Using fractal analysis to assess how species perceive landscape structure

To develop a species-centered definition of landscapes, I suggest using a fractal analysis of movement patterns to identify the scales at which organisms are interacting with the patch structure of the landscape. Significant differences in the fractal dimensions of movement patterns of two species indicate that the species may be interacting with the patch structure at different scales. Fractal analysis therefore permits comparisons of landscape perceptions of different species within the same environment.I tested the utility of this fractal application by analyzing the movement patterns of three species of acridid grasshoppers (Orthoptera) in a grassland mosaic. The largest species moved up to 6 times faster than the two smaller species, and species exhibited different responses to microlandscape structure within 25-m² plots. Further, the largest species exhibited different responses to microlandscape structure in two pastures subjected to different intensities of cattle grazing. This species thus is able to integrate information on landscape structure at broad spatial scales. Fractal analysis of movement patterns revealed that the two small species had significantly more tortuous patterns than the larger species, which suggests that these species are interacting with patch structure at a finer scale of resolution than the large species. Fractal analysis can be used to identify the perceptive resolution of a species; that is, the spatial grain and extent at which they are able to perceive and respond to heterogeneity. Analysis of movement patterns across a range of spatial scale may reveal shifts in fractal dimension that reflect transitions in how species respond to the patch structure of the landscape at different scales.     

Foraging in a fractal environment: Spatial patterns in a marine predator-prey system

Spatial relationships between predators and prey have important implications for landscape processes and patterns. Highly mobile oceanic birds and their patchily distributed prey constitute an accessible model system for studying these relationships. High-frequency echosounders can be used together with simultaneous direct visual observations to quantitatively describe the distributions of seabird consumers and their resources over a wide range of spatial scales, yielding information which is rarely available in terrestrial systems.Recent fine-scale investigations which have used acoustics to study the distribution of foraging marine birds have reported weak or ephemeral spatial associations between the birds and their prey. These results are inconsistent with predictions of optimal foraging, but several considerations suggest that traditional foraging models do not adequately describe resource acquisition in marine environments. Relative to their terrestrial counterparts, oceanic landscapes are structurally very simple, but they generally lack visual cues about resource availability.An emerging view assumes that perceptually constrained organisms searching for food in multiscale environments should respond to patterns of resource abundance over a continuum of scales. We explore fractal geometry as a possible tool for quantifying this view and for describing spatial dispersion patterns that result from foraging behavior. Data on an Alaskan seabird (least auklet [Aethia pusilla]) and its zooplanktonic food resources suggest that fractal approaches can yield new ecological insights into complex spatial patterns deriving from animal movements.     

Landscape patch shape complexity as an effective measure for plant species richness in rural landscapes

The application of landscape patch shape complexity as a predictor ofvascularplant and bryophyte species richness is analysed. Several common complexityindices (shape index, fractal dimension, comparison to the area of the minimumbounding rectangle) are tested for their predictive power for plant speciesrichness. One new robust measure for shape complexity is presented whichovercomes some disadvantages of common complexity measures applied to highresolution analysis of agricultural landscapes based on aerial photographs. Thenew index is based on the number of shape characterising points along apolygons boundary. This new measure shows promising predictive capabilitiesforspecies richness of vascular plants and bryophytes (correlation coefficient:0.85 for vascular plants, 0.74 for bryophytes).This revised version was published online in May 2005 with corrections to the Cover Date.     

