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 relateto growth and survival in the forest. Five to 10 plants of nine herbaceous species were totally excavated inold-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 Cas-cades. Achlys triphylla, Clintonia uniflora, and Smilacina stellata maintain extensive rhizome systems withboth short and long shoots. This growth form allows these species flexibility in exploiting the forest en-vironment. The three species differed in rate of extension growth and rooting depth. Arnica latifolia spreadsby long rhizomes, which persist for only a few years; thus, extensive interconnected stem systems do notdevelop. Rubus lasiococcus and Linnaea borealis have extensive stolon systems with greater potential ratesof 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 threespecies often included the original seedling structure, indicating that seedling establishment is relativelyfrequent. On the six species with extensive vegetative spread, we never found a seedling source; genets areolder than 5-36 yr, and new genet establishment appears to be uncommon. The differences in growth formamong the species help to explain their ability to survive and coexist in the heterogeneous forest floorenvironment.