Abstract
Amazonian forests are extremely heterogeneous at different spatial scales. This review intends to present the large-scale patterns of the ecosystem properties of Amazonia, and focuses on two parts of the main components of the net primary production: the long-lived carbon pools (wood) and short-lived pools (leaves). First, the focus is on forest biophysical properties, and secondly, on the macro-scale leaf phenological patterns of these forests, looking at field measurements and bringing into discussion the recent findings derived from remote sensing dataset. Finally, I discuss the results of the three major droughts that hit Amazonia in the last 15 years. The panorama that emerges from this review suggests that slow growing forests in central and eastern Amazonia, where soils are poorer, have significantly higher above ground biomass and higher wood density, trees are higher and present lower proportions of large-leaved species than stands in northwest and southwest Amazonia. However, the opposite pattern is observed in relation to forest productivity and dynamism, which is higher in western Amazonia than in central and eastern forests. The spatial patterns on leaf phenology across Amazonia are less marked. Field data from different forest formations showed that new leaf production can be unrelated to climate seasonality, timed with radiation, timed with rainfall and/or river levels. Oppositely, satellite images exhibited a large-scale synchronized peak in new leaf production during the dry season. Satellite data and field measurements bring contrasting results for the 2005 drought. Discussions on data processing and filtering, aerosols effects and a combined analysis with field and satellite images are presented. It is suggested that to improve the understanding of the large-scale patterns on Amazonian forests, integrative analyses that combine new technologies in remote sensing and long-term field ecological data are imperative.
Highlights
Amazonia plays a major and yet poorly understood function in the global carbon cycle
Amazonian tropical forest holds about 120 ± 30 Pg of carbon in biomass [1] with an approximate spatial distribution of above ground live biomass ranging from 300 Mg·ha−1 in Central Amazonia and in regions to the east and north, to 100–200 Mg·ha−1 in the transitional and seasonal forests at the southern and north-western edges of the basin [2]
It has been suggested that the higher specific gravity in central and eastern Amazon forests is related to the regular seasonal water availability or El Niño related droughts that occur in this region [23], and more recently, to a certain extent to the soil physical structure and quality [16]
Summary
Amazonia plays a major and yet poorly understood function in the global carbon cycle. Amazonian tropical forest holds about 120 ± 30 Pg of carbon in biomass [1] with an approximate spatial distribution of above ground live biomass ranging from 300 Mg·ha−1 in Central Amazonia and in regions to the east and north, to 100–200 Mg·ha−1 in the transitional and seasonal forests at the southern and north-western edges of the basin [2] Recent results have shown that increased diffuse radiation, caused by the increase of aerosols in the Amazon atmosphere during the dry season, increases forest CO2 uptake [15] Despite these studies, Amazon ecosystem processes cannot be understood in terms of climate alone. A review of climate change effects on tropical forests have been explored elsewhere [17]
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