Ecological Implications of Belowground Morphology of Nine Coniferous Forest Herbs

The morphology of forest herbs was examined to determine how variation in growth form could relate to growth and survival in the forest. Five to 10 plants of nine herbaceous species were totally excavated in old-growth forests in the central Oregon Cascade Mountains. Underground parts were mapped, measured, oven-dried, and weighed. Additional information was derived from sites in the southern Washington Cascades. Achlys triphylla, Clintonia uniflora, and Smilacina stellata maintain extensive rhizome systems with both short and long shoots. This growth form allows these species flexibility in exploiting the forest environment. The three species differed in rate of extension growth and rooting depth. Arnica latifolia spreads by long rhizomes, which persist for only a few years; thus, extensive interconnected stem systems do not develop. Rubus lasiococcus and Linnaea borealis have extensive stolon systems with greater potential rates of spread than the three rhizomatous species. Although they expand rapidly under favorable conditions, they may be displaced by taller herbs. Rubus has larger and deeper roots than Linnaea. Tiarella trifoliata, Valeriana sitchensis, and Erythronium montanum have minimal vegetative spread. Plants of these three species often included the original seedling structure, indicating that seedling establishment is relatively frequent. On the six species with extensive vegetative spread, we never found a seedling source; genets are older than 5-36 yr, and new genet establishment appears to be uncommon. The differences in growth form among the species help to explain their ability to survive and coexist in the heterogeneous forest floor environment.