Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed

EPA Grant Number: R825433C032
Subproject: 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: Packard, Benjamin H
Project Period: October 1, 1996 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research


This project seeks 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.


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. 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.

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. In the past two years investigators have focused on two important tree pathogens in the Lake Tahoe Basin: dwarf mistletoe (Arceuthobium spp.) and white pine blister rust (Cronartium ribicola).

The investigators have concentrated their 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.

To understand patterns of pathogen spread and the effect WPBR may have on host population dynamics, they surveyed 5-needle pine species in 30-40 ha grids in mixed-conifer forests in the central Sierra Nevada and in a subalpine location in the Lake Tahoe Basin, in the northern Sierra Nevada. In addition, we ran transects in 17 different upper montane/subalpine locations around Lake Tahoe. In mixed-conifer forests, results suggest that WPBR incidence is largely dependent on topographic features, that favor environmental conditions suitable for rust infection, as well as the presence of Ribes. In the more environmentally homogenous subalpine location, WPBR incidence was less variable and more uniformly spread. However, across the Lake Tahoe Basin WPBR incidence is quite variable. Much of the variability associated with incidence across the Basin is due to differences in environmental conditions, and possibly genetic heterogeneity and isolation of hosts. Where environmental conditions are favorable for WPBR, we have observed increased mortality among smaller pine recruits.

Expected Results:

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).

Investigators expect to improve restoration planning by examining the interactions of pathogens and insects with human caused changes to forest ecosystems (e.g., fire suppression, logging) to determine the current and future impacts on forest health in the Lake Tahoe Basin.

Supplemental Keywords:

Watershed, ecosystem restoration, conservation, pest complexes, forests, insects, pathogens, biotic stress, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, ENVIRONMENTAL MANAGEMENT, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Water & Watershed, exploratory research environmental biology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Restoration, Resources Management, Aquatic Ecosystem, Monitoring/Modeling, Ecological Effects - Environmental Exposure & Risk, Environmental Microbiology, Ecological Effects - Human Health, Biochemistry, Terrestrial Ecosystems, Ecological Monitoring, Aquatic Ecosystem Restoration, Watersheds, Ecological Indicators, deterministic linkages, ecological effects, ecosystem modeling, pathogens, watershed management, biodiversity, ecosystem assessment, forest ecosystems, Sierra National Forest, conservation, wetland plant species, restoration strategies, wetland restoration, integrated watershed model, ecological assessment, forested basins, pest complexes, aquatic ecosystems, environmental stress, lake ecosysyems, water quality, ecosystem restoration, forests, biotic stress, GIS, watershed forests, ecosystem stress, ecological impact, deforestation, ecological models, forest tenure, lake ecosystem, watershed assessment, aquatic habitat protection , ecological research, restoration planning, watershed restoration, ecological restoration, forest conservation

Progress and Final Reports:

  • 1997
  • 1998
  • 1999 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).
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    R825433C009 Modeling Ecosystems Under Combined Stress
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    R825433C039 Analytical and Biomarkers Core
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    R825433C041 Inorganic Analysis
    R825433C042 Immunoassay and Serum Markers
    R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
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