Jonathan R. Thompson

Reburn severity in managed and unmanaged vegetation in a large wildfire

Debate over the influence of postwildfire management on future fire severity is occurring in the absence of empirical studies. We used satellite data, government agency records, and aerial photography to examine a forest landscape in southwest Oregon that burned in 1987 and then was subject, in part, to salvage-logging and conifer planting before it reburned during the 2002 Biscuit Fire. Areas that burned severely in 1987 tended to reburn at high severity in 2002, after controlling for the influence of several topographical and biophysical covariates. Areas unaffected by the initial fire tended to burn at the lowest severities in 2002. Areas that were salvage-logged and planted after the initial fire burned more severely than comparable unmanaged areas, suggesting that fuel conditions in conifer plantations can increase fire severity despite removal of large woody fuels.

Mixed‐severity fire regimes: lessons and hypotheses from the Klamath‐Siskiyou Ecoregion

Although mixed-severity fires are among the most widespread disturbances influencing western North American forests, they remain the least understood. A major question is the degree to which mixed-severity fire regimes are simply an ecological intermediate between low- and high-severity fire regimes, versus a unique disturbance regime with distinct properties. The Klamath-Siskiyou Mountains of southwestern Oregon and northwestern California provide an excellent laboratory for studies of mixed-severity fire effects, as structurally diverse vegetation types in the region foster, and partly arise from, fires of variable severity. In addition, many mixed-severity fires have occurred in the region in the last several decades, including the nationally significant 200,000-ha Biscuit Fire. Since 2002, we have engaged in studies of early ecosystem response to 15 of these fires, ranging from determinants of fire effects to responses of vegetation, wildlife, and biogeochemistry. We present here some of our important early findings regarding mixed-severity fire, thereby updating the state of the science on mixed-severity fire regimes and highlighting questions and hypotheses to be tested in future studies on mixed-severity fire regimes. Our studies in the Klamath-Siskiyou Ecoregion suggest that forests with mixed-severity fire regimes are characterized primarily by their intimately mixed patches of vegetation of varied age, resulting from complex variations in both fire frequency and severity and species responses to this variation. Based on our findings, we hypothesize that the proximity of living and dead forest after mixed-severity fire, and the close mingling of early- and late-seral communities, results in unique vegetation and wildlife responses compared to predominantly low- or high-severity fires. These factors also appear to contribute to high resilience of plant and wildlife species to mixed-severity fire in the Klamath-Siskiyou Ecoregion. More informed management of ecosystems with mixed-severity regimes requires understanding of their wide variability in space and time, and the particular ecological responses that this variability elicits.

Four Centuries of Change in Northeastern United States Forests

The northeastern United States is a predominately-forested region that, like most of the eastern U.S., has undergone a 400-year history of intense logging, land clearance for agriculture, and natural reforestation. This setting affords the opportunity to address a major ecological question: How similar are todays forests to those existing prior to European colonization? Working throughout a nine-state region spanning Maine to Pennsylvania, we assembled a comprehensive database of archival land-survey records describing the forests at the time of European colonization. We compared these records to modern forest inventory data and described: (1) the magnitude and attributes of forest compositional change, (2) the geography of change, and (3) the relationships between change and environmental factors and historical land use. We found that with few exceptions, notably the American chestnut, the same taxa that made up the pre-colonial forest still comprise the forest today, despite ample opportunities for species invasion and loss. Nonetheless, there have been dramatic shifts in the relative abundance of forest taxa. The magnitude of change is spatially clustered at local scales (<125 km) but exhibits little evidence of regional-scale gradients. Compositional change is most strongly associated with the historical extent of agricultural clearing. Throughout the region, there has been a broad ecological shift away from late successional taxa, such as beech and hemlock, in favor of early- and mid-successional taxa, such as red maple and poplar. Additionally, the modern forest composition is more homogeneous and less coupled to local climatic controls.

