1990) and the Modified

Levene Equal Variance tests (Levene et al. 1960) respectively in the NCSS software package (Number Cruncher Statistical System 2004). The seed production data set was square root transformed in order to meet normality assumptions. A second ANOVA was conducted using the black oak and chestnut oak data sets individually to explore species

× treatment interactions. These analyses were also completed using the “proc mixed” statement in the SAS software package (SAS Institute 2001). To determine differences in chestnut oak seed weight, a GLM-ANOVA was employed along with a Tukey-Kramer multiple comparisons test using the NCSS software package (Number Cruncher

Statistical System 2004). For this analysis, we used only sound seeds from the October

2005 collection in order to minimize temporal differences in seed size. Data for black oak were not available due to low numbers of sound seeds. F-test critical values for all

ANOVA models were considered significant at P = 0.05.

Linear regression of tree size on seed production was analyzed by converting the

DBH to area (m2) in order to standardize production by unit area of the seed traps (0.5

m2). This analysis used trees from the Zaleski site only. Annual mean and individual 16 mean seed production within each treatment was evaluated to determine the coefficient of variation (standard deviation / mean) for the population (CVp) as well as individual trees

(CVi) within each population.

Spearman-Rank correlation coefficients were used to analyze the relation between

environmental variables (Palmer Drought Severity Index, minimum monthly

temperature) and seed production, as well as percent of seeds falling into the sound, aborted and weevil infested categories. The Palmer drought severity index is a numerical value using precipitation and temperature to calculate drought severity (NOAA 2006). A value of zero indicates baseline conditions, and drought is shown as negative values.

Positive values indicate wetter than normal conditions. PDSI values used in this analysis covered the entire southeastern Ohio area for the period of January 2000, through

December 2005.

Results

Seed production varied considerably from year to year in both species of oaks.

ANOVA results show a significant effect of species on seed production, demonstrating a

clear difference in production among the two types of trees. The significant effect of year

and species × year indicate temporal variation in seed production such as would be

expected in species experiencing discrete mast cycles (table 1-1). Overall there was a significant effect of treatments on stand level seed production (P = 0.0544); however, a significant species × treatment interaction indicates that the response is species specific

(P = 0.0139; table 1-1). When analyzed separately, chestnut oak showed a significant 17 response to the treatments (P = 0.0004), while black oak failed to respond (P = 0.7191; table 1-2).

Chestnut oak produced discrete, bimodal variation in seed production with a coefficient of variation (CVp) ranging from 144.7 % in the thin + burn plot, to 241.0 % in

the burn. Among the four treatments there was no significant difference in yearly

variation (table 1-3) indicating that treatments did not influence mast cycle occurrence.

Mast events for this species occurred in 2002 and 2005, during which the greatest number

of seeds were produced in the thin + burn plots at both the Zaleski and REMA sites.

Consequently, the thin + burn treatment also resulted in a reduced mean seed weight

(figure 1-5). Intermast years were characterized by very low numbers of seeds (figure 1-

1). Annual mean production varied from a minimum of 120 seeds per ha in the burn plot

during a nonmast year, to 108,120 seeds per ha in the thin + burn during a mast season.

Synchrony in seed production among the different treatments, including the control plots,

was maintained (figure 1-1). Despite within-year synchrony of the different treatment

plots, there remained considerable variation in seed production among individual trees,

with some trees showing consistently better production during a mast year than others.

The coefficient of variation of mean seed production of individual trees (CVi) per

treatment area across the five years of study ranged from 145.3 percent in the thin plot to

171.0 percent in the burn.

Mast cycles in black oak were much less defined. Mean population level coefficient of variation (CVp) for annual seed production ranged from 93.7 % in the burn,

to 123.5 % in the control, with no significant difference in yearly variation among the

four treatments (table 1-1). A single bumper crop of black oak occurred in 2001. During 18 this time seed production was greatest in the control plot at the Zaleski site, and the thin plot at REMA. Following the 2001 season, black oak seed production became incrementally lower over the next four years. Synchrony among the different treatments, including the control, was maintained in this species also, refuting the hypothesis that treatments could initiate a mast cycle (figure 1-1). Mean seed production among individual trees of each treatment had a coefficient of variation (CVi) ranging from 82.6

percent in the thin to 122.0 percent in the control. Individual variation in black oak was

significantly different from the control in both the thin, and thin + burn treatments (table

1-3).

For chestnut oak, the percentage of seeds damaged by acorn weevil larvae was

considerably lower during mast years than during non-mast years. For this analysis,

aborted (undeveloped) acorns were not considered since it is not possible for them to

have become infested or produce mature seeds. During non-mast years an average of 62

% of developed acorns were weevil damaged compared to just 25 % during a mast year

(table 1-3). Likewise, the percent of sound seeds rose from only 7 % during non-mast

years to 70 % during a mast year.

For black oak, damage by weevils was more constant from year to year. The 2001

bumper crop of black oak seeds suffered from 64 % weevil damage. By comparison, the

average percent of weevil damaged acorns for the remaining four years was 63 %. Sound

seeds comprised 32 % and 18 % of the 2001 and 2002 – 2005 seed crops respectively

(table 1-4).

