Progress 05/08/08 to 06/30/12

Outputs
OUTPUTS: For additional information, please contact Bob Nowak at 775-784-1656 or nowak@cabnr.unr.edu PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
For additional information, please contact Bob Nowak at 775-784-1656 or nowak@cabnr.unr.edu

Publications

• No publications reported this period

Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: We are using satellite remote sensing (Landsat Thematic Mapper) and geospatial analysis techniques to quantify forest mortality in the mixed conifer forests of the Lake Tahoe Basin over environmental gradients, historical fire regimes, forest types, and climatic periods from 1985 to 2010. We downloaded Landsat TM late summer imagery (scenes) for each year from 1985 to 2010, choosing images of highest quality that are snow-free and cloud-free in the Lake Tahoe Basin study area. Pixel values of the 2010 reference image were transformed into reflectance values using the radiometric and geometric characteristics of the image capture through Landsat calibration. Dark object subtraction was then performed to remove "dark pixels" from the scene and standardize pixel values across all spectral bands. The 1985-2009 imagery was then normalized to the 2010 imagery using the IRMAD process in ENVI. Images were then transformed into Normalized Difference Vegetation Index (NDVI). We correlated ground measurements of LAI taken during summer 2010 with NDVI derived from Landsat imagery for the same pixel. Based on the modeled relationship, we then used LAI to define the stocking level of each forested pixel in the Landsat images from 1985-2010. This stocking level is analogous to forest density but uses the top-down sensor geometry of remote sensing to capture the amount of tree foliage in a pixel. We validated our estimation of stocking level against density readings taken with a convex spherical densiometer from 75 30 x 30m plots in varying forest types and environmental positions (slope, aspect, elevation). To estimate reductions in canopy vigor, we compared two single-year values for the Normalized Difference Wetness Index (NDWI) Index to capture gradations of foliage health in forest stands of varying levels of mortality. PARTICIPANTS: Participants include graduate and undergraduate students, professional staff, and a postdoctoral research associate at the University of Nevada, Reno. Assistance from personnel in the Nevada State Lands Division and the Nevada Department of Forestry also occurred. TARGET AUDIENCES: Target audiences include scientists and land managers in the Lake Tahoe Basin and other conifer forests in mountainous regions of the western US. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Although these results are preliminary and do not yet account for the diversity of forest types or environmental settings, the strength of density-dependent mortality seems to be generally stable and relatively low over the 1985-2010 time period. Two notable exceptions are 1986-1987 where a year of normal drought severity index is followed by an unusually wet winter; areas of greater stocking level in 1986 experienced less tree canopy mortality in 1987. Following the dry winter of 1993-1994, the expected density-dependent relationship was observed, where areas of greater stocking level experienced greater tree canopy mortality. However, the relationship between stocking level and tree mortality did not appear to respond in a similar way to other climatically variable time periods. In addition, we have conducted preliminary analyses on the relationships between forest type, historic fire regime, and the strength of density-dependent mortality. To explore forest type influences, we separated the pixels used in the overall analyses into five groups based on dominant cover type and constructed generalized linear models that account for the interaction between stocking level and forest type in forest mortality. We used discrete periods in the time series to capture varying effects of drought and wet cycles, periodicity of drought/wet cycles, recovery from drought, or sudden transition from wet to dry periods. Preliminary analyses show that the variability (i.e. temporal trend) of density-dependent mortality is similar among forest types, although the strength of density-dependent mortality in drought years appears to differ among forest types. Departure from historic fire regime did not show a measurable difference except for the period from 1985-1986, where stands with greatest departure from historical fire regime (i.e. stands historically characterized by frequent surface fires) showed the greatest effect of density-dependent mortality, meaning that in such areas, trees were more likely to experience mortality in denser stands.

