Thomas R. Crow

Microclimate in Forest Ecosystem and Landscape Ecology

Microclimate is the suite of climatic conditions measured in localized areas near the earths surface (Geiger 1965). These environmental variables, which include temperature, light, windspeed, and moisture, have been critical throughout human history, providing meaningful indicators for habitat selection and other activities. For example, for 2600 years the Chinese have used localized seasonal changes in temperature and precipitation to schedule their agricultural activities. In seminal studies, Shirley (1929, 1945) emphasized microclimate as a determinant of ecological patterns in both plant and animal communities and a driver of such processes as the growth and mortality of organisms. The importance of microclimate in influencing ecological processes such as plant regeneration and growth, soil resperation and growth, soil repiration, nutrient cycling, and wildlife habitat selection has became an essential component of current ecological research (Perry 1994). plant regeneration and growth, soil respiration, nutrient cycling, and

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.

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.

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.

A Quantitative Approach to Developing Regional Ecosystem Classifications

Ecological land classification systems have recently been developed at continental, regional, state, and landscape scales. In most cases, the map units of these systems result from subjectively drawn boundaries, often derived by consensus and with unclear choice and weighting of input data. Such classifications are of variable accuracy and are not reliably repeatable. We combined geographic information systems (GIS) with multivariate statistical analyses to integrate climatic, physiographic, and edaphic databases and produce a classification of regional landscape ecosystems on a 29 340-km2 quadrangle of northwestern Wisconsin. Climatic regions were identified from a high-resolution climatic database consisting of 30-yr mean monthly temperature and precipitation values interpolated over a 1-km2 grid across the study area. Principal component analysis (PCA) coupled with an isodata clustering algorithm was used to identify regions of similar seasonal climatic trends. Maps of Pleistocene geology and major soil morphosequences were sued to identify the major physiographic and soil regions within the landscape. Climatic and physiographic coverages were integrated to identify regional landscape ecosystems, which potentially differ in characteristic forest composition, successional dynamics, potential productivity, and other ecosystem-level processes. Validation analysis indicated strong correspondence between forest cover classes from an independently derived Landsat Thematic Mapper classification and ecological region. The development of more standardized data sets and analytical methods for ecoregional classification provides a basis for sound interpretations of forest management at multiple spatial scales.

Characterizing historical and modern fire regimes in Michigan (USA): A landscape ecosystem approach

We studied the relationships of landscape ecosystems to historical and contemporary fire regimes across 4.3 million hectares in northern lower Michigan (USA). Changes in fire regimes were documented by comparing historical fire rotations in different landscape ecosystems to those occurring between 1985 and 2000. Previously published data and a synthesis of the literature were used to identify six forest-replacement fire regime categories with fire rotations ranging from very short (<100 years) to very long (>1,000 years). We derived spatially-explicit estimates of the susceptibility of landscape ecosystems to fire disturbance using Landtype Association maps as initial units of investigation. Each Landtype Association polygon was assigned to a fire regime category based on associations of ecological factors known to influence fire regimes. Spatial statistics were used to interpolate fire points recorded by the General Land Office. Historical fire rotations were determined by calculating the area burned for each category of fire regime and dividing this area by fifteen (years) to estimate area burned per annum. Modern fire rotations were estimated using data on fire location and size obtained from federal and state agencies. Landtype Associations networked into fire regime categories exhibited differences in both historical and modern fire rotations. Historical rotations varied by 23-fold across all fire rotation categories, and modern forest fire rotations by 13-fold. Modern fire rotations were an order of magnitude longer than historical rotations. The magnitude of these changes has important implications for forest health and understanding of ecological processes in most of the fire rotation categories that we identified.

INTEGRATION OF GIS DATA AND CLASSIFIED SATELLITE IMAGERY FOR REGIONAL FOREST ASSESSMENT

New methods are needed to derive detailed spatial environmental data for large areas, with the increasing interest in landscape ecology and ecosystem management at large scales. We describe a method that integrates several data sources for assessing forest composition across large, heterogeneous landscapes. Multitemporal Landsat Thematic Mapper (TM) satellite data can yield forest classifications with spatially detailed information down to the dominant canopy species level in temperate deciduous and mixed forests. We stratified a large region (106 ha) by ecoregions (103–104 ha). Within each ecoregion, plot-level, field inventory data were aggregated to provide information on secondary and sub-canopy tree species occurrence, and tree age class distributions. We derived a probabilistic algorithm to assign information from a point coverage (forest inventory sampling points) and a polygon coverage (ecoregion boundaries) to a raster map (satellite land cover classification). The method was applied to a region in northern Wisconsin, USA. The satellite map captures the occurrence and the patch structure of canopy dominants. The inventory data provide important secondary information on age class and associated species not available with current canopy remote sensing. In this way we derived new maps of tree species distribution and stand age reflecting differences at the ecoregion scale. These maps can be used in assessing forest patterns across regional landscapes, and as input data in models to examine forest landscape change over time. As an example, we discuss the distribution of eastern white pine (Pinus strobus) as an associated species and its potential for restoration in our study region. Our method partially fills a current information gap at the landscape scale. However, its applicability is also limited to this scale.

