Importance of fragmentation-tolerant species as seed dispersers in disturbed landscapes |
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Authors: | Jeffrey E Moore Robert K Swihart |
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Institution: | (1) Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907-2061, USA;(2) Duke Center for Marine Conservation, Duke University Marine Laboratory, 135 Duke Marine Lab Road, Beaufort, NC 28516-9721, USA |
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Abstract: | Forest fragmentation can negatively affect plants if animal seed-dispersers become locally extinct in fragments. We conducted
a 2-year experiment to evaluate the importance of tree squirrels (Sciurus) as seed dispersers for Quercus, Carya, and Juglans, and to assess dispersal consequences in patches where fragmentation-sensitive eastern gray squirrels (Sciurus carolinensis) are absent. We accounted for fates of ∼15,700 seeds from five tree species in four exclosure treatments at 18 fragments
during a high (2003–2004) and low seed (2004–2005) year. Two treatments excluded Sciurus to mimic disperser loss. We sampled nut-tree seedling density at 259 sites across eight watersheds, half of which were too
fragmented to support S. carolinensis, but supported fragmentation-tolerant fox squirrels (Sciurus niger). Autumn-to-spring seed survival was low (∼1%) for all species during low seed production. During high seed production, survival
was higher for Juglans nigra (20%) and Carya ovata (16%) than for three Quercus species (∼4% for Quercus palustris and Quercus rubra in two exclosure types; ∼1% for Quercus alba in all treatments). Survival of J. nigra, C. ovata, and Q. rubra was ≥2.1–7.7 times higher for seeds in exclosures that Sciurus could access. Seed displacement distance was higher in the low seed than the seed-rich year, but the proportion of seeds
surviving to greater distances was higher in seed-rich years for all seed types except Q. rubra. This affirms the importance of masting to seed survival and dispersal, but also suggests an advantage to trees of producing
seed in non-mast years. Seedling densities were comparable in watersheds with and without S. carolinensis. These results demonstrate the importance of tree squirrels as dispersers of nut-bearing trees, but suggest that fragmentation
may not disrupt dispersal of certain species if losing S. carolinensis from disturbed landscapes is compensated for by fragmentation-tolerant fox squirrels (S. niger). |
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Keywords: | Carya Central hardwoods Forest fragmentation Masting Juglans |
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