Home > architecture, school > Landscape Ecology Chapter 4: Causes of Landscape P…

Landscape Ecology Chapter 4: Causes of Landscape P…

Landscape Ecology
Chapter 4: Causes of Landscape Pattern
all quotes obtained from Landscape Ecology, Turner et al., 2001

‘broad-scale variability in the abiotic environment sets the constraints within which biotic interactions and disturbances act.’

‘Climate refers to the composite, long-term, or generally prevailing weather of a region, and climate acts as a strong control on biogeographic patterns through the distribution of energy and water.’ climate affects and determines the landform over long periods (thousands of years), while the landform may control the climate over short periods (immediate) – feedback loop. paleoecology is the study of individuals, populations, and communities of plants and animals that lived in the past and their interactions with and dynamic responses to changing environments – this helps to understand the current interaction of everything in nature and can help to predict the outcome of current interactions or future hypothetical situations.

climate varies w/ latitude and continental position. 32 degrees N coastal may have entirely different climate than 32 degrees N interior. elevation also alters temperature: low elevation coastal water temperature may be drastically different from low elevation interior water temperature, while low elevation coastal and high elevation coastal have different temperature – combination of latitude and continental position create entirely different biomes, and can create different climates locally.

long term climate change: each glacial-interglacial period lasts roughly 100,000 years: ~90,000 yrs of gradual cooling followed by rapid heating and ~10,000 yrs of warmth. earth is currently at the end of a warmth period, meaning the temp should begin dropping soon (part of the 90,000 yr gradual cooling), but buildup of CO2 will offset the cooling and instead incite at least a 2degreeC temp increase.

earth’s biota must respond to temp changes. plant species can respond to climate change by either: evolving and speciating; migrating long distances; or become extinct. glacial-interglacial cycles trigger the disassembly of communities followed by a reassembly that is unpredictable in terms of either species composition or abundance. disturbance regimes are very sensitive to changes in climate : the 44yr fire cycle of northwestern Minnesota become an 88yr cycle with the onset of cooler, moisture conditions created by the onset of the Little Ice Age after 1700CE. different plant species respond to changes in climate according to their own characteristics – climate change does not necessarily affect entire biomes, but the overall composition of the biome may change according to the abilities of each species to withstand change.

landforms range from flat plains to rolling hills to craggly mountains that are nastier than yo mom’s crater face! damn! ‘if different areas are composed of similar landforms w/ similar geology, then soil catenas (a chain of connected objects so arranged that each member is closely related to the preceding and following members) and vegetation types may also be expected to be similar.’
four general effects of landform on ecosystem:
1. elevation, aspect, parent materials, and slope of landforms affect air and ground temperature and the quantities of moisture, nutrients, and other materials available at sites w/in a landscape. (south slopes receive more solar radiation, hence drier, warmer conditions – better conditions for plants.
2. landforms affect the flow of many quantities, including organisms, propagules (A part of a plant that can produce another plant: including seeds, roots and rhizomes), energy, and matter through a landscape. steep non-porous slopes will funnel water more effectively and may be a conduit or path for the dissemination of seeds or erosion paths.
3. landforms affect the frequency and spatial pattern of natural disturbances such as fire, wind, or grazing. certain species may act as a natural fire break; forests decrease wind speed; rivers and creeks delineate fields…
4. landforms constrain the spatial pattern and rate or frequency of geomorphic processes, the mechanical transport of organic and inorganic material, that alter biotic characteristics and processes. landforms significantly contribute to the development and maintenance of spatial heterogeneity across a landscape through their multiple effects on soils, vegetation, and animals.

interaction among organisms may result either homogenous or heterogeneous landscapes. 2 species may compete w/ one resulting victor and a homogenous landscape. other times there may be multiple stable states, where multiple species coexist, but one is dominant. a small change in landscape dynamics may shift conditions to where a different species becomes dominant. example of ecotone edge, where a finger of forest may intrude into a grassland and a finger of grassland may intrude into a forest. conditions are left to chance, and the relationship may change so that the forest overtakes the finger of intruding grass, or vice versa.

competition between vegetation may also form ecotones, even where climatic conditions may favor the growth of both species. as temp. changes from north to south, one may assume that two species of tree would intermingle before becoming exclusively species 1 or species2. but competition between the 2 species may create a distinct boundary resulting in clearly defined separate ecotones.

reaction-diffusion models – growing and competing populations are also dispersing across a uniform environment. the landscape takes on a patchy, periodic spatial distribution. predator-prey models will look patchy if the predator is more successful than the prey at diffusive distribution – the patchiness is all that survives of the prey. this is called diffusive instability.

keystone species: Holling (1992) believes that ‘all ecosystems are controlled and organized by a small number of key plant, animal, and abiotic processes that structure the landscape at different scales.’ example of starfish keeping mussels in check – starfish is the keystone species.

dominant organisms can also affect the composition of the entire landscape, within the confines of the abiotic template. certain tree species may become dominant w/in a landscape, and their shade, water intake and evapotransporation, and leaf and seed dispersal may influence the growth and survival of less dominant surround plant species. a beaver dam creates a pond that may flood and alter up to 13% of the inundated landscape. it can saturate soils, resulting in different plant composition along the shore. american bison used to affect the vegetation along their migration paths b/c of what they ate, recycled, trampled. ‘large mammals will act as a mechnaism in pattern formation. more generally, large mammals often direclty alter vegeation and rates of nutrient recylcing.’ human civilazation? hmmm??

humans have altered land cover (habitat or vegetation type present, such as forest, agriculture, and grassland) according to varied land use (way in which and the purposes for which humans employ the land and its resources). resulting change in land cover by way of land use is – ready for this? – land use change! landscapes we may perceive to be natural today probably have a history of human influence that dates back a long time. in the 1600s, practically the entire eastern half of the contiguous 48 states was covered in forest. now forest is very sporadic, although there are areas of intense regrowth as industry in the eastern US has scaled down, most especially in the northeast.

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