Scott J. Goetz

Cross-scale controls on carbon emissions from boreal forest megafires

Climate warming and drying is associated with increased wildfire disturbance and the emergence of megafires in North American boreal forests. Changes to the fire regime are expected to strongly increase combustion emissions of carbon (C) which could alter regional C balance and positively feedback to climate warming. In order to accurately estimate C emissions and thereby better predict future climate feedbacks, there is a need to understand the major sources of heterogeneity that impact C emissions at different scales. Here, we examined 211 field plots in boreal forests dominated by black spruce (Picea mariana) or jack pine (Pinus banksiana) of the Northwest Territories (NWT), Canada after an unprecedentedly large area burned in 2014. We assessed both aboveground and soil organic layer (SOL) combustion, with the goal of determining the major drivers in total C emissions, as well as to develop a high spatial resolution model to scale emissions in a relatively understudied region of the boreal forest. On average, 3.35xa0kgxa0Cxa0m-2 was combusted and almost 90% of this was from SOL combustion. Our results indicate that black spruce stands located at landscape positions with intermediate drainage contribute the most to C emissions. Indices associated with fire weather and date of burn did not impact emissions, which we attribute to the extreme fire weather over a short period of time. Using these results, we estimated a total of 94.3xa0Tgxa0C emitted from 2.85xa0Mha of burned area across the entire 2014 NWT fire complex, which offsets almost 50% of mean annual net ecosystem production in terrestrial ecosystems of Canada. Our study also highlights the need for fine-scale estimates of burned area that represent small water bodies and regionally specific calibrations of combustion that account for spatial heterogeneity in order to accurately model emissions at the continental scale.

Historical and Projected Climates as a Basis for Climate Change Exposure and Adaptation Potential across the Appalachian Landscape Conservation Cooperative

Global temperatures have risen over the last few decades, and even the most conservative climate models project these trends to continue over the next eighty-five years (IPCC 2013). As climate changes, flora and fauna will be forced to adapt or migrate (Aitken et al. 2008). Many species have been able to adapt to past changes in climate, moving south during glacial periods and north during interglacial periods. However, anthropogenic climate change in most areas is occurring much faster than previous climatic shifts. Flora, in particular, may be unable to adapt or disperse quickly enough to track suitable climate conditions (Corlett and Westcott 2013). Understanding historical and projected future trends in temperature, precipitation, and other climate variables is important for evaluating the current context and likely consequences of climate changes in national parks, and in developing effective strategies for climate adaptation.

Potential Impacts of Climate and Land Use Change on Ecosystem Processes in the Great Northern and Appalachian Landscape Conservation Cooperatives

Ecosystem processes are the physical, chemical, and biological actions or events that link organisms and their environment. These processes include water and nutrient cycling, plant growth and decomposition, and regulation of community dynamics (Millennium Ecosystem Assessment 2003). The ecological characteristics of many parks and protected areas are dependent on the ecosystem functions that result from interactions between ecosystem processes, characteristics, and structures. Ecosystem functions, such as the regulation of water flows, soil retention and formation, and the provisioning of habitat and maintenance of biological diversity, in turn, provide the foundation for the ecosystem services supported by parks and protected areas (Hansen and DeFries 2007). As such, the preservation of ecosystem processes can be an important conservation target that complements conservation goals for species and habitats. Defining these targets is the first step in the Climate-Smart Conservation framework (Glick, Stein, and Edelson 2011; Stein et al. 2014).

Detecting early warning signals of tree mortality in boreal North America using multiscale satellite data

Increasing tree mortality from global change drivers such as drought and biotic infestations is a widespread phenomenon, including in the boreal zone where climate changes and feedbacks to the Earth system are relatively large. Despite the importance for science and management communities, our ability to forecast tree mortality at landscape to continental scales is limited. However, two independent information streams have the potential to inform and improve mortality forecasts: repeat forest inventories and satellite remote sensing. Time series of tree-level growth patterns indicate that productivity declines and related temporal dynamics often precede mortality years to decades before death. Plot-level productivity, in turn, has been related to satellite-based indices such as the Normalized difference vegetation index (NDVI). Here we link these two data sources to show that early warning signals of mortality are evident in several NDVI-based metrics up to 24xa0years before death. We focus on two repeat forest inventories and three NDVI products across western boreal North America where productivity and mortality dynamics are influenced by periodic drought. These data sources capture a range of forest conditions and spatial resolution to highlight the sensitivity and limitations of our approach. Overall, results indicate potential to use satellite NDVI for early warning signals of mortality. Relationships are broadly consistent across inventories, species, and spatial resolutions, although the utility of coarse-scale imagery in the heterogeneous aspen parkland was limited. Longer-term NDVI data and annually remeasured sites with high mortality levels generate the strongest signals, although we still found robust relationships at sites remeasured at a typical 5 year frequency. The approach and relationships developed here can be used as a basis for improving forest mortality models and monitoring systems.