A foundation tree at the precipice: Tsuga canadensis health after the arrival of Adelges tsugae in central New England

Hemlock (Tsuga canadensis) plays a unique role in Eastern forests, producing distinctive biogeochemical, habitat, and microclimatic conditions and yet has begun a potentially irreversible decline due to the invasive hemlock woolly adelgid (Adelges tsugae; HWA) that causes foliar damage, crown loss, and mortality of host trees. Understanding the regional, landscape, site, and stand factors influencing HWA spread and impact is critical for predicting future landscape dynamics and directing effective management. Using aerial photographs, we documented hemlock distribution throughout central Massachusetts and subsampled 123 stands to examine the spatial pattern of HWA and its impact on tree vigor and mortality since its arrival in 1989. In the study region, over 86,000 ha of hemlock forest were mapped in 5,127 stands. White pine (Pinus strobus), red oak (Quercus rubra), red maple (Acer rubrum), and black birch (Betula lenta) were common overstory associates. Hemlock abundance increased from south to north, commonly on western and northwestern slopes. Average stand size was 55 ha, overstory basal area ranged from 23 to 55 m2 ha−1 and overstory stem densities averaged 993 ha−1. By 2004, 40% of sampled stands were infested, but most stands remained in good health overall; only 8 stands contained high HWA densities and only two had lost >50% overstory hemlock. Out of fifteen stand and landscape predictor variables examined, only latitude and winter climate variables were related to HWA density. Cold temperatures appear to be slowing the spread and impact of HWA at its northern extent as HWA infestation intensity and hemlock mortality and vigor were significantly correlated with average minimum winter temperature. Contrary to predictions, there was no regional increase in hemlock harvesting. The results suggest that regional HWA-hemlock dynamics are currently being shaped more by climate than by a combination of landscape and social factors. The persistence and migration of HWA continues to pose a significant threat regionally, especially in the northern portion of the study area, where hemlock dominates many forests.

Scenario Studies as a Synthetic and Integrative Research Activity for Long-Term Ecological Research

Scenario studies have emerged as a powerful approach for synthesizing diverse forms of research and for articulating and evaluating alternative socioecological futures. Unlike predictive modeling, scenarios do not attempt to forecast the precise or probable state of any variable at a given point in the future. Instead, comparisons among a set of contrasting scenarios are used to understand the systemic relationships and dynamics of complex socioecological systems and to define a range of possibilities and uncertainties in quantitative and qualitative terms. We describe five examples of scenario studies affiliated with the US Long Term Ecological Research (LTER) Network and evaluate them in terms of their ability to advance the LTER Networks capacity for conducting science, promoting social and ecological science synthesis, and increasing the saliency of research through sustained outreach activities. We conclude with an argument that scenario studies should be advanced programmatically within large socioecological research programs to encourage prescient thinking in an era of unprecedented global change.

Methods for translating narrative scenarios into quantitative assessments of land use change

In the land use and land cover (LULC) literature, narrative scenarios are qualitative descriptions of plausible futures associated with a combination of socio-economic, policy, technological, and climate changes. LULC models are then often used to translate these narrative descriptions into quantitative characterizations of possible future societal and ecological impacts and conditions. To respect the intent of the underlying scenario descriptions, this process of translation needs to be thoughtful, transparent, and reproducible. This paper evaluates the current state of the art in scenario translation methods and outlines their relative advantages and disadvantages, as well as the respective roles of stakeholders and subject matter experts. We summarize our findings in the form of a decision matrix that can assist land use planners, scientists, and modelers in choosing a translation method appropriate to their situation. Assessments of land use and land cover change often employ narrative scenarios.Detailed evaluation of policy actions and outcomes requires quantitative model output.We review methods of translating narrative scenarios into model-based assessments.A summary table provides guidance for choosing a method suitable for the situation.

Land-use impacts on the quantity and configuration of ecosystem service provisioning in Massachusetts, USA

Summary 1. Meeting fundamental human needs while also maintaining ecosystem function and services is the central challenge of sustainability science. In the densely populated state of Massachusetts, USA, abundant forests and other natural land cover convey a range of ecosystem services. However, after more than a century of reforestation following an agrarian past, Massachusetts is again losing forests, this time to housing and commercial development. 2. We used land-cover maps, ecosystem process models and land-use data bases to map changes (2001, 2006, 2011) in eight ecosystem service variables and to identify ‘hotspots’, or areas that produce a high value of five or more services, at three policy-relevant spatial scales. 3. Water-related services (clean water provisioning and flood regulation) experienced local declines in response to shifting land uses, but changed little when measured at the state level. General habitat quality for terrestrial species declined statewide during the study period as a consequence of forest loss. In contrast, climate regulation (carbon storage) and cultural services (outdoor recreation) increased, driven by continued forest biomass accrual and land protection, respectively. Timber harvest volume had high interannual variability, but no temporal trend. 4. The scale at which hotspots are delineated greatly affects their quantity and spatial configuration, with a higher density in eastern Massachusetts and 10–12% more hotspots overall when they are identified at a town scale as compared to a watershed or state scale. 5. Synthesis and applications. Ecosystem service hotspots cover a small percentage of land area in Massachusetts (25–35% of the state), but are becoming more abundant as urbanization concentrates ecosystem service provisioning onto a diminished natural land base. This suggests that while ecosystem service hotspots are valuable targets for conservation, more are not necessarily better since hotspot proliferation can reflect the bifurcation of the landscape into service and non-service provisioning areas and subsequent loss of diversity across the landscape.

