Plant Ecology

, Volume 177, Issue 1, pp 13–24

Influence of light and soil moisture on Sierran mixed-conifer understory communities


    • Sierra Nevada Research Center, PSW Research StationUSDA Forest Service
  • Brian Oakley
    • College of Forest ResourcesUniversity of Washington
  • Rob Fiegener
    • Department of Environmental HorticultureUniversity of California
  • Andrew Gray
    • Forest Inventory and Analysis, PNW Research StationUSDA Forest Service
  • Michael Barbour
    • Department of Environmental HorticultureUniversity of California

DOI: 10.1007/s11258-005-2270-3

Cite this article as:
North, M., Oakley, B., Fiegener, R. et al. Plant Ecol (2005) 177: 13. doi:10.1007/s11258-005-2270-3


Sierra Nevada forests have high understory species richness yet we do not know which site factors influence herb and shrub distribution or abundance. We examined the understory of an old-growth mixed-conifer Sierran forest and its distribution in relation to microsite conditions. The forest has high species richness (98 species sampled), most of which are herbs with sparse cover and relatively equal abundance. Shrub cover is highly concentrated in discrete patches. Using overstory tree cover and microsite environmental conditions, four habitats were identified; tree cluster, partial canopy, gap, and rock/shallow soil. Herb and shrub species were strongly linked with habitats. Soil moisture, litter depth and diffuse light were the most significant environmental gradients influencing understory plant distribution. Herb cover was most strongly influenced by soil moisture. Shrub cover is associated with more diffuse light, less direct light, and sites with lower soil moisture. Herb richness is most affected by conditions which influence soil moisture. Richness is positively correlated with litter depth, and negatively correlated with direct light and shrub cover. Disturbance or management practices which change forest floor conditions, shallow soil moisture and direct light are likely to have the strongest effect on Sierran understory abundance and richness.


CaliforniaNMS ordinationPatchPlant communityTeakettle Experimental ForestUnderstory diversity

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© Springer 2005