John A. Kupfer

The suitability of montane ecotones as indicators of global climatic change

Because of the difficulties involved with separating natural fluctuations in climatic variables from possible directional changes related to human activities (e.g., heightened atmospheric CO2 concentrations related to fossil fuel consumption), some researchers have focused on developing alternative indicators to detect hypothesized climate changes. It has, for example, been suggested that the locations of ecotones, transitions between adjacent ecosystems or biomes, should be monitored. It is assumed that changes in climate, especially increases in atmospheric temperature, will result in shifts in the location (altitude or latitude) of ecotones as plants respond to the newly imposed climatic conditions. In this article, we address the use of two montane ecotones, the alpine tree-line ecotone and the deciduous/Boreal forest ecotone, in monitoring global climatic change. In so doing, we 1) outline the factors that create and maintain each ecotones position at a given location; 2) assess the projected response of the ecotones to various aspects of global warming; and 3) discuss the usefulness of both ecotones as indicators of global climate change. While it is likely that extended periods of directional climate change would bring about an altitudinal shift in the ranges of montane species and the associated ecotones, we question whether the response at either ecotone will be at a timescale useful for detecting climate change (a few decades) owing to disequilibrium related to upslope edaphic limitations and competitive interactions with established canopy and subcanopy indi viduals. Further, limitations related to the prediction of the complex and interacting effects of projected changes in temperature, precipitation and site water balance on photosynthetic pro cesses of plant species raise uncertainties about the expected responses of both ecotones.

Landscape ecology and biogeography: Rethinking landscape metrics in a post-FRAGSTATS landscape

Landscape pattern indicators or ‘metrics’ provide simple measures of landscape structure that can be easily calculated with readily available data and software. Unfortunately, the ecological relevance of many metrics (i.e. the relationship between metric values and the real-world ecological processes that they are meant to serve as proxies for) is often unproven and questionable, and concerns are regularly voiced that such metrics fail to capture important aspects of landscape function. In this paper, I provide a review of landscape measures that may better link landscape pattern and function, ranging from approaches that extend existing metrics by incorporating a more functional component (e.g. core area measures, least cost distances) to those rooted in graph, network, and electrical circuit theory. While more ‘functional’ approaches are becoming increasingly popular, the selection of appropriate landscape metrics in many applications involves tradeoffs regarding data requirements, ease of calculation, functional basis, and simplicity of interpretation by a range of specialist and non-specialist stakeholders. Regardless, there continues to be a need for landscape metrics because they are seen by many land managers and stakeholders as simple, intuitive tools for assessing and monitoring changes in landscape pattern and, by extension, the effects on underlying ecological processes. Future needs include: (1) the development of more user-friendly landscape analysis software that can simplify graph-based analyses and visualization; and (2) studies that clarify the strengths and weaknesses of different approaches, including the potential limitations and biases in graph and network-based measures.

Application of spherical statistics to change vector analysis of landsat data: southern appalachian spruce-fir forests.

Abstract This study sought to develop a modified change vector analysis (CVA) using normalized multidate data from Landsat TM to examine spruce–fir ecosystems. The introduction of the balsam woolly adelgid ( Adelges piceae ) to the Great Smoky Mountains in the late 1950s resulted in widespread mortality of Fraser fir ( Abies fraseri ), prompting the need for research on disturbance and regeneration. Drawing from methods in spherical statistics, the extended CVA technique measured absolute angular changes and total magnitude of Tasseled Cap indices (brightness, greenness, and wetness). Polar plots and spherical statistics summarized change vectors to quantify and visualize both magnitude and direction of change. Results separated vectors for forest stands by extent and time interval since infestation, as found along the crest of Smokies Range. Changes in the greenness–wetness plane improved prediction of fir class more than brightness–greenness change. Linear discriminant functions found that magnitude and vector angles combined to predict change class 72% correct with three classes and 57% correct in six spruce-fir classes. The technique demonstrates the ability of change vectors in multiple biophysical dimensions to differentiate forest disturbance and regeneration trends as an alternative to nominal forest or land cover classifications. Introduction High elevation conifer forests in the Southern Appalachians are one of the rarest and most endangered forest types in the eastern United States, encompassing only c. 100 km 2 of which 75% is contained within Great Smoky Mountains National Park (Saunders, 1979; White et al., 1993) . These ecosystems, which are dominated by red spruce ( Picea rubens ) and Fraser fir ( Abies fraseri ), have been impacted by a number of human actions in recent decades, the most serious of which has been the introduction of the balsam woolly adelgid ( Adelges piceae ) in the 1950s. Adelgid-caused mortality of mature Fraser firs has surpassed 90% on some mountains (e.g., Mount Mitchell and Mount Collins; Eagar, 1984; Busing et al., 1988; Smith and Nicholas, 1999 ), and the wave of tree deaths has in turn affected avi-faunal communities (e.g., Alsop and Laughlin, 1991; Rabenold et al., 1998 ).

