Progress 09/01/05 to 05/31/09
Outputs
OUTPUTS: Each day, thousands of people visit Lake Tahoe, world renown for its natural beauty and crystalline waters. It is a challenge to both maintain healthy forests and watersheds and to provide safe winter driving conditions for visitors and residents. During winter months, salt and deicing compounds are applied to roads to keep them clear of snow and ice. Sodium chloride (NaCl) is readily available, effective and inexpensive, and it is the deicing compound most commonly used by highway departments. Salt and deicing compounds potentially have a negative effect on forest health. Forests in the Lake Tahoe Basin are comprised of evergreen trees that are more susceptible to salt damage compared to hardwood species because they retain their foliage through the winter months when salt is applied to roads. In addition to the loss of aesthetic value of trees due to salt damage, there is a concern that loss of canopy cover would result in increased erosion of unprotected soils. Soil erosion is a concern in Lake Tahoe where excellent water clarity is desired. The overall goal of this project was to investigate the effect of road applications of salt and deicing compounds by state highway departments on tree health. The specific objectives were to: (1) assess damage caused by salt, biotic, and abiotic agents to trees in roadside plots compared to trees in control plots; (2) compare salt concentrations of soil and vegetation samples collected from roadside plots to vegetation and soil samples collected at control plots; (3) investigate the relationship among environmental factors, salt damage, and tree health. Data were collected from both roadside and control plots to determine the effects of road de-icing salts on the health of conifers on the California side of Lake Tahoe. Fieldwork began in the early spring of 2007 and continued through the fall of 2008. PARTICIPANTS: Participants in the project include undergraduate students, professional staff, and a postdoctoral research associate at the University of Nevada Reno, with assistance from personnel in state departments of transportation. TARGET AUDIENCES: Target audiences include scientists and land managers within the Lake Tahoe basin and other conifer forests within the mountainous regions of the western US plus personnel with state departments of transpioration, especially those responsible for winter highway maintenance and snow removal. PROJECT MODIFICATIONS: No siginifcant modifications to report.
Impacts
We found a clear roadside effect in salt damage to roadside trees. Evidence to support this statement include: (1) symptoms of salt damage were only observed on trees in roadside plots and never in plots located >1000' from the road; (2) sodium and chlorine content of foliage for roadside trees was much higher than that from control plots for both salt-symptomatic and -asymptomatic trees; and (3) the incidence of salt damage declined as distance from the road increased. Our results, coupled with those in the literature, point to aerial deposition of salt on conifer needles as the likely source for salt damage, rather than as uptake from the soil. However, this inference needs to be tested with carefully designed studies. We did not find evidence to support the hypothesis that salt damage is accumulating over time in the Lake Tahoe Basin due to the accumulation of salt in soils. First, ion content of soil samples was very low (well below the level at which damage occurs to conifers) and has not appreciably changed over the 18 years since the last comprehensive study of salt damage in the Lake Tahoe Basin prior to our study. Second, the incidence of salt damage to roadside trees has not significantly increased over the 18-year period. The incidence of salt damage is not simply related to the amount of salt applied to roads. We suspect, however, that the amount of applied salt may influence the severity of salt damage. For example, the severity of salt damage has decreased dramatically in the last 18 years, coincident with a large decrease in salt application. Additional circumstantial evidence supports a relationship between the severity of salt damage and the amount of applied salt, but specific additional studies are needed to clearly determine relationships between amount of salt applied and damage severity. Our results do not support the hypothesis that the presence of disease, insect, or other damaging agents exacerbates salt damage. Furthermore, these other sources of damage are much more often associated with declining tree health than salt damage. Only environmental factors such as distance from the road and slope characteristics of the roadside have major influences on salt damage. The incidence of damage decreases as distance from the road increases, and the severity of damage is greater down slope from the road, especially for steep down slope gradients. Other environmental factors such as soil type, elevation, and aspect did not have consistently significant effects on salt damage. Furthermore, the incidence of salt damage was similar for plots in rural and urban areas. Consistent with previous studies, Jeffrey pine, lodgepole pine, and ponderosa pine had the greatest incidence of salt damage. Sugar pine, red fir, and white fir had lower incidences of salt damage.
