ELEMENT STEWARDSHIP ABSTRACT for

Cornus spp.

North American invasive dogwoods

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Authors of this Abstract: C. Converse; update by Nancy Eckardt © THE NATURE CONSERVANCY 1815 North Lynn Street, Arlington, Virginia 22209 (703) 841 5300 The Nature Conservancy Element Stewardship Abstract For spp. (North American invasive dogwoods)

I: DESCRIPTION

Description: Cornus drummondii is a one to six meters tall growing in thickets (Soper and Heimburger 1982). Tree forms may grow 15 m in height (Fernald 1950, Wilson 1965). The are entire, opposite, and ovate to elliptical. They are distinctly scabrous and have attenuate tips. White borne on loose, flat or rounded corymbs bloom mostly in May and June (Fernald 1950, Stephens 1973, Steyermark 1977, Soper and Heimburger 1982). Slender red pedicels support white subglobose drupes that ripen in August through October.

Cornus racemosa is an ascending shrub 2.5 m high with slender gray to light brown branches. Leaves are simple, opposite, lanceolate, elliptic or narrowly ovate, long- acuminate, 5-10 cm long and 2-4 cm wide tapering to short (3-10mm) petioles. The flowers are small, creamy white and ill-scented in cymes that are nearly as high as they are broad. The is a white drupe less than 6 mm in diameter on a red and in red- stalked raceme-like clusters (Fernald 1950, Soper and Heimburger 1982). Wilson (1965) considers C. racemosa a subspecies of C. foemina; C. foemina subsp. racemosa occurring in the northern half of its range and C. foemina subsp.foemina in the south. C. stolonifera is an ascending to loosely spreading shrub with branches often prostate and freely rooting. Branchlets are green and pubescent, becoming smooth and purplish to bright red, the pith large and white. Leaves are broadly ovate to oblong-lanceolate, simple and opposite, 5-15 cm long and 3-9 cm wide, dark green above, paler to whitened and glabrous beneath. Flowers are small, dull white in flattish-topped cymes. The fruit is a rounded white or bluish drupe, 6 mm or more in diameter (Fernald 1950, Soper and Heimburger 1982). Where they occur together, C. stolonifera may be told from C. racemosa by its flat or rounded, as opposed to pyramidal, , and twigs red with a white pith, as opposed to tan or gray twigs with a white pith becoming brown by the second year (Stephens 1973). (C. stolonifera is now included in the species C. sericea (silky dogwood) by Kartesz (1994 checklist)).

Cornus obliqua is an upright or spreading shrub up to 3 meters high with reddish-brown to grayish bark. The leaves are simple and opposite, lanceolate to narrowly ovate-oblong, with tapering or gradually narrowed bases and gradually acuminate tips, whitish or glaucous beneath. White flowers are borne on terminal round-topped cymes. The fruit is a blue, one-seeded drupe. Fernald (1950) states that C. obligua is similar to C. amomum and the two are often confused. Wilson (1965) considers these as subspecies of C. amomum; C. amomum subsp. obligua occurring in the northeast and midwestern states and C. amomum subsp. amomum restricted to the Appalachian mountains and foothills. Cornus drummondii Cornus sericea Cornus foemina Cornus amomum ssp obligua Cornus obligua

II. STEWARDSHIP SUMMARY

Dogwoods are natural successional components of many woodland ecosystems in North America. Originally kept off the prairies by wildfires, dogwoods are one of various woody species that have invaded prairies and wetlands, at the expense of native prairie and habitat, due to the post-settlement decline in fire. Woody plants have also invaded some floodplains where water diversion has greatly reduced river flow, resulting in reductions in channel width and destruction of wildlife--especially migratory waterfowl--habitat.

Old aerial photos can be helpful in determining historic abundance of woody plants and setting a management goal for desired percent cover. Dogwoods are topkilled by fire but resprout readily, so the key to effective control is repeated burning, possibly in conjunction with cutting and/or herbicide application. Recommended time for burning or cutting is late spring (after dormancy breaks) to late summer (before dormancy sets in). Spring burns are most commonly prescribed, although in early fall fuels in low areas should be drier and produce more intense and complete fires (burn in early fall when dogwood is still green but grasses are dormant). Repeated (annual) burning may not be feasible due to insufficient fuels, but alternating years of cutting and burning can provide adequate control. Time and labor permitting, repeated cuttings over a single season (once in spring after bud break and again in mid-late summer) may be more effective than a single cutting.

Herbicide application may be necessary in the initial recovery phase of management in heavily infested areas. The recommended method of herbicide application is to apply glyphosate in a 10-20% solution or AMS in a concentrated solution to stumps immediately after cutting. These chemicals are recommended because of their relatively low toxicities, lack of persistence in soils, and effectiveness at controlling woody weeds.