Landscape graphs: Ecological modeling with graph theory to detect configurations common to diverse landscapes

In view of the bewildering diversity of landscapes and possible patterns therein, our objectives were to see if a useful modeling method for directly comparing land mosaics could be developed based on graph theory, and whether basic spatial patterns could be identified that are common to diverse landscapes. The models developed were based on the spatial configuration of and interactions between landscape elements (ecosystems, land uses or ecotopes). Nodes represented landscape elements and linkages represented common boundaries between elements. Corridors, corridor intersections, and the matrix were successfully incorporated in the models. Twenty-five landscape graphs were constructed from aerial photographs chosen solely to represent a breadth of climates, land uses and human population densities. Seven distinctive clusters of nodes and linkages were identified and common, three of which, in the forms of a spider, necklace and graph cell, were in >90% of the graphs. These represented respectively the following configurations of patches, corridors and matrix: (1) a matrix area surrounding or adjoining many patches; (2) a corridor bisecting a heterogeneous area; and (3) a unit in a network of intersecting corridors. The models also indicated that the connectivity or number of linkages for several common elements, such as fields and house clearings, was relatively constant across diverse landscapes, and that linear shaped elements such as roads and rivers were the most connected. Several additional uses of this graph modeling, including compatibility with systems dynamics models, are pinpointed. Thus the method is useful in allowing simple direct comparisons of any scale and any landscape to help identify patterns and principles. A focus on the common and uncommon configurations should enhance our understanding of fluxes across landscapes, and consequently the quality of land planning and management.     

Comparison of available soil water capacity estimated from topography and soil series information

We present a simple and generalized method to predict Available Soil Water Capacity (ASWC-TOP) for a given area using a topographic index, defined as ln(/tan), where is the upslope area draining past a certain point per unit width of slope, and is the local surface slope angle. The estimated results (ASWC-TOP) were then compared with the available soil water capacity calculated from soil series information provided by Soil Conservation Service, U.S. Department of Agriculture (ASWC-SCS). The model implementation was tested with three study cases: the Seeley-Swan valley, Montana, with pixel resolutions of 100 m and 1 km, respectively; and the state of Montana, U.S.A., with a pixel resolution of 1 km. A linear relationship exists between ASWC-SCS and ln(/tan). Standard errors between ASWC-TOP and ASWC-SCS were about 4.4 cm in the Seeley-Swan valley and 5.5 cm in the state. The number of pixels with absolute residuals 4 cm between ASWC-TOP and ASWC-SCS accounted for 68.2, 64.4, and 51.9% for the valley 100 m, valley 1 km, and the state respectively. Some of the mismatches between ASWC-TOP and ASWC-SCS may indicate an improvement using this method compared to existing data because the topographic method reflects the higher spatial variation of the inputs. The increasing availability of digital elevation data, at various resolutions, may provide an alternative to soil series for estimating ASWC. The accuracy of ASWC-TOP depends on estimation of mean and maximum ASWC for a study area.     

Coincidences between different landscape ecological zones and growth forms of Cembran pine (Pinus cembra L.) in subalpine habitats of the Central Alps

The forgotten depots of the European Nutcracker (Nucifraga c. caryocatactes) often lead to the development of tufts of Pinus cembra. In many cases the other individuals of such tufts are not suppressed by the fittest one, rather there is an intraspecific coexistence up to the senescent stage of the trees. There are fusions of separate trunks, and so frequently the individual history of older trees can only be reconstructed by studying sutures, crown structures or trunk cross sections. Different types of trunk fusions are worked out. By means of transect counting the occurrence of these multiple trunk trees is documented quantitatively in different landscape ecological zones of the Engadin region (the Grisons, Switzerland). The data base is 3024 counted microsites of Pinus cembra individuals arising from seeds, including 5272 living individuals. These multiple trunk trees significantly play an important role in the landscape ecological zones of recent glacier recession and at the alpine timberline. Their growth forms have a higher biomechanical stability.     

Potential impacts of changing agricultural activities on scenic beauty – a prototypical technique for automated rapid assessment

