Growth Patterns of Some Native Annual and Perennial Herbs in Southern Wisconsin

Abstract

Temporal growth patterns and adaptive characters were studied in 17 perennial, 16 annual, and 4 biennial native herbs for one to three growing seasons in dry—mesic, mesic, and wet—mesic forest and in open barrens in southern Wisconsin. In annuals almost all dry matter produced was retained in aerial organs following the initial growth period. Below—ground weight increased rapidly in early season and then slowly increased or declined. In perennials there was a predominantly upward weight movement during growth initiation and during flowering and fruiting and a downward movement between growth initiation and flowering and preceding aboveground senescence or death. Between autumn and spring, all perennials, including wintergreens, lost weight. Most winter annuals increased in both above— and below—ground dry weight over winter, demonstrating maintenance above the compensation point. Growth patterns of biennials in their first year were similar to perennials and in their second year were similar to annuals. Forest herbs lost less water before wilting, were more succulent, wilted in a shorter time, and had heavier seeds than herbs of open habitats. The seeds of the forest annuals were heavier and germinated more readily than seeds of forest perennials. Although most annuals are pioneer, drought—resistant plants, fores annuals wilted easily and were very succulent. This suggests that stems and leaves of the annuals apparently are supported more by turgor pressure, while the perennial plants are supported more by cell wall thickening. This special dependence of annuals on water correlates with their greater numbers in wet—mesic and mesic forests compared with drier forests. Growth characteristics are discussed for eight forest annuals: Amphicarpa bracteata, Ellisia nyctelea, Floerkea proserpinacoides, Galium aparine, Impatiens pallida, Parietaria pennsylvanica, and Pilea pumila.

Spatiotemporal dynamics ofFloerkea proserpinacoides(Limnanthaceae), an annual plant of the deciduous forest of eastern North America

“…We propose that mortality as a result of intraspecific competition, e.g., for water, may be a significant density-dependent factor. Indeed, our experiment on water stress showed that seedlings and juveniles are sensitive to water stress (see also Struik and Curtis, 1962;Struik, 1965). According to our observations and those of Smith (1983a), Floerkea's root system is limited to the top 3-5 cm of the soil and does not extend horizontally beyond ϳ2-3 cm from the plant.…”

“…Successful Floerkea plants produce an average of only four mature nutlets each (Struik and Curtis, 1962; this study). In other annual species often associated with Floerkea, such as Collinsia verna and Galium aparine (ϳ20 seeds/plant), and Impatiens capensis and I. pallida (ϳ40 seeds/plant), the lack of a long-term persistent seed bank appears to be compensated for by a somewhat larger reproductive output (Struik and Curtis, 1962;Leck, 1979;Kalisz, 1991). The absence of a persistent seed bank and the low reproductive output of Floerkea appear to be compensated for by a high survival of the seeds from dispersal to emergence.…”

“…However, in habitats where there is a high probability for an annual plant to successfully complete its life cycle (e.g., in mature forests), the optimal germinable seed fraction is often high and seed dormancy is much less important (Cohen, 1966;Watkinson, 1978;Carey and Watkinson, 1993). Successful Floerkea plants produce an average of only four mature nutlets each (Struik and Curtis, 1962; this study). In other annual species often associated with Floerkea, such as Collinsia verna and Galium aparine (ϳ20 seeds/plant), and Impatiens capensis and I. pallida (ϳ40 seeds/plant), the lack of a long-term persistent seed bank appears to be compensated for by a somewhat larger reproductive output (Struik and Curtis, 1962;Leck, 1979;Kalisz, 1991).…”

“…These filters may be related to soil moisture and leaf litter patterns, both influenced by microtopography (Struik and Curtis, 1962;Rogers, 1982). We have shown that substrate moisture influences seed germination velocity, although it does not affect overall percentage germination.…”

“…Consequently, the maintenance of a long-lived seed bank seems unlikely for the species, a somewhat uncommon characteristic for an annual plant and one that may place the populations at a high risk of local extinction. Other studies (e.g., Russell, 1919;Curtis, 1959;Struik, 1965;Ornduff and Crovello, 1968;Gauthier and Rousseau, 1973;Parker and Bohm, 1979;Rogers, 1982;McKenna, 1999;McKenna and Houle, 1999) have also considered some aspects of the taxonomy, physiology, and ecology of the species.…”