Weed life history: identifying vulnerabilities - Ecological Management of Agricultural Weeds - page 40

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Weed life history: identifying
vulnerabilities

Weeds from an ecological perspective

Weeds share certain ecological characteristics that distinguish them
from other plants. Specifically, weeds are plants that are especially successful at colo-
nizing disturbed, but potentially productive, sites and at maintaining their abundance
under conditions of repeated disturbance . That is, weeds are the plants that thrive
where soil and climate are favorable to plant growth, but disturbance fre-
quently reduces competition among plants to low levels.Unlike previous con-
ceptions of weediness (Baker, 1965; Harlan & de Wet, 1965; Buchholtz et al .,
1967),this ecologically based definition lacks reference to humans and human
disturbance. The species people refer to as weeds mostly existed prior to
human disturbance, and the repertoire of behaviors that makes them invasive
and persistent in human-dominated habitats largely evolved independently
of human society. Nevertheless, as discussed in Chapter 10, human activities
selectively modify weed characteristics such that weeds are becoming better
adapted to human disturbance regimes.
The subcategory of weeds dealt with in this topic consists of the weeds of
agriculture - specifically, the plants that colonize and increase in the distur-
bances created by farming. These are sometimes termed agrestal weeds, as dis-
tinguished from the ruderal weeds of roadsides, waste piles, and other
non-agricultural disturbances (Baker, 1965). Agricultural weeds share certain
life-history characteristics that adapt them for life on farms (Table 2.1). The
thesis of this chapter is that understanding life-history characteristics provides
insights into how weed management practices work and how they can be improved .In
particular, differences between weeds and crops in germination characteristics, seed size,
growth rate, and susceptibility of different life stages to stress provide weed management
options.
Relative to most ecosystems, agricultural fields are not stressful environ-

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