As a result of the liberalisation of the agricultural market, mountain regions in Central Europe are at great risk of experiencing increasing land abandonment and spontaneous reforestation. Prior to taking measures for landscape maintenance, the ecological and landscape-aesthetic consequences of land abandonment should be analysed. This paper addresses the aesthetic component of such analyses: we investigated whether lay people perceive land abandonment and spontaneous reforestation as a loss or a gain and developed a prototypical technique for rapid aesthetic assessment of reforestation scenarios for vast regions.First, we conducted image experiments to assess the respondents' reactions to increasing levels of reforestation. Based on these experiments we concluded that a medium degree of reforestation is most desirable. Second, we analysed the relationship between scenic beauty and landscape patterns and found that landscape preference values correlate significantly with various quantitative measures of the landscape pattern (e.g., diversity and contagion indices of grey- tone and colour images). Third, we applied a GIS-assisted moving- window technique to transform spatially explicit remote-sensing data (in particular orthophotos) of a test region to spatially explicit data of landscape-pattern indices. Thanks to the significant positive correlation between pattern indices and landscape preference values, the resulting maps can preliminarily be interpreted as beauty-maps of the test-region.     

Boundary dynamics at the aquatic-terrestrial interface: The influence of beaver and geomorphology

Beaver (Castor canadensis) impoundments are used to illustrate the effect of large animals on the boundary dynamics of patch bodies, volumetric landscape units which have surficial boundaries with upper and lower strata, and lateral boundaries with adjacent patches within the same stratum. Patch bodies created by beaver impoundments include the beaver pond, the aerobic soil beneath the pond, and the underlying anaerobic soil. Beaver herbivory in the riparian zone creates an additional patch body concentric to the pond. Beaver and water are the primary biotic and abiotic vectors mediating fluxes across lateral patch body boundaries; vegetation and microbes are the primary biotic vectors mediating fluxes across surficial patch body boundaries. Basin geomorphology affects the permeability of pond boundaries (i.e., their ability to transmit, energy and materials) by affecting the kinetic energy of water, the surface-to-volume ratio of the impoundment, and the movement of beaver between the pond and the riparian foraging zone. We suggest that: (1) permeability of lateral boundaries to abiotic vectors is a function of kinetic energy; (2) within-patch retention of particulate matter transferred by abiotic vectors across lateral boundaries is maximized by a decrease in kinetic energy; (3) lateral patch boundaries between safe refuge and a resource used by an animal vector are most permeable when they are narrow; and (4) total amount of energy and materials transferred across surficial boundaries is maximized by increasing surface area.     

Effects of patch shape on the number of organisms

This study examined effects of habitat patch shape on the abundance of organisms. The effects of patch shape were considered in terms of (1) immigration and emigration of organisms. (2) the amount of available resources in a patch and (3) spatial and temporal heterogeneity of the organisms and environment. I hypothesized that (1) the number of organisms would increase as patch shape elongates because organisms are more likely to encounter an elongated patch, (2) the number of organisms in a patch would remain constant for all patch shapes where the number of organisms in a patch was limited by the amount of resources, because patch shape does not change the patch area that is directly associated with the amount of patch resources, and (3) spatial and temporal variation of the abundance of organisms would increase as patch shape elongates because an elongated patch is more likely to interact with the variable surrounding matrix.Common millipedes,Oxidus gracilis, and their habitat, plywood boards of five shapes (width:length ratio; 11, 14, 19, 136, 1144) with an area of 900 cm² were placed in forest and old field and the number of millipedes appearing under the boards was monitored. Significantly higher mean number of millipedes under the boards was observed at a patch with an elongated shape in the forest and the old field. A significant positive correlation was observed between perimeter length of a patch and the number of millipedes in the old field. The temporal and spatial variation of the number of millipedes was high in the old field. The spatial and temporal variation was higher for boards with elongated shape.     

Gap analysis: concepts,methods, and recent results*

Rapid progress is being made in the conceptual, technical, and organizational requirements for generating synoptic multi-scale views of the earth's surface and its biological content. Using the spatially comprehensive data that are now available, researchers, land managers, and land-use planners can, for the first time, quantitatively place landscape units – from general categories such as Forests or Cold-Deciduous Shrubland Formation to more categories such as Picea glauca-Abies balsamea-Populus spp. Forest Alliance – in their large-area contexts. The National Gap Analysis Program (GAP) has developed the technical and organizational capabilities necessary for the regular production and analysis of such information. This paper provides a brief overview of concepts and methods as well as some recent results from the GAP projects. Clearly, new frameworks for biogeographic information and organizational cooperation are needed if we are to have any hope of documenting the full range of species occurrences and ecological processes in ways meaningful to their management. The GAP experience provides one model for achieving these new frameworks.     

