Forest Resilience, Biodiversity, and Climate Change

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Forest Resilience, Biodiversity, and Climate Changepublished predicted changes for the boreal forestas: increased fire, increased infestation, northwardexpansion, and altered stand composition andstructure. To that list we add reduced old-growthforest and conversion to grasslands and steppeof southern-central dry forests (Thompson et al.1998, Price and Scott 2006). Warming climate hasbeen implicated as a cause for current extensiveoutbreaks of mountain pine beetle (Dendroctonusponderosae) in western Canada and the USA(Taylor et al. 2006). Productivity is expectedto rise, but net carbon losses are likely to occurbefore the end of the century, owing to increaseddisturbances and higher rate of respiration (Kurzet al. 2008). However, significant stocks of biomassand soil carbon will remain. The net exchange andresultant standing stock will depend on, amongother things, changes in fire regimes and forestmanagement activities (Chen et al. 2008). Someareas of the boreal forest are predicted to becomewetter and others drier, with consequently moreor less fire (Johnson 1992, Bergeron and Flannigan1995, Kellomaki et al. 2008). Generally firefrequency has been predicted to increase in theboreal biome (Flannigan et al. 1998) and evidencehas accumulated confirming this prediction inNorth America and Russia (Gillette et al. 2004, Sojaet al. 2007). Our first case-study on lodgepole pine(Pinus contorta) reflects that prediction (table 4).5.1.2 Case-study: western North Americanlodgepole pineLodgepole pine forests are a self-replacing, firedrivenecosystems (Brown 1975) and climatechange is generally predicted to reduce the fire intervalover much of their distribution (Flanniganet al. 2005). However, ecosystem models suggestthat stands may remain as carbon sinks even underincreased fire regimes, in part because of theincrease in production in response to temperature,but also depending on the model selected and theclimate change regime that is modelled (Kashianet al. 2006, Smithwick et al. 2009). Insect infestation,notably mountain pine beetle (Dendroctonusponderosae) can significantly alter the dynamicinfluence of fire, to the point of being the dominantfactor responsible for stand renewal over hugelandscapes (Logan and Powell 2001), and the combinationof fires and insect infestation may lead tonew forest states (Shore et al. 2006). If the insectkilledstands do not burn, then a large amount ofcarbon would enter the detrital pool. In lodgepolepine forests, the impact of climate change on carbonstocks may be marginal depending on infesta-Lodgepole pine (Pinus contorta)killed by themountain pine beetle (in red) inBritish Columbia, Canadation levels and this forest ecosystem may be resilientduring at least the next 50-100 years.5.1.3 Case study: North American borealmixedwoodsA second boreal case-study is from a moisterecosystem where fire has an influence but the fireregime is much more protracted, resulting in broadexpanses of mixed species (hardwood and softwood)forests (table 5). Here, the relatively large numberof species, relative to many other boreal types,appears to increase the resilience of these forests(Girard et al. 2008). However, even in these moremoist systems, fire frequency is predicted to increaseby 50-80% in boreal mixedwoods in the next 50+years, in North America (Krawchuk et al. 2009).Under a high disturbance regime, carbon stocks inmixedwood forests are predicted to be about 16-50%or more of current stocks, depending on location(Price et al. 1999, Bhatti et al. 2001, Ni, 2002, Yarieand Parton 2005). These forests will still providehabitat and most of the same goods and services,but they will most likely change states in response tothe increased disturbance regime. While the casestudypresented is from central Canada, in Finland,increased moisture and elevated temperatures areexpected to result in an increase in production andcarbon sequestration (Kellomaki et al. 2008).5.2 Temperate forest biomeTemperate deciduous forests can be found acrosscentral-western and eastern North America, centraland western Europe, and northern Asia. Theseforests have a four distinct seasons, and a growingseason lasting 150-200 days. The continental climateis subject to a wide range of air temperature variation(i.e. 30 o C to -30 o C), and annual precipitation of 750Credit: T. Gage31
Forest Resilience, Biodiversity, and Climate ChangeTable 4. A case study of expected forest resilience in boreal lodgepole pine(Pinus contorta) forests of western North America under current climate (A) andexpected under climate change (B).Numbers refer to time (yrs) to recover from disturbance (i.e., resilience). A zero suggests that the forest willonly recover to a new state and/or not recover the attribute in question.Biome: BorealEcosystem: Boreal lodgepole pine forest ecosystemA. Current ClimateNatural disturbance regimes:(a) Fire - stand replacing fires 100 yrs,0=not resilient (statechange)Attributes that areindicators of systemchangeDominant canopy speciesStand structure (canopyheight + density; layers)Ecosystem servicesSite/stand (species andstructures)Landscape and/or watershed(stand mixturesand age structure)≤100 ≤100 Resilient≤50 >100 Resilient1. Total carbon ≤50 Resilient Resilient2. Water ≤50 ≤50 Resistant3. Habitat ≤100 Resilient ResilientB. Expected under Climate ChangeNatural disturbance regimes: Fire - stand replacing fires 100 yrs,0= not resilient (statechange)Attributes that areindicators of systemchangeDominant canopy speciesStand structure (canopyheight + density; layers)Ecosystem servicesSite/stand Landscape and/orwatershed≤50 ≤50 ≤ 500 0 01. Total carbon ≤50 (+9 to -37% of ≤50≤50original C stocks)2. Water ≤ 50 ≤ 50 ≤ 503. Habitat ≤100 ≤100 ≤100Bioregion/ecoregionBio(eco)region32
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