Publications

• No publications reported this period

Progress 01/01/10 to 12/31/10

Outputs
OUTPUTS: Maintaining healthy forests and avoiding catastrophic wildfires are important management objectives in the Tahoe Basin. Our goal is to quantify incidence and severity of forest tree diseases and damaging agents in relation to fuel reduction treatments. The specific objectives were to (1) quantify incidence and severity of forest tree diseases and other damaging agents in the study area, (2) quantify changes in incidence and severity of tree diseases and other damaging agents in areas treated to reduce fuels, (3) use remote sensing technologies to quantify tree crown damage related to tree diseases, other damaging agents, or fuel reduction treatments. To accomplish our objectives a total of 70 permanent plots have been installed and surveyed in seven locations in the Nevada portion of the Tahoe Basin. At each location treatments plots were established in areas treated to reduce fuels and control plots were established in untreated areas of similar topography, species composition, and age. Plots consist of 30 m x 30 m squares and were established so that each plot corresponds to a pixel of the Landsat imagery. Plot data recorded included latitude and longitude coordinates, elevation, and percent slope. All trees larger than 4 cm diameter at breast height (dbh) within plot boundaries were tagged and surveyed. Data collected for each tree included: species, dbh, general health rating, dieback rating, incidence and severity of diseases, insect pests, mechanical injury, or salt damage. Dieback is the progressive of shoots, leaves, or roots beginning at the tips in response to pathogens or abiotic stress. Data were analyzed for treatment effects on tree density, tree health, incidence, and severity of forest insects and diseases. PARTICIPANTS: Participants include graduate and undergraduate students, professional staff, and a postdoctoral research associate at the University of Nevada, Reno. Assistance from personnel in the Nevada State Lands Division and the Nevada Department of Forestry also occurred. TARGET AUDIENCES: Target audiences include scientists and land managers in the Lake Tahoe Basin and other conifer forests in mountainous regions of the western US. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The hazardous fuel reduction effects of treatments are apparent. Except for one location, the majority of trees in treated plots were undamaged or healthy and if damaged, damage was limited to no more than a third of the crown. For three locations, the health status of trees was better in treated plots compared to control plots. The interaction between treatment and incidence of insect or disease damage or damage severity were significant. In these three locations, fewer trees were undamaged by insects and diseases (incidence), and the extent of damage (severity) was less in treated plots compared to control plots. For a second set of 3 locations, the health status of trees was not different in control plots compared to treated plots. At these three locations, the interaction between treatment and incidence of insect or disease damage or damage severity was not statistically significant. In the final location, the health status of trees was worse in treated plots compared to control plots. This final location had been prescribed burned > 5 years ago. Many trees were charred and some were attacked by bark beetles. In contrast, trees in control plots were very healthy and undamaged by insects and diseases. After discussing land management treatments in this area, we determined that this location abuts land where a prescribed fire had escaped and damaged trees in study plots, which accounts for the tree damage observed in treatment plots at this location. Dwarf mistletoes were the pathogens causing most damage to trees, both in the number of trees affected and in the extent or severity of damage caused. Thirteen percent of live trees were infected with dwarf mistletoe, and damage extended to more than 2/3 of the crown for 29% of these. Another commonly observed problem was resinosis of white fir (13% of live trees). Other common pathogens included needle diseases and root and butt rots. Insect damage was not observed as frequently as damage from pathogens (<5% trees). Pine needle miner and fir engraver were the most frequently observed insects causing damage to live trees. In conclusion, most trees are healthy and if damaged, damage is limited to a third of the crown. The hazardous fuel reduction effects of treatments are apparent, but the effects of treatments on tree health are more subtle. The effects of fuel reduction treatments vary by location and treatment type. Most treatments had a positive or no significant effect on tree health. In one location, however, tree health status was worse in treated plots compare to control plots, but this appeared to be due to inadvertent post-treatment activities. The incidence of specific forest insects and diseases was affected by tree species composition because many forest pathogens and insects are host specific. Dwarf mistletoes were the most frequently observed pathogens, especially in stands dominated by Jeffrey pine. Resinosis (a symptom of environmental stresses such as drought), root rot, and fir engraver were the insect and disease problems most commonly associated with white fir.

