• Emerging climate-driven disturbance processes: Widespread mortality associated with snow-to-rain transitions across 10° of latitude and half the range of a climate-threatened conifer

      Buma, Brian; Hennon, Paul E; Harrington, Constance A.; Popkin, Jamie R.; Krapek, John; Lamb, Melinda S.; Oakes, Lauren E.; Saunders, Sari; Zeglen, Stefan (John Wiley & Sons, 2016-10-29)
      Climate change is causing rapid changes to forest disturbance regimes worldwide. While the consequences of climate change for existing disturbance processes, like fires, are relatively well studied, emerging drivers of disturbance such as snow loss and subsequent mortality are much less documented. As the climate warms, a transition from winter snow to rain in high latitudes will cause significant changes in environmental conditions such as soil temperatures, historically buffered by snow cover. The Pacific coast of North America is an excellent test case, as mean winter temperatures are currently at the snow–rain threshold and have been warming for approximately 100 years post-Little Ice Age. Increased mortality in a widespread tree species in the region has been linked to warmer winters and snow loss. Here, we present the first high-resolution range map of this climate-sensitive species, Callitropsis nootkatensis (yellow-cedar), and document the magnitude and location of observed mortality across Canada and the United States. Snow cover loss related mortality spans approximately 10° latitude (half the native range of the species) and 7% of the overall species range and appears linked to this snow–rain transition across its range. Mortality is commonly >70% of basal area in affected areas, and more common where mean winter temperatures is at or above the snow–rain threshold (>0 °C mean winter temperature). Approximately 50% of areas with a currently suitable climate for the species (< 2 °C) are expected to warm beyond that threshold by the late 21st century. Regardless of climate change scenario, little of the range which is expected to remain suitable in the future (e.g., a climatic refugia) is in currently protected landscapes (<1–9%). These results are the first documentation of this type of emerging climate disturbance and highlight the difficulties of anticipating novel disturbance processes when planning for conservation and management.
    • A foundation of ecology rediscovered: 100 years of succession on the William S. Cooper plots in Glacier Bay, Alaska

      Buma, Brian; Bisbing, Sarah; Krapek, John; Wright, Glenn (Ecological Society of America, 2017-03-24)
      Understanding plant community succession is one of the original pursuits of ecology, forming some of the earliest theoretical frameworks in the field. Much of this was built on the long-term research of William S. Cooper, who established a permanent plot network in Glacier Bay, Alaska, in 1916. This study now represents the longest-running primary succession plot network in the world. Permanent plots are useful for their ability to follow mechanistic change through time without assumptions inherent in space-for-time (chronosequence) designs. After 100-yr, these plots show surprising variety in species composition, soil characteristics (carbon, nitrogen, depth), and percent cover, attributable to variation in initial vegetation establishment first noted by Cooper in the 1916–1923 time period, partially driven by dispersal limitations. There has been almost a complete community composition replacement over the century and general species richness increase, but the effective number of species has declined significantly due to dominance of Salix species which established 100-yr prior (the only remaining species from the original cohort). Where Salix dominates, there is no establishment of “later” successional species like Picea. Plots nearer the entrance to Glacier Bay, and thus closer to potential seed sources after the most recent glaciation, have had consistently higher species richness for 100 yr. Age of plots is the best predictor of soil N content and C:N ratio, though plots still dominated by Salix had lower overall N; soil accumulation was more associated with dominant species. This highlights the importance of contingency and dispersal in community development. The 100-yr record of these plots, including species composition, spatial relationships, cover, and observed interactions between species provides a powerful view of long-term primary succession.
    • How Landscape Ecology Informs Global Land-Change Science and Policy

      Buma, Brian; Mayer, Audrey; Davis, Amelie; Gagne, Sara; Loudermilk, E. Louise; Scheller, Robert; Schmiegelow, Fiona; Wiersma, Yolanda; Franklin, Janet (Oxford University Press, 2016)
      Landscape ecology is a discipline that explicitly considers the influence of time and space on the environmental patterns we observe and the processes that create them. Although many of the topics studied in landscape ecology have public policy implications, three are of particular concern: climate change; land use–land cover change (LULCC); and a particular type of LULCC, urbanization. These processes are interrelated, because LULCC is driven by both human activities (e.g., agricultural expansion and urban sprawl) and climate change (e.g., desertification). Climate change, in turn, will affect the way humans use landscapes. Interactions among these drivers of ecosystem change can have destabilizing and accelerating feedback, with consequences for human societies from local to global scales. These challenges require landscape ecologists to engage policymakers and practitioners in seeking long-term solutions, informed by an understanding of opportunities to mitigate the impacts of anthropogenic drivers on ecosystems and adapt to new ecological realities.
    • Interpreting multiscale domains of tree cover disturbance patterns in North America

