Scott D. Peckham

Fire as the dominant driver of central Canadian boreal forest carbon balance

Changes in climate, atmospheric carbon dioxide concentration and fire regimes have been occurring for decades in the global boreal forest, with future climate change likely to increase fire frequency—the primary disturbance agent in most boreal forests. Previous attempts to assess quantitatively the effect of changing environmental conditions on the net boreal forest carbon balance have not taken into account the competition between different vegetation types on a large scale. Here we use a process model with three competing vascular and non-vascular vegetation types to examine the effects of climate, carbon dioxide concentrations and fire disturbance on net biome production, net primary production and vegetation dominance in 100 Mha of Canadian boreal forest. We find that the carbon balance of this region was driven by changes in fire disturbance from 1948 to 2005. Climate changes affected the variability, but not the mean, of the landscape carbon balance, with precipitation exerting a more significant effect than temperature. We show that more frequent and larger fires in the late twentieth century resulted in deciduous trees and mosses increasing production at the expense of coniferous trees. Our model did not however exhibit the increases in total forest net primary production that have been inferred from satellite data. We find that poor soil drainage decreased the variability of the landscape carbon balance, which suggests that increased climate and hydrological changes have the potential to affect disproportionately the carbon dynamics of these areas. Overall, we conclude that direct ecophysiological changes resulting from global climate change have not yet been felt in this large boreal region. Variations in the landscape carbon balance and vegetation dominance have so far been driven largely by increases in fire frequency.

Simulated long‐term effects of harvest and biomass residue removal on soil carbon and nitrogen content and productivity for two Upper Great Lakes forest ecosystems

We used the ecosystem process model Biome‐BGC to simulate the effects of harvest and residue removal management scenarios on soil carbon (C), available soil nitrogen (N), net primary production (NPP), and net ecosystem production (NEP) in jack pine (Pinus banksiana Lamb.) and sugar maple (Acer saccharum Marsh) ecosystems in northern Wisconsin, USA. To assess harvest effects, we simulated short (50‐year) and long (100‐year) harvest intervals, high (clear‐cut) and low (selective) harvest intensities, and three levels of residue retention (15%, 25%, and 35%) over a 500‐year period. The model simulation of NPP, soil C accumulation, and NEP agreed reasonably well with biometric and eddy‐covariance measurements of these two ecosystems. The more intensive (50‐year rotation clear‐cuts with low residue retention) harvest scenarios tended to have the greatest NEP (420 and 678 t C ha−1 for the 500‐year interval for jack pine and sugar maple, respectively). All the harvest scenarios decreased mineral soil C and available mineral soil N content relative to the no‐harvest scenario for jack pine and sugar maple. The rate of change in mineral soil C decreased the greatest in the most intensive biomass removal scenarios (−0.012 and −0.072 t C ha−1 yr−1 relative to no‐harvest for jack pine and sugar maple, respectively) and the smallest decrease was observed in the least intensive biomass removal scenarios (−0.002 and −0.009 t C ha−1 yr−1 relative to no‐harvest for jack pine and sugar maple, respectively). The more intensive biomass removal harvest scenarios in sugar maple significantly decreased peak productivity (NPP) in the simulation period.

Detection of Spatial and Temporal Trends in Wisconsin Lake Water Clarity Using Landsat-derived Estimates of Secchi Depth

Abstract The existence of large-scale spatial and temporal trends in Wisconsins lake water clarity is a topic that has not been thoroughly investigated. This study is an effort to reliably detect these trends by utilizing three inventories of satellite-derived lake water clarity predictions for over 2,000 lakes statewide. The data were analyzed statistically on a statewide, regional, lake type, and lake area basis. Statistically significant trends in clarity were found for the state overall, as well as for particular U.S. Environmental Protection Agency Ecoregions, Wisconsin Department of Natural Resources hydrologic lake types, and lake area categories. Results will aid in the establishment of a statewide lake water clarity database and demonstrate the effectiveness of satellite-based assessments in detecting trends in water transparency over the past three decades and into the future. Documenting such trends is essential to targeting and evaluating lake management practices as well as raising public awareness of lake clarity conditions throughout the state.

Estimating the carbon budget and maximizing future carbon uptake for a temperate forest region in the U.S.

