David J. Mladenoff

Sustainable Biofuels Redux

Science-based policy is essential for guiding an environmentally sustainable approach to cellulosic biofuels.

SPATIALLY EXPLICIT AND STOCHASTIC SIMULATION OF FOREST- LANDSCAPE FIRE DISTURBANCE AND SUCCESSION

Understanding disturbance and recovery of forest landscapes is a challenge because of complex interactions over a range of temporal and spatial scales. Landscape simulation models offer an approach to studying such systems at broad scales. Fire can be simulated spatially using mechanistic or stochastic approaches. We describe the fire module in a spatially explicit, stochastic model of forest landscape dynamics (LANDIS) that in- corporates fire, windthrow, and harvest disturbance with species-level succession. A sto- chastic approach is suited to forest landscape models that are designed to simulate patterns over large spatial and time domains and are not used deterministically to predict individual events. We used the model to examine how disturbance regimes and species dynamics interact across a large (500 000 ha), heterogeneous landscape in northern Wisconsin, USA, with six land types having different species environments, and fire disturbance return intervals varying from 200 to 1000 yr. The model shows that there are feedbacks over time between species, disturbance, and environment, resulting in the re-emergence of patterns that char- acterized the landscape before extensive alteration. Landscape equilibrium of species com- position and age-class structure develops at three scales from the initial, disturbed landscape. Over 100-150 yr, fine-grained successional processes cause gradual disaggregation of the initial pattern of relatively homogenous composition and age classes. Species such as eastern hemlock ( Tsuga canadensis), largely removed from the landscape by past human activities, only slowly re-invade. Next, patterns on the various land types diverge, driven by different disturbance regimes and dominant species. Finally, aging of the landscape causes the prob- abilities of larger and more severe fires to increase, and a coarse-grained pattern develops from the disturbance patches. Influence of adjacent land types is shown as fires spread across land type boundaries, although modified in spread and severity. As found by others, altered landscapes are likely to retain their modified pattern for centuries, suggesting that nonequilibrium conditions between tree species and climate will persist under predicted rates of climate change. The results suggest that this modeling approach can be useful in examining species- level, broad-scale responses of heterogeneous landscapes to changes in landscape distur- bance, such as modified management or land-use scenarios, or effects of global change.

Comparing Spatial Pattern in Unaltered Old‐Growth and Disturbed Forest Landscapes

We used geographic information systems (GIS) to analyze the structure of a second-growth forest landscape (9600 ha) that contains scattered old-growth patches. We compared this landscape to a nearby, unaltered old-growth landscape on comparable landforms and soils to assess the effects of human activity on forest spatial pattern. Our objective is to determine if characteristic landscape structural patterns distinguish the primary old-growth forest landscape from the disturbed landscape. Characteristic patterns of old-growth landscape structure would be useful in enhancing and restoring old-growth ecosystem functioning in managed landscapes. Our natural old-growth landscape is still dominated by the original forest cover of eastern hemlock (Tsuga canadensis), sugar maple (Acer saccharum), and yellow birch (Betula allegheniensis). The disturbed landscape has only scattered, remnant patches of old-growth ecosystems among a greater number of early successional hardwood and conifer forest types. Human disturbances can either increase or decrease landscape heterogeneity depending on the parameter and spatial scale examined. In this study, we found that a number of important structural features of the intact old-growth landscape do not occur in the disturbed landscape. The disturbed landscape has significantly more small forest patches and fewer large, matrix patches than the intact landscape. Forest patches in the fragmented landscape are significantly simpler in shape (lower fractal dimension, D) than in the intact old-growth landscape. Change in fractal dimension with patch size, a relationship that may be characteristic of differing processes of patch formation at different scales, is present within the intact landscape but has been obscured by human activity in the disturbed landscape. Important ecosystem juxtapositions of the old-growth landscape, such as hemlock with lowland conifers, have been lost in the disturbed landscape. In addition, significant landscape heterogeneity in this glaciated region is produced by landforms alone, without natural or human disturbances. The features that distinguish disturbed and old-growth forest landscape structure that we have described need to be examined elsewhere to determine if such features are characteristic of other landscapes and regions. Such forest landscape structural differences that exist more broadly could form the basis of landscape principles to be applied both to the restoration of old-growth forest landscapes and the modification of general forest management for enhancing biodiversity. These principles may be particularly useful for constructing integrated landscapes managed for both commodity production and biodiversity protection.

An aggregation index (AI) to quantify spatial patterns of landscapes.