We were unable to discover any significant treatment effect on percentage of

acorns inhabited by weevil larvae in the five years of study (P = 0.5679), nor did we find 19 any significant species × treatment interaction (P = 0.1865; table 1-4). A significant effect of year was expected since weevil infestation percentage changed with seed crop size and significant values for species indicate a difference in percentage of inhabited seeds between the two species of oak trees (P = 0.0232 and 0.0220, respectively; table 1-

4).

Spearman rank correlation analysis of Palmer Drought Severity Index values and minimum monthly temperature was used to determine the influence of weather variables on seed production and predation. For chestnut oak, summer drought had a significant negative effect on percentage of sound seeds (table 1-5). A low minimum temperature during the month of May was negatively correlated with total acorn production (α >

0.001) and positively correlated with percent of acorns experiencing weevil damage (α >

0.001). Conversely, low temperatures during the month of June had a significant positive affect on total acorn crop (α = 0.037) and a reducing affect on weevil damage (α = 0.037).

Tree diameter was generally positively correlated with increase seed production in both species of oak, as would be expected. This finding was most apparent in black oak (r2 =

0.1570) and less so in chestnut oak (r2 = 0.0036; figure 1-2).

For black oak, drought during the months of June (α = 0.037) and October (α >

0.001) of the first growing season had a significant negative effect on percentage of seeds

damaged by weevils. Drought during October of the first growing season and February of

the second season also had a significant negative effect on total seed production (table 1-

6). Low temperatures in March of the first growing season had a significant positive

effect on percentage of sound seeds (α > 0.001) while low temperature the following

November increased seed abortion (α = 0.037). During the second growing season, low 20 temperatures in May had a strong negative correlation with seed abortion (α > 0.001), and to a lesser extent, low temps in July did as well (α = 0.037) (table 1-6). A significant, negative relationship between tree diameter and seed production was observed for black oak trees at the Zaleski site.

Discussion

Over the five year study of seed production, black oak was a superior acorn

producer compared to chestnut oak. It’s important to recognize that black oak acorns are

considerably smaller than those of chestnut oak and therefore likely expend fewer

resources per seed. Similarly, Greenberg (2000) also found chestnut oak to be a poor

producer compared to other oak species.

Effects of the thinning and burning treatments on seed production were species

specific. Whereas black oak acorn production failed to respond to any of the treatments,

chestnut oak responded most heavily to the combination thin + burn treatment. This may

depend on chestnut oak responding to an increase in available light in the thin + burn

plots. Tree mortality induced from the burning treatments provided an increase in canopy

openness compared with that of the thin-only unit. The increase in light presumably adds to the trees potential to accumulate resources for use in flowering. Despite the potential increase, the masting schedule did not change. Trees in the thin + burn unit were still in synch with those of the control and other treatment plots. This observation supports the

theory of an external cue, most likely weather related, that controls the timing of a mast

cycle. If masting occurred immediately following accumulation of resources past a 21 threshold amount, then the masting schedule of trees in the different treatments would have been different (a pattern which we did not observe). The thinning treatments applied in this study were executed such that subdominant trees of non-oak species were preferentially removed. Based on our findings, removing a greater percentage of the forest canopy may increase the efficacy of thinning to enhance seed production in chestnut oak.

Crop size varied significantly over the five years of study. Chestnut oak showed a greater degree of bimodal, yearly variation in seed production than did black oak, making it better suited to the characterization of a mast species. This is similar to results of Sork et al. (1993) who found significantly less yearly variation in black oak as compared to red and white oak. We were unable to demonstrate any significant treatment effect on temporal variation for either species. Likewise, treatments alone failed to initiate a mast crop as was evident by the timing of mast crops in the control plots matching those in the treatments, as well as a discrepancy in the lag time of response in chestnut oak. The correlations between drought and minimum monthly temperature explained some of the variation; however, these two factors would not have been impacted by burning and thinning treatments. Tree size (basal area) was not a determinant of seed production in chestnut oak, though size was negatively correlated with seed production in black oak.

This result is contrary to the findings of Greenberg (2000) who found a positive relationship between seed production and tree size for black, red and white oak.

There was a significant treatment effect on the size of chestnut oak seeds for the

2005 mast season. Seeds in the thin and the thin + burn plots were significantly smaller than those in the control, and burn plots. Interestingly, these plots also produced a greater 22 number of seeds than either the control or burn, suggesting a trade off in seed number versus size. This finding can be explained by a limit in the amount of resources available per seed. Further research is needed to determine whether or not this reduced size has ecological implications for seedling recruitment.

Interspecific synchrony did not occur in our study; instead both species produced crops on different time scales. This is expected given the time difference (1 year vs. 2 years) required to mature seeds. A number of other studies have similarly found a lack of interspecific synchrony (Abrahamson and Layne 2003, Koenig et al. 1994, Sork 1993).

Spatially, both sites experienced the same patterns of production with respect to each species, despite the fact that they were located about 30 km apart. Long distance, intraspecific synchrony has been demonstrated in a number of studies (Liebhold et al.