Hierarchical relationships between landscape structure and temperature in a managed forest landscape

Management may influence abiotic environments differently across time and spatial scale, greatly influencing perceptions of fragmentation of the landscape. It is vital to consider a priori the spatial scales that are most relevant to an investigation, and to reflect on the influence that scale may have on conclusions. While the importance of scale in understanding ecological patterns and processes has been widely recognized, few researchers have investigated how the relationships between pattern and process change across spatial and temporal scales. We used wavelet analysis to examine the multiscale structure of surface and soil temperature, measured every 5 m across a 3820 m transect within a national forest in northern Wisconsin. Temperature functioned as an indicator – or end product – of processes associated with energy budget dynamics, such as radiative inputs, evapotranspiration and convective losses across the landscape. We hoped to determine whether functional relationships between landscape structure and temperature could be generalized, by examining patterns and relationships at multiple spatial scales and time periods during the day. The pattern of temperature varied between surface and soil temperature and among daily time periods. Wavelet variances indicated that no single scale dominated the pattern in temperature at any time, though values were highest at finest scales and at midday. Using general linear models, we explained 38% to 60% of the variation in temperature along the transect. Broad categorical variables describing the vegetation patch in which a point was located and the closest vegetation patch of a different type (landscape context) were important in models of both surface and soil temperature across time periods. Variables associated with slope and microtopography were more commonly incorporated into models explaining variation in soil temperature, whereas variables associated with vegetation or ground cover explained more variation in surface temperature. We examined correlations between wavelet transforms of temperature and vegetation (i.e., structural) pattern to determine whether these associations occurred at predictable scales or were consistent across time. Correlations between transforms characteristically had two peaks; one at finer scales of 100 to 150 m and one at broader scales of >300 m. These scales differed among times of day and between surface and soil temperatures. Our results indicate that temperature structure is distinct from vegetation structure and is spatially and temporally dynamic. There did not appear to be any single scale at which it was more relevant to study temperature or this pattern-process relationship, although the strongest relationships between vegetation structure and temperature occurred within a predictable range of scales. Forest managers and conservation biologists must recognize the dynamic relationship between temperature and structure across landscapes and incorporate the landscape elements created by temperature-structure interactions into management decisions.

Modeling temperature gradients across edges over time in a managed landscape

Landscape management requires an understanding of the distribution of habitat patches in space and time. Regions of edge influence can form dominant components of both managed and naturally patchy ecosystems. However, the boundaries of these regions are spatially and temporally dynamic. Further, areas of edge influence can be defined by either biotic (e.g. overstory cover) vs. abiotic (e.g. microclimate) characteristics, or structural (e.g. vegetation height) vs. functional (e.g. decomposition rates) features. Edges defined by different characteristics are not always concordant; the degree of spatial concurrence varies with time. Thus, edge effects are difficult to generalize or quantify across a landscape. We examined temperature at eight times of the day across the edge between a clearing and a 50-year-old pine stand. We used simple, nonlinear equations to model and predict temperature gradients across this edge over time. The depth of edge influence (DEI) on temperature varied from 0 to 40 m, depending on the patch type and time of day. Two equations were required to model adequately (r 2 >0.50) patterns of temperature at all eight times of the day. Model fit was best at night (r 2 a0.97) and lowest in the afternoon (r 2 a0.50). Parameters for the models could be predicted from local, reference weather conditions. However, these linear relationships varied among parameters and with time of day (0.29r 2 0.99). Model validation was weak, with mean absolute percent error >10% for all day-time combinations. The models tended to underestimate DEI for both patch types, though edge depth was more accurately predicted in the closed-canopy stand than in the clearing. The difference between observed and predicted edge effects was highest at midday in the clearing and during the morning under closed canopy. The models predicted the location of peak temperature and the slope of temperature change (i.e. pattern of temperature variation) across the edge and the range of temperature better than actual values. We suggest that this approach may, therefore, be useful for characterizing edge dynamics if a wider range of local weather conditions could be monitored during initial data collection. The empirical evidence for temporal changes in position and intensity of abiotic edge effects emphasized the need to quantify these dynamics across time and space for sound planning at the landscape scale. # 1999 Elsevier Science B.V. All rights reserved.

Modeling the effects of forest harvesting on landscape structure and the spatial distribution of cowbird brood parasitism

Timber harvesting affects both composition and structure of the landscape and has important consequences for organisms using forest habitats. A timber harvest allocation model was constructed that allows the input of specific rules to allocate forest stands for clearcutting to generate landscape patterns reflecting the “look and feel” of managed landscapes. Various harvest strategies were simulated on four 237 km2 study areas in Indiana, USA. For each study area, the model was applied to simulate 80 years of management activity. The resulting landscape spatial patterns were quantified using a suite of landscape pattern metrics and plotted as a function of mean harvest size and total area of forest harvested per decade to produce response surfaces. When the mean clearcut size was 1 ha, the area of forest interior remaining on the landscape was dramatically reduced and the amount of forest edge on the landscape increased dramatically. The potential consequences of the patterns produced by the model were assessed for a generalized neotropical migrant forest bird using a GIS model that generates maps showing the spatial distribution of the relative vulnerability of forest birds to brood parasitism by brown-headed cowbirds. The model incorporates the location and relative quality of cowbird feeding sites, and the relation between parasitism rates and distance of forest from edge. The response surface relating mean harvest size and total area harvested to the mean value of vulnerability to cowbird brood parasitism had a shape similar to the response surfaces showing forest edge. The results of our study suggest that it is more difficult to maintain large contiguous blocks of undisturbed forest interior when harvests are small and dispersed, especially when producing high timber volumes is a management goal. The application of the cowbird model to landscapes managed under different strategies could help managers in deciding where harvest activity will produce the least negative impact on breeding forest birds.