LANDSCAPE PATTERN- HIGHER LEVEL CONSTRAINTS

Recall from hierarchy topic reading that at different levels in a hierarchy, a variable influencing a process at a focal level may or may not change, but a shift in relative importance of variables occurs

Level of focus constrained by higher level variables Lower level variables often explanatory E.g., leaf litter decomposition from last week. (What is constraint? What are explanatory components?) From Turner, Gardner, and O’Neill 2001

Urban et al. 1987 (Bioscience)- hierarchy of landscape patterns - Result of biotic processes operating in response to disturbance regimes - Within environmental constraints Climate- highest level of atmospheric conditions From Urban et al. 1987

Climate definition -- composite, long-term weather of a region, that acts as the primary control for ecosystem distribution as source of energy and water (Bailey 1995). Response to latitude - variation in solar energy- controls both temperature and moisture distribution. Different temporal scale than weather, e.g., daily fluctuations Higher spatial level than microclimate, e.g., N and S sides of hill

- Continental position- differential heating and cooling of land and water-- Land responds quicker - Prevailing winds, coastal ocean temperatures. - Continent interior- cold month isotherms bend toward equator.       warm month isotherms bend toward pole. - Both above modified by elevation or landform. From Bailey 1998

CLIMATIC REGIME - pattern of diurnal and seasonal fluxes of energy and moisture.

LANDFORM - Next level down in hierarchy of constraints Modifies, is modified by, climate Provide the template for disturbance and biotic responses.

Swanson et al. (1988) - role of landforms and geomorphic processes in structuring landscapes From Bailey 1998

Climate and landform interact at all scales (continental to landscape to site). Because elevation, aspect, and surface texture interrupt air masses, influence energy input from sunlight, and precipitation.

(e.g., Greater insolation on south slopes causes warmer sites, greater evapotranspiration). From Bailey 1998

(e.g., Elevation can cause rain shadow effect in rugged terrain.) From Bailey 1998

(e.g., Elevation can cause rain shadow effect in rugged terrain.) From Bailey 1998

Landforms interact with climate, increase, decrease susceptibility to disturbance. (Constraining lower levels). e.g., sheltering/exposing forest to windthrow, greater vulnerability of ridges to fire ignition, or barriers to fire spread.

Landforms also play role in water movement and concentration, and soil development differences. Topography and gravitational movement of water, and evapotranspiration create a toposequence or catena of soils.

- Weathering of rock and movement of particles down slope results in deeper, finer textured soils. - Greater water holding capacity; productivity. - Greater organic matter development, movement down, continues to build soil. From Bailey 1998

Climate controls biota, soils, resulting ecosystem pattern From Bailey 1998

Climate controls several large scale processes - Hydrologic cycle Landforms and erosion cycles Plant/animal life cycles and distributions Fire and wind disturbance regimes

Hydrologic cycle Pattern of precipitation and evapotranspiration. e.g., pattern of annual streamflow varies in diff. climate regions depending on seasonality of precipitation, temperature, evaporation, transpiration by plants.

Landforms and erosion cycles e.g., Erosion rates vary with rock type, but also whether climate supports soil development, adequate moisture for vegetative cover.

Plant/animal life cycles and biogeographic distribution Life cycles - e.g., periods of activity, dormancy, reproduction, adjust to seasonal patterns of precipitation/moisture

Fire and wind disturbance regimes e.g., amount of plant productivity, frequency and seasonality of dryness influence type of fire regime.

Western ponderosa pine - frequent, low intensity ground fires, trees survive. e.g., boreal forest - infrequent fires, but intense, crown fires, stand initiating.

Whittaker (1952, 1953) sampled vegetation across a range of montane habitats, spanning elevation and aspect differences; microclimatic- landform controlled. Found that species responded individualistically to changing environment. But communities could be discerned within environmental space defined by elevational and aspect gradients.

From Whittaker 1956

Similar to what John Curtis and students were doing here at same time across S. Wisconsin. Not strong topographic gradient here, but sites along moisture/nutrient gradient.

Converted to contour diagrams. Neilson et al. series of papers (1983, 1986, 1987, 1992)- examined large-scale regional and continental climate data spatially and temporally. Used weather station transects across U.S. and major biomes with characteristic composition and physiognomy. Plotted monthly 30 yr. mean temperature and precipitation. Converted to contour diagrams.

