Seedling abundance and diversity following alien grass removal in a disturbed Hawaiian dry forest.
Thaxton, Jarrod*,1, Cole, Colleen1, Cordell, Susan1, Litton, Creighton2, Cabin, Robert3, Sandquist, Darren2, 1 USDA Forest Service, Institute of Pacific Islands Forestry, Hilo, HI2 California State University at Fullerton, Fullerton, CA3 Brevard College, Brevard, NC
ABSTRACT- Tropical dry forests are one of the most endangered forest types worldwide. In Hawaii, lowland dry forests presently cover less than 10% of their original area. Many sites that historically supported native forest are now dominated by alien species. In particular, the invasion of alien grasses such as African fountain grass (Pennisetum setaceum) has degraded remnant dry forests by altering ecosystem processes and limiting native species recruitment. Restoration has focused on grass removal followed by addition of native seeds or seedlings. However, restoration may be more feasible over large areas if grass removal alone results in native seedling establishment. To address this issue, we monitored native and alien seedling abundance and diversity in plots with different time since initiation of grass removal. All plots were located under intact native canopy and in areas that had experienced either short-term grass removal (<5 years), long-term grass removal (8-10 years) or no grass removal. Seedling abundance and diversity changed over time and differed among treatments. Native seedling diversity was highest in long-term grass removal. Results indicate that grass removal alone can be an effective restoration strategy when maintained over several years in areas with native canopy. In a second experiment, we quantified seedling diversity and cover following grass removal in a treeless area adjacent to native forest. We compared plots with different grass removal methods (bulldozing vs. weedwhacking + herbicide) and with or without outplanted native species. Seedling colonization patterns were affected by grass removal method, potentially due to differences in substrate conditions.
Key words: restoration, tropical dry forest, alien species removal
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