Publications
- No publications reported this period
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: We are planning to include information about road use and management in future analyses so that we can draw conclusions about specific causes of damage. These types of information include plow types and speeds used during and after storms, and on a per storm basis. Also traffic information such as numbers of cars and speeds may be useful in drawing conclusions about salt damage on trees. This information can then be used to effectively manage and reduce the effect of salt injury exhibited on roadside trees by altering management activities or possibly planting more resistant species along the roadside. PARTICIPANTS: Participants in this project include undergraduates students, professional staff, and a postdoctorate research associate at the University of Nevada Reno, with assistance from personnel in state departments of transportation. TARGET AUDIENCES: Target audiences are scientisits and land managers within the Lake Tahoe Basin plus personnel with state departments of transportation. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The majority of trees surveyed lacked symptoms of salt damage or other types of injury. In 2007 and 2008, we found evidence of salt damage on 12% and 20%, respectively, of the surveyed roadside trees. In contrast, we found no evidence of salt damage in control plots. The severity of salt damage in affected trees was mostly restricted to less than a third of the crown. We observed year to year differences in the proportion of trees affected by salt damage and the difference coincided with the amount of deicing salts applied to roads. However, the amount of salt applied alone does not explain year to year variation in the amount of salt damage observed. The amount of salt damage that we observed was less than that observed in a previous study in 1990, but the amount of salt applied has been reduced to approximately half of what was applied in 1990. Interestingly, salt damage did not exacerbate the presence and degree of damage caused by pathogens, insects, or other abiotic factors. In fact, although salt damage decreases with increasing distance from roadside, the opposite trend is observed with other types of injury. It is probable that salt-damaged foliage is not a suitable substrate for insects or plant pathogens. Contrary to what we expected, we found little evidence in our analyses that topography was affecting incidence and severity of salt damage. We can mainly conclude that there is a clear roadside effect for salt damage, and that as the distance from the roadside increases, the incidence of salt damage decreases. Salt damage and severity were worse on downhill slopes compared to uphill slopes and increased with (downhill) slope steepness. Soil type and elevation had no significant impact on the incidence or severity of salt damage on roadside trees. Results from our chemical analyses of salt-symptomatic and asymptomatic conifer needles support a roadside effect as well, with greater contents of both sodium and chloride in roadside needles than in those from control plots. Further support for a roadside effect, comes from the fact that even asymptomatic needles on the roadside had a greater salt content than asymptomatic needles in control plots, suggesting that roadside trees are still accumulating more salt while not necessarily manifesting physical symptoms. Results pertaining to salt sensitivity of different tree species are consistent with previous research conducted in the Lake Tahoe Basin. Two-and-three needle pines such as Jeffrey, ponderosa, and lodgepole pines exhibit symptoms of salt damage more frequently than white and red fir. Management alternative could be to remove salt damaged trees from roadsides, thus favoring the more salt tolerant firs.
