State/Transition Models

Question 1

Disturbance Defn

Answer 1

White/Pickett (1985)

any relatively discrete event in time that disrupts ecosystem/community/pop structure and changes resource pools, substrate availability or physical characteristics

Question 2

Abiotic Disturbances…

Answer 2

lightning
fire
wind
blizzars
drought

Question 3

Biotic disturbances…

Answer 3

invasion (prairie dogs)
pathogens (dom sheep –> bighorn)
insects (beetle kill trees)

Question 4

Anthropogenic disturbances…

Answer 4

human caused
ex: mines, fire (not always bad)

Question 5

True/False: disturbance both creates and responds to spatial heterogeneity?

Answer 5

True

Question 6

spatial heterogeneity is…

Answer 6

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)

Question 7

Ecological Resistance is…

Answer 7

capacity for community/population to remain relatively unchanged w/ disturbance introduced

Question 8

Ecological Resilience is…

Answer 8

capacity for community/population to recover after disturbance

Question 9

Succession is…

Answer 9

an orderly process of development, linear

Question 10

Primary succession ends with…

Answer 10

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…

Question 11

how does secondary succession differ from primary?

Answer 11

largely the same but starts with a disturbance

Question 12

Problems with linear succession include…

Answer 12

1. demographic inertia (removal of disturbance may not result in successional progress - plant composition is dynamic)
2. loss of plant materials (overgrazing certain species, drought, competition)
3. fire feedback (grasses increase fire AND are promoted by fire)
4. soil feedback (erosion, loss of seedbank, nutrients)

Question 13

Clements Climax Model (linear succession) issues…

Answer 13

1. doesn’t explain multiple states that are possible
2. doesn’t incorporate processes that result in transitions and threshold changes

Question 14

States Defn

Answer 14

represents one kind of stable plant community and its soil base (ex. grassland, shrubland)

Question 15

Transitions Defn

Answer 15

process of change due to natural or mgmt actions (state <–> state)

Question 16

Threshold Defn

Answer 16

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

Question 17

Alternative States Model implies that:

Answer 17

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)

Question 18

What is an STM? (State and Transition Model)

Answer 18

used to organize and communicate info re: ecosystem change –> especially for implications for management

Question 19

Reference state

Answer 19

the state we want to get back to in an STM

Question 20

Degraded state

Answer 20

requires mgmt/intervention in an STM

Question 21

Land Classification is

Answer 21

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

Question 22

Ecological Land Resource Hierarchy

Answer 22

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

Question 23

MLRA (major land resource area)

Answer 23

geographically lumped by similar climate, soils, geology, biology

278 in US (43/44 in MT)

don’t make distinct mgmt decisions at this level

Question 24

Ecological Sites

Answer 24

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

Question 25

Ecological Site Concept

Answer 25

climatic, geomorphic (form of landscape/earth’s natural features/surface) and edaphic (physical characteristics w/out climate) similarities that predict community dynamics (ecological potential)

Question 26

Ecological Site Descriptions (ESDs)

Answer 26

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)