      Riitters, Kurt; Costanza, Jennifer K.; Buma, Brian (Elsevier, 2017-05-08)
      Spatial patterns at multiple observation scales provide a framework to improve understanding of pattern-related phenomena. However, the metrics that are most sensitive to local patterns are least likely to exhibit consistent scaling relations with increasing extent (observation scale). A conceptual framework based on multiscale domains (i.e., geographic locations exhibiting similar scaling relations) allows the use of sensitive pattern metrics, but more work is needed to understand the actual patterns represented by multiscale domains. The objective of this study was to improve the interpretation of scale-dependent patterns represented by multiscale domains. Using maps of tree cover disturbance covering North American forest biomes from 2000 to 2012, each 0.09-ha location was described by the proportion and contagion of disturbance in its neighborhood, for 10 neighborhood extents from 0.81 ha to 180 km2. A k-means analysis identified 13 disturbance profiles based on the similarity of disturbance proportion and contagion across neighborhood extent. A wall to wall map of multiscale domains was produced by assigning each location (disturbed and undisturbed) to its nearest disturbance profile in multiscale pattern space. The multiscale domains were interpreted as representing two aspects of local patterns – the proximity of a location to disturbance, and the interior-exterior relationship of a location relative to nearby disturbed areas.
    • Key landscape and biotic indicators of watersheds sensitivity to forest disturbance identified using remote sensing and historical hydrography data

      Buma, Brian; Livneh, Ben (IOP Publishing, 2017-07-19)
      Water is one of the most critical resources derived from natural systems. While it has long been recognized that forest disturbances like fire influence watershed streamflow characteristics, individual studies have reported conflicting results with some showing streamflow increases postdisturbance and others decreases, while other watersheds are insensitive to even large disturbance events. Characterizing the differences between sensitive (e.g. where streamflow does change postdisturbance) and insensitive watersheds is crucial to anticipating response to future disturbance events. Here, we report on an analysis of a national-scale, gaged watershed database together with high-resolution forest mortality imagery. A simple watershed response model was developed based on the runoff ratio for watersheds (n=73) prior to a major disturbance, detrended for variation in precipitation inputs. Post-disturbance deviations from the expected water yield and streamflow timing from expected (based on observed precipitation) were then analyzed relative to the abiotic and biotic characteristics of the individual watershed and observed extent of forest mortality. The extent of the disturbance was significantly related to change in post-disturbance water yield (p<0.05), and there were several distinctive differences between watersheds exhibiting post-disturbance increases, decreases, and those showing no change in water yield. Highly disturbed, arid watersheds with low soil: water contact time are the most likely to see increases, with the magnitude positively correlated with the extent of disturbance. Watersheds dominated by deciduous forest with low bulk density soils typically show reduced yield post-disturbance. Postdisturbance streamflow timing change was associated with climate, forest type, and soil. Snowy coniferous watersheds were generally insensitive to disturbance, whereas finely textured soils with rapid runoff were sensitive. This is the first national scale investigation of streamflow postdisturbance using fused gage and remotely sensed data at high resolution, and gives important insights that can be used to anticipate changes in streamflow resulting from future disturbances.
    • Populus tremuloides seedling establishment: An underexplored vector for forest type conversion after multiple disturbances

      Gill, Nathan S.; Sangermano, Florencia; Buma, Brian; Kulakowski, Dominik (Elsevier, 2017-11-15)
      Ecosystem resilience to climate change is contingent on post-disturbance plant regeneration. Sparse gymnosperm regeneration has been documented in subalpine forests following recent wildfires and compounded disturbances, both of which are increasing. In the US Intermountain West, this may cause a shift to non-forest in some areas, but other forests may demonstrate adaptive resilience through increased quaking aspen (Populus tremuloides Michx.) dominance. However, this potential depends on ill-defined constraints of aspen sexual regeneration under current climate. We created an ensemble of species distribution models for aspen seedling distribution following severe wildfire to define constraints on establishment. We recorded P. tremuloides seedling locations across a post-fire, post-blowdown landscape. We used 3 algorithms (Mahalanobis Typicalities,Multilayer Perceptron Artificial Neural Network, and MaxEnt) to create spatial distribution models for aspen seedlings and to define constraints. Each model performed with high accuracy and was incorporated into an ensemble model, which performed with the highest overall accuracy of all the models. Populus tremuloides seedling distribution is constrained primarily by proximity to unburned aspen forest and annual temperature ranges, and secondarily by light availability, summer precipitation, and fire severity. Based on model predictions and validation data, P. tremuloides seedling regeneration is viable throughout 54% of the post-fire landscape, 97% of which was previously conifer-dominated. Aspen are less susceptible to many climatically-sensitive disturbances (e.g. fire, beetle outbreak, wind disturbance), thus, aspen expansion represents an important adaptation to climate change. Continued aspen expansion into post-disturbance landscapes through sexual reproduction at the level suggested by these results would represent an important adaptation to climate change and would confer adaptive forest resilience by maintaining forest cover, but would also alter future disturbance regimes, biodiversity, and ecosystem services.