BackgroundForests of the Midwest U.S. provide numerous ecosystem services. Two of these, carbon sequestration and wood production, are often portrayed as conflicting. Currently, carbon management and biofuel policies are being developed to reduce atmospheric CO2 and national dependence on foreign oil, and increase carbon storage in ecosystems. However, the biological and industrial forest carbon cycles are rarely studied in a whole-system structure. The forest system carbon balance is the difference between the biological (net ecosystem production) and industrial (net emissions from forest industry) forest carbon cycles, but to date this critical whole system analysis is lacking. This study presents a model of the forest system, uses it to compute the carbon balance, and outlines a methodology to maximize future carbon uptake in a managed forest region.ResultsWe used a coupled forest ecosystem process and forest products life cycle inventory model for a regional temperate forest in the Midwestern U.S., and found the net system carbon balance for this 615,000 ha forest was positive (2.29 t C ha-1 yr-1). The industrial carbon budget was typically less than 10% of the biological system annually, and averaged averaged 0.082 t C ha-1 yr-1. Net C uptake over the next 100-years increased by 22% or 0.33 t C ha-1 yr-1 relative to the current harvest rate in the study region under the optized harvest regime.ConclusionsThe forest’s biological ecosystem current and future carbon uptake capacity is largely determined by forest harvest practices that occurred over a century ago, but we show an optimized harvesting strategy would increase future carbon sequestration, or wood production, by 20-30%, reduce long transportation chain emissions, and maintain many desirable stand structural attributes that are correlated to biodiversity. Our results for this forest region suggest that increasing harvest over the next 100 years increases the strength of the carbon sink, and that carbon sequestration and wood production are not conflicting for this particular forest ecosystem. The optimal harvest strategy found here may not be the same for all forests, but the methodology is applicable anywhere sufficient forest inventory data exist.

Simulating the effects of harvest and biofuel production on the forest system carbon balance of the Midwest, USA

Forests of the Midwestern United States are an important source of fiber for the wood and paper products industries. Scientists, land managers, and policy makers are interested in using woody biomass and/or harvest residue for biofuel feedstocks. However, the effects of increased biomass removal for biofuel production on forest production and forest system carbon balance remain uncertain. We modeled the carbon (C) cycle of the forest system by dividing it into two distinct components: (1) biological (net ecosystem production, net primary production, autotrophic and heterotrophic respiration, vegetation, and soil C content) and (2) industrial (harvest operations and transportation, production, use, and disposal of major wood products including biofuel and associated C emissions). We modeled available woody biomass feedstock and whole‐system carbon balance of 220 000 km2 of temperate forests in the Upper Midwest, USA by coupling an ecosystem process model to a collection of greenhouse gas life‐cycle inventory models and simulating seven forest harvest scenarios in the biological ecosystem and three biofuel production scenarios in the industrial system for 50 years. The forest system was a carbon sink (118 g C m−2 yr−1) under current management practices and forest product production rates. However, the system became a C source when harvest area was doubled and biofuel production replaced traditional forest products. Total carbon stores in the vegetation and soil increased by 5–10% under low‐intensity management scenarios and current management, but decreased up to 3% under high‐intensity harvest regimes. Increasing harvest residue removal during harvest had more modest effects on forest system C balance and total biomass removal than increasing the rate of clear‐cut harvests or area harvested. Net forest system C balance was significantly, and negatively correlated (R2 = 0.67) with biomass harvested, illustrating the trade‐offs between increased C uptake by forests and utilization of woody biomass for biofuel feedstock.

Satellite-Based Management Tool for Oak Savanna Ecosystem Restoration

Abstract The structure and function of oak Quercus spp. savanna ecosystems in the North American Midwest were originally maintained by an active disturbance regime (often fire). Subsequent reductions in the frequency of disturbance after European settlement have facilitated rapid, regional conversion of these ecosystems to more closed-canopy forest. Hence, regional-scale management strategies are now needed to restore critical spatial gradients of light, temperature, soil moisture, and soil organic matter for recovery and sustenance of the unique mosaic of understory grass and forb species assemblages that define oak savannas. Tree species composition, distribution, mortality, basal area, and canopy cover are important forest structural parameters that are intrinsically linked to oak savanna restoration ecology. In this benchmark study, we seek to determine whether Landsat-based monitoring protocols can be developed as a tool to guide and monitor regional-scale restoration and management efforts. Using th...