Paul T. Tueller

Empirical patterns of the effects of changing scale on landscape metrics

While ecologists are well aware that spatial heterogeneity is scale-dependent, a general understanding of scaling relationships of spatial pattern is still lacking. One way to improve this understanding is to systematically examine how pattern indices change with scale in real landscapes of different kinds. This study, therefore, was designed to investigate how a suite of commonly used landscape metrics respond to changing grain size, extent, and the direction of analysis (or sampling) using several different landscapes in North America. Our results showed that the responses of the 19 landscape metrics fell into three general categories: Type I metrics showed predictable responses with changing scale, and their scaling relations could be represented by simple scaling equations (linear, power-law, or logarithmic functions); Type II metrics exhibited staircase-like responses that were less predictable; and Type III metrics behaved erratically in response to changing scale, suggesting no consistent scaling relations. In general, the effect of changing grain size was more predictable than that of changing extent. Type I metrics represent those landscape features that can be readily and accurately extrapolated or interpolated across spatial scales, whereas Type II and III metrics represent those that require more explicit consideration of idiosyncratic details for successful scaling. To adequately quantify spatial heterogeneity, the metric-scalograms (the response curves of metrics to changing scale), instead of single-scale measures, seem necessary.

Multiscale analysis of landscape heterogeneity: Scale variance and pattern metrics

Abstract A major goal of landscape ecology is to understand the formation, dynamics, and maintenance of spatial heterogeneity. Spatial heterogeneity is the most fundamental characteristic of all landscapes, and scale multiplicity is inherent in spatial heterogeneity. Thus, multiscale analysis is imperative for understanding the structure, function and dynamics of landscapes. Although a number of methods have been used for multiscale analysis in landscape ecology since the 1980s, the effectiveness of many of them, including some commonly used ones, is not clear or questionable. In this paper, we discuss two approaches to multiscale analysis of landscape heterogeneity: the direct and indirect approaches. We will focus on scale variance and semivariance methods in the first approach and 17 landscape metrics in the second. The results show that scale variance is potentially a powerful method to detect and describe multiple-scale structures of landscapes, while semivariance analysis may often fail to do so especially if landscape variability is dominant at broad scales over fine scales. Landscape metrics respond to changing grain size rather differently, and these changes are reflective of the modifiable areal unit problem as well as multiple-scale structures in landscape pattern. Interestingly, some metrics (e.g., the number of patches, patch density, total edge, edge density, mean patch size, patch size coefficient of variation) exhibit consistent, predictable patterns over a wide range of grain sizes, whereas others (e.g., patch diversity, contagion, landscape fractal dimension) have nonlinear response curves. The two approaches to multiple-scale analysis are complementary, and their pros and cons still need to be further investigated systematically.

Remote sensing technology for rangeland management applications

The future of rangeland resources development and management is dependent upon increased scientific capability. Remote sensing technology can contribute information for a variety of rangeland resource management applications. In future we can expect to see an increased number of professional range managers with expertise in remote sensing. This training will include, in addition to principles of aerial photo interpretation, digital image analysis technology, increased use of geographic information systems, airborne video remote sensing, and the use of newly developing high resolution systems. The data will be obtained from both aircraft and spacecraft. Applications will include inventory, evaluation, and monitoring of rangeland resources and the incorporation of remote sensing data to support and improve the decision processes on the use, development, and management of rangeland

Vegetation science applications for rangeland analysis and management.

1. Introduction.- Basic Vegetation Science Contributions.- 2. Plant synecology in the service of rangeland management.- 3. Ecophysiology of range plants.- 4. Rangeland plant taxonomy.- 5. New plant development in range management.- 6. Successional concepts in relation to range condition assessment.- 7. A role for nonvascular plants in management of arid and semiarid rangelands.- 8. Seedbeds as selective factors in the species composition of rangeland communities.- 9. Modelling rangeland ecosystems for monitoring and adaptive management.- Vegetation Distribution and Organization.- 10. Vegetation-soil relationships on arid and semiarid rangelands.- 11. Vegetation attributes and their applications to the management of Australian rangelands.- 12. The ecology of shrubland/woodland for range use.- 13. Tundra vegetation as a rangeland resource.- 14. Forest rangeland relationships.- 15. Ecological principles and their application to rangeland management practice in South Africa.- 16. Range management from grassland ecology.- 17. Riparian values as a focus for range management and vegetation science.- Vegetation Science Rangeland Applications.- 18. Rangeland vegetation productivity and biomass.- 19. Rangeland vegetation - hydrologic interactions.- 20. Grazing management and vegetation response.- 21. Understanding fire ecology for range management.- 22. Reclamation of drastically disturbed rangelands.- 23. Rangeland vegetation as wildlife habitat.- 24. Revegetation of arid and semiarid rangelands.