2004, Koenig and Knops 1998), and Koenig and Knops (1998) showed synchrony across distances as far as 1000 km. A number of researchers contend that synchrony is maintained across regions by patterns of environmental variation covering large distances, while others point to long distance pollen transfer and gene flow as determinants. A model developed by Satake and Iwasa (2002) demonstrated that environmental variation (Moran effect) in the absence of pollen coupling (grouping of trees by way of pollen exchange) could not maintain distant or regional synchrony by itself. When pollen coupling was incorporated into the model, synchrony was maintained.

Despite the prevalence of synchrony in population level variability, we found a great deal of variation among individual trees within a population. Intraspecific variation is common among mast species of other genera as well (Koenig et al. 2003, Herrera et al.

1998, Rehfeldt et al. 1971). This was particularly evident in chestnut oak, mean 23 individual coefficients of variation values of which were greater than those of black oak.

Though both species showed individual variability, chestnut oak in particular was characterized by a small number of individuals producing the majority of seeds. While there was no significant treatment effect on individual variation in chestnut oak, black oak had significantly less mean individual variation in the thin, and the thin + burn plots compared to the control. This finding is likely representative of a genotype × environment interaction in black oak that allowed trees to respond to the treatments individually by either increasing or decreasing seed production to more closely match the mean, an idea in keeping with that of McCarthy and Quinn (1989). Conversely, in unmanaged, more homogeneous systems, Koenig et al. (1994) found greater individual variation in black oak subgenera compared to white oak subgenera for five species of oaks in central, coastal California. This type of interaction between intrinsic and extrinsic factors as seen in our study has been demonstrated in a number of agricultural crop species (Annicchiarico et al. 2006, Gunasekera et al 2006, Sudaric et al. 2006); however, more studies focusing on this phenomenon in woody tree species are needed.

In considering predator satiation as an ultimate function of mast seeding, we looked at each species individually as well as the combined data from both species, since both contribute to the total amount of seed available to insects. The drop in percentage of acorns harboring weevil larvae from 64 percent for the first four years to 17 percent during the 2005 season coincided with a large chestnut oak mast crop and a very small black oak crop. The 2002 mast crop produced similar amounts of both chestnut oak and black oak acorns; however, the percentage infested with weevil larvae was far greater in black oak than chestnut oak. While individually our data seem to support evidence for 24 predator satiation by mast seeding in chestnut oak, this may be driven by preference for black oak acorns over those of chestnut oak by the dominant seed weevil species.

Furthermore, our data cover only two of the many oak and other masting species (e.g.,

Carya spp., Fagus grandifolia) found in the area which weevils may feed on, any of which may produce a mast crop in a given year as demonstrated by a lack of interspecific synchrony and personal observation. This negates the function of masting as a mechanism for seed predation avoidance. It’s probable instead that pollen coupling is the more likely evolutionary benefit for synchronous masting in temperate, wind pollinated tree species.

Whether or not applications of silvicultural treatments prove useful in regenerating oak forests is unclear. The premises for treatment applications are multi- tiered:

• Thinning and prescribed burning could increase seed production while potentially

reducing predation by insects.

• Prescribed fire would reduce competition from mesic seedlings and saplings, most of

which are less fire tolerant and disturbance adapted than are the oaks.

• By clearing out the under and midstory of the forest, while simultaneously allowing

more light through the canopy, thinning and prescribed burning should increase

seedling recruitment as well as release existing saplings to advancement into larger

size categories. Seedlings and saplings which are top-killed by fire should have an

advantage in resprouting over competing species due to the more extensive rooting of

oaks. 25

Neither our study nor a recent study by Bellocq et al. (2004) found any significant effect of silvicultural treatments on seed predation. We were able to demonstrate a response in seed production to prescribed burning and thinning treatments, but the response was species specific. Bellocq et al. (2004) found shelterwood thinning increased seed production in red oak however, their findings were dependent upon which of two sampling methods were used and so results were inconsistent. The larger question might be whether or not an increase in oak seeds translates into an increase in oak regeneration following disturbance, as so far this assumption remains suspect. Herb layer frequencies of white, chestnut and black oak seedlings have been shown to be more dependent upon xeric soil conditions than on occurrence of fire (Hutchinson et al. 2005). Likewise,

Albrecht and McCarthy (2006) showed oak seedling densities to be unimproved by burning and thinning treatments, while re-sprouting from top-killed saplings, along with germination from the seed bank, caused mesic seedling densities to increase immediately following a prescribed burn treatment.

It is important to remember, when studying oak seedlings, that because of their masting nature, seedling densities are naturally dynamic. A new cohort of seedlings follows each mast cycle with density dependent mortality thinning out their numbers over time. Applications of silvicultural treatments to regenerate oak forests should account for this factor along with pretreatment vegetation structure and composition as important considerations in determining the most efficacious treatment option. In forests where the understory is dominated by mesic species, thinning by itself will likely facilitate the release of those species into larger size classes through accelerated succession (Abrams and Nowacki 1992). Thinning immediately followed by prescribed burning may not 26 allow new oak seedlings the opportunity to establish enough resources to successfully resprout following top-kill. Our recommendation would include an initial prescribed burning and thinning treatment, followed by a second prescribed burn in the spring one or two seasons following the next mast cycle. This would allow the new cohort of oak seedlings time to accumulate resources and maximize their competitive advantage in resprouting from root stores following the second burn treatment.

