New Zealand Journal of Botany abstract
Influence of vegetation structure on spatial patterns of seed deposition by
birds
R. N. FERGUSON
D. R. DRAKE
School of Biological Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand
Abstract The bird-disseminated species in the seed rain and
the soil seed bank were sampled on Mana Island, New Zealand, to assess the
importance of communally roosting starlings (
Sturnus vulgaris) as seed
dispersers. Density and species composition of dispersed seeds were compared
between forested sites and grassland, representing potential perch sites and
non-perch sites, respectively, to determine the influence of vegetation
structure on deposition patterns of bird-dispersed seeds. Mean density of
bird-dispersed seeds falling in forest was 3742 +/- 914 seeds m
-2
compared with 7.7 +/- 1.0 seeds m
-2 in grassland. This enormous
disparity was reflected in the seed bank, with mean densities of 86 852
+/- 16 579 and 883 +/- 189 seeds m
-2 for forest and grassland
sites, respectively. Species richness in forest ranged from 3 to 23 species
0.25 m
-2 for the seed rain, and from 1 to 19 species
0.002 m
-2 for the seed bank. Relative abundance of most species
differed between the seed rain and seed bank. The seed rain was dominated by
native woody species (66.9% relative density of identified species); alien
species comprised 26.6%. Native woody species were proportionally less
important in the seed bank (51.1%) which was instead characterised by an
increased proportion of alien species (45.3%), some of which may have
persistent seed banks. The potential role of frugivorous birds in facilitating
succession from grassland to native forest may be inhibited by a lack of
dispersal of native seeds into grassland areas, and by the longevity of seeds
of alien species in the soil.
Keywords ornithochory; seed bank; seed rain; starlings;
Sturnus vulgaris
B99009
Received 22 February 1999; accepted 14 September 1999
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