Mosaic of patches Agents of patch formation: Environmental constraints (Abiotic) Biotic processes Disturbances (natural and human induced)

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1 Landscape: Mosaic of patches Agents of patch formation: Environmental constraints (Abiotic) Biotic processes Disturbances (natural and human induced) Concepts for Quantification of a Landscape Landscape ecology involves the study of landscape patterns, the interactions among patches within a landscape mosaic, and how these patterns and interactions change over time. Structure, Function, and Change 1

2 Distribution of Flow of Change of Energy Materials Species Structure Function Change Landscape ecology focuses on three characteristics of the landscape: Structure: Refers to the spatial relationships among the distinctive ecosystems, that is, the distribution of energy, materials, and species in relation to the sizes, shapes, numbers, kinds, and configurations of components. (Spatial Pattern) Function: Refers to the interactions among the spatial elements, that is, the flows of energy, materials, and species among the component ecosystems. (Processes) Change: Refers to the alteration in the structure and function of the ecological mosaic through time. (Dynamics) 2

3 Spatial heterogeneity and pattern of a landscape: where it come from why it matters how to characterize it how it changes through time Quantitative analysis of landscape patterns is a necessary. Quantitative Methods Landscape level research requires new methods to 1. quantify spatial patterns; 2. compare landscapes; 3. identify significant differences; and 4. determine relationships of functional processes to landscape patterns. 3

4 Landscape Elements Patches - size, number, shape, location Edges and Boundaries - structure, shape Corridors and Connectivity - pathways, barriers Mosaics - network, fragmentation, pattern, scale Tools for Quantification of Landscape: Landscape Metrics landscape metrics refers to indices developed for categorical map patterns. Landscape metrics are algorithms that quantify specific spatial characteristics of patches, classes of patches, or entire landscape mosaics. Quantitatively measure the landscape including patch size, shape, proximity, edge density, dominance, diversity, fractal dimension, 4

5 Source of Data for Quantification of Landscape 1. Aerial Photography: One of the most widely used types of remote sensing data from which land use/land cover types can be obtained directly. 2. Digital Remote Sensing: Sequences of satellite data can be used to derive estimates of transition frequencies between land use categories. 3. Spatial Database (GIS) Thematic maps 4. Published Data and Censuses 5. Field Survey Patch Size and Number Patches must be defined relative to the phenomenon under consideration. A patch is a relative homogeneous area that differs from its surroundings. Patches have familiar attributes, such as large or small, rounded or elongated, and straight or convoluted boundaries. These attributes in turn have widespread ecological implications for productivity, biodiversity, soil, and water. 5

6 Why are characteristics of patches important? In forestry: affects road construction and erosion In urban planning: affects the size of housing development and natural reserve In aquifer and lake protection: large patch of natural vegetation is required In agriculture, optimum field size has both ecologic and economic implications Conservation planning requires one large patch or several smaller ones Relationships between number and size of patches and biodiversity Matrix A landscape is composed of several types of landscape elements. Of these, a matrix is the most extensive and most connected landscape element type, and therefore plays the dominant role in the functioning of the landscape. 6

7 In order to quantify landscape patterns in a meaningful way, the origins and half-life of dynamic patches should be considered. For example, succession is only one of many processes determining the rate and direction of change in a patch. On land, five basic causes or origins of vegetation patches are evident and wide spread. Remnant patch; Regenerated patch; Introduced patch; Environmental patch (of vegetation); Disturbance patch (Forman, R.T.T ) The five types illustrated assume the original landscape was mature coniferous forest. Thickness of arrow over each patch type is roughly proportional to its persistence or half-life. 7

8 Remnant Patch: Appears when an area escapes disturbance surrounding it (e.g., from fires, loggings, anthropogenic impacts...) Regenerated Patch: A regenerated patch resembles a remnant but instead has re-grown on a previously disturbed site. 8

9 Introduced Patch: Introduced patches are created by human activities (e.g., farming practices, forestry, urban development, infrastructure, Environmental Patch An environmental patch (of vegetation) is caused by the patchness of the environment, such as a rock or soil type. Example: vegetation distribution and bed rock/soil 9

10 Disturbance Patch: A disturbance patch results from alteration or disturbance of a small area (e.g., fire and wind disturbances). The diverse assemblage of patch types composing a landscape has ecological implications. The rate of change varies widely depending on the cause or origin of patch. 10

11 Environmental patches change slowly, reflecting the stability of the substrate. Example: The Lerai Forest in the Ngorongoro Crater is gradually moving from its present location to a nearby well drained area. Although the yellow-barked fever trees are groundwater dependent, Acacia was not to be. When groundwater changes in water table and supplies, the trees will grow, die, or move accordingly. Those that could not adjust quickly would be eliminated. 11

12 Remnant and Disturbance Patches change relatively rapidly, reflecting the rate of succession, and disappear when they converge in similarity with the adjacent vegetation. When the disturbance stops, succession takes over. Regenerated Patch 12