The use of herders’ accounts to map livestock activities across agropastoral landscapes in Semi-Arid Africa

Improved understandings of the agricultural and range ecologies ofsemi-arid Africa require better information on the spatiotemporal distributionof domestic livestock across agropastoral landscapes. An empirical GIS-basedapproach was developed for estimating distributions of herded livestock acrossthree agropastoral territories (around 100 km² each)over a two-year period. Algorithms developed from regression analyses of herdtracking data (with R²s 0.67) are used to transform a morecomprehensive but incomplete set of data generated from herders accounts oftheir herds grazing itineraries (400 herds following 6500 itineraries). Theresulting characterization registers 40 000 days of livestock activitiesacross694 land units (averaging 70 ha) over the study period. This studydemonstrates that rural producers knowledge of their daily extractionpracticescan be translated to fine-grained characterizations of extraction densitiesacross mixed landscapes. The spatiotemporal distribution of livestock that isrevealed by this approach diverges strongly from that predicted bycommonly-usedpoint-diffusion estimation procedures. Instead, the distribution reflects localpatterns of land use, topography, vegetation, settlements, and water points.Grazing and nongrazing times spent in land units are not spatially correlatedand the seasonality of grazing pressure is spatially variable. Therefore, theecological impacts of livestock grazing are spatially variable at fine scalesand there is a significant potential for livestock-mediated nutrient transfersacross agropastoral landscapes. The georeferenced data produced by thisapproachnot only will help evaluate the impact and sustainability of differentmanagement practices but also provides a strong empirical base for improvedspatial modeling of herded livestock.This revised version was published online in May 2005 with corrections to the Cover Date.     

耐抽薹白菜新品种‘寒绿’

‘寒绿’白菜是以自交不亲和系‘WC-03-05-05’和自交系‘WC-02-08-04’杂交育成的一代杂种。株形直立,束腰,株高约25 cm,开展度约25 cm × 27 cm。叶片展开,叶色绿有光泽,叶柄绿色,长且肥厚。单株质量约0.30 kg。田间综合表现佳,耐抽薹,抗病,品质和商品性好。适宜于长江中下游地区春季栽培及北方地区周年生产。     

A proximity-based approach to assessing habitat

Planning for either a single species, multiple species, or ecosystems is greatly dependent on spatial interactions in the landscape. Problems exist for evaluating wildlife habitat changes over large ranges of space and time. This paper illustrates the use of Geographic Information Systems (GIS) to evaluate habitat for a single species, ruffed grouse (Bonasa umbellus), following a time series of forest harvests. A habitat suitability model for ruffed grouse is utilized on a two-township study area in north-central Minnesota to assess the habitat suitability changes over time using an even-aged area-control harvesting plan. The results are presented as a habitat quality change map and a contingency table, representing the movement of habitat class areas between time periods resulting from the proposed harvesting. We developed a neighborhood definition to allow for spatially varying habitat values. This work illustrates the ability to look ahead and around in estimating the impact on wildlife habitat resulting from alternative future management activities.Now with the U.S. Forest Service, Sitka, AK 99835.     

An investigation of uncertainty in field habitat mapping and the implications for detecting land cover change

Land cover data for landscape ecological studies are frequently obtained by field survey. In the United Kingdom, temporally separated field surveys have been used to identify the locations and magnitudes of recent changes in land cover. However, such map data contain errors which may seriously hinder the identification of land cover change and the extent and locations of rare landscape features. This paper investigates the extent of the differences between two sets of maps derived from field surveys within the Northumberland National Park in 1991 and 1992. The method used in each survey was the Phase 1 approach of the Nature Conservancy Council of Great Britain. Differences between maps were greatest for the land cover types with the smallest areas. Overall spatial correspondence between maps was found to be only 44.4%. A maximum of 14.4% of the total area surveyed was found to have undergone genuine land cover change. The remaining discrepancies, equivalent to 41.2% of the total survey area, were attributed primarily to differences of land cover interpretation between surveyors (classification error). Differences in boundary locations (positional error) were also noted, but were found to be a relatively minor source of error. The implications for the detection of land cover change and habitat mapping are discussed.     

