Issues in Ecology Number 6 Spring 2000 intensive forestry today.and in fact.doino so has been seer to another flevated nitrate levels in streams followino har as a waste.The question of how many trees to leave to vest or forest disturbance represent a threat to wate r qua nt and will ity hecsuee e nutrient fouline can lead to a wide reguire further research on the ecological functions of large problems from algal blooms,loss of oxygen.and fish kills to dead wood.Yet retaining trees on site as future sources of degradation of drinking water.In general.forest ecosy large woody debris must be a major component of sustain- tems with higher levels of nitrogen mineralization (release o able forest management nitrogen from decomposing soil organic matter)have been shown to exhibit higher rates of nitrate production and loss Nutrient Cycling and these losses are further increased by the removal of trees Another major factor in sus and corresponding elimination o taining soil quality is maintaining nitrogen uptake by the trees pools of essential plant nutrients Hibbert 1969.Likens et al.1970 and assuring these are steadily Hornbeck et al.1996). available in forms that plants can Computer modeling of nutri use.Undisturbed forests seldom ent requirements for forest growth experience significant losses of nu as well as studies on waters trient stocks u an importan and forest ecosystems agree tha b orestry i n principl rvesting whol anagement practice est in the long- those nutrients t Until rec nd oth he tant nutrient limiti in te rate and boreal fo 177 and by far the majority of research al.1986.Johnson and Todd has focu ised on nitrogen losse sociated with timber harvest and nrona site preparation (Johnson 1992) sites for planting signific ntly im Losses from a harvested site take nact soil fertility esne cially the use three forms:removal of the nitro of heavy equipment to push slash gen contained in the harvested and other organic matter into wood.nitrogen leached and oiles.a practice called windrow eroded from disturbed soil.and ni ne(Powers et al.1990).In a sus During the last 30 years it has become appar trogen volatilized and lost to the logs and atmosphere during slash burning oer woody debris fulfill m tainable forest management pro y eco the gram.therefore.rates of tree re The extent and impact of these Note person in red for scale moval and other management ac losses vary depending on numer- by Jerry Franklin tivities should be planned accord ous site-specific factors such as ni ing to nutrient budgeting tech trogen ava limate and also on management prac niques in order to reduceor deter long-term degrada tices (Col 1995).In the n nitrogen-poor tion of soil nutrients. em u.s. for example. dslash burn ing ogen-ricl as have increased of North A meric nts shov of r h gen ecognized that h 05 proc le due to tree ha soils to stre espe able fron ne has bee into theIssues in Ecology Number 6 Spring 2000 4 intensive forestry today, and in fact, doing so has been seen as a waste. The question of how many trees to leave to sustain soil quality is not easily answered at present and will require further research on the ecological functions of large dead wood. Yet retaining trees on site as future sources of large woody debris must be a major component of sustain￾able forest management. Nutrient Cycling Another major factor in sus￾taining soil quality is maintaining pools of essential plant nutrients and assuring these are steadily available in forms that plants can use. Undisturbed forests seldom experience significant losses of nu￾trient stocks. Thus an important element in sustainable forestry is taking care that management practices do not result in long￾term reductions in a forest’s nu￾trient capital or in the long-term availability of those nutrients to plants. Until recently, nitrogen has been considered the most impor￾tant nutrient limiting tree growth in temperate and boreal forests, and by far the majority of research has focused on nitrogen losses as￾sociated with timber harvest and site preparation (Johnson 1992). Losses from a harvested site take three forms: removal of the nitro￾gen contained in the harvested wood, nitrogen leached and eroded from disturbed soil, and ni￾trogen volatilized and lost to the atmosphere during slash burning. The extent and impact of these losses vary depending on numer￾ous site-specific factors such as ni￾trogen availability and climate and also on management prac￾tices (Cole 1995). In the nitrogen-poor forests of the west￾ern U.S., for example, losses in wood removal and slash burn￾ing far exceed those in leaching, while in more nitrogen-rich eastern forests, leaching losses can be quite high. Watershed-scale studies and harvesting experiments show that total nitrogen lost from a site after clearcutting varies widely among forest types. Since nitrogen is considered the major nutrient limiting tree growth in most systems, post￾harvest losses are regarded as a long-term threat to forest productivity. Nitrogen losses in the form of nitrate leached from soils to streams are especially variable from one forest to another. Elevated nitrate levels in streams following har￾vest or forest disturbance represent a threat to water qual￾ity because nutrient fouling can lead to a wide range of problems from algal blooms, loss of oxygen, and fish kills to degradation of drinking water. In general, forest ecosys￾tems with higher levels of nitrogen mineralization (release of nitrogen from decomposing soil organic matter) have been shown to exhibit higher rates of nitrate production and loss, and these losses are further increased by the removal of trees and corresponding elimination of nitrogen uptake by the trees. (Hibbert 1969, Likens et al. 1970, Hornbeck et al. 1996). Computer modeling of nutri￾ent requirements for forest growth as well as studies on watersheds and forest ecosystems agree that, in principle, harvesting whole trees and using short intervals be￾tween harvests on a site lead to significant reductions in soil nitro￾gen stocks, nitrogen availability, and productivity. Large losses of phosphorus, calcium, magnesium, potassium, and other nutrients also occur in association with whole-tree harvest and short ro￾tations (Kimmins 1977, Smith et al. 1986, Johnson and Todd 1987). Some practices used to clear logging slash and prepare sites for planting significantly im￾pact soil fertility, especially the use of heavy equipment to push slash and other organic matter into piles, a practice called windrow￾ing (Powers et al. 1990). In a sus￾tainable forest management pro￾gram, therefore, rates of tree re￾moval and other management ac￾tivities should be planned accord￾ing to nutrient budgeting tech￾niques in order to reduce or deter long-term degrada￾tion of soil nutrients. Nitrogen Saturation Concerns have increased across much of North America and Europe about the overabundance of nitrogen entering forests due to the human-driven buildup of airborne nitro￾gen. It is now recognized that human activities such as burn￾ing of fossil fuels and production of nitrogen fertilizers have effectively doubled the supply of biologically available nitro￾gen. Thus, research on nitrogen shortages due to tree har￾vest has been augmented by investigations into the effects of Figure 2 - During the last 30 years it has become appar￾ent that logs and other woody debris fulfill many eco￾logical functions and persist for centuries, as in the case of this giant sequoia log. Note person in red for scale. Photo by Jerry Franklin