There is often need to measure aggregation levels of spatial patterns within a single map class in landscape ecological studies. The contagion index (CI), shape index (SI), and probability of adjacency of the same class (Qi), all have certain limits when measuring aggregation of spatial patterns. We have developed an aggregation index (AI) that is class specific and independent of landscape composition. AI assumes that a class with the highest level of aggregation (AI =1) is comprised of pixels sharing the most possible edges. A class whose pixels share no edges (completely disaggregated) has the lowest level of aggregation (AI =0). AI is similar to SI and Qi, but it calculates aggregation more precisely than the latter two. We have evaluated the performance of AI under varied levels of (1) aggregation, (2) number of patches, (3) spatial resolutions, and (4) real species distribution maps at various spatial scales. AI was able to produce reasonable results under all these circumstances. Since it is class specific, it is more precise than CI, which measures overall landscape aggregation. Thus, AI provides a quantitative basis to correlate the spatial pattern of a class with a specific process. Since AI is a ratio variable, map units do not affect the calculation. It can be compared between classes from the same or different landscapes, or even the same classes from the same landscape under different resolutions.

Homogenization of northern U.S. Great Lakes forests due to land use

Human land use of forested regions has intensified worldwide in recent decades, threatening long-term sustainability. Primary effects include conversion of land cover or reversion to an earlier stage of successional development. Both types of change can have cascading effects through ecosystems; however, the long-term effects where forests are allowed to regrow are poorly understood. We quantify the regional-scale consequences of a century of Euro-American land use in the northern U.S. Great Lakes region using a combination of historical Public Land Survey records and current forest inventory and land cover data. Our analysis shows a distinct and rapid trajectory of vegetation change toward historically unprecedented and simplified conditions. In addition to overall loss of forestland, current forests are marked by lower species diversity, functional diversity, and structural complexity compared to pre-Euro-American forests. Today’s forest is marked by dominance of broadleaf deciduous species—all 55 ecoregions that comprise the region exhibit a lower relative dominance of conifers in comparison to the pre-Euro-American period. Aspen (Populus grandidentata and P. tremuloides) and maple (Acer saccharum and A. rubrum) species comprise the primary deciduous species that have replaced conifers. These changes reflect the cumulative effects of local forest alterations over the region and they affect future ecosystem conditions as well as the ecosystem services they provide.

UNDERSTORY SPECIES PATTERNS AND DIVERSITY IN OLD-GROWTH AND MANAGED NORTHERN HARDWOOD FORESTS

Forest management can significantly affect both the diversity and spatial patterning of understory vegetation. However, few studies have considered both diversity and spatial patterning at a stand scale. Our objective was to evaluate the effects of forest management on understory plant communities in northern hardwood forests and assess the processes governing differences in species composition, diversity, and spatial patterns. We sampled understory vegetation (all species ,2 m tall) and percentage of light transmission levels in three forest types in 12 mesic northern hardwood stands in northern Wisconsin and the Upper Peninsula of Michigan, USA: old-growth, undisturbed forests; even-aged forests resulting from clearcut logging (;65-85 yr old); and uneven-aged forests with recent selective logging. Estimated understory species richness per stand, mean species richness per quadrat, and mean percent cover per quadrat were lower in old-growth forest than in even-aged, second- growth forests and lower in even-aged than in uneven-aged, second-growth forests. Dif- ferences in species composition among the three forest types were related to available light and to coarse woody debris; however, differences between the cover of most plant groups were not significant. The mean patch size of species diversity and cover is highly variable and could not be related to forest stand type. However, understory communities in old- growth forests have significantly smaller community patch sizes and larger compositional heterogeneity. Community patch size is correlated with both coarse woody debris and light heterogeneity. Each forest stand type produces a characteristic combination of understory composition, diversity, and spatial patterning of communities. Although harvesting has negligible effects on understory alpha diversity in these mesic hardwood forests, spatial structure is slower to recover and has not recovered in the even- and uneven-aged northern hardwood forests studied. If management objectives include preserving or restoring the ecological character of the forest, harvesting may need to be altered or delayed predicated on the character of the understory.

Linking an ecosystem model and a landscape model to study forest species response to climate warming

No single model can address forest change from single tree to regional scales. We discuss a framework linking an ecosystem process model {LINKAGES) with a spatial landscape model (LANDIS) to examine forest species responses to climate warming for a large, heterogeneous landscape in northern Wisconsin, USA. Individual species response at the ecosystem scale was simulated with LINKAGES, which integrates soil, climate and species data, stratified by ecoregions. Individual species biomass results, simulated by LINKAGES at year 10, were quantified using an empirical equation as species establishment coefficients (0.0-l.0). These coefficients were used to parameterize LANDIS, thus integrating ecosystem dynamics with large-scale landscape processes such as seed dispersal and fire disturbance. Species response to climate warming at the landscape scale was simulated with LANDIS. LANDIS was parameterized with information derived from a species level, forest classification map, and inventory data. This incorporates spatially-explicit seed source distributions. A standard LANDIS run with natural fire disturbance regime and current climate was conducted for 400 years. To simulate the effects of climate change, the differences in species establishment coefficients from current and warmer climates were linearly interpolated over the first 100 years assuming climate warming will occur gradually over the next century. The model was then run for another 300 years to examine the consequences after warming. Across the landscape, the decline of boreal species and the increases of temperate species were observed in the simulation. The responses of northern temperate hardwood species vary among ecoregions depending on soil nutrient and water regimes. Simulation results indicate that boreal species disappear from the landscape in 200-300 years and approximately same amount of time for a southern species to become common. Warming can accelerate the re-colonization process for current species such as found for eastern hemlock, where moisture does not become limiting. However, the re-colonization is strongly affected by available seed source explicitly described on the landscape. These phenomena cannot be simulated with most gap models, which assume a random seed rain.