III. NATURAL HISTORY

Range: C. drummondii is native to North America and presently occurs from Ontario to South Dakota, south to eastern Texas, east to Georgia and north through western Tennessee and Kentucky (Sargent 1947, Fernald 1950, Wilson 1965, Stephens 1973, Soper and Heimburger 1982). Cornus racemosa is native to North America and occurs in dry to moist open sites from central Maine to southern Ontario and Minnesota, south to Delaware, Maryland and Virginia and west to Kentucky, Missouri, and Oklahoma (Fernald 1950). Wilson (1965) lists C. racemosa as a subspecies of C. foemina; C. foemina subsp. racemosa occurring in the northeast U.S. from Maine to Minnesota, south to Missouri and east to Virginia, C. foemina subsp. foemina occurring in the southeast from S. Carolina to west to Arkansas and eastern Texas (Wilson 1965).

C. stolonifera is native to North America and occurs along shores and in thickets from Newfoundland and S. Labrador west to Ohio, Indiana, Illinois, Iowa, Nebraska, and south to New Mexico, Arizona and California (Fernald 1950).

Cornus obligua is native to N. America and occurs in swamps, marshes, wet woods or thickets, and river banks. Wilson (1965) considers C. obligua a subspecies of C. amomum. C. amomum subsp. obligua occurs from Maine south to Massachusetts west through New York (not in Pennsylvania), then further west and south through Ohio, , Indiana, Wisconsin, Illinois, Minnesota, Iowa, Missouri and Arkansas, with a few locations west into Oklahoma, Kansas, and Nebraska. C. amomum subsp. amomum occurs from Pennsylvania south through Virginia, West Virginia, Tennessee, Kentucky, North Carolina, northwestern South Carolina, and northern Georgia, Mississippi and Louisiana.

Habitat: Characteristic habitats of C. drummondii include limestone glades, river bluffs, woodland prairie margins, hillside pastures, sandy stream banks, river bottoms, intermittent streams and ravines of prairies, oak savannas and open woods. It may grow in clay (Soper and Heimburger 1982), silty-clay loam (Bragg and Hulbert 1976), or silty loam soils, and tolerates extremes in topography and moisture. Rough-leaved dogwood also grows along roadsides, in ditches, and in fencerows (Mohlenbrock and Voigt 1959, Wilson 1965). Occasionally it is planted in windbreaks (Carpenter 1940, Stephens 1973) and for wildlife food and habitat (Brinkman 1974).

Cornus racemosa (gray dogwood) occurs in thickets and moist soil in riparian zones, roadsides, on sandy slopes and limestone ridges (Soper and Heimburger 1982).

C. stolonifera grows in low, damp ground along shores, river flats, marshes, damp open woods, and roadsides (Soper and Heimburger 1982). In Wisconsin, Haglund (pers. comm.) described C. stolonifera as an inhabitant of sedge meadows, calcareous fens, wet mesic prairies, and stream banks.

Cornus amomum subsp. obligua and C. amomum subsp. amomum occur in similar habitats, but C. amomum subsp. obligua tends towards more open areas than C. amomum subsp. amomum (Wilson 1965).

Ecology: Sexual reproduction: These dogwoods probably reach sexual maturity in three to four years. There is one viable seed per drupe in all four species (Stephens 1973). A complex of hybrids exists between C. drummondii, C.racemosa (C. foemina subsp. racemosa) and C. foemina (subsp. foemina). The hybrids have high pollen viability, robust growth, and fruit sometimes larger and more plentiful than that of the parent (Wilson 1965).

Seed dispersal: Seeds are dispersed by a variety of birds, including crows, vireos, redheaded woodpeckers and bluebirds (Ridley 1930), autumn through winter (Stephens 1973). Availability of perching sites may be important in dispersal. Smith (1975) included C. racemosa in his study of re-vegetation of forest openings, and found that most seeds were deposited by birds within 25 meters of the seed source, often in the shade near perching sites. About 25% of the dispersed seeds left the study area after consumption by long-distance flying birds.

