Jl. Gonzalez-andujar et al., Modeling effects of spatial patterns on the seed bank dynamics of Alopecurus myosuroides, WEED SCI, 47(6), 1999, pp. 697-705
A spatially explicit metapopulation neighborhood model was extended to enco
mpass the seed bank dynamics of the annual weed Alopecurus myosuroides Huds
. (blackgrass), growing in U.K. winter wheat crops established after noninv
ersion tillage. The effects of the initial spatial pattern of infestation,
herbicide, and combine harvesting on seed bank densities and on expected yi
eld losses of the infested crop were studied within a 634 m(2) area. In the
absence of herbicide, all seed bank populations were large and typical of
values in the literature; those with patchy initial distributions spread qu
ickly over the entire held. The effects of intraspecific competition ensure
d that even after 10 yr, the average seed bank density from three patterns
with the same initial density consistently retained the same rank order: th
e initially uniform pattern consistently ranked largest; a patchily distrib
uted moderate infestation ranked next; a more patchily distributed heavy in
festation ranked least. Expected grain yield losses sometimes exceeded 40%.
With the introduction of a herbicide, seed densities declined exponentiall
y but the rank order with regard to spatial pattern remained. Relatively de
nse patches occasionally persisted for longer than 10 yr. The economic thre
shold for treatment was achieved within 2 and 5 yr, depending on the infest
ation pattern, but the model predicted that it would take many more than 10
yr before infestations could be completely eliminated. The effects of harv
esting by combine were modeled. In all cases, the speed of the spread of in
festation along a row appeared to be largely due to the combine rather than
to natural dispersal or other cultivation practices. The proportion of see
ds removed by the combine was an important determinant of the number of yea
rs required to drive the population below the economic threshold and of the
probability of long-term eradication of the weed metapopulation.