Publications
- No publications reported this period
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Progress 01/01/07 to 12/31/07
Outputs
Located in the Sierra Nevada Mountains, Lake Tahoe is an area rich in biological diversity and is characterized by its natural beauty and pristine water clarity. Lake Tahoe is also an environmentally sensitive area that has struggled with balancing an increasing number of visitors each year with the safety of winter road conditions. De-icing salt (i.e., sodium chloride and/or brine typically combined with sand) is commonly applied to roads to keep them free from snow and ice. The effects of de-icing salts have previously been shown to cause damage to conifer species existing along roadsides. The objectives of the current studies are to determine the degree of salt injury to roadside vegetation and the long-term impacts of de-icing salts on roadside vegetation in the Tahoe Basin. Study plots were established in Nevada and California among 3 land use categories (rural, urban, and control) and located among 5 different soil groups. During the 2006 field season, 242 plots
were established and a total of 5799 trees were surveyed for disease and salt damage. Visual surveys revealed salt damage apparent to some degree on 48% of roadside trees, and 1/3 of those trees also exhibited signs of diseases and insects. Chemical analysis of soil and vegetation samples were performed on samples collected at 80 plots. Chemical analysis of soils indicated a small but significant difference in soil pH for roadside plots when compared to control plots, but no difference was found for comparisons of electrical conductivity, which is a measure of dissolved salts in the soil. Sodium and chloride content in plant tissue from roadside plots that exhibited salt damage was significantly different from control plots. Although no evidence of salt damage was found in control plots, the amount of both healthy and diseased trees on roadside plots was lower than those on control plots, suggesting that salt damage partially replaces other disease-causing agents. We conclude that a
roadside effect does exist for trees exhibiting symptoms of salt damage, and further field data collection are planned to confirm the trends found here as well as to determine if specific environmental factors may increase salt damage.
Impacts
48% of the trees surveyed in roadside plots in the Lake Tahoe Basin had some evidence of salt damage. However, the severity of this injury was relatively minor, i.e., less then one third of the crown displayed salt damage. More than half of the salt-injured trees also have some other type of injury. Roadside plots also had fewer healthy trees (~12%) compared to controls. These results indicate a reduction in tree health associated with roads. The method of salt damage is still unknown because we are not observing high levels of salts in the soils. We suspect that salt injury occurs through direct foliar absorption of salts that are aerially-deposited on the leaves. Also, a general decline in tree health within the Basin may exacerbate salt injury. However, these hypotheses need further testing. We will continue to collect data through 2008. With our data plus information on external environmental factors (e.g., precipitation, salt application rates and amounts, traffic
and plow speeds), we will use a statistical model to help determine factors mainly responsible for the salt damage on the conifers in the Tahoe Basin. This knowledge can then be used to design mitigation measures.
Publications
- No publications reported this period
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Progress 01/01/06 to 12/31/06
Outputs
We have established and completed measurements and surveys for 210 plots on the Nevada side of Lake Tahoe. This includes GPS coordinates for all plot corners and trees, labeling and measurement of all trees (DBH and distance from baseline), and comprehensive salt, disease, and insect surveys for each of the nearly 5000 trees in our study plots on the Nevada side of the lake. The remaining 40 plots proposed for study in Nevada are on private property. Multiple letters have been sent to these landowners, and we have been denied access to six of the properties and have had no response from the remaining. On the California side of Lake Tahoe, we have begun establishing plots on state lands and have completed 29 to date. We have or are in the process of gaining permission to work on Federal, State, and NGO lands in California and mailed requests to private land owners in Placer and El Dorado counties. All GPS coordinates recorded thus far have been added to the ArcView GIS
database that contains detailed information for the Lake Tahoe Basin. Our tree measurement and survey data is currently being entered into spreadsheets and prepared for spatial and statistical analysis. Also, permanent tree tags are being made that will be placed on all surveyed trees during next years' survey. Foliage samples have been collected from 80 study plots in Nevada for a total of 429 samples. These samples were collected from both salt-symptomatic and salt-asymptomatic trees in urban, rural, and control plots. They are now being analyzed for sodium and chloride content. Preliminary analysis of data to date suggest that approximately 49% of the trees in plots located near roads showed evidence for salt damage to needles. About one third of these trees with salt damage also had damage from insects, fungi, or other diseases. For comparison, over half the trees in plots located at least 1000 feet from roads had damage from insects, fungi, or other diseases. Thus, salt damage is
not the only factor that is adversely affecting trees in the Lake Tahoe Basin. Incidence of salt damage was most pronounced within 0-30 feet of the road and was also affected by slope and slope location. Trees uphill from the road had lower incidence of salt damage, and the steeper the slope uphill, the less severe was the salt damage. In contrast for trees downhill from the road, steeper downhill slopes tended to have more severely impacted trees. Tree species also differed in their apparent sensitivity to salt damage, with Jeffrey and white pines among the most sensitive and white fir and incense cedar among the least sensitive.
