Defining a regional approach for invasive plant research and management - Invasive Plants: Ecological and Agricultural Aspects - page 133

an important factor accounting for the ability of P. recta to dominate certain
forest and meadow sites in northeastern Oregon.
Seed dispersal
Dwire et al. [65] quantified seed production and measured seed dispersal of P.
recta in different habitats in northeast Oregon. Seed dispersal was measured by
using sticky traps that surrounded individual source plants. Seed production,
distance of seed dispersal, and timing and duration of seed dispersal were
measured. Results indicated that the 83% of the seeds that were produced dis-
persed within 60 cm from the mother plant. This is an insufficient distance to
adequately explain the rapid spread of P. recta across the region and dispersal
over longer distances than 60 cm appears to be critical for P. recta spread.
Newbert and Caswell [66] and Caswell et al. [67] indicate that dispersal of rel-
atively few seeds at the edge of an expansion 'wave' can account for the rapid
spread of many invasive organisms (Fig. 5). Therefore we are initiating other
studies to identify mechanisms of longer-distance dispersal of this and other
plant species.
Figure 5. Hypothetical relationship of dispersal distance to dispersal wave speed.
Dispersal and herbivory
Domestic and wild mammal and avian herbivores may contribute to plant inva-
sions by seed transport of invasive plants into previously uninhabited sites
through endozoochory [68]. This phenomenon occurs when animals consume
seeds in one area and later regurgitate or defecate them in another. Invasive
species with thick seed coats dispersed by endozoochory, in addition to bene-
fiting from transport, may have enhanced germination as a result of scarifica-