Differences in vegetation structure, species composition, and soil microbial communities among forests of different successional ages and types in the Lake Tahoe Basin

Old-growth forests are increasingly rare ecosystems believed to be distinct from seral, less mature forests. Ecologists have developed definitions of old growth to distinguish their ecological properties from those of younger stands. An alternative to defining old growth stands, is to study forests of different ages in order to characterize variability common to successional stages.{09}The Lake Tahoe Basin offers an opportunity to study forest succession within a single, large ecosystem. I studied the structural, compositional and microbial characteristics in two ages, seral and old growth, and four types of forest Jeffrey pine, white fir, red fir, and mixed conifer.; Seral forests in the Lake Tahoe Basin had greater total basal area and log biomass than old-growth forests. Old growth forests had greater overstory and understory tree density than seral forest with total tree density being twice as high in old growth. Old growth also had deeper duff layers.; The sera] forests in Tahoe maintain an herb diversity, richness, and abundance similar to that of old-growth forests. A rainshadow effect in the Basin required the shrub data be split into the east (dry) and west (wet) sides of the Basin. On the east side, seral forests had greater shrub richness than old-growth forests. East-side mixed conifer had greater shrub richness than east-side red fir and west-side white fir had greater shrub richness than west-side mixed conifer. Indicator species included the herb Arabis rectissima for seral forests, a white fir indicator shrub Ribes roezhi, and a Jeffrey pine indicator shrub Purshia tridentata. If Tahoe Basin seral forests were managed towards old growth modest changes in composition could be expected, including a decrease in the occurrence of exotic species.; For soil microbes, Thiobacillus had a greater presence in seral forests throughout the Basin. Bacteria levels in Tahoe's seral forests appear to be higher than those found in other seral conifer forests, while the amount of microbial biomass overall is on par with that found in other studies.