Biology and anthropology of plant invasions - Invasive Plants: Ecological and Agricultural Aspects - page 209

community (neighbors), with which the individual phenotype interacts.
Disturbance of plant communities can be human-mediated or not. Disturbance
possesses dimensionality. Disturbance can be understood by considering the
biological community structure, and the abiotic environment, influencing the
community at a locality (the population) and microsite (the individual) (Tab. 1).

Vulnerability to disturbance
The susceptibility and sensitivity of a locality or microsite to invasion varies
with the robustness and resistance of a local community. The vulnerability of
habitats to invasion is often a function of the extent of direct and indirect dis-
turbance by humans.
Ironically, many agroecosystems have stable weed communities that resist
invasion by new species. Weed populations often are stable due to the high,
consistent level of disturbance management of these controlled systems.
Population shifts are most likely to occur in these agriculture fields when crop
management tactics change, e.g., introduction of new herbicides or herbicide
resistant crops [5]. Disturbed habitats are often more vulnerable to invasion
due to the fact that direct and indirect disturbance can change the ecological
balance within these unmanaged biological communities, creating new oppor-
tunities (e.g., plant community changes due to the loss of large herbivores with
human colonization of North America).

Table 1. Dimensions of disturbance regimes (spatial, temporal, biological community, abiotic envi-
ronment), disturbance factors within each dimension, and examples of factors

Disturbance Disturbance factor Examples

dimension

Spatial • proximity of effect: direct or • direct, localized: lightning

indirect strike spot in field

• localized or widespread • indirect, widespread: highway

• heterogeneity and fragmentation corridor effects on adjacent forests

• variable erosion and drainage
effects with landscape elevation

Temporal • severity: quantity, frequency • cycles: annual winter soil freezing

and duration • crashes: yearly tillage of crop field

• regularity and predictability of • catastrophes: removal of tropical

patterns rain forests

Biological • competitive neighbor interactions • competitive exclusion by earliest

community • specificity and vulnerability: emerging seedling in field

sensitivity and resistance • response to predators, parasites

• change in biodiversity and diseases

• increase in prairie fires with loss of
large herbivores

Abiotic • resource availability • drought

environment • inhibitors and stress • herbicides

• climate and weather • winter freezing of soil