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1999 Progress Report: Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
EPA Grant Number: R825433C032Subproject: this is subproject number 032 , 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: Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
Investigators: Rizzo, David
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 identify major pest complexes (pathogens, insects) associated with overstory and understory mortality, and reduced vigor in both late seral/old-growth (LSOG) and early seral forest stands in the Tahoe basin.
Progress Summary:If we are to obtain an accurate idea of the effects of abiotic (e.g., drought, fire) and human-induced stress factors (e.g., pollution, urbanization, timber management) on forest ecosystems, we must have a detailed picture of naturally occurring biotic stress factors. Many pathogens and insects are considered to be major pests of forest ecosystems and, therefore, detrimental to management goals. However, the fact that many of these organisms are native to these sites (with the exception of white pine blister rust) indicates that they may also play key roles in ecosystem functions (e.g., directing succession, maintaining biodiversity, decomposition, or providing food for wildlife). While the importance of pathogens and insects in natural forests has been acknowledged by ecologists, relatively few studies have directly assessed their role in the dynamics of these ecosystems.
Graduate student Patricia Maloney is studying two comparable forests that differ in their level of human impacts. In the Lake Tahoe watershed, studies of late-seral/old-growth forest stands will provide baseline data on the importance and distribution of pest organisms prior to Euroamerican settlement, while studies of early seral stages will detect current patterns of mortality and stress. In addition, we have examined pest incidence and host mortality at a study site in Baja California, a system which has not received large human impacts. The Sierra San Pedro Martir (SSPM) has no history of logging or fire exclusion unlike the forests of the Sierra Nevada and the Tahoe Basin. The SSPM also has mixed-conifer forests much like the Sierra Nevada and the Lake Tahoe Basin. The combination of data from all of our study sites will contribute to current models which relate to ecosystem health.
Fire exclusion policies in the Tahoe Basin have increased understory tree densities in the lower montane zone by favoring white fir regeneration. Selective logging and increased competition (due to increased densities) have resulted in a decline in importance of Jeffrey pine and sugar pine in seral Lake Tahoe forests. Similarities in overstory canopy structure and composition between late-seral Tahoe and SSPM forests may be indirect evidence of presettlement overstory forest structure and composition (See M. Barbour report). Old-growth makes up such a small proportion (< 5 %) of lower montane forest in the Lake Tahoe Basin that the condition of these forests must be seen in the context of the entire forested landscape of the basin, including sites that have been logged in the past (i.e., seral sites).
Based on surveys in 1997 and 1998, overall cumulative mortality (including standing dead and down trees) in the lower montane zone of the Basin was approximately 21 % for late-seral/old growth and 29 % for seral stands. Mortality, however, was variable at smaller spatial scales and ranged from 6 % to 44 % in the 31 sampled stands (17 old-growth, 16 seral stands). The majority of the standing dead trees in the Basin have died during the most recent drought (1987-1992), although a number of trees that had died prior to this drought were still found on the sites. Mortality was most common in the 20-50 cm dbh size class. This was also the most common size class at most sites and overall mortality was fairly evenly distributed throughout different size classes. White fir makes up the largest percentage (78 % in seral stands, 62 % in old growth stands) of dead stems in the lower montane forests of the Basin.
While much tree mortality in the Lake Tahoe Basin can be indirectly attributed to the short-term effects of the recent drought and the long term effects of fire suppression, the proximal cause of death of most trees in the basin is due to a number of insects and pathogens. For each of the major conifer species, overall pathogen and insect incidence is generally lower on late-seral/old-growth sites as compared to seral stands. On seral sites, as a whole, 39 % and 49 % of all Jeffrey pine and white fir stems, respectively, were identified with some pest species. Old growth sites, as a whole, had pest incidence of 23 % and 34 % on Jeffrey pine and white fir. However, there was wide variation in pest incidence from site to site and between the different pest species and these overall differences between seral and late-seral/old growth stands were not statistically significant.
Epidemic levels of bark beetles are clearly the most important cause of tree death in the past ten years in the basin. Forest service reports show increased mortality of Jeffrey pine due to the Jeffrey Pine beetle (Dendroctonus jeffreyi) and white fir due to the fir engraver beetle (Scolytus ventralis) between 1987 and 1993. The annual rate of mortality in the basin due to bark beetles has declined since the drought ended in 1992-1993. While overall bark beetle-caused mortality in the Lake Tahoe Basin was very high during the drought, it was not unusual when placed in the context of bark beetle mortality in forests statewide. Significant numbers of trees were killed by bark beetles during the drought on the Modoc Plateau, the Southern Cascades region, the eastside of the Sierra Nevada and in the mountains of southern California.