Germination: Germination usually occurs in the spring following seed production and dispersal to a favorable site, but may be delayed a year due to a dormant embryo, hard pericarp (Brinkman 1974), and possible chemical inhibition by the pulp (Goodwin 1948). Mechanical and chemical scarification and stratification techniques are used commercially to stimulate germination in dogwood (Brinkman 1974). C. racemosa and C. stolonifera are described by Krefting and Roe (1949) as having "double dormancy", or requiring two periods of stratification for germination. C. stolonifera seeds that were treated first with acids then with cold stratification experienced almost 100% germination, whereas germination was much lower for those seeds receiving cold treatment only. However, seeds of both species that were twice stratified by passage through quail or pheasant gut plus cold treatment also gave relatively low percent germination. The authors suggested that this was due to a large amount of variability in the extent of scarification from the bird gizzards. Some seeds are injured or overstratified in the bird gut and some are left unscathed or understratified (Krefting and Roe 1949). Smith (1975) described C. racemosa as fruiting abundantly but having very low germinability, depending instead on vegetative reproduction to enhance its propagation. Germination tests of scarified and stratified C. drummondii seeds have shown a 25% germination in three samples after 50 days (Brinkman 1974).

Seedling establishment: Some Cornus spp. shrub seedlings are tolerant of variable light intensities, and may become established in woodland edges, within woods, or in open areas (Gatherum et al. 1963, Smith 1975). Seedlings may invade grasslands alone or with other woody plants (McClain per. comm.).

Asexual reproduction: C. drummondii, C. racemosa, C. stolonifera and C. obligua reproduce most successfully by vegetative growth following seedling establishment. Thickets may expand by adventitious underground shoot growth or rhizomatous growth (Stephens 1973, Wilson 1965, Smith 1975).

Populations: Dogwood invasion of grasslands from swales, ravines, and woodland edges of floodplains is accelerated by vegetative reproduction and tolerance to wind, full exposure or partial shade, and dry soils (Pound and Clements 1900, Costello 1931, Steyermark 1940, Albertson and Weaver 1945, Weaver 1965, Duxbury 1982). From the time of initial woody invasion of Kansas range study sites, C.drummondii increased coverage from 6% in 15 years to 54% in 45 years on slopes with rock outcroppings. It also became a dominant shrub during a 25 to 45 year period on other slopes and on lower loamy upland sites (Bragg 1974). Thickets may be of dogwood alone, or mixed with pre- occurring species such as smooth sumac (Rhus glabra) and coral berry (Symphori carpus orbiculatus) (Aikman 1928, Albertson and Weaver 1945, Bragg and Hulbert 1976, Ewert pers. comm.).

As density within a dogwood thicket increases, groundcover vegetation decreases and may become entirely absent (Aikman 1928, Weaver 1965). Annual weeds sometimes grow beneath dogwood (Duxbury 1982, Nyboer pers. comm. 1983), and bur oak (Quercus macrocarpa) may invade dogwood thickets (Albertson and Weaver 1945, Aikman 1928). Dogwood may persist and sometimes dominate the understory of woods (Duxbury 1982).

Impacts: Cornus spp. are natural early successional components of many woodland ecosystems in North America. They have many adaptions that enable them to take advantage of open areas, including a large number of seeds, vigorous seedlings and rapid subsequent growth, dispersal by birds, and high tolerance to adverse conditions such as drought and shade (Smith 1975, citing Auclair and Cottam 1971). Rapid and extensive cloning by rhizomatous growth allows dogwood species to create dense thickets which crowd out desired grasses, sedges and forbs, and alter wildlife habitat. Invasion of dogwood, along with other woody species, into prairies and wetlands became more extensive mainly due to the post-settlement decline in wildfires.

Woody plant invasion of floodplains is a concern in some areas, particularly in the western U.S., where stream diversion has greatly reduced the flow in rivers. Water diversion can reduce river flow to the extent that dogwoods and other woody plants invade the floodplain, reducing river channel width and drastically altering wildlife habitat. For example, woody plant invasion, including C. drummondii, willows (Salix spp.), green ash (Fraxinus pensylvanica) and black locust (Robinia pseudoacacia), has reduced channel area of the Platte River in Nebraska by 50-85%, resulting in a loss of up to 97% of the roosting habitat for sandhill and whooping cranes and many other migratory birds (Currier 1987).

IV. MANAGEMENT/MONITORING

Management Requirements: Management goals are often to reduce abundance of dogwood in a prairie or wetland to an acceptable level rather than achieve complete eradication. Acceptable levels are usually determined by investigating the historical distribution of the dogwoods and other woody plants at a site. Fire: The most advantageous time to burn for control of dogwoods is unknown. Adams and Anderson (1982) found that both summer (July 14) and winter (March 12) burns eliminated C. drummondii from their shady plots, but they indicated that the March burn was more effective in general woody plant control. Toney (pers. comm.) suggested late April burns in Missouri, and Nyboer (pers. comm. 1987) recommended burning in the spring after budbreak. Launchbaugh and Owensby (1978) recommended two to three years of consecutive spring burns; April 15-25 in the south and April 20-May 1 in the north. Haglund (pers. comm.) suggested that in the fall, when dogwood is still green but grasses are dormant, there would be more fine, dry fuels and a greater possibility of low humidity and high temperatures effecting hotter fires than in spring. Reuter (1986) stated that prescribed burning in peatlands (sedge meadows) is most effective in early spring when frost and/or high soil moisture reduce the chance of a peat-destroying fire.