Publications

• Munck IA, Bennett CM, Camilli KS, Nowak RS. (2010). Long-term impact of de-icing salts on tree health in the Lake Tahoe Basin: environmental influences and interactions with insects and diseases. Forest Ecology and Management 260:1218-1229.

Progress 01/01/09 to 12/31/09

Outputs
OUTPUTS: Maintaining healthy forests is a desired management objective in the Lake Tahoe Basin because healthy forests are critical to the beauty and water clarity of Lake Tahoe. Avoiding catastrophic wildfires is another desired, important management objective in the area. Our goal is to quantify incidence and severity of forest tree diseases and damaging agents in relation to fuel reduction treatments. The specific objectives were to (1) quantify incidence and severity of forest tree diseases and other damaging agents in the study area, (2) quantify changes in incidence and severity of tree diseases and other damaging agents in areas treated to reduce fuels, (3) use remote sensing technologies to quantify tree crown damage related to tree diseases, other damaging agents, or fuel reduction treatments.To accomplish our objectives, 35 permanent plots were installed and surveyed in 2008 and resurveyed in 2009. In 2009, 35 additional permanent plots were installed and surveyed for a total of 70 plots in 7 locations. At each location treatments plots were established in areas treated to reduce fuels and control plots were established in untreated areas of similar topography and stand structure. All trees larger than 4 cm diameter at breast height (dbh) within plot boundaries were tagged and surveyed. Detailed information has been collected for 2,465 trees (2,245 live trees and 220 dead trees). Data collected for each tree included: species, dbh, incidence and severity of diseases, insect pests, mechanical injury, or salt damage. The severity of forest diseases and other damaging agents was assessed using a scale from 0 to 3. The following crown damage severity ratings were given to each tree: "0" if no damages were observed, "1" if <1/3 of the crown was damaged, "2" if 1/3-2/3 crown damaged, "3" if >2/3 crown damaged. A general health rating (good, fair, poor, or dead) was also assigned to each tree based on the proportion of the crown with dieback or foliage discoloration. This second rating was independent of the presence or absence of damaging agents. PARTICIPANTS: Participants include graduate and undergraduate students, professional staff, and a postdoctoral research associate at the University of Nevada, Reno. Assistance from personnel in the Nevada State Lands Dividion and the Nevada Department of Forestry also occurred. TARGET AUDIENCES: Target audences include scientists and land managers in the Lake Tahoe Basin and other conifer forests in mountaineous regions of the western US. PROJECT MODIFICATIONS: No significant modifications to report.

Impacts
The hazardous fuel reduction effects of treatments are apparent. For example, control plots compared to treated plots have greater tree densities and more dead trees. Although there is no specific sanitation goal when selecting trees to be thinned, severely damaged trees are preferentially removed. As a result, the severity of insect and disease damage is greater in control plots than in treated plots. This is particularly obvious for severely damaged trees. A greater proportion of trees are severely damaged by diseases or insects in control plots (6.4%) compared to treated plots (2.4%). In contrast to the more obvious hazardous fuel reduction effects of treatments, the effects of treatments on tree health were more subtle. Overall, the majority of trees in both treated (67%) and control (65%) plots were in good health. In addition, the severity of insect and disease damage is generally limited to less than a third of the crown. The health status of trees, however, varied by location. The presence of specific insects and diseases was influenced by tree species composition. The most important pathogen in locations dominated by Jeffrey pine was dwarf mistletoe, Arceuthobium campylopodum. At these locations pine needle miner, Coleotechnites sp., was the most commonly observed insect pest.The most important forest health problem at locations within the Jeffrey pine- white fir forest type was drought stress or environmental stress resulting in resinosis of white fir (30% trees). Other frequently observed diseases in the Jeffrey pine-white fir forest type include: dwarf mistletoes, needle diseases (i.e. Elytroderma needle cast), root, and butt rots (i.e. Heterobasidion annosum). Insect damage was not observed frequently in this forest type (<5% trees). In the mixed conifer forest type, a mix of insects and disease problems was also present. White fir is the most common tree species and as a result, resinosis (>29% trees) and fir engraver (~15% trees), Scolytus ventralis, were the most commonly observed forest health problems at this location. Other frequently observed diseases included dwarf mistletoes, cankers, and rots.

