“Litterfall and Leaf Area Index Measurements Before and After Selective Loggingin Tapajos National Forest, Santarem - Para - Brasil ”

1Figueira, A.M.S.;1Sousa,C.A.; 1Maia,A. 2Rocha, H.; 2Juarez,R.; 2Freitas, H.; 3Goulden, M.; 3Menton, M.; 3Miller, S.D.1Universidade Federal do Pará – Campus de Santarém- PA, 2Universidade de S. Paulo, 3University of California, Irvine

Biophysical processes and the generation of surface fluxes (water, energy

and CO2) 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 CO2 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 CO2 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 var iation 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 CO2 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-1yr-1).

The integrated litterfall observations prior to logging suggest an

overall LAI of 5m2m2 (Fig.6), which agrees with independent

assessments of LAI made by fisheye photography during 2001

(5.86m2m2).

Leaf biomass and Leaf Area Index:

In order to evaluate the production of leaves and other litter components,

we installed 30 1m2 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

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Figure 3. Area x weight

y = 81.586x + 54.188

R2 = 0.91

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Figure 7. Leaf fall before and after logging

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Leaves beforelogging

Leaves afterlogging

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 m2m2 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

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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 sitesSantarem, Para

LBA = Large Scale Biosphere-Atmosphere Experiment in Amazonia

Antonio Oviedo for advice on collectionmethodology, Jose Mauro Moura for assistancewith field work, CNPq and LBA for financialsupport.

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 duringABRACOS. In: Gash, J.C; Nobre, C. ; Roberts J.M. ; Vitoria R.L. (eds) 1996. Amazonian deforestation and climate. John&Wiley&Sons, UK. 611p.