Carbon storage in old-growth forests of the Mid-Atlantic: toward better understanding the eastern forest carbon sink.

Few old-growth stands remain in the matrix of secondary forests that dominates the eastern North American landscape. These remnant stands offer insight on the potential carbon (C) storage capacity of now-recovering secondary forests. We surveyed the remaining old-growth forests on sites characteristic of the general Mid-Atlantic United States and estimated the size of multiple components of forest C storage. Within and between old-growth stands, variability in C density is high and related to overstory tree species composition. The sites contain 219 ± 46 Mg C/ha (mean ± SD), including live and dead aboveground biomass, leaf litter, and the soil O horizon, with over 20% stored in downed wood and snags. Stands dominated by tulip poplar (Liriodendron tulipifera) store the most live biomass, while the mixed oak (Quercus spp.) stands overall store more dead wood. Total C density is 30% higher (154 Mg C/ha), and dead wood C density is 1800% higher (46 Mg C/ha) in the old-growth forests than in the surrounding younger forests (120 and 5 Mg C/ha, respectively). The high density of dead wood in old growth relative to secondary forests reflects a stark difference in historical land use and, possibly, the legacy of the local disturbance (e.g., disease) history. Our results demonstrate the potential for dead wood to maintain the sink capacity of secondary forests for many decades to come.

Is There Potential for the Historical Range of Variability to Guide Conservation Given the Social Range of Variability

Using the historical range of forest conditions as a reference for managing landscapes has been proposed as a coarse-filter approach to biodiversity conservation. By emulating historical disturbance processes, it is thought that forest management can produce forest composition and structure similar to the conditions that once supported the native biota. A recent project was designed to integrate social and ecological findings to investigate the important relationships between the state of ecological understanding of a region, the state of the regions biodiversity, and the state of the regions social understanding of how it might be managed for biodiversity conservation into the future. The project relied on established concepts of the historical range of variability (HRV) and developed the concept of the social range of variability to help explain the interaction of social and ecological assessments, particularly their interaction to create future ranges of variability. The Oregon Coast Range, where a rich history of HRV research has been completed starting with paleoecological reconstructions of the historical fire regime, was one of five sites in the United States that were selected as case studies. We found land development and impending climate change to be major hurdles impeding the use of the HRV as a management regime. We also found that the complexities and uncertainties of management preclude the use of any single tool to tackle landscape-scale challenges and suggest that land management needs to become a continuous process of negotiation.

Initial census, woody seedling, seed rain, and stand structure data for the SCBI SIGEO Large Forest Dynamics Plot

Abstract We present data from the first five years (2008–2012) of the establishment of the 25.6-ha Smithsonian Conservation Biology Institute (SCBI) Large Forest Dynamics Plot, comprising the initial woody stem census, woody seedling plot surveys, seed rain, and dendrochronological data. The plot is in mature secondary mixed deciduous forest 5 km south of Front Royal, Virginia, USA. The initial plot census enumerated 38 932 free-standing living stems and 29 991 living individuals ≥1 cm dbh comprising 62 species, 38 genera, and 26 families, along with an additional 1248 dead/missing standing stems, for a total of 40 180 stems. Dominant canopy trees include tulip poplar (Liriodendron tulipifera), hickories (Carya spp.), oaks (Quercus spp.), white ash (Fraxinus americana), and black gum (Nyssa sylvatica). Prominent understory components include spicebush (Lindera benzoin), pawpaw (Asimina triloba), American hornbeam (Carpinus caroliniana), witchhazel (Hamamelis virginiana), and eastern redbud (Cercis canaden...