Landscape ecology and biogeography

The growing recognition that spatial scale and heterogeneity affect ecological processes has focused heightened attention over the last decade on principles from the field of landscape ecology. Landscape ecologists, drawing on principles from a diverse array of disciplines and fields, including physical and human geography, focus explicitly on the interrelation between landscape structure (i.e., pattern) and landscape function (i.e., processes). In this article, I discuss the application of landscape ecological principles to a specific and pressing issue: nature reserve design and functioning. To do so, I outline and review five landscape ecological themes with relevance to reserve design and management: reserve distribution, reserve shape, landscape corridor design and functioning, boundary dynamics, and reserve functioning. I particularly stress: 1) the role that landscape ecological theories may have in integrating existing principles from applied biogeography and population biology, and 2) the unique insights provided by a landscape ecological approach. Finally, I argue that biogeographers, because of our distinct skills, need to be more active in the development and advancement of landscape ecological theory.

Incorporating spatial non-stationarity of regression coefficients into predictive vegetation models

The results of predictive vegetation models are often presented spatially as GIS-derived surfaces of vegetation attributes across a landscape or region, but spatial information is rarely included in the model itself. Geographically weighted regression (GWR), which extends the traditional regression framework by allowing regression coefficients to vary for individual locations (‘spatial non-stationarity’), is one method of utilizing spatial information to improve the predictive power of such models. In this paper, we compare the ability of GWR, a local model, with that of ordinary least-squares (OLS) regression, a global model, to predict patterns of montane ponderosa pine (Pinus ponderosa) basal area in Saguaro National Park, AZ, USA on the basis of variables related to topography (elevation, slope steepness, aspect) and fire history (fire frequency, time since fire).The localized regression coefficients exhibited significant non-stationarity for four of the five environmental variables, and the GWR model consequently described the vegetation-environment data significantly better, even after accounting for differences in model complexity. GWR also reduced observed spatial autocorrelation of the model residuals. When applied to independent data locations not used in model development, basal areas predicted by GWR had a closer fit to observed values with lower residuals than those from the optimal OLS regression model. GWR also provided insights into fine-scale controls of ponderosa pine pattern that were missed by the global model. For example, the relationship between ponderosa pine basal area and aspect, which was obscured in the OLS regression model due to non-stationarity, was clearly demonstrated by the GWR model. We thus see GWR as a valuable complement to the many other global methods currently in use for predictive vegetation modeling.

Observed and modeled directional change in riparian forest composition at a cutbank edge

Lateral migrations of river meanders create transient, spatially transgressive edges where the advancing cutbank edge encroaches upon interior floodplain forest communities. This spatial movement of edge toward the forest interior should initiate directional changes in species composition within a forest plot as it is affected by a changing microclimate and hydrological regime. We found that cutbank edge and forest interior sites in an Iowa floodplain contained markedly different plant assemblages. Species commonly associated with later stages of succession dominated interior sites while cutbank edge sites favored secondary, successional species. Assuming that the cutbank edge sites once contained vegetation similar to that surveyed in the floodplain interior, the observed changes in community structure accompanying channel migration are suggestive of retrograde succession, or retrogression. To link cutbank erosional processes with retrogressional processes, we modified a computer simulation model already in use for floodplain environments. We incorporated the changing edge effects and compared model projections with the data collected from the field sites using detrended correspondence analysis. Without changes, the simulation projected a site compositionally similar to the sampled interior forest. When the changes were initiated, the simulated site progressively took on compositional characteristics similar to the riparian edge sites. Because we included only those forcing functions that would be initiated by cutbank erosion, the model supports the hypothesis that the spatially progressive edge effect results in a directional change in forest community composition analogous to retrogression. Our results demonstrate an interesting linkage between successional and fluvial-geomorphic processes and indicate that site dynamics may be controlled differently in landscapes where sites are progressively created and destroyed than where recurrent disturbances affect the same site.

Sensitivity of landscape metrics to classification scheme

Landscape metrics are a standard tool in the study and monitoring of landscape pattern and change, but their statistical properties and behaviour across a range of classification schemes and landscapes, as well as their sensitivity to changing landscape patterns, are still not fully understood. We therefore investigated the sensitivity of 24 metrics to a number of land cover classes for three Arizona landscapes with different spatial patterns. To do so, we applied unsupervised classification of remotely sensed data with two different nominal spatial resolutions to generate maps containing 2–35 classes. We calculated metric values for these thematic maps and classified the metrics into six groups using principal components analysis. For each group, the nature and sensitivity of responses to differences in resolution, landscape pattern, and classification detail were assessed. Our results indicated that many metrics behaved predictably with increasing classification detail, increasing or decreasing at rates that were often relatively similar and independent to sensor and landscape pattern. At lower class numbers, metrics were most sensitive to increasing classification detail, and the effects of classification scheme were most erratic and sensitive to resolution and underlying landscape pattern. Overall, this study provides a descriptive overview of the sensitivity of common metrics to changes in classification scheme, as well as a first attempt to draw some generalizations about the importance of classification scheme in conjunction with resolution effects.