13 Regenerated Patch Disturbance Patch: results from alteration or disturbance of a small area. 13

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15 Disturbance may be a single or repeated event. Repeated or chronic disturbance, such as tractor plowing or daily local pollution, maintains the patch over time. Each landscape element contains an edge, the outer area exhibiting the edge effect, i.e. dominated by species found only near the border. The inner area of a landscape element is considered the interior or core, and is dominated by species live away from the border. The edges combined compose the boundary or boundary zone. A border is the line separating the edges of adjacent landscape elements. 15

16 Landscape ecology principles in landscape architecture and land-use planning by W.E. Dramstad, J.D. Olson, R.T.T. Forman, Island Press

17 Patch Size: Large or Small... Dramstad, et al., Dramstad, et al.,

18 Dramstad, et al., Patch Locations: Where... Dramstad, et al.,

19 Eastern Arc Mountains: a unique chain of isolated mountains that are directly influenced by the climatic effects of the Indian Ocean and the great age of the mountains. These mountains are recognized as globally important hot spots for forest biodiversity and are major national, regional and local sources of hydropower, water, and forest products. Dramstad, et al.,

20 October 2, 1972 Landsat TM Spring Brook Tall Grass Prairie Restoration Site May 30, 1985 Landsat TM October 10, 1997 Landsat TM Land Cover Change in Naperville Area between 1985 and 1997 Agriculture Urban Spring Brook Prairie Restoration Site 20

21 Boundaries and Edges Three mechanisms produce vegetation boundaries in landscape. A patchy physical environment (e.g., mosaic of soil or landforms ) Natural disturbance (e.g., wild fire ) Human activities (e.g., clear cutting, housing development ) In many cases, natural disturbance and human activities sharpen an existing boundary, thus increase contrast in landscape. Edge Structure: Dramstad, et al.,

22 Dramstad, et al., Dramstad, et al.,

23 Dramstad, et al., Dramstad, et al.,

24 Corridors and Connectivity Corridors perform five major functions in landscape: habitat, conduit, filter, source, and sink. Corridor acts a conduit when objects move along it. Corridor is a filter or barrier when objects are inhibited from crossing between patches on opposite sides. Conduit fluxes may be either inside or alongside a corridor. Corridors and Connectivity Nature creates corridors in the form of streams, ridges, and animal trails Example: bare rock range land brush along the creak. 24

25 Corridors and Connectivity Nature creates corridors in the form of streams, ridges, and animal trails Example: The Badlands Wall Appalachian Trail 25

26 Corridors and Connectivity Humans create roads, power-lines, ditches, walk trails Corridors and Connectivity Humans create roads, power-lines, ditches, walk trails 26

27 Stone walls Corridors and Connectivity As a source (i.e., an area or reservoir that gives off objects) of effects on neighboring patches, corridor may harbor herbivores that feed on crops, predators that control crop pests, trees that disperse seeds, and hunters that hunt in the matrix. As a sink (i.e., an area or reservoir that absorb objects) for fluxes from neighboring areas, corridor may accumulate wind-blown sediment and snow, subsurface mineral nutrients, and animals from the matrix. 27

28 Dramstad, et al., Dramstad, et al.,

29 Mosaic Patterns The overall structural and functional integrity of a landscape can be understood and evaluated in terms of both pattern and scale. Ecological health of a landscape is the overall connectivity of the natural systems present. Corridors often interconnect with one another to form networks, enclosing other landscape elements. Networks in turn exhibit connectivity, circuitry, and mesh size. Mosaic Patterns A common landscape pattern is fragmentation, which is considered as one of several land transformation processes, which together may produce isolation of habitat. Fragmentation also results from natural disturbances, but has become an international policy issue because of the widespread alternation of land mosaics by human activities. 29

30 Mosaic Patterns The spatial scale at which fragmentation occurs is important when identifying strategies to cope with continued habitat loss and isolation. For example, fragmented habitat at a fine scale may be perceived as intact at a broader scale. Only by recognizing and addressing landscape changes across different scales can planners and designers maximum protection of biodiversity and natural processes. Gross, et al., Map showing connectivity of natural landscapes in the United States. The thickness of red lines indicates magnitude of cumulative movement, assuming that animals avoid human-modified areas. The surface underneath the pathways depicts the averaged cost distance surfaces, or the overall landscape connectivity surface. Colors range from green through yellow and purple to white, where green is greatest connectivity (lowest travel cost) and white indicated lowest connectivity (highest travel cost). National Park Service units are outlined in black. 30

31 Mosaic Patterns In landscape, context is usually more important than content, i.e., the surrounding mosaic has a greater effect on patch functioning and change than do the present characteristics within the patch. Context includes three components: adjacency neighborhood, and location within a landscape Dramstad, et al.,

32 Dramstad, et al., Dramstad, et al.,

33 Chicago Wilderness Example: Is a regional nature reserve, comprising of 200,000 acres of protected natural lands in the metropolitan region. It is the globally significant concentration of rare natural communities--the woodlands, forests, grasslands, streams and wetlands. Landscape Composition and Configuration. 33

