American Scientist

Natural Change and Human Impact in Madagascar. Steven M. Goodman and Bruce D. Patterson, eds. 432 pp. Smithsonian Institution Press, 1997. $35 paper.

The microcontinent of Madagascar is the world's second most recently discovered major landmass (after New Zealand), and there's little doubt that in a comparatively short time human activities have made a remarkable impact on the fauna, flora and landscapes of this 1,600-kilometer-long island, which is separated from the southeast African coast by some 480 kilometers of water. Objective assessment of the extent of this human impact, however, has been a long time coming. Perhaps this can be ascribed to two preponderant historical influences. Back in the late 18th century, the naturalist Philippe Commerson described the island as "the naturalists' promised land ... [where] ... you meet bizarre and marvellous forms at every step." Here we have an influential vision of a pristine natural paradise, untainted by the vile hand of man. In stark contrast, not much more than a century later the botanist Henri Humbert was moved to subtitle his review of Madagascar's vegetation "The destruction of an insular flora by [anthropogenic] fire." The portrait painted by Humbert was of an island that had been entirely covered by an amazingly species-rich variety of forests until the arrival of humans, with their graze-hungry cattle and slash-and-burn agriculture, set in motion a vast and rapid process of wholesale destruction.

Paradise in peril: a metaphor bound to appeal to anyone who knows Madagascar and its astonishing flora and fauna, and who has witnessed the island on fire each October, just before the rains arrive. At that time of year cattle herders ignite the grasslands to encourage the growth of new shoots, and in nighttime satellite images the island shows up more clearly than in daylight, as an almost uniform blaze of light. Yes; from the arid, xerophytic and highly endemic formations of the southwest of Madagascar, to the lush rain forests of the east, one can today see the island's native habitats inexorably disappearing in the face of cutting (some of it industrial) and burning. As indeed we could 30 years ago, at which time we were all saying, "In thirty years everything will be gone."

To take but one example, however, in the more than two centuries during which such descriptions have been made, not a single Malagasy mammal species that has been scientifically described in the living state is now known to have become extinct. The conclusion is unavoidable that the Malagasy environment is under extraordinary stress, and that habitats are disappearing daily. But, equally clearly, it has proved more resilient than Humbert or many of his successors would ever have imagined.

Madagascar is one of the world's most significant centers of botanical and zoological endemism, tending to be poor in major taxa but extremely rich within those taxa represented. Nonetheless, the huge variety of endemic species that are surviving today pales in comparison to what existed before human beings arrived on the island not too much more than 1,000 years ago. This loss of species in relatively recent times is particularly (though far from exclusively) evident among Madagascar's primates, of which at least a dozen species are now known only as subfossils. Particularly striking is the fact that these now-disappeared lemurs consist virtually exclusively of forms that were somewhat to hugely larger in size than those surviving today—a pattern that also appears to apply among other extinct vertebrates.

To some researchers the conclusion is thus evident that the species that became extinct were the slower-moving and thus more vulnerable forms that were at the same time most attractive to the human hunters to whom they succumbed. Others, however, have argued that climatic and consequent environmental changes also played a role, perhaps a critical one, in their disappearance. Until recently the evidence was exclusively inferential, but during the past decade or two various workers have begun specifically to investigate the extent to which the landscape and biota of Madagascar owe their modern form to the activities of people as opposed to natural agents. The result of a symposium held at Chicago's Field Museum in 1995, this valuable volume reports on much of this research. At the same time it considers aspects of the origin of the Malagasy biota and its future prospects.