There are very few records of mortality patterns in Lake Tahoe Basin forests prior to the arrival of Euroamericans. A comparison, however, of Lake Tahoe Basin forests with SSPM forests indicates that overall mortality is significantly lower at SSPM than in the Lake Tahoe Basin. Estimates of cumulative mortality range from 4 % to 15 % of all trees on the SSPM sites. SSPM forests appear to have escaped the most recent drought without extensive bark beetle outbreaks and, therefore, much lower mortality than was reported for the forests of California. In addition, mortality on SPM sites appears to be concentrated in the larger size classes; over 90 % of the dead trees are larger than 50 cm dbh. This contrasts with the data presented here for old growth forests in the Lake Tahoe Basin in which approximately 60% of the mortality was in the 20 to 50 cm dbh size class. Stand thinning in the SSPM is occurring earlier in stand development due to the effects of fire at the seedling stage. In contrast, stand thinning in the Lake Tahoe Basin is taking place at a much later point in stand development when trees are larger than 20 cm dbh. Insects and diseases have largely replaced fire as the main stand thinning agent in the Lake Tahoe Basin, while insects, diseases, and fire maintain tree diversity (evenness) in the SSPM forests.
In 1999, we have concentrated our efforts in the subalpine zone looking at the distribution of an introduced pathogen. White pine blister rust (WPBR) caused by Cronartium ribicola is an exotic pathogen that infects and kills 5-needle pine species. In the Lake Tahoe Basin there are three species that are affected by this disease: sugar pine (Pinus lambertiana), western white pine (Pinus monticola) and whitebark pine (Pinus albicaulis). Western white pine grows in the transition zone between upper montane and the subalpine zone, whereas whitebark pine exists only in the subalpine zones. These two species are important components of these subalpine habitats and are valued for their roles in watershed protection and wildlife food at these higher elevations. Loss of these species from the subalpine landscape would have major ecological consequences. Twenty transects, located all throughout the Lake Tahoe Basin, have been established to determine the distribution and intensity of WPBR. A larger intensive study plot, that will cover an area of approximately 25 hectares, will be sampled to determine the spatial distribution and the pattern of spread of this disease.
Future Activities:This winter we intend to synthesize a wide range of data sets on forest tree mortality in the Lake Tahoe Basin. We will be collaborating with the US Forest Service remote sensing lab to integrate their coarse scale mortality numbers with our fine scale mortality numbers for the lower montane zone. This remote sensing data has previously been unavailable to us.
Pathogens and insects will always be a part of Lake Tahoe forest ecosystems and any management strategies designed to restore natural processes will need to take into consideration the effects on pest species. In theory, restoring forests to their natural densities should mitigate most serious pest outbreaks (e.g., reduced bark beetle epidemics during drought periods). However, procedures such as thinning dense understories and prescribed burns have the potential to increase pest incidence in some instances. For example, thinning may potentially mitigate pest problems by lowering stand densities and relieving the potential for drought and competition-induced stress. Such operations, however, often damage residual trees and can increase the buildup of root disease inoculum due to saprobic survival in stumps. The ecological consequences of these restoration methodologies are not well understood. Therefore, we are involved with an experiment to study the effects of logging (to reduce the fuel loads) and prescribed burning to restore open, late seral stage stands on the Teakettle Experimental Forest near Dinky Creek in the Sierra National Forest.
We also intend to continue work with WPBR in the subalpine zone. All transects and plots established will allow for long-term monitoring to determine rates of infection and mortality. Also, observations of individual trees that do not become diseased may be potential resources of genetic material to screen for resistance to WPBR.
Supplemental Keywords:Ecosystem Protection/Environmental Exposure & Risk, ENVIRONMENTAL MANAGEMENT, Water, INTERNATIONAL COOPERATION, Scientific Discipline, RFA, ECOSYSTEMS, Ecosystem/Assessment/Indicators, Water & Watershed, exploratory research environmental biology, Restoration, Aquatic Ecosystem Restoration, Aquatic Ecosystems & Estuarine Research, Terrestrial Ecosystems, Ecological Monitoring, Aquatic Ecosystem, Ecological Indicators, Biochemistry, Environmental Microbiology, Ecological Effects - Human Health, Watersheds, Ecological Effects - Environmental Exposure & Risk, Ecosystem Protection, Monitoring/Modeling, Resources Management, water quality, ecological impact, lake ecosystem, forest tenure, watershed management, watershed restoration, ecosystem modeling, ecological restoration, deforestation, ecological research, aquatic habitat protection , pest complexes, ecosystem restoration, wetland restoration, forested basins, wetland plant species, conservation, GIS, forest ecosystems, aquatic ecosystems, ecosystem assessment, environmental stress, pathogens, vegetation , lake ecosysyems, biotic stress, deterministic linkages, ecological assessment, forest conservation, forests, restoration strategies, ecosystem stress, watershed assessment, ecological models, watershed forests, Sierra National Forest, biodiversity, ecological effects, restoration planning
Progress and Final Reports:
Original Abstract
2000 Progress Report
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