This project is primarily focused on understanding the ecology and nutrient cycling of Catskill forests and the responses of the forests to stresses such as air pollution and introduced pests.
Nitrate Loss from Catskill Watersheds
This project is primarily focused on understanding the ecology and nutrient cycling of Catskill forests and the responses of the forests to stresses such as air pollution and introduced pests.
Small forested watersheds in the Catskills can vary up to 17-fold in the concentration of nitrate in streamwater (Lovett et al. 2000). This is important because nitrate is a significant acidifying agent in the streams, and can cause harmful algal bloom when it is delivered to downstream estuaries and coastal waters. We are investigating the cause of nitrate variation through comparative studies in Catskill watersheds. Most of the variance in watershed nitrate export can be explained by the carbon to nitrogen ratio (C:N) of the watershed soils, and this ratio appears to be mainly controlled by the tree species composition of the watershed (Lovett et al. 2002).
Sugar maples, in particular, seem to create soils with a low C:N ratio, which leads to high rates of nitrate release to stream water, while soils under red oak and eastern hemlock have higher C:N ratios and lower nitrate release (Lovett et al 2004, Lovett and Mitchell 2004, Christenson et al. 2009). Other factors may also inhibit nitrate production under oak soils, such as abiotic retention of nitrogen (Fitzhugh et al. 2003a and 2003b). Increasing accumulation of nitrogen in the soils from continued atmospheric deposition may result in decreased ability of oak forest soils to retain nitrogen (Templer et al. 2005).
Patterns of Atmospheric Deposition
Air pollutants are deposited not only in rain and snow, but also as gases, particles, and fog droplets. Knowing the rates and patterns of deposition is critical to evaluating ecosystem response to the pollutants
Because of their relatively high elevations and their proximity to sources of pollution on the east coast and in the Midwest, the Catskill Mountains receive among the highest rates of sulfur and nitrogen deposition in the Northeast (Ollinger et al. 1993).
We have found that high-elevation ecosystems of the mountains receive higher rates of precipitation, dry deposition (particles and gases) and cloud water deposition than low-elevation areas (Weathers et al. 2000, Lovett et al. 1999). Forest edges at high elevation are particularly exposed to pollutant deposition, and may receive up to four times the pollutant load of forests at low elevations (Weathers et al. 1995, Weathers et al. 2000).
Effects of Beech Bark Disease on Catskill forests
The beech bark disease, which was introduced to North America from Europe, is caused by a combination of a scale insect and a fungus. The insect penetrates the bark of the trees to feed, and the tiny holes it leaves behind allow the fungus to become established. Once infected with the fungus, most trees die.
The disease affects nearly every beech tree in the Catskills, and it is especially prevalent in the mid-elevation forests (Griffin et al 2003). One of the effects of the disease has been a reduction in the Catskill's beech population, resulting in an increase in beech's major competitor, sugar maple. We have studied a sequence of stands that range from healthy mixed beech-maple forest to stands where once-dominant beech trees have succumbed to beech bark disease and been replaced by maples. We have found that as the disease progresses and the beech are replaced by sugar maple, there are associated changes in carbon and nitrogen cycling such as increased soil respiration, increased litter decomposition, and increased nitrate production (Hancock et al. 2008, Lovett et al. in press).
We are also studying several hundred plots in the Catskills of New York and the White Mts. of New Hampshire to understand the tree species change caused by the beech bark disease and its implications for carbon storage and nitrogen retention in the forest.
- Publications