Hope C. Humphries

Changes in alpine vegetation over 21 years: Are patterns across a heterogeneous landscape consistent with predictions?

One significant unanswered question about biotic responses to climate change is how plant communities within topographically complex landscapes will respond to climate change. Alpine plant communities are strongly influenced by topographic microclimates which can either buffer or compound the effects of more regional climatic changes. Here, we analyzed species changes over 20+ years in a complex alpine landscape with pronounced gradients in microtopography and consequently large variation in temperatures, snow depths, and nitrogen availability across small (10 m) scales. Using data from long-term monitoring plots from six community types, we asked how species composition and functional diversity changed over time in these different areas of the landscape, and whether fine-scale heterogeneity allowed species to move in response to temporal changes in the environment. We found site-wide patterns of increasing species and functional diversity. However, the majority of variability in composition over time was...

Tree spatial patterns and environmental relationships in the forest–alpine tundra ecotone at Niwot Ridge, Colorado, USA

Forest–alpine tundra ecotones (FTEs) are dynamic transition zones between forest and alpine tundra ecosystems that play an important role in regulating ecological processes, which are in turn directly influenced by the spatial patterns of trees and environmental constraints such as topography and climate. Our objectives were to characterize the spatial patterns of tree species and size classes, determine whether spatial patterns of trees differed among three FTE types, and examine FTE- and tree-environmental relationships in our study area on Niwot Ridge, CO, USA. Overall, spatial aggregation was more extensive for seedlings than saplings or trees. Distributions were largely random in limber pine but were highly aggregated in Engelmann spruce and especially subalpine fir, reflecting these species’ relative shade tolerance and expected sequence of establishment following disturbance. Fragmented and patchy tree distributions were observed in the FTE with the most heterogeneous topography, characterized by high relief and associated physical disturbances. The least patchy distributions were associated with the FTE containing a relative absence of disturbance. Intermediate levels of tree aggregation were associated with low topographic relief and presence of meadows and wetlands. Our results emphasize the importance of spatial structure as an initial controlling factor of vegetation pattern in FTEs occurring in the same landscape.

Suitability for conservation as a criterion in regional conservation network selection

The process of selecting candidate areas for inclusion in a regional conservation network should include not only delineating appropriate land units for selection and defining targets for representing features of interest, but also determining the suitability of land units for conservation purposes. We developed an explicit rating of conservation suitability by applying fuzzy-logic functions in a knowledge base to ecological condition and socio-economic attributes of land units in the interior Columbia River basin, USA. Suitability was converted to unsuitability to comprise a cost criterion in selecting regional conservation networks. When unsuitability was the sole cost criterion or was combined with land area as cost, only about one-third of the area selected was rated suitable, due to inclusion of unsuitable land to achieve representation of conservation targets (vegetation cover-type area). Selecting only from land units rated suitable produced networks that were 100% suitable, reasonably efficient, and most likely to be viable and defensible, as represented in our knowledge-based system. However, several conservation targets were not represented in these networks. The tradeoff between suitability and effectiveness in representing targets suggests that a multi-stage process should be implemented to address both attributes of candidate conservation networks. The suitability of existing conservation areas was greater than that of most alternative candidate networks, but 59% of land units containing conservation areas received a rating of unsuitable, due in part to the presence of units only partially occupied by conservation areas, in which unsuitability derived from conditions in non-conserved areas.

Methods for Determining Historical Range of Variability

Previous chapters have emphasized the dynamic nature of ecosystems, including the occurrence of periodic disturbances. Consequently, current ecosystem composition, structure, and function are likely to operate within ranges of variability that arise from climatic variability, disturbance, and the effects of human activities (Bourgeron and Jensen, 1994; Kaufmann et al., 1994; Morgan et al., 1994; Cissel et al., 1998). Understanding the magnitude and direction of anthropogenic impacts requires knowledge of the range of fluctuations historically experienced by ecosystems as a result of variability in climatic conditions, disturbance regimes, and their interactions (Swetnam and Betancourt, 1998). Therefore, the determination of the historical range of variability (HRV) in key ecosystem patterns and processes is an important part of ecological assessments and results in the characterization of the range of variability in conditions to which ecosystem components (e.g., species) are adapted (Bourgeron and Jensen, 1994; Morgan et al., 1994; Swanson et al., 1994). HRV provides a baseline for evaluating anthropogenic changes and a means for identifying the potential for surprise events to occur (Holling, 1986). Historical conditions serve as a model of the functioning of ecosystems under unmodified disturbance regimes and alternative land-use scenarios. Ecosystem patterns and processes operate at multiple hierarchically structured spatial and temporal scales, and therefore the determination of HRV should be conducted at scales that both meet the objectives of the assessment and are appropriate for the patterns and processes of interest (Bourgeron et al., 1994).