34 Landscape Structure Landscapes are distinguished by spatial relationships among components. A landscape can be characterized by both its composition and configuration (landscape pattern). These two aspects of a landscape can independently or in combination affect ecological processes and organisms. Landscape Composition Landscape composition refers to features associated with the presence and amount of each patch type within the landscape, but without being spatially explicit or does not explain the placement or location of patches within the landscape mosaic. It s about the presence and absence of species and habitats. 34

35 Landscape Configuration Landscape configuration refers to the physical distribution or spatial character and arrangement, position, orientation of patches within the landscape. Some aspects of configuration, such as patch isolation or patch contagion, are measures of the placement of patch types relative to other patch types, the landscape boundary, or other features of interest. Certain aspects of configuration, such as shape and core area, are measures of the spatial character of the patches. Quantifying a landscape, such as the mean patch core area across the landscape, could provide a good index to landscape suitability for the relative species 35

36 Quantification of a landscape, or describe landscape in a meaningful quantitative way. Number of Patches? Average Patch Size? Patch Density? Edge Index? Quantification of a landscape, or describe landscape in a meaningful quantitative way. Number of Patches? Average Patch Size? Patch Density? Edge Index? 36

37 Mean patch size is a function of the number of patches in the class and total class area. In contrast, patch density is a function of total landscape area. The two landscapes could have the same number and size distribution of patches for a given class and thus have the same mean patch size; yet, if total landscape area differed, patch density could be different between landscapes. Alternatively, two landscapes could have the same number of patches and total landscape area and thus have the same patch density; yet, if class area differed, mean patch size could be very different between landscapes. These differences defines landscape patterns in a quantitative way. Challenging? 37

38 One big patch vs. Several Small Patches? Number of Patches? Average Patch Size? Patch Density? Edge Index? One big patch vs. Several Small Patches? Number of Patches? Average Patch Size? Patch Density? Edge Index? 38

39 Classes of Landscape Patterns Landscape patterns can be quantified in a variety of ways depending on the type of data collected, the manner in which it is collected, and the objectives of the investigation. Broadly considered, landscape pattern analysis involves four basic types of spatial data corresponding to different representations of landscape pattern. Spatial point patterns; Linear network patterns; Surface patterns; and Categorical (or Thematic) map patterns (1) Spatial Point Patterns Which represent collections of entities where the geographic locations of the entities are of primary interest, rather than any quantitative or qualitative attribute of the entity itself. Typically, the points would be labeled by species, and perhaps further specified by their sizes (a marked point pattern). 39

40 (g/m 2 ) National Soil Survey Soil Organic Carbon Calculations (Total soil organic carbon content value in unit of g/m 2, 13, 000 pedon points)

41 The goal of point pattern analysis is to determine whether the points are more or less clustered than expected by chance and/or to find the spatial scale(s) at which the points tend to be more or less clustered than expected by chance (Greig-Smith 1983, Dale 1999). (2) Linear Network Patterns Which represent collections of linear landscape elements that intersect to form a network (corridors that connect nodes). Often, the nodes and corridors are further characterized by composition (e.g., vegetation type) and spatial character (e.g., width). 41

42 The geographic location and arrangement of nodes and corridors are of primary interest. The goal of linear network pattern analysis is to characterize the physical structure (e.g., corridor density, mesh size, network connectivity) of the network, and a variety of metrics have been developed for this purpose (Forman 1995). (3) Surface Patterns Which represent quantitative measurements that vary continuously across the landscape; there are no explicit boundaries (i.e., patches are not delineated). The data can be conceptualized as representing a three-dimensional surface, where the measured value at each geographic location is represented by the height of the surface. 42

43 A familiar example is a digital elevation model (DEM), but any quantitative measurement can be treated this way (e.g., plant biomass, leaf area index, soil nitrogen, density of individuals). (3) Surface Patterns In many cases the data are collected at discrete sample locations separated by some distance. Interpolation techniques exist that permit the modeling of these spatial patterns. 43

44 IDW (Inverse Distance Weighting) Spline Kriging Cokriging Interpolation of land surface temperature (4) Categorical (or Thematic) Map Patterns Which represent data in which the system property of interest is represented as a mosaic of discrete patches. A familiar example is a map of land cover types, wherein the data consists of polygons (vector format) or grid cells (raster format) classified into discrete land cover classes. Patches may be classified and delineated qualitatively through visual interpretation of the data or digital image classification. An edge in this case is an area where the measured value changes abruptly (i.e., high local variance or rate of change). 44

45 LANDSCAPE METRICS Landscape metrics refer exclusively to indices developed for categorical map patterns. Landscape metrics focus on the characterization of the geometric and spatial properties of categorical map patterns represented at a particular scale. Landscape metrics are algorithms that quantify specific spatial characteristics of patches, classes of patches, or entire landscape mosaics. 45

46 LANDSCAPE METRICS Landscape metrics fall into two general categories: 1. To quantify composition of the map without reference to spatial attributes, and 2. To quantify spatial configuration of the map, requiring spatial information for their calculation (McGarigal and Marks 1995, Gustafson 1998). FRAGSTATS 46