Technical Report #182.
Scheffler, P.Y., L.W. Pratt, D. Foote, and K.N. Magnacca. 2012. A
preliminary study of effects of feral pig density on native Hawaiian
montane rainforest vegetation.
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This study aimed to examine the effects of different levels of pig
density on native Hawaiian forest vegetation. Pig sign was measured
across four pig management units in the 'Ōla'a Forest from 1998 through
2004 and pig density estimated based upon pig activity. Six paired
vegetation monitoring plots were established in the units, each pair
straddling a pig fence. Percent cover and species richness of understory
vegetation, ground cover, alien species, and preferred pig forage plants
were measured in 1997 and 2003 and compared with pig density estimates.
Rainfall and hunting effort and success by management personnel were
also tracked over the study period. Vegetation monitoring found a higher
percentage of native plants in pig-free or low-pig areas compared to
those with medium or high pig densities, with no significant change in
the percent native plant species between the first and second monitoring
periods. Differences between plots were strongly affected by location,
with a higher percentage of native plants in western plots, where pig
damage has historically been lower. Expansion of this survey with more
plots would help improve the statistical power to detect differences in
vegetation caused by pigs. Because of the limited vegetation sampling in
this study, the results must be viewed as descriptive. We compare the
vegetation within 30 X 30 m plots across three thresholds of historical
pig density and show how pig densities can change in unanticipated
directions within management units. While these results cannot be
extrapolated to area-wide effects of pig activity, these data do
contribute to a growing body of information on the impacts of feral pigs
on Hawaiian plant communities.