Conclusion

In terms of numbers, black oak is a superior seed producer to chestnut oak and also exhibits less yearly variation. Chestnut oak produces discrete mast cycles characterized by a large degree of yearly variation at the population and individual level.

Of the silvicultural treatments implemented in this study, the combination of thinning and burning resulted in the greatest increase in seed production in chestnut oak, though the burning treatment resulted in a larger seed size. None of the treatments showed any effect on overall seed production in black oak; however, treatments decreased variation of seed production among individual black oak trees, which may be indicative of a genotypic response. The application of treatments to the forest did not stimulate the occurrence of a mast cycle, as might have been expected and likewise they had no effect on yearly variability within the populations for either species. Treatments did not influence seed predation by acorn weevils, the dominant seed predator, for either species.

In determining whether or not thinning and prescribed burning treatments will be useful in regenerating oak forests, a number factors including pretreatment vegetation and site conditions (xeric vs. mesic) must be considered. From a forest management perspective, identification of the best seed producers, particularly with respect to chestnut 27 oak, prior to any stand level silvicultural applications may be the best technique for promoting increased oak seed production and putatively enhanced oak regeneration. 28

2.5e+6 Control A Thin B 2.0e+6 T & B Burn

1.5e+6

1.0e+6

5.0e+5

0.0 2001 2002 2003 2004 2005 2001 2002 2003 2004 2005

2.5e+6 C D 2.0e+6 Number of Acorns / ha

1.5e+6

1.0e+6

5.0e+5

0.0 2001 2002 2003 2004 2005 2001 2002 2003 2004 2005

3.5e+5 A B 3.0e+5

2.5e+5

2.0e+5

1.5e+5

1.0e+5

5.0e+4

0.0

2001 2002 2003 2004 2005 2001 2002 2003 2004 2005 3.5e+5 C D 3.0e+5

Number of Acorns/ ha 2.5e+5

2.0e+5

1.5e+5

1.0e+5

5.0e+4

0.0

2001 2002 2003 2004 2005 2001 2002 2003 2004 2005

Figure 1-2. Seed production for individual chestnut oak trees at the Zaleski and REMA study sites combined. (A) control, (B) thin, (C) thin and burn and (D) burn.

3.5e+5 A B 3.0e+5

2.5e+5

2.0e+5

1.5e+5

1.0e+5

5.0e+4

0.0

2001 2002 2003 2004 2005 2001 2002 2003 2004 2005 3.5e+5 C D 3.0e+5

Number of Acorns / ha of Acorns Number 2.5e+5

2.0e+5

1.5e+5

1.0e+5

5.0e+4

0.0

2001 2002 2003 2004 2005 2001 2002 2003 2004 2005 Figure 1-3. Seed production for individual black oak trees at the Zaleski and REMA study sites combined. (A) control, (B) thin, (C) thin and burn and (D) burn.

300 A y = 24.74x + 38.23 r2 = 0.0036 250

200

150

100

50 Trap Area 2

300 B y = 194.41x + 73.11 2 250 r = 0.1570

Number of Acorns / 0.5 m 0.5 / Acorns Number of 200

150

100

0.0 0.1 0.2 0.3 0.4 0.5 Seed Tree Basal Area (m2)

8 b a a 6 a

4 Mean Weight (g)

n = 33 n = 73 n = 366 n = 118 2

0 Control Thin Thin & Burn Burn

3000

Unsound Chestnut Oak 2500 Sound

2000

1500

1000

500

3000 Black Oak 2500

2000

1500

1000

Number of Acorns 500

3000 Chestnut & Black Oak 2500

2000

1500

1000

500

0 20012002200320042005

Table 1-1. Repeated measures analysis of variance outlining the effects of species, treatment and year on acorn production by black oak and chestnut oak in two southeastern Ohio forests.

Effects Num. df Den. df F P Species 1 39 124.00 0.0001 Treatment 3 39 2.77 0.0544 Year 4 39 18.78 0.0001

Species × Treatment 3 39 4.02 0.0139 Species × Year 4 39 55.76 0.0001 Treatment × Year 12 39 1.86 0.0724 Species × Treatment × Year 12 39 1.55 0.1477

Table 1-2. Repeated measures analysis of variance of silvicultural treatment effect on acorn production in two species of oaks over five years of study. Effect Num. df Den. df F P Chestnut oak Treatment 3 19 9.77 0.0004 Year 4 19 78.52 0.0001 Treatment × Year 12 19 3.36 0.0091 Black oak Treatment 3 19 0.45 0.7191 Year 4 19 20.25 0.0001 Treatment × Year 12 19 1.06 0.4430

