Abstract
Separating the threats that habitat loss and habitat fragmentation pose to biodiversity is challenging because these processes usually occur simultaneously. Additionally, their importance may be underestimated due to time-delayed extinction. In central Texas savannas, woody plant encroachment reduces the amount of habitat available to herbaceous species while fragmenting remaining habitat. We examined the relationships between present species richness and present and past habitat amount and fragmentation (measured as fractal dimension) using a series of aerial photographs taken over nearly 60 years. We show that woody plant encroachment, a common phenomenon in savannas worldwide, reduces the diversity of herbaceous vegetation through both habitat loss and fragmentation. Habitat loss has the strongest impact on species richness over short time spans and small spatial scales in these savannas. Habitat fragmentation, however, has the strongest impact over longer time spans and larger spatial scales and generates long-term extinction debts. We also demonstrate that examining habitat loss and habitat fragmentation across different time periods and at different spatial scales is essential for understanding their joint and individual effects on plant community composition.
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Acknowledgments
We thank S. Meadows, G. Casares, L. Aguilar, H. Gillespie, and H. López-Fernández for assistance with field work; the staff at Balcones Canyonlands National Recreation Area, Pedernales Falls State Park and Freeman Ranch (Texas State University) for access to research sites; Texas Natural Resources Information System for allowing us to scan historical aerial photographs in their collection; D. Murray and J. White for providing scanned aerial photographs of Balcones in 1951 and 1980; and three anonymous reviewers. We are grateful for funding from a National Science Foundation (NSF) Doctoral Dissertation Improvement Grant (DEB-0710348 KMA and NLF), NSF Graduate Research Fellowship Program (KMA), and Ariel Appleton Fellowship from the Research Ranch Foundation (KMA).
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Communicated by K. Harper.
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Alofs, K.M., González, A.V. & Fowler, N.L. Local native plant diversity responds to habitat loss and fragmentation over different time spans and spatial scales. Plant Ecol 215, 1139–1151 (2014). https://doi.org/10.1007/s11258-014-0372-5
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DOI: https://doi.org/10.1007/s11258-014-0372-5