Madagascar, it is now known, has been far distant from Africa since at least the mid-Cretaceous period. D. W. Krause, J. H. Hartman and N. A. Wells discuss the implications of this for the island's colonization by vertebrates, pointing out the possible significance of seamounts in the Mozambique Channel as potential island-hopping points. Of equal importance, they report on the Gondwanan aspect of the fauna they have recently begun to recover from terrestrial Late Cretaceous deposits in the island's northwest, and conclude that a pattern of waif dispersal to Madagascar has been characteristic ever since the late Mesozoic. That the immigrants found abundant ecological opportunities awaiting them is evident from the island's current endemic diversity, touched on (although no more) in several contributions that appear early in the book. Thus C. J. Raxworthy and R. A. Nussbaum focus on patterns of endemism among reptiles in eastern Madagascar (and find that they don't match classical categorizations of the vegetation zones); E. L. Simons surveys lemur origins, introduces the extinct lemurs and highlights the plight of several extant taxa; and P. P. Lowry II, G. E. Schatz and P. B. Phillipson revisit the classification of Malagasy vegetation types, concluding that even areas of "natural" vegetation are by now deeply penetrated by invading species.

One of the most curious Malagasy landforms is represented by "lavaka," deep erosion gullies that form on poorly vegetated laterite surfaces. N. A. Wells and B. R. Andriamihaja examine the complex processes by which lavaka are formed and find, contrary to received wisdom, that they do not invariably result from anthropogenic processes. This leads to a discussion of natural and human effects on the Malagasy landscape by D. A. Burney, who convincingly argues that since long before the arrival of human beings the history of Madagscar has been one of dynamic and fluctuating change, rather than the one of stability that was for so long assumed. In this view, ecological change on the island (including extinctions) has been the result of a large number of factors (including, latterly, human activities), all of which continue to operate in a process that poses an ongoing threat to those endemic species that still remain.

Several contributions examine aspects of species extinction and ecological degradation in greater detail. R. D. E. MacPhee and P. A. Marx kick off with a thoughtful but controversial essay on the potential role of disease in faunal extinctions worldwide, extending their argument to Madagascar only by implication. L. R. Godfrey, W. L. Jungers, K. E. Reed, E. L. Simons and P. S. Chatrath use "niche morphometrics" to compare past and present primate communities n the island, and they show that the extinctions were highly selective. S. M. Goodman and L. M. A. Rakotozafy conclude that the disappearance of many water birds in western and southwestern Madagascar predated human arrival. O. Langrand and L. Wilme examine the (deleterious) effects of forest fragmentation on bird diversity.

From the human perspective, H. T. Wright and J.-A. Rakotoarisoa look at evidence for early settlement in five areas of Madagascar, and find that locally its effects varied widely. Rakotoarisoa then discusses how the development of societies altered the relationships between people and environment, as does C. Radimilahy, drawing examples from the northwestern site of Mahilaka. R. E. Dewar's useful contribution is concisely summarized in its title, "Were People Responsible for the Extinction of Madagascar's Subfossils, and How Will We Ever Know?" To the latter half of his question his answer appears to be, "with difficulty."

The final section of the book looks to the future. P. C. Wright surveys the prospects for conservation in Madagascar from the vantage point of Ramomafana National Park, detailing several lessons learned there that will be advantageously applied elsewhere. A. F. Richard and S. O'Connor take a broader island-wide perspective, examining the goals of effective conservation programs and ways of attaining them. They do not shrink from the evident difficulties, but end their remarks, and the volume, on an optimistic note.

This collection does an enormous service in pulling together the work of so many of the small band of researchers who are actively engaged in research on the multifarious processes and victims of environmental degradation in Madagascar. At the same time, it shows clearly that what we do know is but the tiniest fraction of what we do not. Partly because of our fragmented knowledge, it is not an easy entry into the field it surveys. But entry could nonetheless have been made easier; although the symposium from which it emerged necessarily focused on specific problems and studies, the published book would be more readily accessible to the nonspecialist reader if it included a section surveying the threatened biota of Madagascar in a more systematic way than is found in any of the contributions published here. Don't let this put you off, though; despite its spotty coverage this book is a landmark in the study of the interactions of people and biota on one of the world's most singular landmasses.—Ian Tattersall, Anthropology, American Museum of Natural History