Homage Due


Global Patterns of Plant Diversity: Alwyn H. Gentry's Forest Transect Data Set. Miller, O. P., and J. S. Miller . 2002 . Monographs in systematic botany. Missouri Botanical Garden Press , St. Louis . 335 pp. $45.00. ISBN 0-915279-12-6 .

This unusual book is the legacy of the vision and hard work of Alwyn Gentry, whose life was cut short by a tragic airplane accident in 1993. This book is perhaps the best testimony to this Missouri Botanical Garden scientist's remarkable career, similar in trajectory to those of some of the great tropical botanists of the nineteenth and twentieth centuries. In most cases, these botanists began their studies and careers in systematics, either in floristics or in taxonomic revisions. Grappling with the biodiversity within a group or region was the springboard for speculation and research on the broader questions of ecology and evolution. Such nineteenth-century greats as Joseph Hooker and A. H. Ridley and twentieth-century luminaries as A. J. H. Corner and C. G. G. J. van Steenis come to mind. Late in the twentieth century, the study of biodiversity in the tropics took on a new urgency as we became more aware of its fragility in the face of enormous pressures for extraction and development. Systematists again rose above their original research foci to grapple with issues of evolution and conservation. The work of Peter Ashton on the Dipterocarpaceae, speciation in the tropics, and then sustainable tropical forestry, as well as that of Ghillean Prance on the Lecythidaceae and biodiversity conservation in the Neotropics, are two good examples. Gentry's own director, Peter Raven, moved beyond his systematic knowledge of the Onagraceae to forge new ideas in evolution and became a leading spokesperson on the threats of extinction and the need to conserve biodiversity.

We can only speculate on how much further Alwin Gentry would have gone in his research on the origins of plant diversity in the Neotropics and his path-breaking work in strategies for conserving biodiversity. Unlike Raven, Gentry wasn't the administrative type, perhaps too plainspoken and lacking in the needed elegance, but he would have continued to help discover more biodiversity hotspots and new concepts about the forces creating plant and ecological diversity in the tropics. Botanists, conservationists, and many others still grieve his loss a decade later.

The problem faced by plant biologists concerned with the questions of how plant diversity evolved in the tropics and what determines the gradients in this diversity has been the variety of techniques employed to sample diversity in different locations. It has been extremely difficult—in most cases impossible—to compare the results of such surveys. One of Gentry's major achievements was to establish a single method for the rapid assessment of tree diversity in forests. He originally established the method to aid in his own studies of diversity within the Bignoniaceae, including the lianas of such importance in this plant family. The standard quadrat methods underestimate species diversity in any given forest location. Gentry's method, however, sampled an area of 0.1 ha through the use of repeated transects ( 10 2 × 50 m subplots ), each proceeding in a random direction from the end of the previous one. Gentry found that a single site of a species-rich tropical rainforest could be sampled in a few days. Gentry was also realistic, however, in his low expectation of others quickly adopting his method, so he established an international database pretty much by himself. He visited forest sites on all continents, from low to high latitudes and from dry to wet climates, completing a total of 211 transects.

Gentry's development of this technique, along with his unparalleled practical ability to identify plant groups ( Gentry & Vasquez 1993 ), became powerful tools in researching the constraints on diversity in forests and in assessing biodiversity hotspots. Importantly, Murray Gell-Mann and Ted Parker discussed the impending loss of diversity on a birding trip in Venezuela in 1985 and proposed the establishment of the Rapid Assessment Program ( RAP ) that became an early program of Conservation International. As a board member of the McArthur Foundation, Gell-Mann also was instrumental in the provision of funds for RAP in its formative days, and Gentry and Parker were among the founding participants in this revolutionary program. They participated in five such RAPs before their deaths. Another 19 have been completed since that time, still using Gentry's transect method ( http://www.biodiversityscience.org ).

Global Patterns of Plant Diversity, written by two former colleagues of Gentry's at the Missouri Botanical Garden, documents the development of the transect technique and summarizes the results for a total of 226 sites ( 15 added by colleagues ). These sites span a latitude range from over 50° north to 40° south and cover all continents, excluding Antarctica. Most of the sites are tropical, and particularly Neotropical. Specimens collected from the transects were well-vouchered: over half of Gentry's some 80,000 personal accessions were related to his transect surveys. This field research was a monumental task, made possible only by Gentry's vision, courage, and exceedingly demanding work ethic.

The bulk of the book consists of one-page summaries of the 226 sites, providing environmental data, lists of important taxa, and estimates of biomass and tree diversity. I had initially thought this section would be boring, but I frequently found myself visiting different sites to compare them with my own impressions of what would be there. The summary provides an example of the impressive transect database established by the Missouri Botanical Garden ( http://www.mobot.org/research/applied_research.explan.html ), which provides the species lists for each site, including numbers of individuals and bole diameters, and the herbarium numbers of Gentry's vouchers. Ultimately, all the latter will be downloadable as high-resolution images. Thus, the book provides an entry to one of the most important comparative databases on forest diversity ever established. Descriptions of transects are preceded by a lengthy section of photographs of many of the sites, most of murky and mediocre quality. Gentry was a far better botanist than photographer.

Although Gentry was able to use some of the results of this comparative survey during his life—for example, his valuable paper on tree species richness in forests of the upper Amazon ( 1988 )—the most important analyses came after his death, done partly by collaborators who had worked with him. Notable is a landmark paper on factors influencing the diversity and dynamics of tropical rainforest species by one of the authors of this book, Oliver Phillips ( Phillips et al. 1994 ). Givnish ( 1999 )  used these surveys to add to the arguments on the causes of latitudinal gradients in taxonomic diversity. These transect data continue to be used in path-breaking research in tropical plant ecology and evolutionary biology ( Enquist & Niklas 2000; Enquist et al. 2002 ).

This book describes a remarkable program of research of enormous value for studies in conservation biology and evolutionary ecology. It is ultimately a better testimony to the remarkable character and achievements of Alwyn Gentry than the many obituaries that followed his tragic end. The book is sturdily bound and of reasonable price, and it should be in the hands of ecologists and conservation biologists interested in questions of biodiversity, particularly of tropical plants.

David W. Lee