Allochthonous ecosystems

In extreme deserts with precipitation of less than 10–20 mm/yr, biocoenoses occur which are void of producers but show ecosystem functions such as food chains and energy flow. Since they are fed by the importation of allochthonous organic material the term allochthonous ecosystems is proposed to designate these systems. The application of this term to other incomplete ecosystems without producers is discussed.     

Induction of vertical zones in sub-alpine valley forests by avalanche-formed fuel breaks

Vertical zonation of forests in high mountains is normally explained in terms of climatic variation, but avalanche tracks can act as fuel-breaks in southern Alberta Rocky Mountain forests. This is an additional way of explaining the spruce-fir (Picea engelmannii (Parry) Engelm. - Abies lascioparpa (Hook.) Nutt.) and lodgepole pine (Pinus contorta Dougl. var. latifolia Wats.) communities of the upper and lower sub-alpine zones. The hypotheses are that: 1) Fires start more often at lower than high altitude and that, as they spread into high valleys, 2) they are halted where avalanche tracks reach the valley bottom from both slopes. Also, (3) the average return interval of fires will be greater above this avalanche block, and 4) vegetation above the block will consist primarily of near-climax, fire-intolerant communities. These hypotheses were tested using the Highwood Pass (50 °21 N, 114 °26W) in the Rocky Mountains of southern Alberta, Canada. Maps of avalanche tracks and past fires, a point-centered quarter survey of forest stands, and disturbance histories established by increment coring were used to test the hypotheses which were all upheld. Thus avalanche tracks are one of the complex of factors limiting fires in the sub-alpine zone of the Alberta Rocky Mountains. The results, additionally, imply that vertical vegetation zones in temperate high mountains are influenced, not only by climatic factors, but also by avalanches and other landforms.     

Model description of dynamics of disturbance and recovery of natural landscapes

We consider the dynamic simulation model of landscapes proposed by Turner et al. (1993). In this model a landscape, represented by a square grid of 100×100 cells, is exposed to disturbances of a fixed size at random locations at specified time intervals. The affected area recovers through a series of seral stages and achieves a mature stage unless it is affected again by successive disturbances. Two non-dimensional parameters, determining the dynamics of the model, are T, the ratio of the disturbance interval to the time of recovery and S, the ratio of the size of the disturbance to the size of the landscape. The main outcomes of analysis are the means and standard deviations of the areas occupied by different seral stages. We show that these characteristics of the system can be calculated analytically. This facilitates the understanding of the results of the computer experiments, the analysis of the asymptotic behaviour of the system (for example when the disturbances become increasingly small but very frequent, T,S1) and of more complex regimes of external disturbances, e.g., of the combined effects on a landscape from several types of disturbances with different spatial and time scales.     

Scale of heterogeneity of forage production and winter foraging by elk and bison

The relationship between fine-scale spatial patterns of forage abundance and the feeding patterns of large ungulates is not well known. We compared these patterns for areas grazed in winter by elk and bison in a sagebrush-grassland landscape in northern Yellowstone National Park. At a fine scale, the spatial distribution of mapped feeding stations in 30 m × 30 m sites was found to be random where there were no large patches devoid of vegetation. In areas similar to the mapped sites, the underlying spatial distribution pattern of biomass was also determined to be random. At a broad scale, forage biomass differed among communities across the northern range but forage quality did not. These results suggest that ungulates are feeding randomly within forage patches (fine scale) but may select feeding sites based upon forage abundance at broader, landscape scales. Contrary to what has been suggested in other systems, ungulates were not overmatching at finer scales.