Estrutura do dossel e sazonalidade do índice de área foliar em ambientes de terra firme na Amazônia Central, com uso do LiDAR portátil terrestre
The objective of this study was to investigate the structural differences of the canopy and its seasonal variation in four environments of terra firme in the Central Amazon. Structural attributes of the forest canopy were obtained, using a rangefinder LiDAR, which provides the distance to the last...
| Autor principal: | Rosa, Diogo Martins |
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| Grau: | Dissertação |
| Idioma: | por |
| Publicado em: |
Instituto Nacional de Pesquisas da Amazônia - INPA
2020
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| Assuntos: | |
| Acesso em linha: |
https://repositorio.inpa.gov.br/handle/1/5148 http://lattes.cnpq.br/8326494777353994 |
| Resumo: |
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The objective of this study was to investigate the structural differences of the canopy and its seasonal
variation in four environments of terra firme in the Central Amazon. Structural attributes of the forest
canopy were obtained, using a rangefinder LiDAR, which provides the distance to the last return for
each of 1,000 pulses per second. The sensor was aimed upwards and held 1m above the forest floor to
obtain 150m long forest canopy profiles at a constant walking speed. Each of four different forest types
that comprise a toposequence (catena) was profiled, with six replicates (total 900m of transect per type)
at monthly intervals for a full year. From the highest to the lowest, the catena compartments were:
plateau on well drained clay-loam; upper slope on well drained clay-loam; gentle lower slope on white
sand (tall campinarana forest); and seasonally waterlogged riparian zone on white sand (baixio forest).
For each 150m transect, the canopy structure profile was represented by a 2D point cloud containing the
positions (x, z) of ~ 345,000 LiDAR last-returns. The main features extracted were: (1) top-of-canopy
height in each 1m horizontal interval; (2) the mean and standard deviation (roughness) of these 150
maximum heights per transect; (3) canopy openness; (4) vertical profiles of leaf area density (LAD); (5)
the fraction of the total leaf area index (LAI) contained in the highest 5m and in the highest 10m of the
canopy and in the highest 6m and in highest 11m of the understory; and (6) the average LAI per transect
and the LAI of each 1m horizontal interval, the latter used to construct frequency histograms. From the
baser of the catena toward the plateau, top-of-canopy height and top-of-canopy roughness both increase.
Vertical profiles of the leaf area density are bimodal in all four forest types, with higher concentrations
of leaves in the lower understory and in the upper canopy. The upper canopy leaf density mode gradually
decreases from the riparian forest toward the plateau, as expected from the increasingly irregular topof-canopy surface. The lower understory´s leaf density is greatest in the waterlogged riparian forest and
lowest in the tall white-sand forest. The first 5m of upper canopy (below the highest return at each
horizontal transect interval of 1m) contains 54-60% of the leaf area of the forest. The first 10m of upper
canopy contain 79-86% of the leaf area. Canopy openness and the LAI (using six transect averages per
forest type) do not vary between the four forest types. Over the full year, three significant changes in
LAI were detected when all four forest types were lumped (repeated-measures analysis of the 24
transects per month). First, there was an LAI increase of 2.9% from 15/Mar to 15/Aug/2015 (wettest
month to first dry month); then a drop of 2.0% from 15/Aug to 15/Oct (two driest months of the 2015
El Niño); and finally there was an LAI increase of 3.7% as precipitation gradually increased from
15/Oct/2015 to 15/Jan/2016. Over the full year (15/Mar/2015- 15/Mar/2016) there was a small but
significant increase in the LAI (3% ± 2%). There was no seasonal change of the LAI in the understory
(1 to 5/11m above the ground). When lumping all forest types, seasonal amplitude of LAI (between the
smallest and largest of the 13 monthly averages) was only 4.8%, indicating that LAI alone should have
little influence on the seasonality of the forest canopy photosynthetic capacity, even in a severe El Niño
year. However, the frequency histograms of the LAI classes, obtained for 900 intervals of 1m from the
six transects of each of the four forest types, had a truncated upper tail in every month, indicating
saturation in the detectability of high values of LAI. Therefore, the seasonal variation of LAI was
probably underestimated. Saturation may also impede detecting LAI differences between the forest
types |