“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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litt
er(
g/m
2)
leaves
wood
reproducts tissues
miscellaneous
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Figure 3. Area x weight
y = 81.586x + 54.188
R2 = 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)
are
a (
cm
2)
Figure 7. Leaf fall before and after logging
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Sept Oct Nov Dec Jan Feb Mar April May
Month
Leaf
Litt
er P
rodu
ctio
n (g
/m2)
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
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 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.