Landscape Ecology - Lecture
Notes
Landscape Pattern and
Ecosystem Processes
[From Bailey 1996]
I. Mechanisms for
movement of energy, materials and species in landscape mosaics
A. Major vectors
(1) Wind
- Carries heat energy, water, dust, pollutants, nutrients,
propagules, organisms, etc.
(2) Water
- Carries mineral nutrients, seeds, insects, sewage,
fertilizers, pollutants, etc.
(3) Flying animals (e.g., birds, bats, bees)
- Carry fruits, seeds, spores and insects in feathers, feet,
and the gut
(4) Ground animals (e.g., mammals, reptiles)
- Carry seeds, fruits, spores, insects, etc.
(5) People (use of vehicles)
- Carry organisms, seeds, fruits, spores, insects, nutrients,
etc.
B.
Main forms (or forces) of movement
II. Landscape
pattern and spatial distribution of energy and materials
- The spatial distribution of biomass, ecosystem productivity,
and biogeochemical processes are closely related to the spatial
pattern of the landscape (e.g., vegetation types, hydrological
regime, topographic variation, disturbance regime, climatic
variation, etc.)
- Main causes:
- Climatic factors (temperature, precipitation)
- Soil heterogeneity
- Topographic variations
- Animal activities (e.g., selective foraging)
[From Bailey 1996]
- Example: Ecosystem properties and processes vary
spatially across the landscape.
III. Movement of
nutrients and energy among ecosystems is affected by landscape
pattern
- Both the composition and configuration of landscapes (e.g.,
land cover types, diversity, connectivity, and boundary
characteristics) affect flows of materials, energy, and
organisms in landscape mosaics.
- Flows of different types affected by and affect landscape
pattern
- Ecosystem processes: primary productivity,
biogeochemical cycling, decomposition
Figure caption: Movement of nutrients and major
pathways between ecosystems on the Rhode River watershed,
Maryland (Drawn based on data from Peterjohn and Correll
1984; cf. Turner et al. 2001)
- Margalef's (1963) hypothesis: In considering flows
between adjacent ecosystems or elements, the younger may
operate as a source of energy or material, and the more mature
as a sink or recipient (also see Risser 1990).
- Example: Lateral flows in landscapes and effects on
ecosystem processes
- Stury area and field sampling
- The
universal soil loss equation (USLE):
A = f(R, K, L, S. C) or:
A = f(R, K, L, S. C, P)
A - amount of soil eroded
R - rainfall intensity
K - soil erodability factor
L - length of the slope
S - angle of the slope
C - vegetation cover
P - supporting practices factor
The Universal Soil Loss Equation (USLE) does not account for
landscape heterogeneity, a measure of spatial configuration or
juxtaposition of landscape units needs to be incorporated
(Risser 1990). Efforts have been made to incorporate
landscape heterogeneity into the universal soil loss equation,
resulting in revised universal soil loss equations (RUSLE).
- Example:
Land use and land cover change alters the spatiotemporal
pattern of ecosystems (e.g., urbanization)
IV. Effects of landscape
fragmentation on ecosystem dynamics
[Excerpt from J. Wu (2009). Ecological dynamics in fragmented
landscapes. In: Simon A. Levin (ed). Princeton Guide to
Ecology. Princeton University Press, Princeton.]
Ecosystem
ecology, the study of energy flow and material cycling
within an ecosystem composed of the biotic community and its
physical environment, traditionally has adopted a systems
perspective, which emphasizes stocks, fluxes, and interactions
among components without explicit consideration of spatial
heterogeneity within the system and effects of the landscape
context. With the rapid development of landscape ecology
since the 1980s, more and more ecosystem studies have adopted a
landscape approach that explicitly deals with within-system
spatial heterogeneity and between-system exchanges of energy and
matter.
An increasing
number of recent studies have shown that landscape fragmentation
can influence ecosystem dynamics in several ways. First, the loss and creation
of patches directly change the spatial distribution of pools and
fluxes of energy and materials in the landscape (e.g., biomass,
ecosystem productivity, nutrient cycling, decomposition,
evapotranspiration). Second,
the altered configuration of landscape elements, particularly
introduced edges and boundaries, may not only affect the flows
of organisms but also the patterns of lateral movements of
materials and energy within and among ecosystems (e.g.,
hydrological pathways and erosion-deposition patterns). Third, landscape
fragmentation can affect ecosystem processes through
microclimatic modifications due to altered surface energy
balance (e.g., changes in albedo, radiation fluxes, soil
temperature, soil moisture, wind profile and pattern) especially
near the boundaries of remnant patches (edge effects). Fourth, all the effects of
landscape fragmentation on population dynamics and species
persistence have bearings on ecosystem processes because both
plants and animals play an important role in ecosystem
processes.
Landscape approach to ecosystem dynamics
A landscape
approach to ecosystem dynamics is characterized by the explicit
consideration of the effects of spatial heterogeneity, lateral
flows, and scale on the pools and fluxes of energy and matter
within an ecosystem and across a fragmented landscape (Turner
and Cardille 2007). This new approach to ecosystem studies
highlights the fact that ecosystems are neither homogeneous
internally nor closed externally. Such a perspective seems
in sharp contrast with the traditional equilibrium view that
ecosystems are self-regulatory, self-repairing, and homeostatic,
and is particularly appropriate when fragmented landscapes are
considered. Guided by this spatial approach, several key research questions have
emerged: How do the pools of energy and matter and the rates of
biogeochemical processes vary in space? What factors
control the spatial variability of these pools and
processes? How do land use change and its legacy affect
ecosystem processes? How do patch edges, boundary
characteristics, within-system spatial heterogeneity, and the
landscape matrix influence ecosystem dynamics and
stability? How do ecosystem processes change with scale
and how can they be related across scales (i.e., scaling)?
How do the responses of populations and ecosystem processes to
landscape fragmentation interact? How do the composition
and configuration of fragmented landscapes affect the
sustainability of landscapes in terms of their capacity to
provide long-term ecosystem services?
A landscape
approach to ecosystem dynamics promotes the use of remote
sensing and GIS in dealing with spatial heterogeneity and
scaling in addition to more traditional methods of measuring
pools and fluxes commonly used in ecosystem ecology. It
also integrates the pattern-based horizontal methods of
landscape ecology with the process-based vertical methods of
ecosystem ecology, and promotes the coupling between the
organism-centered population perspective and the flux-centered
ecosystem perspective.
V. Future directions
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