Early gap successional pathways in a Fagus‐Acer forest preserve: pattern and determinants

. Many theories of forest succession imply that terrestrial plant community composition within a region tends to converge toward a climax community. That is, given similar climatic and edaphic conditions, succession at different sites within an area will lead to comparable species compositions, a pattern referred to as successional convergence. In this study, we examine changes in plant composition within forest canopy gaps over a 17-yr period to identify potential patterns of successional convergence and to ascertain the factors controlling the successional pathway. To do so, we: (1) sampled 36 forest canopy gaps in Hueston Woods Nature Preserve in 1977, 1981, 1985, 1989 and 1993, (2) evaluated changes in the similarity of gap composition over this period, and (3) examined gap composition in each year as a function of variables describing gap habitat, seed source proximity, and disturbance history. Results indicated an initial pattern of successional divergence, with gaps exhibiting increased dissimilarity over the first 10–12 years of succession. We attribute this initial period of divergence to the effects of differential seed inputs from edge individuals and heterogeneity of available light due to differences in gap size. Recent surveys, however, indicated that gap composition has become more similar as competition within gaps has become more intense. In these samples, gap composition is closely linked to site conditions, including slope, soil conditions, and site exposure. Finally, while these patterns may suggest equilibrium-oriented dynamics, non-equilibrium processes such as repeat disturbances are also evident at Hueston Woods and will likely play an important role in determining future successional pathways.

Regionalization of forest pattern metrics for the continental United States using contiguity constrained clustering and partitioning

Abstract Technological advances have created new opportunities for defining and mapping ecological and biogeographical regions on the basis of quantitative criteria while generating a need for studies that evaluate the sensitivity of ecoregionalizations to clustering methods and approaches. In this study, we used a novel regionalization algorithm, regionalization with dynamically constrained agglomerative clustering and partitioning (REDCAP), to identify hierarchical regions based on measures of forest extent, connectivity, and change for 2109 watersheds in the continental U.S. Unlike regionalizations developed using non-spatial clustering techniques, REDCAP directly incorporates a spatial contiguity constraint into a traditional hierarchical clustering method, resulting in contiguous regions that optimize a homogeneity measure. Results of our analyses identified nine- and eighteen-class Forest Pattern Regions that reflected the influence of natural and anthropogenic factors structuring forest extent and fragmentation. Because these regions are defined by the forest pattern metrics themselves, rather than pre-defined political or ecological units, they provide a valuable means for visualizing forest pattern information and quantifying forest patterns across a large, diverse geographic area. In contrast, regionalizations of the same data using two non-spatial methods ( k -means clustering and non-spatial average linkage clustering) resulted in more homogeneous classes composed of many discontiguous units. While it should not be viewed as a replacement for non-spatial clustering techniques, REDCAP provides an alternative approach to developing ecological regionalizations by placing greater emphasis on maintaining the spatial contiguity of units, a property that may be desirable in many broad-scale regionalizations because it reduces data complexity and facilitates the visualization and interpretation of ecological or biogeographic data.

Complexity of Successional Pathways in Subalpine Forests of the Selway-Bitterroot Wilderness Area

Abstract We examined forest structure and composition in four watersheds in the Selway-Bitterroot Wilderness Area, Idaho and Montana, to better understand the complexity of successional processes following stand-replacing fires in subalpine forest ecosystems. Dendrochronological analyses of more than 1,100 trees were used to identify the timing of establishment of major forest species at sites that had experienced different intervals since the last fire. This was coupled with analyses of forest structure and composition using nonmetric multidimensional scaling. A conceptual model of stand development is presented to highlight our findings. Lodgepole pine (Pinus contorta var. latifolia Dougl.) dominated most overstories for the first 100–200 years but persisted as a canopy dominant for more than 250 years in some stands. As forests increased in age, Engelmann spruce (Picea engelmanii Parry) and subalpine fir (Abies lasiocarpa [Hook.] Nutt.) became more prominent in the overstory. Whitebark pine was present in some young stands and older stands but was most often represented as dead standing trees killed during twentieth-century mountain pine beetle outbreaks. Understory composition was a function of time-since-fire but showed considerable variation that is likely tied to seed arrival, environmental conditions, and establishment. Our results suggest that short fire intervals may limit the development of lodgepole pines capable of producing serotinous cones, leading to young forests dominated by spruce or fir. However, intervals longer than the lifespan of lodgepole pine (as long as 350 years) could also lead to early dominance by spruce or fir following fire. These results refine our understanding of the temporal development of subalpine communities following stand-replacing fires and have implications for the implementation of long-range management goals in these habitats.