Impacts
The Lake Tahoe Basin is world renowned for its natural beauty, water clarity, and winter sports activities. However, the increasing resident population and visitor use require clear roadways during the winter and hence the application of anti-icing and de-icing salts. During 1990, salt effects on vegetation adjacent to highways in the Tahoe Basin were studied. 15% of trees were salt-affected, but 1/3 of these trees had evidence for other damage. 30% of trees exhibited damage from non-salt related causes, and 55% did not exhibit any symptoms of salt, drought, disease, insect, or other damage. Thus, salts negatively impact roadside vegetation, but previous drought conditions may have made plants more susceptible to salt injury. Furthermore, salt content of soils was not abnormally high. Thus, although salts play some role in roadside vegetation damage, existing data from the Tahoe Basin also suggest that the role may be minor. Comparisons of results from our new study
with those obtained from the previous study will be used to evaluate the potential long-term impact of salts on roadside soil salinity, the health trends of vegetation along highways, and the maximum potential impact of salts on vegetation in the Tahoe Basin. Our improvements in sampling protocols (e.g. addition of new control plots, additional sampling of targeted soils and species) will strengthen the research and improve our ability to discern the damage due to salts.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
We tried to locate the original study plots from the 1990 study, but (1) RCI does not have any records in their archives (their records only go back 10 years); and (2) there was virtually no sign of original plots in the field. Using the maps and tables prepared by RCI, we were able to find the approximate locations of all the original NV plots, but many of the plots in urban areas now have homes or businesses on them. Thus, we concluded that we will have to re-establish plots and that some of the original plots are no longer usable. Next, we conducted a feasibility study to determine if sufficient plots were available to conduct a proper, scientifically controlled study on each soil type in both Nevada and California. We also determined that the study should have 3 types of study plots (along roads in urban areas, along roads in rural areas, and control [>1000 feet off-road] in rural areas) and 2 sets of preplanned comparisons (urban road vs. rural road plus rural
road vs. rural off-road). Note that "control plots in an urban area" do not exist. This effort entailed building an ArcGIS database and maps that included roadways, soil type, elevation, and land ownership. We concluded that sufficient plots were available for the following types of study plots in each soil type and State: Soil Type B: Urban road, rural road, control in both CA & NV; Soil Type C: Urban road, rural road, control in CA only; Soil Type D: Rural road & control in NV only; Soil Type E: Rural road & control in NV only; Soil Type H: Rural road & control in both CA & NV.
Impacts
The Lake Tahoe Basin is world renowned for its natural beauty, water clarity, and winter sports activities. However, the increasing resident population and visitor use require clear roadways during the winter and hence the application of anti-icing and de-icing salts. During 1990, salt effects on vegetation adjacent to highways in the Tahoe Basin were studied. 15% of trees were salt-affected, but 1/3 of these trees had evidence for other damage. 30% of trees exhibited damage from non-salt related causes, and 55% did not exhibit any symptoms of salt, drought, disease, insect, or other damage. Thus, salts negatively impact roadside vegetation, but previous drought conditions may have made plants more susceptible to salt injury. Furthermore, salt content of soils was not abnormally high. Thus, although salts play some role in roadside vegetation damage, existing data from the Tahoe Basin also suggest that the role may be minor. Comparisons of results from our new study
with those obtained from the previous study will be used to evaluate the potential long-term impact of salts on roadside soil salinity, the health trends of vegetation along highways, and the maximum potential impact of salts on vegetation in the Tahoe Basin. Our improvements in sampling protocols (e.g. addition of new control plots, additional sampling of targeted soils and species) will strengthen the research and improve our ability to discern the damage due to salts.
Publications
- No publications reported this period
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