A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Bamboo-dominated forests of the southwest AmazonNelson(1), B.W.; Oliveira(1), A.C.A.; Silveira(2), M.; Smith(1), M.; Vidalenc(1), D.;França(1), M.B.; Miranda(3), I. & Kalliola(4), R.Studies of bamboo-dominated terra firme forests covering ~180,000 km 2 of thesouthwest Amazon, conducted since 1996, have resulted in five completed theses byBrazilian students that address several LBA themes: spectral pattern of Amazonforests, biomass modeling, mapping of erodable soils, and the possible role of groundfire in expansion/maintenance of a natural plant community. Guadua weberbaueriand close congeners -- all of which are basally erect and distally climbing by use ofspines -- dominate the forest canopy but are hollow and only 4.3-7.1 cm diameter(DBH) when mature. On the terra firme, G. weberbaueri appears to be associatedwith 2:1 clay in concentrations high enough to impede percolation in the rainy season,leading to mechanical erosion of soil and seasonally high suspended sediment loads instreams even under primary forest cover. When bamboo is mature, the forest canopyhas higher near infrared reflectance and higher normalized difference vegetationindex, using Landsat TM images, than bamboo-free forests. Within patches of 10 2 –10 4 km 2 , G. weberbaueri synchronously reproduces and dies 25-30 years aftergerminating, then slowly reestablishes itself from the single massive seed crop.During the first 10 years the canopy appears spectrally similar to bamboo-free forest.After experimental cutting and burning of all bamboo stems and all trees under 10 cmDBH, G. weberbaueri showed more rapid height and biomass recovery than all otherresprouting pre-existing species taken together and by three years post-burn hadexceeded the density of bamboo stems in an unburned forest. Though ground firethus favors G. weberbaueri over other species, such fires are rare in southwestAmazon forests and appear unnecessary for bamboo establishment and dominance.The main agent of forest disturbance is the bamboo itself, using its short-lived culmsas expendable weapons to shade and topple trees. As a consequence, the bamboodominatedforest has lower basal area of large trees, 30-50% less total biomass,apparently higher tree turnover, more fast-growing trees, lower average wood density,lower tree diversity per unit area, and much lower numbers of palms, compared withforest on similar soil not yet colonized by bamboo.Affiliations at time of research:1. INPA-National Institute for Amazon Research – Ecology Course; Manaus, AM2. University of Brasília – Ecology Course; Federal University of Acre3. CTA – Centro dos Trabalhadores da Amazônia; Rio Branco, AC4. University of Turku, Finland