Table 1-3. Minimum, maximum and coefficient of variation, (CVp, CVi) values for annual mean acorn production totals, and mean individual tree production for two species of oak under four different treatments. Data from five years of study, 0.5m2 seed fall trap area per tree. n = number of individual trees. Annual mean Individual mean Treatment Min Max CVp Min Max n CVi Chestnut oak Control 0.25 11.94 161.9 0.40 21.20 16 150.1 Thin 0.11 15.32 189.5 0.60 15.60 19 145.3 T & B 0.18 54.06 144.7 0.60 48.00 17 145.4 Burn 0.06 14.39 241.0 0.20 20.80 18 171.0

Black oak Control 5.35 49.35 123.5 1.40 43.00 20 122.0 Thin 8.82 23.35 98.1 1.40 37.20 17 82.6 T & B 6.84 21.63 105.2 1.40 39.80 19 90.9 Burn 10.17 33.39 93.7 8.80 29.80 18 93.4 Note: Coefficient of variation (CV) is the standard deviation divided by the mean (σ / x) and is reported as a percentage. 37

Table 1-4. Analysis of variance of silvicultural treatment effects on percentage of sound vs. weevil infested acorns of black and chestnut oak in two experimental forests in southeastern Ohio. Effect df F P Species 1 834.24 0.0220 Treatment 3 0.81 0.5679 Year 4 10.03 0.0232 Species × Treatment 3 3.14 0.1865

Table 1-5. Correlation coefficients and associated P-values of Palmer Drought Severity Index (PDSI) and minimum monthly temperatures on acorn production totals and category (sound, aborted, weevil, other) for two species of oak in southeastern Ohio. Chestnut Oak PDSI – Values Minimum Temp. June July August May June July Total -0.300 -0.600 -0.500 -1.000 0.872 0.900 0.624 0.285 0.391 *<0.001 0.054 0.037 Sound -0.900 -1.000 -0.900 0.600 0.667 0.700 *0.037 *<0.001 *0.037 0.285 0.219 0.188 Aborted 0.200 0.100 0.300 -0.300 -0.205 0.500 0.747 0.873 0.624 0.624 0.741 0.391 Weevil 0.300 0.600 0.500 1.000 -0.872 -0.900 0.624 0.285 0.391 * <0.001 0.054 *0.037 Other 0.700 0.900 0.800 0.700 -0.564 -0.900 0.188 *0.037 0.104 0.188 0.322 *0.037

Black Oak PDSI – Values Minimum Temp. June‡ Oct‡ Feb§ March‡ Nov‡ May§ July§ Total -0.800 0.900 -0.900 0.400 -0.300 0.600 -0.700 0.104 *0.037 *0.037 0.505 0.624 0.285 0.188 Sound -0.100 -0.300 -0.300 1.000 -0.100 0.000 -0.100 0.873 0.624 0.624 *<0.001 0.873 1.000 0.873 Aborted 0.400 0.700 0.700 0.000 0.900 -1.000 0.900 0.505 0.188 0.188 1.000 *0.037 *<0.001 *0.037 Weevil -0.900 1.000 -1.000 0.300 -0.400 0.700 -0.600 *0.037 *<0.001 *<0.001 0.624 0.505 0.188 0.285 Other 0.100 0.300 0.300 1.000 0.100 0.000 0.100 0.873 0.624 0.624 *<0.001 0.873 1.000 0.873 * Indicates significant at α = 0.05 ‡ First growing season § Second growing season

Chapter 2: Curculionid Weevil Diversity in Two Experimental

Oak Forests in Southeastern Ohio.

Introduction

A major concern of researchers and forest managers in the eastern U.S. is the lack

of natural regeneration of oak species. Throughout the eastern forests, the canopy

dominant oaks are poised to be replaced by more mesophytic species, namely red maple

(Acer rubrum L.), tulip poplar (Liriodendron tulipifera L.), sassafrass (Sassafras albidum

(Nutt.) Nees), and sweet gum (Liquidambar styraciflua L.). These species dominate the understory sapling layer, preventing oak seedlings from progressing toward advanced size classes. A number of studies have linked this trend to fire suppression policies of the

last 80 – 100 years, as many species of oaks are thought to be fire adapted. In light of this

knowledge, recent studies have focused on the use of prescribed fire in conjunction with

fire surrogates (i.e., thinning) as a method to enhance natural oak regeneration from seed.

Results of these treatments on the vegetation structure have been mixed. What is not

known is the effect that stand level treatments may have on invertebrate seed predators,

particularly acorn weevils (Coleoptera: Curculionidae). Acorn weevils are the major seed predator of oak species in the central and eastern United States. Damage to seed crops can vary anywhere from 0 – 100 % based on tree species and seed crop size (Miller and

Schlarbaum 2005, Riccardi et al. 2004, Gibson 1972, 1982; Christisen 1955). It is possible that a prescribed burn conducted during the spring might destroy adult weevils as they emerge from the soil, as well as those residing near the soil surface. It is also 40 possible that by clearing out the leaf litter, prescribed burning may actually increase predation on weevils by removing their cover. The white footed mouse and the short tailed shrew, both of which are common in eastern deciduous forests, are major predators of weevils (Anderson and Folk 1993, Semel and Anderson 1988). A reduction in acorn weevil populations would potentially enhance oak regeneration by decreasing seed predation.

