Forest/Meadow Health Research Progress and Plans Michael Barbour, Elise Kelley, and Kathren Murrell Center for Ecological Health Research University of California, Davis      More than 20 relictual stands of pristine old-growth forest in the Tahoe Basin have been located and quantitatively described in terms of physical habitat features, vegetation structure, species composition, canopy cover, basal area and biomass of snags, biomass of coarse woody debris, litter depth on the forest floor, carbon-nitrogen-phosphorus content in the mineral soil, and a profile of microbial groups present in the soil (as estimated from their biochemical signatures). These stands represent four of the most prominent forest types in the Basin: Jeffrey pine, mixed conifer, white fir, and red fir forests. Riparian and mixed subalpine forest types were not examined because of their small cumulative areas.      The old-growth stands have been compared to a similar number of mid-seral Basin stands located by the Forest Service in the1990s. We visited these sites and quantified them with the same methods used for old-growth stands. Our objective was to find attributes and values that would serve to cleanly delimit the transition from seral to old-growth biotic conditions. We have been able to identify several such attributes, including the ratio of understory tree density to overstory tree density, the density of snags, the biomass of coarse woody debris, the density of trees > 75-100 cm dbh, soil phosphorus content, and the array of microbial groups present in the soil. These Basin-specific attributes can be used to quantitatively define what is meant by the expression, "old-growth forest" in the Tahoe Basin.      A similar number of meadows in the Basin have been randomly located for quantitative description in terms of: physical attributes (including evidence of disturbance by livestock grazing or human trampling, community and habitat diversity, plant species diversity, the species composition of every community identified, and the nature of forest stand dynamics and patterns of species change at the meadow/forest edge, where wetland transitions to upland. These data remain to be analyzed in 2001-2.      The next research step, planned for 2001-3, is to place what is known about the erosive nature of surfaces beneath various vegetation types into a quantitative model of erosion for a representative watershed in the Basin. The obvious choice is the Ward Creek watershed because this watershed has the best data record for sediment load carried at various points of Ward Creek through the watershed, and also because the diverse vegetation has recently been mapped by the Forest Service at a scale of 1:10,000. Included among the vegetation types are meadows and the four major forest types for which we have descriptive, defining data.      Our objective is to reconstruct, from the model, the amount of sediment load that would have exited a pre-contact, old-growth-dominated Ward Creek watershed. By comparing the reconstructed amount to known current amounts in the post-contact, largely seral-dominated watershed, we may be able to predict the result of a Basin-wide management plan that would move seral forests to old-growth status on sediment loading to the entire lake. (Furthermore, we can also predict the C-N-P nutrient content of that sediment load, since we have measures of these nutrients in the topsoil of old-growth and seral forests.)      We imagine that old-growth stands create more stable forest floor conditions, but a quantitative interpretation of that prediction has never been attempted. Once the absolute relationship between sediment/nutrient diminishment and old-growth status is known, management decisions about old-growth restoration can be based on something more objective than imagined predictions of ecosystem-wide consequences. Without such information, managers have no objective reason to choose among the diverse targets proposed for the ultimate percent of forested area to be in old-growth status (20-85%).