Ecosystem Characterization and Ecological Assessments

Ecological assessments are an important component of any strategy for making or reevaluating land management and regulatory decisions (see Chapters 1, 9, and 35; also Slocombe, 1993; Jensen and Bourgeron, 1994; Bourgeron et al., 1995). An important objective of ecological assessments is the identification, location, and description of the biotic and abiotic features of a landscape. Landscape features exhibit heterogeneity at a variety of scales (Turner et al., 1995). This heterogeneity is characterized by identifying relevant patterns and the processes that produce patterns in a landscape (Bourgeron and Jensen, 1994). Distinct patterns and processes occur at a variety of spatial and temporal scales of organization (see Chapter 2). For ecological assessments, an explicit understanding is needed of the scaled relationships of biological and biophysical characteristics from site to regional scales (Lessard, 1995; Lessard et al., 1999). Therefore, the characterization process is a multiscaled approach conducted within a hierarchical framework (Bourgeron and Jensen, 1994; Hann et al., 1994; Bourgeron et al., 1995; Jensen et al., 1996).

The forest–alpine ecotone: a multi-scale approach to spatial and temporal dynamics of treeline change at Niwot Ridge

Background: Current understanding of treeline or forest-alpine ecotone (FAE) dynamics does not fully explain past and present FAE patterns and their underlying processes, nor allow prediction of their response to climate change. Aims: We address the overarching hypothesis that the FAE is a mosaic of distinct landscape units of vegetation and landforms that result in differential responses to climate change. We focus on climate-related, landscape and vegetation characteristics, but also consider the effect of landscape heterogeneity on biogeochemistry and overall resilience of the FAE to climate change. Results: There are three distinct FAE land units at Niwot Ridge, generated by different interactions of climate with vegetation, landforms and topography. Within these FAEs, a process of self-organisation takes place from organism to patch to landscape scales, and is modulated by positive and negative feedback loops along an elevation gradient. The underlying controls cannot be attributed solely to temperature, but to a combination of interactions along a physical/biotic gradient. Conclusions: FAE dynamics result from interactions among mechanisms and processes at the microsite, patch and landscape scales: (1) tree persistence; (2) forest patch establishment; (3) drivers of patch forest configurations and (4) resilience, increasing along a gradient of biotic control.

Sensitivity Analysis of Land Unit Suitability for Conservation Using a Knowledge-Based System

The availability of spatially continuous data layers can have a strong impact on selection of land units for conservation purposes. The suitability of ecological conditions for sustaining the targets of conservation is an important consideration in evaluating candidate conservation sites. We constructed two fuzzy logic-based knowledge bases to determine the conservation suitability of land units in the interior Columbia River basin using NetWeaver software in the Ecosystem Management Decision Support application framework. Our objective was to assess the sensitivity of suitability ratings, derived from evaluating the knowledge bases, to fuzzy logic function parameters and to the removal of data layers (land use condition, road density, disturbance regime change index, vegetation change index, land unit size, cover type size, and cover type change index). The amount and geographic distribution of suitable land polygons was most strongly altered by the removal of land use condition, road density, and land polygon size. Removal of land use condition changed suitability primarily on private or intensively-used public land. Removal of either road density or land polygon size most strongly affected suitability on higher-elevation US Forest Service land containing small-area biophysical environments. Data layers with the greatest influence differed in rank between the two knowledge bases. Our results reinforce the importance of including both biophysical and socio-economic attributes to determine the suitability of land units for conservation. The sensitivity tests provided information about knowledge base structuring and parameterization as well as prioritization for future data needs.

Elements of Ecological Land Classifications for Ecological Assessments

An ecological land classification (ELC) is the product of the formal definition of land-based ecosystems and ecosystem complexes (Rowe and Sheard, 1981; Sims et al., 1996), based on the ecological and mapping principles of ecosystem characterization (see Chapters 2 and 3). In addition to the specific requirements of ecosystem characterization (see Chapter 3), constructing an ELC requires making decisions about the classification concepts to follow and the specific uses of the ELC (Grossman et al., 1999). In practice, the classification process is a balance between science and art (Sims et al., 1996).

The Integrated Restoration and Protection Strategy of USDA Forest Service Region 1: A Road Map to Improved Planning

Core design components of the Ecosystem Management Decision Support system were used to develop and implement the integrated restoration and protection strategy of the Northern Region of the U.S. Department of Agriculture Forest Service. Scenarios that spatially optimized hazardous fuel reduction, protected developed recreation values, and improved watershed conditions are presented to illustrate how the evaluation and decision modeling capabilities of the decision support system can be used sequentially in both strategic and tactical planning.