Spatiotemporal remote sensing of ecosystem change and causation across Alaska

Contemporary climate change in Alaska has resulted in amplified rates of press and pulse disturbances that drive ecosystem change with significant consequences for socio-environmental systems. Despite the vulnerability of Arctic and boreal landscapes to change, little has been done to characterize landscape change and associated drivers across northern high-latitude ecosystems. Here we characterize the historical sensitivity of Alaskas ecosystems to environmental change and anthropogenic disturbances using expert knowledge, remote sensing data, and spatiotemporal analyses and modeling. Time-series analysis of moderate-and high-resolution imagery was used to characterize land- and water-surface dynamics across Alaska. Some 430,000 interpretations of ecological and geomorphological change were made using historical air photos and satellite imagery, and corroborate land-surface greening, browning, and wetness/moisture trend parameters derived from peak-growing season Landsat imagery acquired from 1984 to 2015. The time series of change metrics, together with climatic data and maps of landscape characteristics, were incorporated into a modeling framework for mapping and understanding of drivers of change throughout Alaska. According to our analysis, approximately 13% (~174,000xa0±xa08700xa0km2 ) of Alaska has experienced directional change in the last 32xa0years (±95% confidence intervals). At the ecoregions level, substantial increases in remotely sensed vegetation productivity were most pronounced in western and northern foothills of Alaska, which is explained by vegetation growth associated with increasing air temperatures. Significant browning trends were largely the result of recent wildfires in interior Alaska, but browning trends are also driven by increases in evaporative demand and surface-water gains that have predominately occurred over warming permafrost landscapes. Increased rates of photosynthetic activity are associated with stabilization and recovery processes following wildfire, timber harvesting, insect damage, thermokarst, glacial retreat, and lake infilling and drainage events. Our results fill a critical gap in the understanding of historical and potential future trajectories of change in northern high-latitude regions.

Vulnerability of Tree Species to Climate Change in the Appalachian Landscape Conservation Cooperative

Forests of the Appalachian Landscape Conservation Cooperative provide critical ecological and management functions. The moist climate of the eastern United States fosters productive stands that store relatively high amounts of carbon; for example, the Appalachian Landscape Conservation Cooperative (Appalachian LCC) accounts for only 7.6 percent of the contiguous United States but contains 18.8 percent of its aboveground forest biomass (derived from Kellndorfer et al. 2012). The Appalachian Mountains create substantial topographic and microclimatic diversity, and forests in the southern Appalachian LCC have some of the highest levels of endemic mammal, bird, amphibian, reptile, freshwater fish, and tree species biodiversity in the conterminous United States (Jenkins et al. 2015). Forest types vary from commercial pine plantations in the south to temperate hardwoods in the central Appalachians to high-elevation spruce-fir forests in the north.

Potential Impacts of Climate Change on Vegetation for National Parks in the Eastern United States

Forests in the eastern United States have a long history of change related to climate and land use. Eighteen thousand years ago, temperatures were considerably lower and glaciers covered much of the area where deciduous forests currently grow. As glaciers retreated and temperatures rose, tree species advanced from southern areas (Delcourt and Delcourt 1988) and may also have dispersed from low-density populations near the edge of the Laurentide ice sheet (McLachlan, Clark, and Manos 2005). A variety of other processes have also influenced the distribution of tree species. Derechos, tornadoes, and fires cause frequent, small- to intermediate-scale disturbances that are important influences on canopy structure and species composition, while larger disturbances, such as hurricanes, cause less frequent but more extensive changes (Dale et al. 2001).

Human and natural controls of the variation in aboveground tree biomass in African dry tropical forests

Understanding the anthropogenic and natural controls that affect the patterns, distribution, and dynamics of terrestrial carbon is crucial to meeting climate change mitigation objectives. We assessed the human and natural controls over aboveground tree biomass density in African dry tropical forests, using Zambias first nationwide forest inventory. We identified predictors that best explain the variation in biomass density, contrasted anthropogenic and natural sites at different spatial scales, and compared sites with different stand structure characteristics and species composition. In addition, we evaluated the effects of different management and conservation practices on biomass density. Variation in biomass density was mostly determined by biotic processes, linked with both species richness and dominance (evenness), and to a lesser extent, by land use, environmental controls, and spatial structure. Biomass density was negatively associated with tree species evenness and positively associated with species richness for both natural and human-modified sites. Human influence variables (including distance to roads, distance to town, fire occurrence, and the population on site) did not explain substantial variation in biomass density in comparison to biodiversity variables. The relationship of human activities to biomass density in managed sites appears to be mediated by effects on species diversity and stand structure characteristics, with lower values in human-modified sites for all metrics tested. Small contrasts in carbon density between human-modified and natural forest sites signal the potential to maintain carbon in the landscape inside but also outside forestlands in this region. Biodiversity is positively related to biomass density in both human and natural sites, demonstrating potential synergies between biodiversity conservation and climate change mitigation. This is the first evidence of positive outcomes of protected areas and participatory forest management on carbon storage at national scale in Zambia. This research shows that understanding controls over biomass density can provide policy relevant inputs for carbon management and on ecological processes affecting carbon storage.