Protagonists of Healthy Ecosystems

Abstract

Large Herbivore Ecology, EcosystemDynamics and Conservation.Danell, K., R. Bergstr¨om, P. Duncan,and J. Pastor, editors. 2006. CambridgeUniversity Press, New York,NY. Conservation Biology Series 11.522 (xvi + 506) pp. {$}130.00 (hardcover).ISBN 0-521-83005-2. {$}65.00(paperback). ISBN 0-521-53687-1.Large mammalian herbivores are ofconcern to conservationists for theirown sake and because of the substantialimpacts they exert on vegetation,habitat conditions for other species,and ecosystem processes such as nutrientcycling. The stimulus for thisbook seems to have been the concernof European forest managers for theimpacts of expanding populations ofdeer and other ungulates on forest regeneration.Its chapters, however, reviewcurrentunderstanding of a comprehensiverange of ecological topicsbearing on this problem, from foragingbehavior through to predation.And, as Iain Gordon states in the finalchapter, ``large herbivores play avital role in the functioning of healthyecosystems.''Literature addressing the consequencesof grazing and browsing bylarge herbivores is quite widely scattered,and the chapters in general doan excellent job of synthesizing currentknowledge and understanding.The majority of the contributors arebased in Europe, and the remainderin North America, with just a singlerepresentative from south of theTropic of Cancer. The geographicalscope of the coverage, however, isnot narrowly north temperate zonebecause many of the contributorshave worked in other parts of theworld. Although these authors integratenorthern hemisphere findingswith those from Africa and SouthAmerica, for them Africa is representedmostly by the Serengeti ecosystem---a nutrient-rich and grassyextreme of the actual range of savannawoodlands in Africa.Nevertheless, ecologists and protected-area managers based in thesouth will gain much from the contentsof the various chapters, especiallythose in Africa worriedabout the impacts of elephants andrhinoceroses. I found two contributionsespecially interesting becauseof how thoroughly they challengedestablished dogma. Vera, Bakker, andOlff assembled evidence indicatingthat northern European (and perhapsNorth American) woodlandsof the past largely took the formof a ``wood-pasture'' mosaic, maintainedby the grazing impacts ofthe ancestors of domestic cattle andhorses, rather than the extensiveclose-canopy forests that are soughtby managers.Ward explains howherbivoresaffect even arid-land vegetationand outlines how the effect ofgrazing on the expansion of shrubthicket operates mainly during yearsof high rather than low rainfall. Bothof these chapters have major managementimplications. In the penultimatechapter Gordon addresses someof the issues in translating scientificunderstanding into management application,interpreted through conceptsof ecosystem health.Some striking contrasts emergingfromthe chapters remain unresolved.Forest managers in temperate latitudeshave viewed the demonstrablysevere impacts of large herbivoresas disastrous for forest establishmentand biodiversity, but couldbe persuaded by the broad ecologicalperspective of this book thatthese form part of a cyclic successionto be encouraged. Savanna managersin Africa south of the Serengetihave expected that some balance betweentrees and grasses would beretained in ecosystems with abundantbrowsers, but are confrontedby encroaching woody plants, andeven elephants seem to promote onlyshrubs. Are African trees and shrubsthat much tougher in their ability toresist browsing? Or are we in thesouth not recognizing the long timescales involved in the cyclic transitions?The concluding chapter suggeststhemes for further research,building on the scientific foundationprovided by earlier chapters, toguide more enlightened managementof the complexities of herbivore--ecosystem interactions.