Diego Antunes Campos

Wide variability in the rainfall regime and drought is characteristic of semi-arid regions. A better understanding of this variability can aid decision-making in the short, medium and long term. The aim of this study was to identify long-term patterns and trends in rainfall and temperature through the use of temporal patterns, in addition to assessing the duration of wet and dry periods. Daily historical series of rainfall and temperature for the district of Iguatu, Ceará were used. For rainfall, the annual and monthly climate normal (1974-2018) was calculated, in addition to the number of consecutive dry days (CDD) during the rainy season. The annual mean value for the maximum, mean, and minimum temperatures (1996-2017) was also calculated. Wide interannual variability in the rainfall was found, with very wet years (1985; 2009 and 2011) and very dry years (1979; 1983 and 1993) interspersed with periods of around average rainfall. When analysing the total occurrence of dry spells by class, it was found that events of from 5 to 10 days were the most frequent, and tended to reduce in number over the period under investigation. There was also an increase in the number of longer events, those over 16 days. Maximum annual temperatures show an increasing trend over the years, with minimum temperatures showing the smallest increases. It was concluded that extreme rainfall events are common, and alternate between rainy years and years of drought. The increase in maximum temperature and the reduction in rainfall express the extreme climate variability that may be a consequence of climate change.

Increases in water scarcity due to climate change, especially in dry regions, can affect the dynamics of successional species. In view of the longest sequence of dry years (2010–2019) to have occurred in the Brazilian semi-arid region, with a consequent reduction in water availability, the influence of rainfall distribution on the production of above-ground plant biomass was investigated in a Dry Tropical Forest (DTF). This natural change monitoring experiment was conducted over 11 years (2009–2019) in a fragment of DTF under regeneration for 40 years, in the district of Iguatu, Ceará, Brazil. All living individuals of the woody component with a Diameter at Ground Level (DGL) ≥3 cm and a height (h) ≥100 cm were measured during 2009–2010, 2015–2016, 2018–2019. Biomass production was calculated using an allometric equation defined for DTF species. A mean mortality rate of 134 ind. ha⁻¹ yr⁻¹ was registered, with a recruitment of 39 ind. ha⁻¹ yr⁻¹, generating a mean deficit of 95 ind. ha⁻¹ yr⁻¹. The mean reduction in biomass was 3.26 Mg ha⁻¹ yr⁻¹. Climate conditions during consecutive dry years have a direct effect on the mortality and recruitment of woody species, with a recruitment/mortality ratio of 0.11. Shrubby-tree individuals of smaller diameter showed less resilience to the cumulative effect of drought.

Management of tropical dry forests in Brazil expanded 450% in the two latest decades; but little is known about the dynamics of these areas. Thus, the objective of this work was to evaluate if the recovery of mean original biomass stocks (MOBS) is a consistent criterion to define cut cycles in a managed forest for charcoal production, and determine the remaining biomass and its contribution to soil carbon stocks. The study was conducted at the Ramalhete Settlement, in General Sampaio, CE, Brazil, in 2018. The explorable shrubby-arboreous biomass (ESAB) and the ESAB mean annual increases (ESAB -MAI) were determined in five areas subjected to clearcutting after 3, 5, 8, 11, and 15 years, and in a preservation area with 40 years of regeneration. Each area was divided into seven plots (20 × 20 m), totaling 42 plots. The ESAB of the plots were compared and the remaining biomass (branches, stumps, and litterfall) in a recently explored area was calculated and converted into organic carbon. The remaining biomass of branches had higher contribution to soil carbon stocks, followed by the litterfall, and stumps. The carbon stocks of the branch component were 3.4-fold higher than those of the litterfall. The recovery of the MOBS of an area after clearcutting should not be used as a criterion to define the cut cycle, since these original carbon stocks do not represent the maximum ESAB production possible in the area; the biodiversity and amount of ESAB in the classes of larger diameter are more adequate criteria.

This work is focused on characterizing and understanding the aboveground biomass of Caatinga in a semiarid region in northeastern Brazil. The quantification of Caatinga biomass is limited by the small number of field plots, which are inadequate for addressing the biome's extreme heterogeneity. Satellite-derived biomass products can address spatial and temporal changes but they have not been validated for seasonally dry tropical forests. Here we combine a compilation of published field phytosociological observations with a new 30m spatial resolution satellite biomass product. Both data were significantly correlated, satellite estimates consistently captured the wide variability of the biomass across the different physiognomies (2-272 Mg/ha). Based on the satellite product we show that in year 2000 about 50 percent of the region had very low biomass (<2 Mg/ha) and that the majority of the biomass (86%) is concentrated in only 27% of the area. Our work confirm other estimates of biomass 39 Mg/ha (9-61 Mg/ha) and carbon 0.79 PgC. The satellite products together with ground based estimates has the potential to improve forest management in Caatinga and other seasonally dry tropical forests through improved approximation of spatial variability, how they relate to climate, and support numerical modeling experiments in semiarid regions.