# Biomass Dynamics in a Fragment of Brazilian Tropical Forest (Caatinga) over Consecutive Dry Years
## 1 Introduction  
The dryland domain represents 41.5% of the world's surface [1]. These regions are home to 14.4% of the world's population and their sustainability depends on, among other factors, the scarce water availability [1]. The potential evapotranspiration to rainfall ratio is greater than one, with a five to eight month dry season and a Thorthwaite's aridity index of 0.65 [1]. Vegetation is typically rangeland and savanna-steppe [2]. The most striking feature of dry regions is the water deficit that predominates for 8 to 10 months of the year [3]. According to the latest simulation models, climate change may increase this area by 11 to 23% by the end of the 21 st century, with the largest increase occurring in semi-arid regions [3]. Dry Tropical Forests (DTFs) are part of this domain and account for 42% of tropical and subtropical forest resources, occupying around 2.7 million km\({}^{2}\) distributed across the globe [4]. Tropical dry forests (TDFs) are located in regions of tropical dry climate, with average monthly temperatures above 18 \({}^{\circ}\)C, annualprecipitation below the 1800 mm isohyet, and rainfall events concentrated within four to seven months characterizing a long period of continuous dry days (CDDs) [5]. This characteristic may be aggravated by possible changes in climate. In Brazil, the DTF is known as Caatinga, and is located in the northeast of Brazil within the limits of the semi-arid region [6]. It has an area of approximately 844 thousand km\({}^{2}\) and a population of 27 million people [6]. Areas of Caatinga are generally exploited for firewood, agriculture and pasture, and subsequently abandoned, starting the process of regeneration [7]. This process gives rise to new forest fragments that present a high rate of recruitment and high density of new individuals, with small individuals that show quick growth with a large increase in biomass [8; 9]. In DTFs the biomass dynamics during the early processes of succession of succession are dominated by more tolerant species to drought that are better able to cope with the harsh environment during the initial stages of succession [10; 11]. This dynamic of vegetation biomass depends on several factors, such as species composition and variability [12], the soil, the level and type of anthropogenic disturbance and the rainfall pattern [13; 14; 15]. Among the determinants of biomass production, changes in water availability are the most limiting on the dynamics of successional species [12; 16]. Successive years of drought and the frequent occurrence of short dry spells impair the ability of plants to recover [13]. During drought, trees reduce their evapotranspiration through mechanisms of water-deficit tolerance, such as stomatal closure and deciduousness [17]. When climate conditions exceed the limits of plant tolerance due to an increase in temperature, vapor pressure and water deficit [10], the probability of tree mortality of some trees may increase. Long periods of drought can generate several problems, such as xylem hydraulic failure [18] embolisms that cut off the water supply, leading to tissue mortality [19]. However, a lack in long-term data on droughts caused by climate change limits the understanding on tree mortality patterns in TDFs. In general, studies have investigated forest mortality in the short term without assessing long-term mortality [15]. From 2010-2019, the Brazilian semi-arid region experienced the longest period of drought reported, and little is known about the biomass dynamics due to a reduction in water availability during this period. Based on this, this study assessed the biomass generated from this period by different species of plants in a Dry Tropical Forest in the Caatinga Phytogeographic Domain (DTF/CPD). Also, we determine the resilience of some species to this dry period.