Showing papers by "Scott J. Goetz published in 2018"

Plant functional trait change across a warming tundra biome

Abstract: The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature-trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.

Animals and the zoogeochemistry of the carbon cycle

Abstract: BACKGROUND Modern advances in remote-sensing technology are providing unprecedented opportunities to accurately measure the global distribution of carbon held in biomass within ecosystems. Such highly spatially resolved measures of biomass carbon are intended to provide an accurate inventory of global carbon storage within ecosystems. They are also needed to test the accuracy of carbon cycle models that predict how global changes that alter biogeochemical functions—such as carbon assimilation via photosynthesis, carbon losses via plant and microbial respiration, and organic matter deposition in soils and sediments—will affect net ecosystem carbon uptake and storage. Emerging ecological theory predicts that wild animals stand to play an important role in mediating these biogeochemical processes. Furthermore, many animal species roam widely across landscapes, creating a spatial dynamism that could regulate spatial patterning of vegetation biomass and carbon uptake and soil carbon retention. But such zoogeochemical effects are not measured by current remote-sensing approaches nor are they factored into carbon cycle models. Studies are now providing new quantitative insights into how the abundance, diversity, and movement of animal species across landscapes influence the nature and magnitude of zoogeochemical affects. These insights inform how to account for animals in remote-sensing applications and in carbon cycle models to more accurately predict carbon exchange between ecosystems and the atmosphere in the face of global environmental change. ADVANCES Zoogeochemical effects have been measured using manipulative experiments that exclude or add focal wild animal species or along landscape gradients where animal abundances or diversity vary naturally. Our review of these studies, which cover a wide diversity of taxa (vertebrates and invertebrates and large- and small-bodied organisms) and ecosystems, reveals that animals can increase or decrease rates of biogeochemical processes, with a median change of 40% but ranging from 15 to 250% or more. Moreover, models that embody zoogeochemical effects reveal the potential for considerable under- or overestimates in ecosystem carbon budgets if animal effects are not considered. The key challenge, in light of these findings, is comprehensively accounting for spatially dynamic animal effects across landscapes. We review new developments in spatial ecosystem ecology that offer the kind of analytical guidance needed to link animal movement ecology to geospatial patterning in ecosystem carbon uptake and storage. Considerations of animal movement will require highly resolved spatially explicit understanding of landscape features, including topography, climate, and the spatial arrangement of habitat patches and habitat connectivity within and among ecosystems across landscapes. We elaborate on advances in remote-sensing capabilities that can deliver these critical data. We further review new geospatial statistical methods that, when combined with remote-sensing data and spatial ecosystem modeling, offer the means to comprehensively understand and predict how zoogeochemical-driven landscape processes regulate spatial patterns in carbon distribution. OUTLOOK There is growing interest to slow climate change by enlisting ecological processes to recapture atmospheric carbon and store it within ecosystems. Wild animal species are rarely considered as part of the solution. Instead, it is often held that managing habitat space to conserve wild animals will conflict with carbon storage. Our integrative review offers a pathway forward for deciding when and how conserving or managing a diversity of animal species could in fact enhance ecosystem carbon uptake and storage. Such understanding informs international climate and biodiversity initiatives such as those described by the United Nations Convention on Biological Diversity and national biodiversity strategies and climate action plans. All of these initiatives require better resolution of how biodiversity effects on ecosystem structure and biogeochemical functioning will become altered by global change.

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

Abstract: 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 24 years 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.

Missing pieces to modeling the Arctic-Boreal puzzle

Abstract: Author(s): Fisher, JB; Hayes, DJ; Schwalm, CR; Huntzinger, DN; Stofferahn, E; Schaefer, K; Luo, Y; Wullschleger, SD; Goetz, S; Miller, CE; Griffith, P; Chadburn, S; Chatterjee, A; Ciais, P; Douglas, TA; Genet, H; Ito, A; Neigh, CSR; Poulter, B; Rogers, BM; Sonnentag, O; Tian, H; Wang, W; Xue, Y; Yang, ZL; Zeng, N; Zhang, Z | Abstract: NASA has launched the decade-long Arctic-Boreal Vulnerability Experiment (ABoVE). While the initial phases focus on field and airborne data collection, early integration with modeling activities is important to benefit future modeling syntheses. We compiled feedback from ecosystem modeling teams on key data needs, which encompass carbon biogeochemistry, vegetation, permafrost, hydrology, and disturbance dynamics. A suite of variables was identified as part of this activity with a critical requirement that they are collected concurrently and representatively over space and time. Individual projects in ABoVE may not capture all these needs, and thus there is both demand and opportunity for the augmentation of field observations, and synthesis of the observations that are collected, to ensure that science questions and integrated modeling activities are successfully implemented.

Cross‐scale controls on carbon emissions from boreal forest megafires

Abstract: 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, 3.35 kg C m-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 94.3 Tg C emitted from 2.85 Mha 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.