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Post date: Oct 18, 2013 5:19:51 PM
How many tree species are in the ~6-million-km2 of Amazon rainforest? And how many of them are rare or common? These are the kind of questions that have plagued the minds of many scientists since early explorers like Alfred Russel Wallace stepped into the Amazon basin more than 100 years ago. According to this study published today in Science, there are almost 400 billion of trees in this region distributed in roughly 16,000 tree species. The surprising finding is that only 1.4% of the total estimated tree species (227 "hyperdominant" species) account for the estimated ~400 billion total trees.
Previously, plant ecologists have studied patterns of diversity at a regional scale in the Amazon; however an assessment of the rarity and commonness of Amazonian tree species escaped a continental analysis because of the lack of a comprehensive dataset. Given the vast extension of the Amazon region as a whole, counting every tree there would take many lifetimes. In 1953 a formal attempt to answers these questions was first formulated by J. M. Pires et al. for a small area in the Brazilian Amazon. They recognized the need to apply a formal statistical model of species rarity and commonness to predict abundance based on field data. A paper published in PNAS on 2008 by Hubbell et al. followed on the steps of Pires' et al. paper and using a statistical model of the distribution of rare and common species attempted to come up with a first estimation of the total number of trees in the Amazon Basin, reaching to an estimated number of ≈12,500 tree species.
Today a new paper published in the journal Science by core authors Hans ter Steege, Nigel Pitman, Daniel Sabatier, and Christopher Baraloto (along with collaborators) achieved a finer level of analyses into these questions by using a network of tree inventory plots collected through more than 20 years of field work.
An exemplary collaborative study involving more than 120 scientists in nine countries covering the greater Amazon (the Amazon region plus the Guiana Shield region). They established 1170 floristic plots on which every tree larger than 10 cm in diameter were measured, counted, and identified to species. Peruvian plant researchers that have participated in this study include: Abel Monteagudo, Percy Núñez Vargas, Euridice Honorio, Rodolfo Vásquez, Nállarett Dávila, Roosevelt Garcia, Marcos Rios Paredes, Italo Mesones, Isau Huamantupa, and Elvis Valderrama.
Source: ATDN plots
This formidable dataset was used to estimate for the fist time the total number of species covering this hyper-diverse region as well as the number of individual trees that may occur in each of the major habitat types present there (terra firme, flooded forests, swamps, and white-sand forests). This study found that there are almost 400 billion of trees in this region distributed in roughly 16,000 tree species. The surprising finding is that only 1.4% of the total estimated tree species (227 "hyperdominant" species) account for the estimated ~400 billion total number of trees.
“In essence, this means that the largest pool of tropical carbon on Earth has been a black box for ecologists, and conservationists don't know which Amazonian tree species face the most severe threats of extinction,” said Nigel Pitman, Robert O. Bass Visiting Scientist at The Field Museum in Chicago, and second co-author on the study.
The study was led by Hans ter Steege, researcher at the Naturalis Biodiversity Center in South Holland, Netherlands. “We think there are roughly 16,000 tree species in Amazonia, but the data also suggest that half of all the trees in the region belong to just 227 of those species! That's a much smaller number than anyone anticipated, and it really helps simplify our work,” said ter Steege.
These results have big implications for tree conservation strategies and basic studies in ecology, biogeography, and ecosystem processes in the region. We now know the names of the "hyper-dominant" species in each region on which to focus for instance carbon ecosystem studies, or the rarest of rarest tree species on which to direct our efforts to improve our basic understanding of their ecology and natural history to prevent them from extinction.
PDF: Hyperdominance in the Amazonian tree flora. Science. 2013.
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