“Litterfall and Leaf Area Index Measurements Before and After Selective Logging in Tapajos National Forest, Santarem - Para - Brasil ” 1 Figueira, A.M.S.; 1 Sousa,C.A.; 1 Maia,A. 2 Rocha, H.; 2 Juarez,R.; 2 Freitas, H.; 3 Goulden, M.; 3 Menton, M.; 3 Miller, S.D. 1 Universidade Federal do Pará – Campus de Santarém- PA, 2 Universidade de S. Paulo, 3 University of California, Irvine Biophysical processes and the generation of surface fluxes (water, energy and CO 2 ) inside an ecological system are associated with the physical structure of the canopy and the amount of green biomass (biological component) which regulate both the radiation balance within the canopy and canopy-atmosphere energy and CO 2 exchanges. As such, one of the key parameters in the estimation and quantification of these fluxes is Leaf Area Index (LAI), defined as leaf area pr unit of ground area (Montheith, 1973). The effect of perturbations such as logging on these processes is not well understood. This study examines the seasonal variability of litter biomass (leaves, flowers, fruits, and wood) and LAI before and after selective logging in order to better understand the effects of logging on forest structure. This study is done in conjunction with the LBA eddy-flux covariance study “Measuring the Effects of Logging on the CO 2 and Energy Exchange of a Primary Forest in the Tapajos National Forest”. Litterfall varied seasonally from September 2000 to September 2001, with comparatively high rates beginning in May and continuing through the dry season (from July to December). Comparison of cumulative rainfall and cumulative leaf fall (Fig.6) shows that litterfall increases when rainfall decreases. The temporal variation of dry weight and leaf area (using the equation in Figure 3), shows a peak of leaf fall between November and December, which coincides with the end of the dry season (Fig.5). Eddy-flux tower data show an increase in CO 2 uptake in January and February which coincides with increased photosynthesis for new leaf production following dry season leaf senescence in November and December. Annual litterfall rates were 10.5 T ha -1 yr -1 , most of it leaves (6.3Tha -1 yr -1 ). The integrated litterfall observations prior to logging suggest an overall LAI of 5m 2 m 2 (Fig.6), which agrees with independent assessments of LAI made by fisheye photography during 2001 (5.86m 2 m 2 ). Leaf biomass and Leaf Area Index: In order to evaluate the production of leaves and other litter components, we installed 30 1m 2 litterfall traps (Fig.1), (the number recommended by Newbould (1997)), which were arrayed at 25-m intervals along two east- west transects in an 18-ha block (300m N-S, 600m E-W) upwind of the eddy covariance tower. Litter was collected bi-weekly (Fig.2) beginning in September 2000. The material was separated into leaves, wood and other parts (mainly flowers and fruits), oven dried and weighed. Prior to oven drying, the subsample’s leaf area was determined using a computer scanner (scanner HP Scanjet 6300C, output resolution 300) and image processing software (Rootedge). The relationship between weight and area measured was calculated for each subsample and used to derive an equation (Fig.4) which is used to estimate total leaf area for each litterfall trap. Introduction Methods Preliminary Post-Logging Results Figure 5. Litterfall - FLONA Tapajós Km83 0.00 10.00 20.00 30.00 40.00 50.00 60.00 Sep-00 Oct-00 Oct-00 Nov-00 Nov-00 Dec-00 Dec-00 Jan-01 Jan-01 Jan-01 Feb-01 Feb-01 Mar-01 Mar-01 Apr-01 Apr-01 May-01 May-01 Jun-01 Jun-01 Jul-01 Jul-01 Jul-01 Aug-01 time litter(g/m2) leaves wood reproducts tissues miscellaneous - Figure 3. Area x weight y = 81.586x + 54.188 R 2 = 0.91 20.00 520.00 1020.00 1520.00 2020.00 2520.00 3020.00 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 weight (g) area (cm2) Figure 7. Leaf fall before and after logging 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 Sept Oct Nov Dec Jan Feb Mar April May Month Leaf Litter Production (g/m2) Leaves before logging Leaves after logging Pre-Logging Results Preliminary results after logging show a fall in leaf litter production of about 13,5% compared to the same period before selective logging (Fig.6). This result corresponds with the results of hemispherical photography that found a decrease from 5 LAI to a mean of 4,3 m 2 m 2 in the 3 months following the cut. We will continue to monitor post-logging litterfall and LAI dynamics. Figure 6.Fallen leaves x Rainfall - FLONA Tapajos km 83 0 1 2 3 4 5 6 0.00 100.00 200.00 300.00 400.00 500.00 600.00 Days since Sept 24, 2000 Cumulative leaf fall Cumulative Rainfall (m) Figure 2: Litterfall collection Figure 1: Litterfall trap Figure 3. Samples of leaves Acknowledgments LBA-Ecologia sites Santarem, Para LBA = Large Scale Biosphere-Atmosphere Experiment in Amazonia Antonio Oviedo for advice on collection methodology, Jose Mauro Moura for assistance with field work, CNPq and LBA for financial support. References: Monteith, J.L.1973. Principles of environmental physics. Edward Arnold ed. London Newbold, P.J., 1967. Methods of estimating the primary production of forests. IBP Handbook Nº 2, Blackwell Scientific Publication, Oxford. Roberts, J.M. Cabral, O.R.M., da Costa, J.P.; Mc William, A..L.C.;Sa, T.D.A.1996. A overview of the leaf area index and physiological measurements during ABRACOS. In: Gash, J.C; Nobre, C. ; Roberts J.M. ; Vitoria R.L. (eds) 1996. Amazonian deforestation and climate. John&Wiley&Sons, UK. 611p.