Efeito das variações climáticas e hidrológicas no padrão de crescimento diamétrico da espécie arbórea Macrolobium acaciifolium (Benth.) Benth. (Fabaceae) em florestas alagáveis por águas claras na Amazônia Oriental

Abstract

Hydro-climatic variability still lacks information in different regions of the Amazon basin, and the development of homogeneous pre-instrumental time series is a challenge given the limited distribution of meteorological stations in time and space in the largest watershed on Earth. Thus, the use of dendrochronology in tropical forests for studies related to climate (dendroclimatology) has been gaining attention in recent decades. In this study, individuals of the tree species Macrolobium acaciifolium (Fabaceae) growing in the floodplains (igapós) of the Tapajós River in the east of the Amazon were sampled to obtain a tree-ring chronology. The chronology developed for the study site had a period of 77 years (1941-2016) of robust information and presented tree rings sensitive to the flooding regime of the igapós. The annual pattern of radial growth of the species showed significant correlations with climatic and hydrological variables. According to the results, the mean annual increment indicated a significant positive correlation with the maximum level of the Tapajós River (r=0.69 and p<0.001) for the period from 1973 to 1993. This pattern was different from those reported in dendroclimatic studies from central Amazon region where tree-ring chronologies of M. acaciifolium presented a significant correlation with the duration of the terrestrial phase. Correlation maps generated between the tree-ring chronology and drought indices, indicated not only the influence of local precipitation, but also of the regional precipitation regime covering the southern regions of the Amazon Basin and central-west and southeastern region of Brazil during the first quarter of the year. Thus, hydro-climatic conditions in the headwaters of the rivers draining to the Tapajós (Juruena and São Manoel), located in the State of Mato Grosso, express a strong relationship with diameter increment during the rainy season. The performance of the South Atlantic Convergence Zone (SACZ), one of the mechanisms of the monsoon system during the rainy season in South America, was evidenced from the correlation between the chronology and the maximum monthly temperature in January. The results suggest that the variation of the precipitation regime and hydrological cycle is triggered by ENSO-events (El Niño-Southern Oscillation, especially the Niño 1+2 region) and the variation of sea surface temperature (SST) of the Tropical Atlantic influencing tree growth. The correlation of the SSTs of the South Atlantic with the chronology is more evident in the first half of the year and, from July onwards, the correlation with the SSTs of the Equatorial Pacific begins to manifest until reaching its peak in October, November and December. Thus, the study suggests that the climatic and hydrological variability of the study region may not correspond to the general context of the Amazon basin.