Gibson (1969) lists 27 species of weevils in the genus Curculio as occurring in

America north of Mexico. Many of these species exhibit a morphological specificity to a particular host type (Hughes and Vogler 2004). Adult Curculio can be found from April to November in southern states with a slightly lower active period farther to the north.

Toward the end of the summer, females excavate a hole into developing acorns using their extended rostrum and deposit an egg. Eggs hatch in 5 -14 days and larvae feed from within the pericarp for approximately two weeks. After seed drop, larvae exit the acorn and burrow into the ground where they will overwinter. Diapause may last from one to five years depending on the species; however, one or two years is common (Gibson

1969). Conotrachelus, another major genus of seed infesting weevils, generally emerges later in the summer and oviposits in acorns at the end of August and early September.

Many species in this genus require a preexisting oviposition hole or damage to the nut as they are unable to chew through the pericarp on their own. Conotrachelus larvae also feed within the pericarp before emerging from the seed and burying into the soil. Not all weevil species breed in seeds, many simply oviposit in or on the soil surface, or on the surface of leaves or other parts of a tree. Larvae of these species generally feed on roots, or the inner bark of the tree (Evan 1959, Blatchley and Leng 1916). 41

The purpose of this study is to determine if stand level treatments affect the diversity and abundance of adult weevils in two managed, oak dominated hardwood forests in southeastern Ohio. Specifically, we wish to address the following questions 1) what species of weevils occur in the area and how are populations structured? 2) Do the silvicultural treatments employed reduce weevil abundance?

Methods

Study Site

This study utilized the silvicultural treatments initiated by the U.S. Forest Service

at the Ohio Hills site of the National Fire and Fire Surrogate (FFS) study. The two study

locations were at the Zaleski State Forest (39°35′5″N; 82°37′0″W) and the Raccoon

Ecological Management Area (REMA) (39°20′0″N; 82°39′0″W) both of which are

located in Vinton County, southeastern Ohio. The area lies within the unglaciated region

of the Alleghany plateau and the forest type is classified as mixed - mesophytic by Braun

(1950). Canopy tree basal area consists of approximately 85 % percent oak at both the

Zaleski and REMA sites (2000; data on file USDA Forest Service NE research Station,

Delaware, OH). Soils are acidic and well drained, composed mostly of sandstone,

siltstone and shale (Boerner et al. 2003). The climate in this area is humid continental

with a mean yearly temperature of 11.6 ºC and mean annual rainfall of 97.84 cm (NOAA

2006). The warmest month is July with a mean temperature of 23.9 ºC and the coldest is

January with a mean temperature of 2.1 ºC. 42

Sampling Design

Each of the two study sites was divided into four 20 ha treatment plots consisting of 1) an untreated control 2) thinning only 3) thinning followed by prescribed fire and 4) prescribed fire only. Thinning was conducted in the winter of 2000 - 2001 with a 30 % reduction in basal area. Thinning treatments were applied from below, meaning that subdominant trees of non-oak species were preferentially removed. Prescribed burning treatments were conducted in the spring of 2001 and a second burning was performed four years later in the spring of 2005. Fires were low intensity, consuming mainly leaf litter and 1 – hr woody fuels (Iverson et al. 2004). Within each treatment unit, six pyramid style (Tedders and Wood 1995) insect traps were set up. Traps were constructed from 6.4mm fiberboard and were left unbaited and neutral brown in color. The traps were placed in areas containing a high number of apparently healthy oak trees, mainly black

(Quercus velutina Lam.), white (Q. alba L.) and chestnut oak (Q. prinus L.) but often including some red oak (Q. rubra L.) and hickory (Carya spp.) species as well. Traps were checked for presence of adult weevils every 7 – 10 days for a period of twelve weeks beginning in early July and continuing through September. All Curculionids were placed in ethanol and brought back to the lab. Identification of insects to species level was completed using taxonomic keys. For Curculio species, we used Gibson (1969). For all other genera, we used Blatchley and Leng (1916) and Kissinger (1964). Where possible, species identified using the taxonomic keys were confirmed with verified specimens from the Ohio University collection. 43

Statistical Analysis

Effects of stand level silvicultural treatments on weevil abundance were analyzed with a mixed model Analysis of Variance (ANOVA) using the NCSS statistical software package (Number Cruncher Statistical System 2004). Weevil genus and treatment

(control, thin, thin and prescribed burn, prescribed burn) were fixed effects and site

(Zaleski, REMA) was a random effect.

Simpson’s Diversity Index was calculated for each of the treatments at both the

Zaleski State Forest and REMA field sites using the following equation:

S nn ii − ))1(( Ds = ∑ i=1 NN − ))1((

where ni is the number of individuals of the ith species, and N is the total number of

individuals. The final value (Ds) was reported as a reciprocal (1 / Ds) so that the value

increases with greater diversity. One-way ANOVA was used to explore differences in

diversity among the different treatments. Both of the ANOVA model F – tests were

considered significant at a critical value of P = 0.05. Assumptions of normality and

equality of variance for both ANOVAs were tested using the D’Agostino Omnibus test

(D’Agostino et al. 1990) and the Modified Levene Equal Variance tests respectively

using the NCSS software package (Number Cruncher Statistical System 2004). Both data

sets met all assumptions. 44

Results

Overall, we identified twenty six different species of Curculionid weevils

representing nine genera from five different tribes and two subfamilies (table 2-1).

