Threats and Strategies for Global Biodiversity Conservation

Fire Plays a Role in Ecosystems and SocietyThis section introduces the concepts of fire-dependent,fire-sensitive and fire-independent ecosystems and explainswhat a fire regime is and how fire regimes can be alteredin each of these three different ecosystem types. Theconsequences of altering fire regimes, for both ecosystemsand humans, need to be understood in order to effectivelyconserve biodiversity.The ecological role of fire around the world ranges froma process that strongly drives ecosystem structure andfunction (fire-dependent ecosystems—see Box 3) to havingno evolutionary significance (fire-independent ecosystems).The role of fire in human society ranges from acceptanceand use as a land management practice to fear of its threatto lives, property and livelihoods. Even societies that usefire as a land management tool often greatly fear fire whenit is perceived as “out of control.” In some ecosystemswildfire has natural selection significance, and the humanuse of fire as a land management tool may have longstandingcultural significance (Myers 2006, Pyne 1982,Yibarbuk 1998, Goldammer and de Ronde 2004). In manyplaces, periodic burning is used to maintain natural fireregimes—those that are consistent and compatible with theadaptations of species and natural processes—that help tosustain and rejuvenate ecosystems (Hassan et al 2005).Evidence suggests that human induced fires accelerate thetrend of ecosystem transformations caused by climatechange in the long term (Kershaw et al. 2002).Box 2. Agriculture and Human Land Use: The Advancing Front of Fire in the Amazon BasinOne-third of the global area thatburns annually is in the tropics(Mouillot and Field 2005). While“natural” fire is not unprecedentedin tropical systems, most are sensitiveto too frequent fire because it isdetrimental to ecosystem health.Most often fires in tropicalbroadleaved forests are set byhumans, either intentionally to clearforest patches and manage pastureand agricultural fields, or by accidentwhen intentional fires escape fromthese fields (Nepstad et al. 1999).Farmers and ranchers use fire as alabor-saving practice that can quicklyclear a patch of forest. Initial inputsof potassium and carbon from burnedmaterial can create fertile soil in thefirst growing season, and sometimeslonger. These changes in land use intropical broadleaved forests tend tocreate drier conditions, leading toincreased susceptibility of the forestto understory fires and a higherincidence of fires overall (Alencaret al. 2004). The loss of forest covercan then render the soil susceptibleto erosion and eliminate the principalsource of nutrients. When farmersabandon less fertile ground, landclearing is expanded to new areas.In Amazonia, large-scale fire patternsoften follow major human colonization,which causes large-scale patternsof deforestation (Skole and Tucker1993), road construction (Lauranceet al. 2001, Nepstad et al. 2001),and logging activities (Cochraneet al. 1999, Nepstad et al. 1999).Land uses in the region area primary source of “too much fire”in these forests, which is furtherexacerbated by climatic fluctuations.A study near Paragominas, a 35-yearoldranching and logging center ineastern Amazonia, found that 91% ofthe standing forest area that burnedover the 10-year study period caughtfire during El Niño SouthernOscillation (ENSO) years, whensevere drought may have increasedboth forest flammability and theescape of agricultural fires (Alencaret al. 2004). This study also concludedthat the percentage of forest thathad been previously logged or burned,forest fragment size, distance tocharcoal pits, distance to agriculturalsettlements, proximity to forest edge,and distance to roads were correlatedwith forest understory fire. Forestfragment degradation and distanceto ignition sources accuratelypredicted the location of 80% ofthe forest fires observed during theENSO event of 1997–1998. We canexpect that increases in fire activitywill continue to occur in response tofuture rural development programsplus the additional impact of climatechange in this region. These fires arecausing biodiversity loss, degradinglocal air quality and human health,creating regional haze, and changingwater supplies, not to mention theeconomic losses.The expansion of fire into tropicalsystems not generally accustomedto fire (and which also harbor muchof the world’s biodiversity andsequestered carbon), could destroyglobally-unique habitats and disruptglobal climate systems. The patternswe see in the Amazon are replicatingthemselves across similar habitattypes around the world. Othergeographies will have their own suiteof issues, including how human landuses have reduced the amount ofecologically appropriate fire, withoften catastrophic results for humancommunities and the environment.3