ISSUES IN ECOLOGY NUMBER THIRTEEN SPRING 2010 land will likely vield greater carh Box 2.CO-BENEFITS OF FORESTS Afforestation can have negative conse Our report focuses on forestss een through the lens of carbon,and only car Pla ica fore roth of ood for productsand fuel to ofset fossil fuel usere far from the on suchas lower species diversity(if trees are asons forests are valuable.Forests also prov many othe ecosystem se parei to the native coramflow cm.dd com of peak streamflow and an increase in base streamflow servation.Americans are stronaly attached to their forests.n o2Caenmeggctorcabonwoudconetwitotherco-beneisg ng lands to forest reduces revenue from agricultural pr Even simple oxide (a and piodiversity compared to crops or livestock pasture pecause the powerful sCO)will increase of harvest or stand-replacing disturbance is much less for forests. ent:d creasing Th avest reducing ch they ar more carbon in the forest.The greater the longer timeframes and larger landscapes leads incre in ca to an ha in carbo n st ncrease in stru tural and species diversity.On the other hand.the nn sed risk ut o a455o or ca ss due to ance and 60 years (Figure 7).A 50-year increase from compensate for the reduction in forest product generated. h The 4.Forest m ment:increasing ests where varies with forest growth rducing the on iom,anothertmtele r-year harves,but only to20%0 interval (Figure ct for sho se forest ater eff ege time.Reducing harvest amounts in these sys- tation,fertilizing,planting tems trom complete removal 200 ity.Yield nhetennnitweemUn ed Sta 150 harvests coul pressive.In pine mova e most suitable in improved wood growth 0 50 100150200 high potential to store carbon such as those an show 100%6 gains for Harvest Interval (Years) with long-lived species and slowly decompos- wood growth.For southern The Ecological Society of Americaesahq@esa.org esa 7© The Ecological Society of America • esahq@esa.org esa 7 ISSUES IN ECOLOGY NUMBER THIRTEEN SPRING 2010 land will likely yield greater carbon accumulation rates but fewer benefits in terms of biodiversity. Afforestation can have negative conse￾quences, too. Planting forests where they were not present historically can have drawbacks such as lower species diversity (if trees are planted in native grassland), changes in water table, and a higher energy absorption com￾pared to the native ecosystem. In addition, afforestation generally reduces streamflow regardless of the ecosystem type because trees use more water than grass or crops. Conversion of agricultural or grazing lands to forest reduces revenue from agricultural prod￾ucts. If afforestation efforts include the addi￾tion of nitrogen fertilizer, emissions of nitrous oxide (a greenhouse gas roughly 300 times as powerful as CO2) will increase. 3. Forest management: decreasing carbon loss Lengthening the harvest interval or reducing the amount removed in a harvest will store more carbon in the forest. The greater the increase in harvest interval over the current level, the higher the increase in carbon stor￾age. For example, a five-year increase in the harvest interval would lead to a 15% increase in carbon storage if the harvest interval was changed from 25 to 30 years, but only a 4% increase if the interval was changed from 55 to 60 years (Figure 7). A 50-year increase from 25 to 75 years would increase carbon storage 92% (Figure 7). The carbon impact of reducing the amount of trees removed in a harvest also varies with the harvest interval. For example, reducing the harvest from 100% to 20% of the live trees would increase the average forest carbon stock by 97% for a 25-year harvest interval, but only by 30% for a 100-year harvest interval (Figure 7). Some natural forests are dominated by small disturbances that kill a few trees at a time. Reducing harvest amounts in these sys￾tems from complete removal of trees to simply a percentage, for example, could mimic the natural disturbance regime common to the northeastern and midwestern United States. In addition, reducing harvests could be desirable in public forests that are managed for multiple purposes, such as recreation, biodiversity, and water. These strategies would be most suitable in forest regions with active management and a high potential to store carbon, such as those with long-lived species and slowly decompos￾ing dead plant matter, which are common in the Pacific Northwest. The carbon benefit of either of these practices will depend on the temporal and spatial scales at which they are administered – applying these practices over longer timeframes and larger landscapes leads to greater carbon benefits. In addition to an increase in carbon storage, benefits of decreased harvesting also include an increase in structural and species diversity. On the other hand, the costs are an increased risk of carbon loss due to disturbance and the potential for increased harvesting elsewhere to compensate for the reduction in forest products generated. 4. Forest management: increasing forest growth In addition to afforestation, another strategy for increasing carbon storage is to increase the growth rate of existing or new forests. Management practices that can increase forest growth include: regenerating harvested or damaged forests, controlling competing vege￾tation, fertilizing, planting genetically improved trees, and selecting species for superior productivity. Yield gains from these practices can be impressive. In pine forests in the southern U.S., tree breeding has improved wood growth (and carbon storage rate) by 10-30%, and fertilization can show 100% gains for wood growth. For southern Box 2. CO-BENEFITS OF FORESTS Our report focuses on forests seen through the lens of carbon, and only carbon. However, forests are managed for many purposes, and carbon storage and the growth of wood for products and fuel to offset fossil fuel use are far from the only reasons forests are valuable. Forests also provide many other ecosystem ser￾vices that are important to the well-being of the U.S. and its inhabitants: protec￾tion of watersheds from erosion, nutrient retention, good water quality, reduction of peak streamflow and an increase in base streamflow, wildlife habitat and diversity, recreational opportunities and aesthetic and spiritual fulfillment, and biodiversity conservation. Americans are strongly attached to their forests. In some cases, managing strictly for carbon would conflict with other co-benefits of forests. The option of avoided deforestation retains the co-benefits of forests and the carbon in forest ecosystems, while afforestation adds these co-benefits in addition to increasing carbon storage. Even simple forests, such as planta￾tions, generally reduce erosion, regulate streamflow, and increase wildlife habitat and biodiversity compared to crops or livestock pasture because the frequency of harvest or stand–replacing disturbance is much less for forests. Figure 7. Average carbon stored on a landscape will vary with the time between harvests (harvest interval) and how much biomass is removed each harvest. Lengthening the harvest interval will have a greater effect for harvests where removals are high (blue arrows show an increase in harvest interval from 25 to 75 years). Decreasing harvest intensity from 100% of trees to 20% of trees (black arrows) will have a greater effect for shorter harvest intervals. (Courtesy of Mark E. Harmon, Oregon State University, 2009.) 20% Removal 100% Removal 0 50 100 150 200 Harvest Interval (Years) 200 150 100 50 0 Carbon Storage (Mg/ha)