Species abundance plots indicate dominance by a few species with the majority of lesser

species represented by only a few individuals (figure 2-1). The Asiatic oak weevil (C.

castaneus Roelofs) was the most abundant species at both study sites, comprising 61

percent of the weevils caught at Zaleski and 64 percent at REMA. A greater number of

weevils were caught at Zaleski than at REMA and likewise Zaleski exhibited a slightly

higher Simpson’s diversity index value than did REMA with 1/Ds = 2.44 and 1/Ds = 2.29 for the two sites respectively Diversity was highest in the control at Zaleski (1/Ds = 3.24) and the Thin at REMA (1 / Ds = 3.19; table 2-2). There was no significant difference in weevil diversity among the different treatments (data not shown).

Weevil occurrence changed through time, and the two study sites were not always

consistent. Both sites experienced a sharp rise in activity beginning in August and

reaching a peak the first week in September, after which time both experienced a decline

with the most significant reduction occurring at Zaleski (figure 2-2a). This trend is driven

by occurrence of the most common species, C. castaneus, which does not oviposit in

acorns. When we exclude C. castaneus for the purpose of focusing on acorn infesting

weevil activity, we find a decline at Zaleski and a modest rise at REMA in late summer.

In general, the number of weevils captured remained low even during prime oviposition

period for the seed infesting weevils. This is likely due to their activity being focused

more in the tree canopy (figure 2-2b). 45

Of the nine genera, two are considered to be the most important pests of oak acorns; these include the genus Conotrachelus and genus Curculio. Both genera were found in all treatment plots at both study sites and statistically both locations were similar in their numbers, though Conotrachelus was more abundant than Curculio (figure 2-3, table 2-2). There was no effect of silvicultural treatments in these forests on occurrence of either genus, which rejects our hypothesis that prescribed fire in the spring would reduce weevil occurrence. Likewise, we observed no significant treatment × genus interaction indicating that both genera were similarly unaffected by them (table 2-3).

Discussion

C. castaneus, the Asiatic oak weevil, was the most abundant weevil encountered.

This species was introduced to North America from Japan and first detected in New

Jersey in 1933. Ferguson et al. (1991) found black, white and red oak, along with sugar

maple (Acer saccharum Marsh) to be the preferred host trees versus other hardwood

species such as ash (Fraxinus spp.), basswood (Tilia americana L.), and hickory (Carya

spp.). Additionally, they found that weevils fed black and red oak leaves lived longer and

produced more eggs than those fed white oak or sugar maple. In situ studies of host tree

associations by Frederick and Gering (2006) substantiate the claim that C. castaneus prefers oak and maple other hardwood tree species. C. castaneus weevils have been shown to negatively affect oak regeneration by feeding on the fine roots and leaves of oak seedlings which reduced seedling growth (Sander 1990).

Species in the genus Curculio are regarded as primary seed infesting weevils of

oaks as well as other nut tree species, since they do not require previous insect or other 46 damage to a seed for oviposition. Curculio weevils are host specific, and of the more than nine species captured in our study, at least five are known to feed on oaks common to the central hardwood forest. Though none of the remaining species we encountered are exotic, native Curculio weevils may still play a significant role in the reduced regenerative ability of oaks by destroying a large percentage of the acorn crop in any given year.

Conotrachelus weevils are also a major contributor to the destruction of acorn crops, though most species may be restricted to previously infested or damaged acorns

(Gibson 1964, Beers et al. 2003). The most abundant species, C. naso, is known to oviposit in acorns, particularly those of the white oak subgroup (Leucobalanus) in addition to Crataegus and Malus species.

Larvae of the genus Cryptorhynchus are bark borers and adults are generally found on the bark and dead twigs of oaks, hickory, birch (Betula spp. L.) and others.

Weevils in the genus Otidocephalus primarily breed in galls found on oaks and other tree species. Piazorhinus scutellaris is found on oaks where it is thought to mine the leaves.

Eulechriops minutus, Piazorhinus scutellaris and Psomus spp. are known to occur on oak as well as hickory and ash; however, it is not clear whether or not they breed within the seeds of either species (Blatchley and Leng, 1916).

Temporal change in weevil occurrence at our study sites was apparent. REMA saw an increase in weevil activity from late August to early September, coinciding with the early stages of acorn maturation for both sub-groups of oak species. This is the prime oviposition period for acorn infesting weevils in the Curculio and Conotrachelus genera.

Generally, seeds that drop earlier in the season are more likely to harbor weevil larvae 47 than those which fall later, suggesting that trees may preferentially shed infested acorns early to avoid wasting resources (Yu et al. 2003, Miller and Schlarbaum 2005).

