PARENT SESSION
Organized Oral Session 50: Dynamics of disturbed and undisturbed tropical rain forests
Organizer(s): A Huth and J Groeneveld
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 511 B, Level 5, Palais des congrès de Montréal
How large is an intermediate scale disturbance?
Chambers, Jeffrey 1, 3, Smith, Marie-Louise2, Felsemburgh, Cristina3, Plourde, Lucie4, Campanella, Richard1, Higuchi, Niro 3, 1 Tulane Unviersity, New Orleans, LA3 INPA, Manaus, Brazil2 USDA Forest Service, Durham, NH4 Complex Systems Research Center, Durham, NH
ABSTRACT- An improved understanding of tree mortality and canopy gap formation dynamics is important for a number of fields of ecological inquiry. For example, the intermediate disturbance hypothesis states that too little disturbance results in the loss of weaker species through competitive exclusion, and too much disturbance results in the loss of late-successional species. This leads to an important question: What is the minimum gap size required to initiate classical secondary succession? Addressing this question can shed light on the creation and maintenance of biodiversity and also how carbon balance varies with disturbance frequency at the landscape scale. Field based investigations have generally been limited to gaps smaller than 0.1 ha, and these localized gaps are often too small to drive niche differentiation among colonizing tree species and the initiation of secondary succession. However, remote sensing investigations have detected much larger gaps (blowdowns) at the landscape scale ranging from 5 to 3,000 ha. This leaves a critical break in the study of gap dynamics from about 0.1 to 5.0 ha. This talk highlights use of spaceborne imaging spectroscopy to quantify spatial variability in intermediate-scale gap dynamics (blowdowns) in the Central Amazon. A blowdown which occurred in 1999 was clearly identified on both hyperspatial (Ikonos) and hyperspectral (Hyperion) images. The Hyperion image was minimum noise fraction (MNF) transformed to reduce spectral dimensions for analyses, and pixels representing the purest blowdown endmembers were extracted. Spectral unmixing was carried out using a robust method, and the fractional abundance of blowdown-like spectral reflectance was mapped. Three of these blowdown sites were located in the field using a GPS receiver and inventory plots were established where all trees (> 5 cm diameter) were identified to species. A comparison of species composition with primary forest plots showed unique vegetation characteristic of early successional seres, dominated by classical pioneers species. Results demonstrate that intermediate-scale canopy gap blowdowns may play an important role in driving landscape scale niche differentiation, with important implications for biodiversity and forest carbon balance.
Key words: canopy gaps, carbon balance, biodiversity