From Neilson et al. 1992

- Interpreted seasonal changes along transects in terms of biome ecotones affecting distribution of plant formations and species.   From Neilson et al. 1992

- Also did temporal transects for given locations to examine climate changes and species establishment "windows". Suggested that at ecotones, gradients converge, less habitat amplitude for a regional plant formation or species. - Interaction with landforms- in heterogeneous landscape, smaller suitable habitats.       But greater habitat patch diversity.       E.g., (species) jack pine in Wis. vs. boreal forest.       (Communities) prairie/forest border From Neilson et al. 1992

Stephenson (1990) described past studies using annual energy (temperature) and precipitation to relate climate to vegetation Either directly, or indirectly through ratios Relate climate to vegetation formations (physiognomy- plant growth form, e.g., graminoid, shrub, trees- needle-leaved evergreen vs. broad-leaved deciduous.

Many used potential evapotranspiration- Given climate and energy (annual temp.) available at a site, evaporative water loss assuming complete plant cover and unlimited water available. Assumes temp. and precip. independent- does not distinguish well between climates with similar annual energy and moisture, but different seasonal distribution. e.g., PNW and NE U.S.- similar, but different vegetation.

- Stephenson used WATER BALANCE- actual evapotranspiration and deficit. ACTUAL EVAPOTRANSPIRATION- evaporative loss with prevailing energy and available, not unlimited, water. and DEFICIT (diff. of potential and actual evapotranspiration). Climate as sensed by plants- interaction of energy and water in the environment.

- better accounts for seasonal interaction of water and energy balance. - E.g., better discriminates sites of conifers vs. hardwoods in regions with similar mean annual temp. and precip. but diff. seasonal interactions of water and energy. Found better relationship of vegetation patterns and water balance than traditional approach- From Stevenson 1990

Below large scale geomorphology or landform levels, Landscape position has been shown to be important in causing pattern in many different systems, many systems with relatively little relief.

Lakes in a toposequence in northern Wisconsin (Kratz et al. 1991). Great Plains grasslands (Sala et al. 1988; Woodmansee 1990 in Zonneveld and Forman; Arctic tundra terrestrial toposequenceShaver et al. in Turner and Gardner 1991).

Bogs and patterned peatlands in cool temperate regions are another example of a large, complex landscape system that is controlled by close climate and landform interaction, with a major role played by above and below ground hydrology. Most simply, small bogs are wetlands. Like other wetlands- within upland matrix- water table at or near surface. Landform controlled at this simple level, assuming relatively constant climate.

Larger peatland landscapes can be very complex Large areas- matrix. Cool wet climate, low evapotranspiration. Flat or slightly sloping, poor substrate permeability. Low oxygen, decomposition- peat accumulation. Can also occur on steeply sloping landforms, under right climate.

Ombrotrophic bogs - low pH, largely on woody peat, low nutrient availability, largely atmospheric inputs of water and nutrients. Minertrophic bogs or fens - groundwater inputs, higher nutrient avail. and pH. Large differences on within-peatland formations, species composition.

From Glaser

David Foster found similar patterns in Labrador peatlands, as well as biological mechanisms responsible for development of finer scale patterns of open water over time, within the bog vegetation. This finer scale pattern was different than that in Minnesota. Presumably because of greater seasonal drying in Minnesota which affects an entire flat peatland. More constant moisture in Labrador allows development of finer-scale heterogeneity caused by differential peat accumulation and vegetation degradation.

Foster and King (1986) studied forest vegetation pattern in Labrador, looking at climate and landform interactions. Studied fire and physiography role in distribution of paper birch forest patches within matrix of spruce-fir. Found nearly all birch forest patches on steep slopes of ridges with high moisture.

From Turner, Gardner, and O’Neill 2001 - Lightning strikes hit ridge tops in spruce-fir, which is more fire susceptible. - Fires move down ridges, opening patches for birch colonization. - fires stopped by existing birch patches, or wetlands/streams in valley bottoms. - birch intolerant, succeeds to spruce-fir after 100 yrs.   Figure 4.6 Distribution of Betula papyrifera forests (black) on the hillslopes and canyon walls of the St. Augustine River Valley, southeast Labrador. Adapted from Foster and King 1986. From Turner, Gardner, and O’Neill 2001

Foster and Boose (1992)- related study in New England used GIS to analyze correlates of severe hurricane damage to forests. Found slope and aspect highly correlated with increasing damage. As well as tree height and species composition. Damaged stands 3% in topographically protected sites, 31% intermediate, 66% exposed. Damage increased linearly with tree height.

Eric Grimm (1984) studied Big Woods of SE Minnesota Region of mesic forest within oak/prairie transition Historically puzzling location for elm, maple, basswood Found no correlation of pre-European vegetation with climate gradient Landform (fire breaks), and soils most important.

We will look in more detail at research examining ecosystem processes that relate to landscape and landform pattern a little later in the course. From Bailey 1998