Landscape Ecology: Structure and Analysis

• Landscape ecology is the study of relationships between landscape structures, patterns, and processes.
• A landscape consists of a heterogeneous area composed of distinctive patches (landscape elements) arranged in a mosaic.
• Landscape ecology is a highly interdisciplinary field.

Landscape Structure

• Landscape structure includes the size, shape, composition, number, and position of patches (landscape elements).
• A patch is a relatively homogeneous area that differs from its surroundings.
• Patches form the mosaic that constitutes landscape structure.
• The matrix is the element in a landscape that is spatially the most continuous.

Bowen and Burgess Analysis in Ohio

• Bowen and Burgess analyzed six Ohio landscapes.
• They found that forest cover, forest patch size, forest patch density, and forest patch shape varied across these landscapes.
• Patch shape is quantified using the formula: S = P / 2√(πA)
  • S = Patch shape
  • P = Patch perimeter
  • A = Patch area
• An increasing value (above 1) represents a less circular shape.

Ecotones and Edge Effects

• Edges of patches are typically not sharply defined.
• Ecotones are physical and biological transitions between patches.
• Ecotones often support a mix of species.
• Edge effect refers to the distinct ecological conditions and higher species richness found in ecotones compared to either ecosystem.
• Species associated with ecotones are called "edge" species.
• Species not found in ecotones are "interior" species.

Fractal Geometry

• Perimeter estimates of a complex shape depend on the size of the measuring device used.
• Smaller features are more likely to be detected with smaller measuring devices.
• Milne measured the perimeter of Admiralty Island from two perspectives.
  • Bald eagle: perimeter is 760 km
  • Barnacle: perimeter is 11,000 km

Landscape Processes

• Landscape structure influences processes such as the flow of energy, materials, and species between ecosystems within a landscape.
• Landscape processes are responsible for many ecological phenomena.
  • Dispersal of organisms
  • Extinction of local populations
  • Flux of water between groundwater and lakes

Landscape Structure and Dispersal

• Landscape structure can influence the movement of organisms.
• The rate of movement of individuals between subpopulations making up a metapopulation can affect the persistence of a species.
• Human activity often results in habitat fragmentation.

Landscape Structure and Small Animals

• Diffendorfer et al. studied the effect of patch size on the movement of three small mammal species.
• Animals were predicted to move farther in more fragmented landscapes because they must move farther to obtain resources.
• Animals were predicted to stay longer in more isolated patches.
• Results supported the hypothesis that animal movements decrease with habitat fragmentation.

Habitat and Butterfly Populations

• Hanski et al. found that butterfly density is significantly affected by the size and isolation of habitat patches.
• Population size in a patch increased with patch area.
• Population density decreased as patch area increased.
• Isolated patches had lower butterfly densities.
• Isolated populations are partially maintained by immigration.

Habitat Corridors

• Connecting habitat fragments with corridors is used to mitigate the effects of fragmentation.
• Haddad and Baum studied the influence of corridors on butterflies associated with early successional habitats.
• Corridors increased movements between patches.
• Higher densities were found in patches connected by corridors.
• Corridors also affect pollination and seed dispersal.

Origins and Change of Structure

• Geological processes like volcanism, sedimentation, and erosion are primary sources of landscape structure.
• McAuliffe showed that bajadas in the Sonoran Desert are a complex mosaic of distinctive landforms.
• They found a wide range of soil types, ages, and structures.
• Soil structure influences perennial plant distributions.
• Plant distributions map clearly onto soils of different ages.

Climate and Mosaic Structure

• Bajada soil mosaic consists of patches of material deposited in floods from nearby mountains.
• Material is eroded from mountain slopes and deposited as alluvium on bajadas.
• Alluvial deposits gradually change depending upon the climate.
• Water transports both clay particles and CaCO3.
• Soil structure indicates the flow of water was highly episodic.

Organisms and Landscape Change

• Organisms that influence the structure of landscapes, ecosystems, or communities are called ecosystem engineers.
• Humans are dominant landscape modifiers.
• Forests are often converted to agricultural land (for example, Cadiz Township forest dropped from 93.5% to 3.4%.)
• In eastern North America, abandoned farms have also been known to revert to forest, increasing forest cover.
• Similar patterns can be found in parts of Europe.
• Hulshoff found Dutch forest and heathland coverage changed over time, as well as the number and average area of patches.
• Cadiz Township was losing forest while Netherlands was gaining.
• These differences were due to the development of agricultural economy in Cadiz Township versus the collapse of sheep-raising economy in the Netherlands.

Beavers and Change

• Beavers modified nearly all temperate stream valleys in the northern hemisphere.
• Beaver activity changed the boreal forest landscape of the Kabetogama Peninsula to a complex mosaic of ecosystems.
• Beavers reduced the area of boreal forest and increased nutrient retention.
• Ponds and meadows trap material and rising waters trap nutrients.
• Beaver activity causes alterations in biogeochemical processes.

Fire Effects

• Minnich used satellite photos to reconstruct the fire history of Southern California and Northern Baja from 1971 to 1980.
• The landscape consisted of a patchwork of old and new burns.
• Similar climates had different fire histories.
• Fire suppression in Southern California allowed more biomass accumulation and resultant large fires.
• Small burns were thus more frequent in Northern Baja.

This lesson covers landscape ecology, focusing on the relationships between landscape structures, patterns, and processes. It defines key terms like patches and matrix, and explores how landscape structure includes the size, shape, and composition of landscape elements. It also references the Bowen and Burgess analysis in Ohio.