Issues in Ecology Number 6 Spring 2000 forest management should consider the mosaic of fores Another maior research task is to determine what sain patches on the landscape and the connectedness of habitat in biodiversity actually accrue from retaining mature g for forest species in plannine future cuts in uity.results to date show that Forests managed for timber harvest can be fragmented with remnant old trees support a greater abundance of some by roads as well as clearcuts.Roads may affect biodiversity old-growth-associated species than do uniformly youn in a number of ways princinally hy creating barriers to move stands and also sustain some species not found at all i ment.access routes for predators (including humans).and young stands (Hansen et al.1995,Peck and McCune 1997 corridors for invasions by noxious weeds and pathogens(Perry Schowalter 1995). 1988.Small and Hunter 1988).Nu Ecosystems are sensitive to change merous studies have shown that popu in the number and kinds of species lation sizes of bears,wolves,moose found in their communities.Because and mountain lions decline as roac species can vary dramatically in thei density increases(e.g..Brocke et al contribution to ecosystem function 1989) ing.the identity of the species present The spread of both native and in a com unity is important.Declir exotic pests and pathogens in many ngs到 ecies richnes can lead to dete forest systems can be linked to sim on in overa ecosys plific ng6emanom the em ores on arcuts and upy partic web (gra id have est 99 tre P dN with the fre ity of long-term success in ntly viewed de ing forests against pests and pathd ods are mportant because the eens is to encou naintenance act as bio a diverse set of controls such as oc logical dams following disturbance. curs in nature vide unique habitat and food for ure 5.Interior of old orowth Doualas.fir stand animals.and modulate fire severity. Structural Complexitu showine the structural complexity of natural for research has demonstrated tha LANDSCAPE-LEVEL ISSUES IN structural complexity is an important ests provided by multiple canopy layers.snags.and fallen logs.Mt.Baker-Snoqualmie National Forest. foREST MANAGEMENT PLAN feature of natural forest ecosystems Photo by Jerry Franklin. NING (e.g..Perry 1994).Vegetation of While most forestry research ha different heights provides a variety of habitats for the rich focused on the management of individual stands.most im diversity of species associated with healthy torests.Iree har portant forest policy issues require consideration of land vesting usually reduces elements of this structural scape-l mena and concerns (se also the Commit including mu Itiple canopy layers, dead snags.an rge faller tee Report 99).Sustainab stry necess logs(Figure 5). Ecologists gating how tates tha much structural complexity is larger spatial s Ices su es on edg the ests in rder to tat fr nd fects em functic d,the ailurIssues in Ecology Number 6 Spring 2000 8 forest management should consider the mosaic of forest patches on the landscape and the connectedness of habitat for forest species in planning future cuts. Forests managed for timber harvest can be fragmented by roads as well as clearcuts. Roads may affect biodiversity in a number of ways, principally by creating barriers to move￾ment, access routes for predators (including humans), and corridors for invasions by noxious weeds and pathogens (Perry 1988, Small and Hunter 1988). Nu￾merous studies have shown that popu￾lation sizes of bears, wolves, moose, and mountain lions decline as road density increases (e.g., Brocke et al. 1989). The spread of both native and exotic pests and pathogens in many forest systems can be linked to sim￾plification and fragmentation of the forest during harvesting, certain re￾planting practices on clearcuts, and the ready travel corridors provided by extensive road networks. Prob￾lems with pathogens and tree-eating insects in forestry have often been as￾sociated with widespread planting of a single tree species (Perry 1998). From an ecological standpoint, the strategy with the greatest probabil￾ity of long-term success in protect￾ing forests against pests and patho￾gens is to encourage maintenance of a diverse set of controls such as oc￾curs in nature. Structural Complexity Research has demonstrated that structural complexity is an important feature of natural forest ecosystems (e.g., Perry 1994). Vegetation of different heights provides a variety of habitats for the rich diversity of species associated with healthy forests. Tree har￾vesting usually reduces elements of this structural diversity, including multiple canopy layers, dead snags, and large fallen logs (Figure 5). Ecologists are currently investigating how much structural complexity is necessary and whether forest management practices such as long cutting rotations and variable-retention harvesting (which leaves more live trees, snags, and downed logs on a cutover site) can maintain eco￾logically important structural features while still allowing timber harvest (Franklin et al. 1997). Despite gaps in our understanding, sustainable forestry strategies should seek to return managed forests to the structure more typical of natural forests in order to assure protection of biodiversity and ecosys￾tem functioning. Another major research task is to determine what gains in biodiversity actually accrue from retaining mature green trees in perpetuity. Results to date show that young stands with remnant old trees support a greater abundance of some old-growth-associated species than do uniformly young stands, and also sustain some species not found at all in young stands (Hansen et al. 1995, Peck and McCune 1997, Schowalter 1995). Ecosystems are sensitive to changes in the number and kinds of species found in their communities. Because species can vary dramatically in their contribution to ecosystem function￾ing, the identity of the species present in a community is important. Declin￾ing species richness can lead to dete￾rioration in overall levels of ecosys￾tem functioning. Loss of functional groups or reductions in the number of species that occupy a particular level in the food web (grazers, brows￾ers, predators, decomposers) can also cause declines in ecosystem function￾ing (Tilman et al. 1997). Two impor￾tant groups of species in conifer-domi￾nated forests are hardwood trees and shrubs, which are present at one or more stages of succession and are fre￾quently viewed as weeds. Hard￾woods are important because they enhance nutrient cycling, act as bio￾logical dams following disturbance, provide unique habitat and food for animals, and modulate fire severity. LANDSCAPE-LEVEL ISSUES IN FOREST MANAGEMENT PLAN￾NING While most forestry research has focused on the management of individual stands, most im￾portant forest policy issues require consideration of land￾scape-level phenomena and concerns (see also the Commit￾tee of Scientist Report 1999). Sustainable forestry necessi￾tates that individual stands be managed in the context of larger spatial scales. Issues such as regulation of water yields, conservation of biological diversity, and maintenance of aquatic ecosystems require the application of principles from landscape ecology. These principles include concern for size and shape of forest patches, edge effects, and connectivity that is, the movement of organisms and materials through the landscape. Lack of attention to these landscape-scale concerns in stand-by-stand planning can lead to further habi￾tat fragmentation and cumulative negative effects on forest communities. Indeed, the failure to consider larger landscape Figure 5 - Interior of old-growth Douglas-fir stand showing the structural complexity of natural for￾ests provided by multiple canopy layers, snags, and fallen logs. Mt. Baker-Snoqualmie National Forest. Photo by Jerry Franklin.