Reuter (1986) reported that prescribed burning alone was no less adequate for controlling invasive in the Summerton Bog sedge meadow in Wisconsin than cutting in conjunction with hand-torching, and costs as much as 15% less than the latter treatment. Of the shrubs present in the study plots, C. stolonifera was most vigorous as a resprout and showed rapid first and second season recovery (Reuter 1986). Haglund (pers. comm.) noted that repeated burning (every other year for perhaps 10 years) would be required to achieve the desired level of scattered shrubs in the Summerton Bog sedge meadow. Resprouting is likely following burns, and problems with fire management result when fuels are insufficient to allow annual burning (Aldous 1929, McClain pers. comm., Nyboer pers. comm. 1987). Carbohydrate reserves in woody plants may reach pre-treatment levels if several years are allowed between burns. Fire may be combined with cutting and herbicide controls, especially during initial recovery phase management.

Cutting: The season of cutting probably influences resprouting ability. In Appalachia, midsummer (July) cutting of Cornus florida resulted in clumps of resprouts 2.5 feet shorter and 1.5 feet narrower, 3 years after cutting, than of those cut in winter. Tallest resprouts were of plants cut in March (Buell 1940). Cutting in May, or May and August, for two or three consecutive years is recommended for rough-leaved dogwood control in Missouri (Toney pers. comm.). Nyboer (pers. comm. 1983) also suggested multiple cuttings in one growing season. According to McGrath (pers. comm.), repeated cutting, even in conjunction with burning, does not fatally stress dogwood and it will continue to resprout and come back. Herbicides may be necessary to achieve good control during the initial recovery phase of management. McGrath (pers. comm.) reported that excellent control of C. racemosa and C. obligua (synonymous with C. amomum) can be achieved by cutting and herbicide application followed with burning. He recommended slowly working down large clumps by cutting thin (approx. 10 ft. wide) strips around the clump periphery and painting cut stumps with herbicide, burning the following spring, and then repeating the cycle until desired control is achieved. The control scheme would look something like this:

Year 1: Cut 10 ft. wide ring around patch and paint cut stumps with herbicide. (Summer cutting recommended although any time is OK.). Year 2: Burn in spring (after budbreak).

Year 3: Cut another 10 ft. wide strip and apply herbicide to cut stumps.

Year 4: Burn in spring.

After the stand has been reduced to an acceptable level, burning and cutting alone should maintain desired abundance, and burning frequency may possibly be reduced (McGrath pers. comm.). Nyboer (pers. comm.) also stated that cutting and herbicide application followed by burning is the best procedure for control of Cornus spp., although in some areas (presumably milder infestations) cutting alone or spring burning (after dormancy breaks) followed by mid-late summer cutting (July-August) may be adequate.

CHEMICAL CONTROL

Detailed information on herbicides are available in such publications as the Herbicide Handbook, published by the Weed Science Society of America (Ahrens 1994) or USDA (1984), and will not be comprehensively covered here. The Weed Science Society publication gives specific information on nomenclature, chemical and physical properties of the pure chemical, use recommendations and precautions, physiological and biochemical behavior, behavior in or on soils and toxological properties for several hundred chemicals. In applying herbicides it is recommended that a dye be used in the chemical mixture to mark the treated plants and thus minimize waste.

Chemical: Various herbicides have been tested and found useful for control of dogwoods, especially when used in conjunction with cutting and burning. Glyphosate is effective in a 20% solution in water put on cut stumps (McGrath pers. comm.) and can be used over water on C. stolonifera in the formulation marketed as RODEO, or on drier upland sites in the formulation ROUNDUP. McGrath (pers. comm.) suggested that a lower concentration may give adequate results, although it had not been tested. Nyboer (pers. comm. 1987) recommended treating cut stumps with a 10-20% solution of glyphosate or triclopyr in water; the higher concentration to be used on larger stems.

