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1999 Progress Report: Pre-contact Forest Structure
EPA Grant Number: R825433C031Subproject: this is subproject number 031 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: Pre-contact Forest Structure
Investigators: Barbour, Michael
Institution: University of California - Davis
EPA Project Officer: Levinson, Barbara
Project Period: October 1, 1996 through September 30, 2000
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
RFA: Exploratory Environmental Research Centers (1992)
Research Category: Center for Ecological Health Research , Targeted Research
Description:
Objective:To reconstruct old-growth forest vegetation of the Lake Tahoe watershed as it existed prior to significant Euroamerican contact (approximately 1850) and to quantify any changes since then that might have important ecological links to lake water quality.
Progress Summary:We completed a survey of approximately 400 vegetation polygons mapped by the Forest Service in 1970 as potentially containing pristine old-growth forest. Ten percent of those poly-gons did, in fact, contain such vegetation and those stands were quantitatively sampled, every species being measured for at least canopy cover. We subjected the 38 stands to multivariate analyses, including cluster analysis, ordination, and simple linear regression against a dozen environmental factors. We also analyzed current aerial photographs of all basin vegetation, reduced the types to 36 (18 west-side + 18 east-side), and prepared GIS summary statistics on the area of each. We summarized modern vegetation data for nearly 800 forest plots taken by the Forest Service in its Forest Inventory Analysis (FIA) on-going program, in order to have a quantitative summary of seral, second-growth forests that could be compared to our 38 plots of pristine old-growth. Finally, we attempted to recreate pre-contact forest structure and composition by: (1) summarizing land office records of witness trees, recorded during surveys in the 1870s; (2) analyzing data collected by Dr. Alan Taylor on the number and size of stumps left by clearcut harvests of old-growth forests that existed in the 1870s on the east side of Lake Tahoe; and (3) and interpreting anecdotal statements of early professional foresters at the turn of the century. We also worked as part of a watershed assessment research team, convened by the Forest Service, to summarize current ecosystem health in the Lake Tahoe basin; that work expanded our accomplishments for this past year. Finally, we have begun to quantitatively characterize the immediate neighborhoods of each old-growth stand, developing a numerical scale that expresses the ecological distance of that neighborhood from old-growth status and the suitability of that neighborhood for such active management activities as prescribed fire and thinning.
Conclusions to date. By augmenting my on-the-ground survey with an interpretation of remotely sensed data, Dr. Fites Kauffman and I have prepared a map of relictual old-growth forest in the basin. We used such criteria as the size of individual tree crowns, total canopy cover, the number of large-crowned trees per hectare, and the absence of any obvious past disturbance. The total area came to 2138 ha, and it includes forests in all three elevation zones (lower montane, upper montane, subalpine) and in both parts of the basin. This area equals 4.5% of the forested area of the basin. Based on data from national parks on the west side of the Sierra Nevada, pre-contact old-growth area probably accounted for only 55% of forested area because of such natural disturbances as blow-downs, avalanches, and crown fires. If this estimate is correct, then old-growth area in the basin has been reduced to one-tenth of its pre-contact area. While there is scientific consensus that optimal species richness results from a mosaic of old-growth and second-growth patches, there is no consensus as to the optimal ratio of old-growth to second-growth areas. I would personally guess that the current Tahoe basin ratio of 1:21 is too low, but that a restoration target of 1:0.8 may be unnecessarily high.
We classified the vegetation in two ways: according to traditional phytosociological methods that include the entire flora, and according to typical American-style methods that emphasize dominance. The phytosociological approach generated two associations with three subassociations each (6 communities); the dominance approach generated four series. Regressions and ordinations showed that the most significant environmental factors that separated these communities and explained gradients of vegetation change were: (1) position east of the Sierra Nevada crest; (2) annual precipitation; (3) elevation; (4) slope aspect; (5) date of complete snow melt; (6) litter depth; and (7) degree of soil profile development.
