Full text
| |
| Author(s): |
Giovana Mendonça Cabianchi
Total Authors: 1
|
| Document type: | Master's Dissertation |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB) |
| Defense date: | 2010-06-11 |
| Examining board members: |
Maria Victoria Ramos Ballester;
Renato Marques;
Fabio Poggiani
|
| Advisor: | Maria Victoria Ramos Ballester |
| Abstract | |
The objectives of this study were to estimate litterfall production and decomposition, macronutrients and to evaluate the structure and floristic composition of a varzea Forest in a region under strong anthropogenic influence in southwest Amazonia. Knowledge about these processes is extremely important, since they provide information on ecosystem net production, nutrient cycling and can serve as basis for degraded áreas restoration based on adequate management strategies. Litter was sampled biweekly from September 2005 to August 2007, while decomposition was measured during one year. Floristic survey and forest structure measurements were done in August 2009. Average annual litter production was 12.7 t ha-1, with strong seasonality and higher production during drier months. In terms of different litter fractions production followed the order leaves>>branches>miscellaneous. Average annual C deposition via litterfall was 5.4 t ha-1. Proportionally, almost twice as much C returns to the forest ground in the drier season. Average annual N deposition was 199.6 kg ha-1, which is related to relatively high litterfall deposition. Nutrient use efficiency (NUE) was 57.9, a value that can be considered relatively low, indicating that nitrogen supply is not a limiting factor in this forest. C:N ratios were high in both seasons, with maximum (40) occuring at the beginning of dry season, which probably influenced and promoted low decomposition rates, specially during drier months. Average annual k was 0.9 for litterbags and 0.7 based on litter accumulation. During decomposition N imobilization and slow C release predominated. Partial carbon budget indicates that around 342.3 kg C ha-1 are cycled via litterfall, representing 34.2% of net ecosystem exchange. For the forest inventory all individuals with diameter at the breast height (DBH) >3.2 cm were measured, totalling 2.170 individuals. Trees with DBH < 20.0 cm represent 49.1% of the forest. A progressive decrease in individuals as diameter size increase indicated that this forest is stable or even growing. The floristic composition was based on 266 individuals with DBH > 10 cm, composed of 43 species, 17 families and 4 unidentified species. Major families were Leguminoseae (30.2%), Palmae (9.3%), Anonaceae (7.0%) e Sapotaceae (7.0%). Shannon-Winer index (H) was 3.2. Basal area was 24.3 m2 ha-1. These values are similar to other findings in the south and southwest of the Amazon and lower than those of the central Amazon. Smaller basal area indicates smaller forest biomass and consequently smaller CO2 emission in case of fires in this region (AU) | |