Currier (1987) reported 100% control of C. drummondii on study plots in the Platte River floodplain after mowing and subsequent application of a 1 1/2% solution of glyphosate as a foliar spray. Elwell et al. (1974) observed limited control of C. drummondii 4 years after application of picloram as a foliar spray at 1-1.5 lbs/A. McNab and Mayer (1969) observed 13% mortality using the same procedure with picloram plus 2,4-D (TORDON 101). Tebuthiuron, usually applied as pellets, shows effective control of C. drummondii by causing multiple defoliation the first and second year of application, and finally no resprouting (Baker et al. 1980, Streitzke 1978). Currier (1987) reported greater than 95% control of C. drummondii on floodplain islands in the Platte River using tebuthiuron pellets. Tebuthiuron and picloram are highly persistent in the environment and therefore present more of a hazard to nearby plants and wildlife than some other chemicals, such as glyphosate, that break down more rapidly.

A growth state called vegetative maturity occurs in late September in C. stolonifera (Crabtree and Fuchigami 1979, Fuchigami, et al. 1977). Studies showed that herbicides applied before the onset of vegetative maturity are more effective at controlling and preventing resprouting of C. stolonifera (Crabtree and Fuchigami 1979).

Species/ Herbicide Application Application Date/ Control Reference Rate Method Location C. drummondii/ Picloram 1-1.5lb/A Spray June/OK 30--40% Elwell et al., 1974 after 4 years

C. racemose/ AMS as strong paint stems Feb/IL 100% Packard, 1983 as possible cut 3” from unpub. in water ground

C. drummundii/ Glyphosate 10-20% painted after July/August Good Nyboer, 1984 cutting IL

C. racemose Triclopyr stronger on cutting unpub. larger stems

C. racemose Glyphosate 20% Painted after Summer/IN excellent if C. obligua Cutting in conjunction McGrath, 1987 wi/burning

C. drummondii Glyphosate 1.5% Foliar spray NE 100% Currier 1987 Unpub.

C. spp., prob. Triclopyr 4 lb/100 sprayed on summer 100% C. florida gallons oil uncut stem’s many states Fears, 1980 lower 18”

C. florida Triclopyr 20-30% sprayed on various 100% Hall & Hendler in oil uncut stem’s seasons/OH 1985 lower 12-15”

C. florida 2,4-D 1 ml or 1” spacings Feb/NC 13% McNab & calibrated around stems Moyer, 1969 stem injections

C. florida 2,4-D with concentrate 1” spacings Feb/NC 53% McNab & Picloram per incision around stems Moyer, 1969

Monitoring Requirements: Dogwood populations should be monitored for maintenance of desired levels of abundance in their natural habitats. Where possible, present day levels of abundance can be checked against old aerial photos. Rate of spread can be monitored by counting stems along transects and/or marking outer edges of thickets or clumps each year.

Management Research Programs: High school students in Akron, Iowa are conducting a 5- year study (1985-1989) of various cutting and burning schedules on Cornus spp. Contact: Ron Wilmont, Akron Westfield Community School, Kerr Drive, Akron, Iowa 51001. 712/568-2020.

Management Research Needs: 1. Identification of vegetative maturity in the various Cornus spp. through defoliation experiments and application of results to cutting, burning, and chemical management. 2. Measurements of thicket spread. 3. Applicability of C. florida control to other Cornus species.

V. INFORMATION SOURCES

Acknowledgements: We are indebted to all the botanists and ecologists who took the time to provide the information necessary for the preparation of this Element Stewardship Abstract.

Bibliography:

Adams, D.E. and R.C. Anderson. 1982. Differential response of woody and herbaceous species to summer and winter burning in an Oklahoma grassland. The Southwestern Naturalist 27(1):55-61.

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McClain, William. 1983. District Heritage Botanist, IL Dept. Conservation. Telephone conversation with Carmen K. Converse, TNC, MRO. Nov. 11, 1983.

McGrath, D. 1987. Director of Stewardship, Indiana Field Office, TNC. Telephone conversation with N. Eckardt, TNC, MRO. July 28, 1987.

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______. 1983. Natural Heritage Biologist. Telephone conversation with C.K. Converse, TNC, MRO.

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Steyermark, J.A. 1977. Flora of Missouri. Ames, Iowa: Iowa State University Press.

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Toney, Thomas. 1983. Prairie biologist, Missouri Dept.of Conservation. Telephone conversation with C.K. Converse, TNC, MRO. Nov 29, 1983.

Weaver, J.E. 1965. Native vegetation of Nebraska. Lincoln, NE: University of Nebraska Press.

Wilson, J.S. 1965. Variation of three taxonomic complexes of the Cornus in eastern United States. Trans. Kansas Academy of Sci. 67(4): 747-817.

VI. DOCUMENT PREPARATION & MAINTENANCE

Edition Date:87-10-20

Authors: C. Converse; update by Nancy Eckardt