State/Transition Models Flashcards
Disturbance Defn
White/Pickett (1985)
any relatively discrete event in time that disrupts ecosystem/community/pop structure and changes resource pools, substrate availability or physical characteristics
Abiotic Disturbances…
lightning
fire
wind
blizzars
drought
Biotic disturbances…
invasion (prairie dogs)
pathogens (dom sheep –> bighorn)
insects (beetle kill trees)
Anthropogenic disturbances…
human caused
ex: mines, fire (not always bad)
True/False: disturbance both creates and responds to spatial heterogeneity?
True
spatial heterogeneity is…
uneven distribution of species and landscape features
ex: strong wind event might create variability in vegetation cover (which then results in mature trees/new growth)
Ecological Resistance is…
capacity for community/population to remain relatively unchanged w/ disturbance introduced
Ecological Resilience is…
capacity for community/population to recover after disturbance
Succession is…
an orderly process of development, linear
Primary succession ends with…
climax community, stable
ex: pioneer stage (bare, lichen, small annual, grasses) to intermediate stage (grasses, shrubs, trees) to climax stage (shade-tolerant trees).
100’s of years…
how does secondary succession differ from primary?
largely the same but starts with a disturbance
Problems with linear succession include…
- demographic inertia (removal of disturbance may not result in successional progress - plant composition is dynamic)
- loss of plant materials (overgrazing certain species, drought, competition)
- fire feedback (grasses increase fire AND are promoted by fire)
- soil feedback (erosion, loss of seedbank, nutrients)
Clements Climax Model (linear succession) issues…
- doesn’t explain multiple states that are possible
- doesn’t incorporate processes that result in transitions and threshold changes
States Defn
represents one kind of stable plant community and its soil base (ex. grassland, shrubland)
Transitions Defn
process of change due to natural or mgmt actions (state <–> state)
Threshold Defn
points art which an abrupt change occurs in the structure/function of an ecosystem
*once you move past a threshold it is VERY difficult to go back
Alternative States Model implies that:
multiple alternate states can be stable
(looks more like a roller coaster than a straight line - with thresholds at the peaks, system states in the valleys, and resilience on the trek up the hill)
What is an STM? (State and Transition Model)
used to organize and communicate info re: ecosystem change –> especially for implications for management
Reference state
the state we want to get back to in an STM
Degraded state
requires mgmt/intervention in an STM
Land Classification is
compartmentalizing or classifying diff component of the landscape (ex: soil stratification, climate, plant composition)
Why?
1. used to build STM’s
2. gives us site potential
3. gives us info on where we are and where we want to go
Ecological Land Resource Hierarchy
Inverted triangle (most general, largest at top)
Land resource region
Major land resource area
land resource unit
general ecological sites
ecological sites
community/state
patch
MLRA (major land resource area)
geographically lumped by similar climate, soils, geology, biology
278 in US (43/44 in MT)
don’t make distinct mgmt decisions at this level
Ecological Sites
a kind of land with specific physical characteristics (soil, climate) which differs from other kinds of land in its ability to produce distinctive kinds/amounts veg. in response to mgmt.
*divides landscapes into basic units for study/mgmt
Ecological Site Concept
climatic, geomorphic (form of landscape/earth’s natural features/surface) and edaphic (physical characteristics w/out climate) similarities that predict community dynamics (ecological potential)
Ecological Site Descriptions (ESDs)
reports that provide detailed info about an eco-site
provide land use suitability (potential)
compile in a catalog maintained by ESIS (eco site info system)
