Forest structure and the relationship between light environment above and below the canopy in the Tapajˇs National Forest.
Parker, Smithsonian Environmental Research Center, firstname.lastname@example.org
Fitzjarrald, University at Albany, SUNY, email@example.com
Sampaio, LBA-ECO, Santarem, firstname.lastname@example.org
Canopy structure influences the balance, spatial and temporal distribution, and spectral quality of radiation incident on the forest. To understand the details of these interactions in primary moist forest at km67 in the Tapajˇs National Forest, Brazil (2░51' S, 54░58' W), we combined continuous high-frequency pyranometer and quantum sensor measurements above and below the canopy (an array) with observations of canopy structure made with a portable LIDAR system deployed from the forest floor. We describe the whole canopy budget of Photosynthetic Photon Flux Density (PPFD), the canopy reflectance and understory transmittance of PPFD, and the balance of direct and diffuse fractions. We examine the dependence of transmittance, sunfleck probability and duration on solar elevation angle, season, and sky conditions.
From co-located measurements of PPFD and LIDAR structure along a 1000m transect we show the relationship between transmittance and overhead cover, surface area density, and local canopy height. From the distribution of local maximum heights (the hypsograph) we estimate the mean vertical pattern of within-canopy transmittance and absorbance. We constructed "transfer
functions" to describe the light environment and budget at km67. The
brightness classes are 1 (<30%), 2 (30-60%), 3 (60-90%), and 4 (>90%) -
pecrcentage of inciming light relative to modeled clear conditions.
We depict penetrance to the understory as well as reflectance
from the top. For this analysis half-hour averages of the
calibrated subcanopy array means were used.