WHITE PAPER F14-SO-WP-SILV-45 Climate Change and Carbon Sequestration: Vegetation Management Considerations 1 David C. Powell; Forest Silviculturist Supervisor’s Office; Pendleton, OR Initial Version: DECEMBER 2011 Most Recent Revision: MARCH 2017 Background/Context ........................................................................................................... 2 Fig. 1: Projected increase in wildfire area burned ..................................................................... 3 Fig. 2: Restoration objectives for dry forests ............................................................................. 4 Fig. 3: Thinning and low-severity fire reduce the risk of stand-replacing fire ........................... 5 Introduction ........................................................................................................................ 6 Fig. 4: Projected scenario for temperature and precipitation change for Washington ............ 7 Fig. 5: Reconstructed, 2000-year chronology of Palmer Drought Severity Index ..................... 9 Silvicultural activities and climate change ........................................................................ 10 Table 1: Selected life-history traits for conifers of the Blue Mountains .................................. 11 Climate change and HRV ................................................................................................... 12 Climate change summary ................................................................................................. 13 Table 2: Climate change adaptation strategies ....................................................................... 17 Forest carbon analysis ...................................................................................................... 18 Silvicultural activities and carbon sequestration .............................................................. 24 Table 3: Carbon accounting by NEPA alternative .................................................................... 27 Figure 6: Estimated post-treatment C stocks by individual treatment unit ............................ 27 Appendix 1: Site specific information for carbon analysis ............................................... 28 References ........................................................................................................................ 33 Appendix 2: Silviculture white papers ............................................................................ 102 Revision history ............................................................................................................... 105 1 White papers are internal reports; they receive only limited review. Viewpoints expressed in this paper are those of the author – they may not represent positions of the USDA Forest Service. 1 BACKGROUND/CONTEXT The Intergovernmental Panel on Climate Change (IPCC) (IPCC 2014), the most recent National Climate Assessment (Melillo et al. 2014), and other sources suggest that the magnitude and pace of climate change in forest ecosystems will be unprecedented. Cli- mate change is capable of changing forests to meadows or shrublands, and changes of this extent will trigger a cascade of associated impacts on plants, wildlife, and other eco- system components. For the Blue Mountains ecoregion, monthly average temperature during the 21st century is projected to increase by ~3.3°C in winter (December-February) and 5.0°C in summer (June-August). Projected changes in precipitation vary substantially among models, but the central tendency is for increased precipitation (~15%) in winter (Novem- ber-February) and decreased precipitation (~17%) in summer (June-September) (Mau- ger and Mantua 2011). Changes in temperature and precipitation will have important implications on soil moisture, water availability, and streamflow timing for the Blue Mountains. Projections for the end of this century show a 69-72% decrease in April 1st snowpack, with snow- melt occurring at least 3 weeks earlier than now. Projected changes in soil moisture, which have important implications on tree growth and stand vigor (Grant et al. 2013), show increases in average winter amounts (12-13% for January-April) and decreases in average summer storage (4-7% for June to September) (Mauger and Mantua 2011). IPCC concluded with high confidence (8 out of 10 chance) that “disturbances such as wildfire and insect outbreaks are increasing and are likely to intensify in a warmer future with drier soils and longer growing seasons, and to interact with changing land use and development affecting the future of wildland ecosystems” (Parry et al. 2007, page 56). Since about 1990, it has become increasingly obvious that changing climatic condi- tions are causing ripple effects, many of which are being expressed as variations in dis- turbance regimes. As wildfires become larger and as wildfire season lengthens, for ex- ample, land managers now recognize that climate change is more than just a ‘continen- tal’ problem – it is also occurring at geographical scales commensurate with their man- agement activities (fig. 1). Since climate change is a broad-scale phenomenon in many respects, and because natural resource management activities occur at fine scales, there is uncertainty about whether climate change should be addressed in environmental analysis documents for land management projects. Some managers believe that projects have little potential to influence climate change one way or another, so including it in environmental analyses is either irrelevant (at best) or misleading (at worst, because including it suggests that projects have the potential to affect it). 2 Figure 1 – Projected increase in wildfire area burned with a mean annual temperature increase of only 1° C (1.8° F), shown as a percentage change relative to median annual area burned dur- ing 1950-2003 (source: Climate Central 2012, as adapted from fig. 5.8 in National Research Council 2011). Results are aggregated to eco-provinces (Bailey 1995) of the western United States; the Blue Mountains occur in a large brown zone (upper central portion) with projected burn-area increases of at least six times. Climate-fire models were derived from National Cli- matic Data Center climate division records; observed burn-area data follows methods described in Littell et al. (2009). This map is alarming because when comparing the 1970-99 and 2070-99 time periods, an increase in average temperature of 3.3 to 9.7°C is projected, and the increase will be greatest in summer during fire season. This figure suggests that future wildfire effects could continue to be problematic unless thinnings and other density-management treatments are implemented to reduce stand density levels and thereby provide fire-safe forest conditions (figs. 2, 3). As noted in many other assessments, “the most extensive and serious problem related to health of national forests in the interior West is the overaccumulation of vegetation, which has caused an increasing number of large, intense, uncontrollable and catastrophically destructive wildfires” (GAO 1999). In the climate change context shown here, “lower stand densities may be necessary in a warmer climate to achieve the same level of reduced intertree competition as was achieved in the past” (Peterson et al. 2011). Or, to put it another way, residual-tree density after thinning must be lower now to achieve the same level of stand protection provided by higher densities in the past (retaining 60 square feet of basal area now, for example, provides a comparable level of protection as was obtained from 80 square feet historically). In a climate change context, existing stand densities should be reduced all the way down to the lower limit of the management zone, as specified in Cochran et al. (1994) and Powell (1999). After thinning, prescribed fire should be used periodically to preclude establishment of additional tree regener- ation (‘ingrowth’), and thereby maintain stand densities at the lower levels most congruent with a warmer and dryer future. 3 Figure 2 – Restoration objectives for dry forests (from Powell 2014a). Mechanical thinning and prescribed fire are effective treatments for increasing climate-change resilience for dry-forest ecosystems (Johnson et al. 2011, McIver et al. 2013, Stephens et al. 2009, Youngblood 2010). It is becoming increasingly evident that if dry forests are to be made resilient to climate change, their restoration is needed on a scale unprecedented in recent history (Franklin and Johnson 2012, USDA Forest Service 2012). What might qualify as dry-forest restoration? I believe a suc- cessful restoration outcome for dry forests includes the following six elements, taken primarily from Agee and Skinner (2005), Covington (2003), and Powell (2014a). 1) Species composition, forest structure, and stand density occur within their historical ranges of variation. 2) Both trees and forests express indicators of high vigor, such as high sap flow, increased ra- dial growth, good seedling height growth, and high foliar nitrogen levels. 3) Stands and landscapes have high fire resistance, high capacity to accept and absorb fire, and high competency to exhibit positive ecosystem responses to fire’s ecological benefits. 4) Forests exhibit high resilience to insects and diseases at a landscape scale – individual tree stands in a landscape do experience insect and disease activity, but it occurs at characteris- tic levels when evaluated in a landscape context. 5) Landscapes are effectively buffered for