Edge of the Amazon Jul-Aug 2011—One: The Amazon is not a “rainforest”.

Everything’s packed below me in the cargo hold now, no more planning, no more “this one, or that one?”.  As I think of the lack of instrumentation in my luggage, there is a palpable sense of levity in my mind.  Last year I took a Mercedes’ worth of plant emission measuring machinery, which of course functioned about as well as a Mercedes would in the middle of the Amazon without a mechanic for a thousand miles (except us).  During that field course, we learned how to assault the tropical forest at every possible scale with an army of techs and an arsenal of instruments in order to chip a few comprehensible blocks from its fractal-like, breathing ramparts of mystery.  Not this time.  This time I go traditional, with a handful of tools not unlike Alwyn Gentry was using decades ago to map the baffling diversity of flora of northwest Amazonia.

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Gear for the trip: tapes and string for forest survey transects, hand and modified pole pruners (in PVC pipe), string and weights for the big slingshot (in PVC pipe) to launch lines into high branches and pull up a rope-based chain saw, leav scanner, plant books, waterproof notebooks, and outdoor gear (maybe Al Gentry didn’t bring a packraft!).  But dangit, I forgot the scale! I hope I can get one in Santarem.

The Amazon is not a “rainforest”.  The forest changes dramatically from the Andean slopes in the west, where six meters of annual rainfall is common, to the east where, closer to the mouth of the Amazon river, forests drink from 1.5 meters of rainfall per year and face a long dry season.  Just outside the river basin, several hundred centimeters of rain sustain tropical dry forests and savanna.  The species that make up the “plant community” at a given site are different from one site to the next along this gradient of precipitation.  These different communities are adapted to their particular climates, and have different ways of processing carbon and water.  The amazon processes so much carbon and water that changes in those communities and their functions can have global impacts on climate.

My aim is to understand how tropical plant communities will respond to environmental change so that we can take appropriate actions toward species conservation, and improve our ability to predict feedbacks between forests and climate.  On this trip to Brazil, I’ll be conducting surveys of the plant communities at forest edges (hence “Edge of the Amazon ”), such as where some of the forest has been cut to make way for a road or pasture.  Where a forest has an edge like this, that edge is hotter and drier than the interior due to more exposure to sun and wind.  These “edge effects” are enough to change the plant community (species composition) and change the way the community processes carbon and water.  So these provide an opportunity to see both how communities respond to climatic changes (hotter and drier), and how much diversity can be maintained at forest edges in different climates.  I’ll compare forest-edge to forest-interior communities at two different sites along the west-east rainfall gradient: the Tapajos National Forest near Santarem (drier forest) and the Ducke Reserve outside of Manaus (wetter forest).

I predict that edges of forests in the drier environment (Tapajos site) will be less altered by these edge-effects, and so may be more robust to such environmental changes.  For species that exist both in the forest and at the edges, I’ll look at characteristics of their leaves and wood to see what strategies some species are able to use to survive in an altered climate.