Rangeland Monitoring Using Remote Sensing

Monitoring vast landscapes has, from the beginning of rangeland management, depended on peoples judgements. This is no longer tenable, but a more effective method has yet to be devised. The problem is how to do an economical inventory that will detect ecologically important change over extensive land areas with acceptable error rates. The error risk is a function of adequate sample numbers and distribution for each indicator monitored. Of all of the indicators identified for monitoring, ground cover and its inverse, bare ground, may be the most discussed. Ground-cover measurements address soil stability and watershed function which are first-priority ecological concerns; are well adapted to remote sensing frameworks thus allowing extensive, unbiased, economical sampling; and, the measurements, especially when done by computer image analysis, have the potential to reduce or avoid the human-judgement factor. Data collection through remote sensing appears the most logical approach to acquiring appropriately distributed information over large areas in short time periods and on random sites far removed from easy ground access. The value of satellite and high-altitude sensors for landscape-level evaluations, such as plant community distribution, is well established but these tools are inadequate for inventory and measurement of details needed for valid conclusions about range condition. New advances in low-altitude remote sensing may give us the ability to accurately measure bare ground and perhaps other indicators. Combining information from high and low-altitude sensors appears to offer an optimal path for developing a practical system for cost-effective, data-based, rangeland monitoring and management.

Remote sensing science applications in arid environments

Abstract Remote sensing in aridland/rangeland regions has developed to meet the need for low cost management information over large expanses of land. Applications include rangeland management, watershed analysis, antidesertification, wildlife habitat management, mine waste reclamation, management of the arid land-irrigated agriculture interface, and outdoor recreation. Unique remote sensing problems in arid regions are related to sparse vegetation, multiple species, and considerable bare ground. Thus spectral interpretations must consider: multiple intermingled green and senescent species; considerable bare ground which includes cryptogamic soil crusts and powdery, endurated, or salinized surfaces; standing dead vegetation; litter; and shadows. Pixel modeling will be required in these heterogeneous environments. In particular, the lack of greenness tends to preclude the application of vegetation indices based on infrared/red ratios. New interpretation approaches to scene understanding, such as those included in this issue, should lead to useful procedures for aridlands.

Effects of fire on bark beetle presence on Jeffrey pine in the Lake Tahoe Basin

An investigation into the effects of low intensity, late-season prescription fire on Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and associated short-term presence of various bark beetles of the family Scolytidae was completed on forests along the north edge of Lake Tahoe, Nevada. A total of 38 permanent 0.040-ha plots were located among five different prescription burn sites treated during October 1997. An additional twenty-seven 0.040 ha plots were located in adjacent unburned forest stands. All trees within-study plots were visited thrice between June and October of 1998. Results showed a highly significant correlation between burning and bark beetle presence. Over 24% of trees in prescription burn plots were attacked by one or more species of bark beetle. Less than 1% of all non-burned trees were similarly attacked. Highly significant multiple logistic regression models were developed for each of the two occurring species of Dendroctonus and a composite model for all observed species of Ips. The indirect burn severity measurements of crown scorch, duff consumption, and bole scorch were highly significant; other tested variables were species specific or not significant.

Plant succession following chaining of pinyon juniper woodlands in eastern Nevada.

Highlight: This study was undertaken to determine some of the long-term effects of secondary succession on tree control in pinyon-juniper woodlands by cabling and chaining with “debris in place,” a technique used for about two decades. Plant species representative of all the successional stages we observed following treatment exist simultaneously from treatment. These observed changes were primarily changes in relative abundance resulting 4i-om differences in the growth rates and competitive abilities of the species concerned. Competitive ability appears directly related to the length of time following treatment that a species is able to maintain an increased growth rate. The trees maintain this increased growth for two to three times as long as any understory species studied. The result is a steady reduction of understory cover and production beyond the fifth to eight year following treatment, depending on site.

Effects of Changing Spatial Scale on the Results of Statistical Analysis with Landscape Data: A Case Study

Abstract The effect of scale on spatial analysis has long, but sporadically, been recognized in human geography and more recently and acutely in landscape ecology. As the number of studies directly and systematically addressing scale effects is still limited, it remains unclear how results of different statistical analyses are affected by changing scale for different landscapes, or whether or not such effects can be predicted and, if so, in what situations. However, it is certain that erroneous conclusions may result if scale effects are not considered explicitly in spatial analysis with area-based data. With widespread use of remote sensing data and GIS, a better understanding of the issue of scale effects is much needed. The main purpose of this study, therefore, was to examine how results of statistical analysis respond to a systematic change in the scale of analysis. Specifically, we investigated how the relationship between landscape metrics (local landcover diversity and richness indices) and indepe...

Taxonomic determination, distribution, and ecological indicator values of sagebrush within the pinyon juniper woodlands of the Great Basin.

Highlight: Various sagebrush taxa are major understory components of most Great Basin pinyon-juniper woodlands. Improved understanding of their identification, distribution, and ecological indicator significance is necessary to interpret site differences for these ranges. Morphology within sagebrush taxa is so variable that chromatographic determination is more easily and objectively relied upon for identification. Big sagebrush is so widespread and liely genetically diverse that sub-specific designations are more helpful in reading site conditions. The various sagebrush taxa are found in particular situations in Great Basin woodlands. Climatic differences explain the basin-wide distributions much more than geologic, landform, or soil conditions. Soils and exposure become more important on the local scale. Presence of a particular sagebrush taxon within pinyon-juniper woodlands can be used for comparisons of site favorableness provided one understands the general distribution of the other sagebrush taxa.