We were unable to demonstrate any significant effect of silvicultural treatments on Curculio and Conotrachelus weevil diversity at either of the two study sites. These results are similar to those of Bellocq et al. (2005) who found no effect of shelterwood thinning on acorn predation by insects in central Ontario, Canada. Similarly, Moretti et al. (2004) found that single and repeated fires had no significant effect on the number of

Curculionids in temperate, deciduous forests of the Southern Alps. In southeastern Ohio, employing treatments of prescribed fire and thinning to regenerate oak stands has shown mixed results. Some oak species respond to treatments with an increase in seed production, while others show no response (Lombardo and McCarthy, unpublished). Data from a subsequent study indicated no significant difference in the percentage of chestnut oak and black oak acorn predation by weevils among treated and untreated plots; however, larger crop sizes resulted in lower predation percentages. (Lombardo and

McCarthy, unpublished). This finding is consistent with the economies of scale theory of masting in tree species, whereby a larger crop size results in a greater number of acorns escaping predation, and is in accordance with Miller and Schlarbaum (2005) and Yu et al.

(2003), both of whom found that the percentage of predation by weevils declines with increasing acorn crop size.

In our study, prescribed burning was conducted in the spring, presumably during the time when many species of weevils would be emerging from the soil; however, we found no significant treatment effect on weevil diversity or abundance. Moretti et al.

(2004) demonstrated a significant reduction in weevil species richness in temperate, 48 deciduous forests of the Southern Alps that had been burned repeatedly over the last 30 years by fires occurring in the winter. The discrepancy between their results and ours may be attributable to differences in fire intensity or the particular weevil taxa involved.

The low intensity of the prescribed burns used in our study may not have attained sufficient temperatures at or below the soil surface to cause a reduction in weevil population. In our area, it is possible that a burn early in the fall, during the period of acorn drop might exhibit a greater efficacy in reducing weevil occurrence by destroying the insects residing within the acorns or in the process of burying into the soil.

100 Zaleski REMA

1 Abundance (log)

0.1

0.01

Species Sequence

120 A Zaleski REMA 100

0 July 2 July 3 July 4 Aug 1 Aug 2 Aug 3 Aug 4 Sept 1 Sept 2 Sept 3 Sept 4

120 B Zaleski REMA 100 Number of Weevils Captured of Weevils Number

0 July 2 July 3 July 4 Aug 1 Aug 2 Aug 3 Aug 4 Sept 1Sept 2Sept 3Sept 4

Figure 2-2. Change in occurrence of 26 species of Curculionid weevils by week over an 11 week period at the Zaleski and REMA experimental forests in southeastern Ohio. Numbers on x axis indicate week of the month. Weevils were captured using pyramid style insect traps (24 traps / location). A) including C. castaneus, B) excluding C. castaneus. 51

60 Zaleski Curculio Conotrachelus 50

0 Control Thin Thin & Burn Burn 60 REMA

Number of Weevils of Number 50

0 Control Thin T & B Burn

Figure 2-3. Total number of weevils in the genus Curculio and Conotrachelus captured in each of the four silvicultural treatment areas at the Zaleski and REMA experimental forests in southeastern Ohio. 52

Table 2-1. List of species and total number of individuals of Curculionid weevils captured at two study locations, the Zaleski State Forest (Z) and the Raccoon Ecological Management Area (R), in Vinton Co. southeastern Ohio. Species Control Thin T & B Burn Z R Z R Z R Z R Subfamily: Curculioninae Tribe: Cryptorhynchini Conotrachelus anaglypticus 16 4 9 7 16 9 26 4 Conotrachelus falli 0 1 0 1 0 1 Conotrachelus geminatus 1 0 1 0 Conotrachelus juglandis 1 1 Conotrachelus naso 10 5 6 28 6 6 5 7 Conotrachelus posticatus 21 22 4 7 10 5 13 3 Cryptorhynchus bisignatus 0 1 Cryptorhynchus fallax 1 0 Cryptorhynchus lapthi 1 0 Cryptorhynchus parochus 1 0 Micromastus spp. 3 0 1 0

Tribe: Curculionini Curculio caryae 0 1 1 0 Curculio confusor 0 1 Curculio humeralis 0 1 1 0 0 3 Curculio iowensis 0 1 1 2 2 1 Curculio neocorilus 1 0 Curculio pardalis 1 0 2 0 4 4 2 3 Curculio sulcatulus 1 Curculio timidis 1 3 0 1 Curculio spp. 2 0 0 1 0 1

Tribe: Otidocephalini Otidocephalus chevrolatii 1 0 Otidocephalus spp. 1 0 1 0 3 0 2 0

Tribe: Prionomerini Piazorhinus scutellaris 0 1

Tribe: Zygopini Eulechriops minutus 1 0 Psomus spp. 1 1 0 1

Subfamily: Entiminae Cyrtepistomus castaneus 56 61 45 42 112 49 71 96

Table 2-3. Analysis of variance for silvicultural treatment effects on occurrence of two genera of acorn weevils in two managed oak forests in southeastern Ohio. Effects df F P Site 1 1.30 0.2925 Genus 1 23.04 0.0020 Treatment 3 0.01 0.9990 Treatment × Genera 3 0.99 0.4522 55

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