Both social and engineering factors must be further explored and scrutinized across the globe—as should notions of justice related to flooding impacts and responses.
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Edited by William J. Sutherland, University of Cambridge, Cambridge, United Kingdom, and accepted by the Editorial Board February 4, 2014 (received for review June 25, 2013)
Significance
Megafaunas have been decimated worldwide during the last 50,000 y, with poorly understood ecosystem consequences. In Europe, the ability of the extinct megafauna to generate structurally diverse vegetation within the temperate forest biome is controversial and has important implications for conservation management. We used paleoecological beetle data to reconstruct the abundance of large herbivores and the vegetation structure in Great Britain before and after the megafaunal extinctions. We found indications of high abundances of large herbivores and a mosaic of closed forest and wood–pasture vegetation in the last interglacial period and primarily closed forests with lower herbivore abundance in the early Holocene. These findings support an important role for large herbivores in driving vegetation dynamics and in current efforts to promote landscape diversity through rewilding.
Abstract
The impact of large herbivores on ecosystems before modern human activities is an open question in ecology and conservation. For Europe, the controversial wood–pasture hypothesis posits that grazing by wild large herbivores supported a dynamic mosaic of vegetation structures at the landscape scale under temperate conditions before agriculture. The contrasting position suggests that European temperate vegetation was primarily closed forest with relatively small open areas, at most impacted locally by large herbivores. Given the role of modern humans in the world-wide decimations of megafauna during the late Quaternary, to resolve this debate it is necessary to understand herbivore–vegetation interactions before these losses. Here, a synthetic analysis of beetle fossils from Great Britain shows that beetles associated with herbivore dung were better represented during the Last Interglacial (132,000–110,000 y B.P., before modern human arrival) than in the early Holocene (10,000–5,000 y B.P.). Furthermore, beetle assemblages indicate closed and partially closed forest in the early Holocene but a greater mixture of semiopen vegetation and forest in the Last Interglacial. Hence, abundant and diverse large herbivores appear to have been associated with high structural diversity of vegetation before the megafauna extinctions at the end of the Pleistocene. After these losses and in the presence of modern humans, large herbivores generally were less abundant, and closed woodland was more prevalent in the early Holocene. Our findings point to the importance of the formerly rich fauna of large herbivores in sustaining structurally diverse vegetation in the temperate forest biome and provide support for recent moves toward rewilding-based conservation management.
Footnotes
- ↵1To whom correspondence may be addressed. E-mail: chris.sandom81{at}gmail.com or svenning{at}biology.au.dk.
Author contributions: C.J.S. and J.-C.S. designed research; C.J.S. performed research; M.D.D.H. provided specialist information on beetles; C.J.S., M.D.D.H., and J.-C.S. analyzed data; and C.J.S., R.E., and J.-C.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. W.J.S. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1311014111/-/DCSupplemental.
Freely available online through the PNAS open access option.
Large herbivores and interglacial ecosystems
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