Phenological differences in Tasseled Cap indices improve deciduous forest classification

Remote sensing needs to clarify the strengths of different methods so they can be consistently applied in forest management and ecology. Both the use of phenological information in satellite imagery and the use of vegetation indices have independently improved classifications of north temperate forests. Combining these sources of information in change detection has been effective for land cover classifications at the continental scale based on Advanced Very High Resolution Radiometer (AVHRR) imagery. Our objective is to test if using vegetation indices and change analysis of multiseasonal imagery can also improve the classification accuracy of deciduous forests at the landscape scale. We used Landsat Thematic Mapper (TM) scenes that corresponded to Populus spp. leaf-on and Quercus spp. leaf-off (May), peak summer (August), Acer spp. peak color (September), Acer spp. and Populus spp. leaf-off (October). Input data files derived from the imagery were: (1) TM Bands 3, 4, and 5 from all dates; (2) Normalized Difference Vegetation Index (NDVI) from all dates; (3) Tasseled Cap brightness, greenness, and wetness (BGW) from all dates; (4) difference in TM Bands 3, 4, and 5 from one date to the next; (5) difference in NDVI from one date to the next; and (6) difference in BGW from one date to the next. The overall kappa statistics (KHAT) for the aforementioned classifications of deciduous genera were 0.48, 0.36, 0.33, 0.38, 0.26, 0.43, respectively. The highest accuracies occurred from TM Bands 3, 4, and 5 (61.0% for deciduous genera, 67.8% for all classes) or from the difference in BGW (61.0% for deciduous genera, 67.8% for all classes). However, the difference in Tasseled Cap classification more accurately separated deciduous shrubs and harvested stands from closed canopy forest. Our results indicate that phenological change of forest is most accurately captured by combining image differencing and Tasseled Cap indices.

Old-growth forest landscape transitions from pre-European settlement to present

We conducted a multi-temporal spatial analysis of forest cover for a 9600 ha landscape in northern Wisconsin, U.S.A., using data from pre-European settlement (1860s), post-settlement (1931), and current (1989) periods. Using GIS we have shown forest landscape changes and trajectories that have been generally described in aggregate for the norther Great Lake States region. We created the pre-European settlement map from the witness tree data of the original federal General Land Office survey notes. The 1931 cover was produced from the Wisconsin Land Economic Inventory, and the 1989 cover map was based on color infrared photography. We used GIS to analyze 1) land area occupied by different forest types at different dates, 2) temporal transitions between dates and their driving proceses, and 3) successional trajectories with landforms and spatial associations of forest types. Over the 120 year period, forest cover has changed from a landscape dominated by old-growth hemlock (Tsuga canadensis) and hardwood forests (Acer saccharum, Betula alleghaniensis) to largely second-growth hardwoods and conifers. The former dominant hemlock is largely eliminated from the landscape. From 1860 to 1931, large-scale disturbances associated with logging were the dominant processes on the landscape. Early successional forest types covered much of the landscape by the 1930s. From 1931 to 1989, succession was the dominant process driving forest transitions as forest types succeeded to a diverse group of upland hardwood and conifer forest types. If successional trajectories continue, a more homogeneous landscape may develop comprised of both a northern hardwood type dominated by sugar maple, and a boreal conifer/hardwood forest.

Assessing potential gray wolf restoration in the northeastern United States : A spatial prediction of favorable habitat and potential population levels

The northeastern United States was previously identified under the U.S. Endangered Species Act (ESA) as a potential location for restoration of a population of the endangered eastern timber wolf or gray wolf (Canis lupus). The gray wolf has been protected under the ESA since 1974. We used Geographic Information Systems (GIS) and a logistic regression model based on regional road abundance to estimate that the Northeastern states from Upstate New York to Maine contain >77,000 km 2 of habitat suitable for wolves. Using current habitat distribution and available ungulate prey (deer and moose), we estimate the area is capable of sustaining a population of approximately 1,312 wolves (90% CI = 816-1,809). This estimate is equivalent to new, much higher potentials estimated for northern Wisconsin and Upper Michigan, where wolves are rapidly recovering in the U.S. Midwest. Potential wolf densities vary from a low of 53,500 km 2 ) is capable of supporting approximately 1,070 wolves (90% CI = 702-1,439). Such large areas are increasingly rare and important for wolf recovery if populations large enough to have long-term evolutionary viability are to be maintained within the United States. However, large-scale restoration of a top carnivore like the wolf has other consequences for overall forest biodiversity in eastern forests because wolf recovery is dependent on high levels of ungulate prey, which in turn have other negative effects on the ecosystem. In the United States, planning for wolf restoration in the Northeast should take advantage of experience elsewhere, especially the upper Midwest.