From: Halpern, C. B., S. A. Evans, and S. Nielson. 1999. Soil seed banks in young, closed-canopy forests of the Olympic Peninsula, Washington: potential contributions to understory reinitiation. Canadian Journal of Botany 77:922-935.

During early stand development, coniferous forests of the coastal Pacific Northwest commonly pass through a period of dense shade and intense competition during which the abundance and diversity of understory plants decline dramatically. In young, managed forests, silvicultural thinning has been proposed to enhance the structural and floristic diversity of the understory. Although germination of buried seeds is likely to be stimulated by thinning, we know little about the composition of the soil seed bank in these forests. We employed the greenhouse emergence method to assess the potential contribution of the seed bank to understory reinitiation in 40- to 60-yr-old, closed-canopy forests on the Olympic Peninsula, Washington. Seed banks were well-developed (610-7009 germinants per sq. m), containing 46 native and exotic species representing a diversity of life forms. However, many common forest understory species were absent; only 11 species were typical understory plants and these comprised <10% of all germinants. In contrast, 30% of all species and 50% of all germinants were exotic, ruderal forbs. Wind-dispersed annuals and perennials dominated litter samples whereas ruderal forbs and graminoids with limited dispersal dominated soil samples. Our results suggest that silvicultural thinning will enhance the establishment of ruderal, exotic species, but will contribute little to the regeneration from buried seed of the vast majority of forest understory plants.

Young, closed-canopy forest on the Olympic Peninsula, Washington. Note the absence of understory plants.	Monitoring seedling emergence from forest litter and soil samples.
	Contribution of open-site and forest understory taxa to the litter and soil seed bank of three young stands on the Olympic Peninsula, Washington. Seeds in the litter (the transient seedbank) and in the soil (the persistent seed bank) are dominated by ruderal, open-site species.

From: Lezberg, A. L., J. A. Antos, and C. B. Halpern. 1999. Below-ground traits of herbaceous species in young, coniferous forests of the Olympic Peninsula, Washington. Canadian Journal of Botany 77:936-943.

Variation in below-ground traits of herbaceous species may influence their ability to persist and spread during and after the closed-canopy period of forest development. In 40- to 60-yr-old closed-canopy, coniferous forests of the Olympic Peninsula, Washington, we excavated root and rhizome systems of 11 herbaceous species to compare morphology, vegetative spread, and proportion of biomass in below-ground structures. All species were perennial and most were rhizomatous; four species were nonclonal. Of the seven clonal species, only three had clonal fragments with lateral spread >30 cm. The proportion of total biomass in below-ground structures varied considerably among species (21 to 85%), and was higher for deciduous than for evergreen species. For species with high proportional biomass below ground, the ability to store resources or to acquire new resources through lateral spread of underground organs may contribute to persistence in dense coniferous forests. Plants that persist through canopy closure are likely to comprise a major portion of the understory plant cover once forest canopies begin to open. However, the extent to which they can increase in cover via vegetative spread varies markedly among species; only two species appear to have the potential for rapid vegetative expansion following canopy opening.

A clonal fragment of Maianthemum dilatatum showing extensive rhizome development with numerous interconnected ramets