Publications

• No publications reported this period

Progress 01/01/08 to 12/31/08

Outputs
OUTPUTS: Maintaining healthy forests is a desired management objective in the Lake Tahoe Basin because healthy forests are critical to the beauty and water clarity of Lake Tahoe. Avoiding catastrophic wildfires is another desired, important management objective in the area. Few studies have quantified the incidence and severity of forest tree diseases and other damaging agents throughout the Tahoe Basin. Our goal is to quantify incidence and severity of forest tree diseases and damaging agents in relation to fuel reduction treatments. The study area will include study sites in Lake Tahoe Nevada State Parks and US Forest Service lands within the Nevada portion of the lake. Our specific objectives are to (1) quantify incidence and severity of forest tree diseases and other damaging agents in the study area, (2) quantify changes in incidence and severity of tree diseases and other damaging agents in areas treated to reduce fuels, (3) use remote sensing technologies to quantify tree crown damage related to tree diseases, other damaging agents, or fuel reduction treatments. Plots established and surveyed during 2008 will also be surveyed in 2009. At least 24 additional new plots will be established and surveyed in 2009. The effects of fuel reduction treatments on forest health might take some time to manifest. Thus, new plots established during 2009 will be located in areas where fuel reduction treatments have been applied more than one year ago. Data from these plots might capture the long term effects of fuel reduction treatments on forest health. PARTICIPANTS: Participants include graduate and undergraduate students, professional staff, and a postdoctorate research associate at the University of Nevada Reno. TARGET AUDIENCES: Target audiences include scientists and land managers in the Lake Tahoe Basin. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
To accomplish our objectives, 36 new, 30 x 30 m2 square plots have been established and surveyed during the field sampling season of 2008. Plots are located in three different locations. Two are in the northeastern shores of Lake Tahoe, near Sand Harbor and Tunnel Creek respectively (Figure 1). The last location is in the southeastern part of the Lake near Van Sickle Park (Figure 2). Two sets of six plots were established at each location. At each location, one set of plots are in areas where fuel reduction treatments had already taken place or were soon to be treated. The other set of plots are located in untreated areas with similar topography, tree species composition, and tree density as treated areas and will serve as control plots. The latitude and longitude coordinates of the corners of each plot were located with a GPS unit (1 m accuracy) and temporarily marked with pin flags. Plots were established so that each plot corresponds to a pixel of the IKONOS multispectral imagery. A corner of each plot was marked with a metal stake. Plot data that was recorded included latitude and longitude coordinates, elevation, percent slope, and canopy cover. Canopy cover was measured with a densitometer at plot center. Canopy measurements were taken at an arms length of the plot center in the four cardinal directions: north, east, south, and west. All trees larger than 4 cm diameter at breast height (dbh) within plot boundaries were tagged and surveyed. Detailed information has been collected for 1,347 trees. Trees were individually tagged so they can be identified and resurveyed. Data collected for each tree includes: species, dbh, incidence and severity of diseases, insect pests, mechanical injury, or salt damage. The severity of forest diseases and other damaging agents was assessed using a scale from 0 to 3. The following crown damage severity ratings were given to each tree: "0" if no damages were observed, "1" if <1/3 of the crown was damaged, "2" if 1/3-2/3 crown damaged, "3" if >2/3 crown damaged. A general health rating of 1-4 was also assigned to each tree based on the proportion of the crown with dieback or foliage discoloration. This second rating was independent of the presence or absence of damaging agents. All data collected during the 2008 sampling season has been entered into an electronic database. We will conduct analyses to explore how basal area, dbh, tree density, species, and soil type affect the incidence and severity of forest diseases or other damaging agent. To quantify changes in measured tree health parameters caused by fuel reduction treatments, data collected from areas treated to reduce fuels will be compared to data collected in untreated areas (control plots). Field collected data will be compared to data acquired with remote sensing technologies to quantify tree crown damage.

Publications

• No publications reported this period