Easterliness is an important ecological factor because it is highly correlated with annual precipitation. At a given elevation, annual precipitation drops by 50% as one moves from the western part of the basin to the eastern part. The western shore of the lake (1900 m) receives an average of 750-1000 mm whereas the eastern shore receives only 500-650 mm. In the subalpine zone (2600 m), the western portion receives 1000-1500 mm, whereas the eastern portion receives only 650-900 mm. Winter snowpack and melt date are other important factors for vegetation because they too have wide ranges in the basin. As one moves upslope from lake level to the subalpine, that is in the distance of only 700 m elevation change, mean winter snowpack depth rises from 0.5 m to 3.5 m and snowpack duration increases from <130 days to 250 days. We have used a model developed and used successfully by Dr. Ed Royce for the southern Sierra Nevada, to predict snowpack depth and duration in the basin.
The 18 west-side and 18 east-side vegetation types mapped and measured for area with the help of Dr. JoAnn Fites Kauffman of the Forest Service, included forest and non-forest types. Pristine old-growth forests are significantly less dense and have lower amounts of basal area in the eastern portion of the basin, compared to the western. Areas occupied by several forest and non-forest types are asymmetrically distributed in the two portions: meadows, for example, are much more abundant in the west as is the white fir forest series and the mixed subalpine woodland series. Conifer forests cover 58% of the watershed's 82,000 ha, leaving the rest to meadows, montane chaparral, riparian forest, aspen woodland, and barren rock outcrops. Linkages between vegetation and lake water quality in the basin, therefore, are only half explained by forest cover, and attention should be paid in the future to other vegetation types, especially meadows (nearly 6000 ha).
Historic data from clearcut stumps, land office survey records, and anecdotal forest survey accounts uniformly confirm that the pre-contact ratio of fir:pine in the lower montane zone of the basin was close to 1:1. This ratio is quite different from the modern ratio of fir:pine in basin old-growth forests that range from 10:1 to 40:1 in the oldest cohort, and that exceed 40:1 in cohorts younger than 200 yr. Modern seral forests in the basin, as sampled in the FIA program, are also highly dominated by fir and contain tree densities 4 times that of the old-growth stands. Old-growth forest fuel, as approximated by the weight of coarse woody debris (snags and logs >25 cm diameter), averaged 58 metric tons per hectare and several stands had levels >150 metric tons per hectare. Finer fuels would probably add an equivalent biomass, but they were not measured. Although high, these values are not outside the range of modern forests throughout the northern Sierra Nevada and the southern Cascades.
Future Activities:A manuscript describing methods, results, and conclusions, was submitted to the Journal of Vegetation Science in July 1999. It includes forest health data (disease incidence and tree mortality) accumulated by Dr. David Rizzo. An oral presentation of the same material was presented in August at the annual meeting of the International Association of Vegetation Science in Bilbao, Spain.
Our next objectives are three-fold: (1) to link forest vegetation more closely to models of lake water quality; (2) to quantify meadow vegetation, the leading non-forest vegetation type in the basin; and (3) to apply our techniques to management issues in the basin. In order to link our vegetation data to water quality, we need to extrapolate some functional attributes of old-growth and second-growth forests. For example, if we could estimate the volume of water transpired by such forests, the differences could be added to hydrological models; if rooting depths differed among forest dominants, that information would be valuable to hydrological models; if the rate of litter decomposition, litter erosion, soil erosion, or overland flow of water differed among forest types, that also would be valuable information for hydrological and water quality models. One of my graduate students has already begun a study of basin meadows, including their hydrology, work supported last year by the Forest Service. With regard to management issues, the TRPA and the Forest Service both desire to move seral forest stands towards old-growth status. We suggest that a place to begin is by using the 38 pristine old-growth stands as nuclei around which neighborhood vegetation can be managed towards old-growth status. We predict that there will always be monetary constraints on restoration activities, and therefore this work can begin only around some few of those stands. We propose to develop a quantitative scale by which neighborhoods can be assessed in terms of their ecological distance from old-growth status, combined with their potential for being actively managed by such techniques as prescribed fire and thinning. Such factors as distance from human habitations, ease of access, and uniformity of terrain would be part of this assessment--as would biotic traits of the vegetation.
