Description
Cornus drummondii is a shrub 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 leaves are entire, opposite, and ovate to elliptical. They are distinctly scabrous and have attenuate tips. White flowers 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.
Habitat
Characteristic habitats 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).
Ecology
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 plant 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).
Reproduction
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.
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). Some seeds are injured or overstratified in the bird gut and some are left unscathed or understratified (Krefting and Roe 1949). 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 pers. comm.).
Asexual reproduction: C. drummondii, C. racemosa, C. stolonifera and C. obliqua 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).