Dynamics of Weed Populations by Roger Cousens

By Roger Cousens

Weeds have ecological attributes that confer the power to intervene with human actions. Roger Cousens and Martin Mortimer position weed administration inside of an ecological context, with the focal point at the manipulation of inhabitants measurement. they think about the dynamics of abundance and spatial distribution at either geographic and native scales, and examine the fundamental techniques of dispersal, copy and mortality including the criteria that effect them. The authors exhibit how administration modifies styles of habit which are intrinsic to populations, and word the evolution and administration of resistance to herbicides. This ebook offers weed technology with the conceptual foundation that has formerly been missing. It additionally provides ecologists and botanists entry to the wide database at the inhabitants ecology of weeds.

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The rate of increase, in terms of area added per unit time, will be given by the slope of the area versus time curve, d^4/d/; the instantaneous rate of increase, in terms of proportional increase in area per unit time, will be (dA/dt)/A. Consider the early phase of range expansion, before spread starts to become limited by site availability. If radial expansion away from a source is constant, we would expect (from simple algebra) the total area occupied to increase as a function of the square of time, and a plot of the square root of area against time will be linear.

Other predators, such as the cochineal insect Dactylopius opuntiae, are currently providing control in areas where C. cactorum has been less effective. Presumably, had the weed originally been imported with its predators, it would not have spread as rapidly, nor would it have totally dominated habitats. Spar Una anglica, cord grass, provides a notable example of an immigrant colonising a previously unoccupied habitat. It is a rhizomatous, deeply rooting, perennial grass which has become widespread as a pioneer species in salt marshes in the United Kingdom.

Another excellent example is provided by Forcella & Harvey (1988), who described the spread of several species in north-western USA from herbarium specimens (Fig. 5). They identified four dominant invasion routes, depending on the location of the initial invasion point. Invasions began (a) around Portland, Oregon, on the west coast and then spread eastwards, (b) in central Are there recognisable phases in the invasion process? 29 1880-1890 1891-1900 1901-1910 1911- 1921-1930 1971-1 Fig. 5. Spread of Bromus japonicus in north western USA, compiled from herbarium records (from Forcella & Harvey, 1988).

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