Biodiversity Hotspots through Time: Using the Past to Manage the Future . , , and . 2007 . Philosophical Transactions of the Royal Society Biological Sciences . Volume 362 , 167 – 333 . ISSN 09628436 .
“Time present and time past are both perhaps contained in time future.” T. S. Eliot was not thinking about conservation biology when he wrote those words in the poem Burnt Norton in 1935. But he could have been. The habitats, landscapes, and biotas of today have been shaped by dynamic processes that operated in the past as well as by those that are operating today. But we live in a forward-looking culture in which we are often too impatient to consider the past before protecting, managing, or even designing habitats for the future. Does this matter? The editors and authors of this special issue of Philosophical Transactions of The Royal Society Biological Sciences think it matters very much indeed. They seek to prove their case in some of the most difficult circumstances—by examining mostly tropical and Neotropical terrestrial settings. Diversity in these places is high, but the past biotas and environments are difficult to reconstruct.
Most of the authors reach into the archaeologist's or paleoecologist's toolkits to generate proxy records of environmental change and a temporal framework for the dates and rates of those changes. Lakes, soils, archaeological sites, and whole landscapes are the archives of information about the past, and charcoal, pollen, stable isotopes, and human artifacts are the proxies or surrogates for past biotas and conditions.
The stage is set with an excellent opening paper on the relevance of long-term (>50 years) ecological studies. Four of the 12 papers that follow focus on the Amazon and 5 others focus on areas in South or Central America. The Congo region has a paper, as do South Africa and New Guinea.
The opening paper by Willis et al. sets the bar very high, arguing for the importance to conservation biology of long-term studies for understanding extinction, establishing baselines and targets for restoration, managing for climate change, and dealing with invasions. This paper is better read as a call to move from understanding to action than as a prospectus for the papers that follow, few of which can realize the ambitions of Willis et al.
The papers that follow are best at documenting past conditions. Such efforts provide baselines against which to measure European-era impacts, document the long, long history of human modification of landscapes and biotas, and provide insight into how floras responded to climate change in the past.
The most frequent discovery is that humans have been significant modifiers of their environment for a very long time. Glaser sees the signature of human activity in Amazonian soils; Heckenberger et al. review and document the human impact on Amazonian landscapes; and Bush et al. make the important point, on the basis of the record of charcoal in Amazonian lakes, that human impacts were profoundly different in degree and in kind from those occurring today. Human-caused fire in the Congo (Brncic et al.) and in the highlands of southern Brazil (Behling and dePatta Pillar) is discussed in papers in which the authors try to tease apart the influences of climate change and human activity. Haberle uses the pollen record in the highlands of New Guinea to infer that early Holocene changes in agricultural practice shaped changes in biodiversity. Indeed, it seems tougher to make the case that a particular place is pristine than it is to show that humans have left their mark. Yet however often such important discoveries are made, it is not clear what should be done with this information. Habitats cannot be restored to their prehuman condition, and indigenous people cannot be required to continue their activities unchanged. Perhaps the lesson is that all landscapes have been shaped, if not well managed, by human activities and that a sustainable future depends on better active management. Allowing landscapes to go back to their “natural” condition is no longer an option.
Demolishing the myth of a pristine, pre-European Eden serves an additional purpose: it may be problematic to substitute space for time in guiding restoration efforts. As Chazdon et al. illustrate in their study of secondary succession in tropical forests, so-called chronosequences are affected by many factors other than their age since disturbance. Admittedly, their sequences span only decades, so short-term ecological noise can obscure truly long-term trends. There can scarcely be any corner of the globe that has been untouched by human activity.
A few papers focus on the development of better proxies for past conditions. Weng et al. attempt to relate pollen diversity to vegetation diversity along an elevational gradient in the Andes, and Young and León examine the sensitivity of Andean tree lines as indicators of disturbance and climatic change. Gillson and Duffin cleverly show how fossil pollen can be used to produce quantitative estimates of the cover of woody vegetation in African savannahs.
Callicott et al. provide a useful reminder than the notions of biodiversity and biocomplexity are human constructs that serve to connect society with nature. And those connections can be used to support efforts to preserve and protect what remains of nature—from the heavily exploited Big Thicket of east Texas and upper Botanamo River basin of Venezuela to the relatively undisturbed Cape Horn region of Chile.
Mayle et al. provide the most explicit consideration of the application of a historical perspective to conservation strategies, sorting out the effects of climate, geomorphology, and human activity in lowland Bolivia. A key innovation is their use of the record of past vegetation change coupled with models for future climate in the region. Although downscaling of global models remains an important issue, these authors are among the few to have taken up the challenge to show how knowledge of the past can be incorporated into conservation strategies for the future.
This special issue of the Philosophical Transactions of the Royal Society Biological Sciences demonstrates that paleoecologists and archaeologists are eager to put their science to work to benefit conservation. The collection also documents the importance of better communication and teamwork. Conservation efforts will benefit greatly once managers and planners understand what the historical record can provide and once paleoecologists and archaeologists understand what is needed. Both sides still have a way to go, but this is an important beginning.