Supplemental Keywords:Ecosystem Protection/Environmental Exposure & Risk, ENVIRONMENTAL MANAGEMENT, Water, INTERNATIONAL COOPERATION, Scientific Discipline, RFA, ECOSYSTEMS, Ecosystem/Assessment/Indicators, Water & Watershed, Restoration, Aquatic Ecosystem Restoration, Aquatic Ecosystems & Estuarine Research, Terrestrial Ecosystems, Ecological Monitoring, Aquatic Ecosystem, Ecological Indicators, Biochemistry, Environmental Microbiology, Watersheds, Ecosystem Protection, Ecology and Ecosystems, Resources Management, water quality, ecological impact, lake ecosystem, forest tenure, watershed management, watershed restoration, ecosystem modeling, ecological restoration, deforestation, ecological research, aquatic habitat protection , ecosystem restoration, wetland restoration, forested basins, wetland plant species, conservation, GIS, forest ecosystems, aquatic ecosystems, ecosystem assessment, environmental stress, vegetation , lake ecosysyems, deterministic linkages, ecological assessment, forest conservation, forests, anthropogenic stress, restoration strategies, ecosystem stress, watershed assessment, ecological models, watershed forests, biodiversity, ecological effects, restoration planning
Progress and Final Reports:
Original Abstract
Final Report
Main Center Abstract and Reports:
R825433 EERC - Center for Ecological Health Research (Cal Davis)
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R825433C001 Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
R825433C002 Sacramento River Watershed
R825433C003 Endocrine Disruption in Fish and Birds
R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
R825433C005 Fish Developmental Toxicity/Recruitment
R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
R825433C009 Modeling Ecosystems Under Combined Stress
R825433C010 Mercury Uptake by Fish
R825433C011 Clear Lake Watershed
R825433C012 The Role of Fishes as Transporters of Mercury
R825433C013 Wetlands Restoration
R825433C014 Wildlife Bioaccumulation and Effects
R825433C015 Microbiology of Mercury Methylation in Sediments
R825433C016 Hg and Fe Biogeochemistry
R825433C017 Water Motions and Material Transport
R825433C018 Economic Impacts of Multiple Stresses
R825433C019 The History of Anthropogenic Effects
R825433C020 Wetland Restoration
R825433C021 Sierra Nevada Watershed Project
R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
R825433C025 Regional Movement of Toxics
R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
R825433C031 Pre-contact Forest Structure
R825433C032 Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
R825433C033 Subalpine Marsh Plant Communities as Early Indicators of Ecosystem Stress
R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
R825433C035 Border Rivers Watershed
R825433C036 Toxicity Studies
R825433C037 Watershed Assessment
R825433C038 Microbiological Processes in Sediments
R825433C039 Analytical and Biomarkers Core
R825433C040 Organic Analysis
R825433C041 Inorganic Analysis
R825433C042 Immunoassay and Serum Markers
R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
R825433C045 Microbial Community Assays
R825433C046 Cumulative and Integrative Biochemical Indicators
R825433C047 Mercury and Iron Biogeochemistry
R825433C048 Transport and Fate Core
R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
R825433C053 Currents in Clear Lake
R825433C054 Data Integration and Decision Support Core
R825433C055 Spatial Patterns and Biodiversity
R825433C056 Modeling Transport in Aquatic Systems
R825433C057 Spatial and Temporal Trends in Water Quality
R825433C058 Time Series Analysis and Modeling Ecological Risk
R825433C059 WWW/Outreach
R825433C060 Economic Effects of Multiple Stresses
R825433C061 Effects of Nutrients on Algal Growth
R825433C062 Nutrient Loading
R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
R825433C064 Chlorinated Hydrocarbons
R825433C065 Sierra Ozone Studies
R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
R825433C067 Terrestrial - Agriculture
R825433C069 Molecular Epidemiology Core
R825433C070 Serum Markers of Environmental Stress
R825433C071 Development of Sensitive Biomarkers Based on Chemically Induced Changes in Expressions of Oncogenes
R825433C072 Molecular Monitoring of Microbial Populations
R825433C073 Aquatic - Rivers and Estuaries
R825433C074 Border Rivers - Toxicity Studies