Synchronism of Production and Degradation of Litter in Fragment of Dry Tropical Forest in Paraiba, Brazil

The litter is an important way of returning the organic matter to the soil, through the cycling of the nutrients, aiding in the development of the vegetation present in the ecosystems. The study aimed to estimate the spatio-temporal variation of deposition, accumulation and decomposition of the litter present in the preserved caatinga vegetation, located in the RPPN Fazenda Tamanduá in Santa Terezinha-PB, Brazil and the interference of climatic variables in the dynamics of these events. The research was conducted at RPPN Fazenda Tamanduá, in Santa Terezinha-PB, Brazil. The deposition of litter on 20 collectors of 1.0 m × 1.0 m was collected monthly in two periods: period I (August/2015 to July/2016) and period II (August/2016 to July/2017), the collected material was separated into leaves, branches + barks, reproductive and miscellaneous fractions. To estimate the rate of decomposition the litter accumulated on the forest floor was quantified using a 0.5 m × 0.5 m metal frame. The deposition of the total litter in periods I and II was 2,356.83 kg ha and 1,163.67 kg ha, respectively. The leaf fraction was the one that contributed the most during the two collection periods. The analysis of the data allowed to conclude that the total litter deposition in the two periods is in line with the average production for the Caatinga. The increase in precipitation provided higher deposition of litter after the rainy season. Due to several factors, the decomposition of litter in the caatinga is slower than in other biomes.

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Climat
The data o the INME meteorolog spreadshee   (Brazil, 1978 From the K value, the average renewal time estimated by 1/K and the time required for decomposition of 50% (t 0.5) and 95% (t 0.05) of the litter, estimated by the equation of Shanks and Olson (1961).

Statistical Analysis
Aiming to reduce the coefficient of variation between the weights of the fractions deposited in the 20 collectors installed, at the end of the experiment, the values were added to each four collectors, after which the average was calculated, resulting in five monthly repetitions. The experimental design used to analyze litter deposition was in causalized blocks, with treatments in a 24 × 2 factorial arrangement (months × periods), with five replications.

Climate Variables
The climatic data were measured during the experimental period, allowing to identify the possible influences of the climatic variables in the litter deposition process, being available in Table 1. Table 1. Climate variables recorded and monthly litter production at RPPN Fazenda Tamanduá, Santa Terezinha-PB, Brazil, during period I (August/2015 to July/2016) and period II (August/2016 to July/2017) The total rainfall during the two study periods was 1,096.4 mm, period II contributed 583.3 mm, with the highlight being the month of March/2017, which recorded the highest rainfall. In period I, total precipitation was 513.1 mm, with the largest contribution in January/2016 with 193.3 mm (Table 1). It is possible to notice that the distribution of rainfall during the experimental period was irregular and that the rainy season was concentrated in the months of January to June of both years; from this period a drastic decrease in rainfall rates occurred.

Variables (Months/Year) Rainfall (mm) Temperature (°C) Wind speed (m s -1 ) Relative humidity (%) Insolation (h)
In relation to temperature ( The highest recorded values of wind speed (Table 1), during the two experimental periods were in the months of August to December, in the remaining months it is possible to observe that the speed of the winds remains practically constant. In the period when the velocity of the winds was higher corresponding to the same one in that the plants have a smaller amount of leaves, providing greater fall of the branches and barks.
The relative humidity of the air (Table 1), in the period I and period II, the months of October and November presented the lowest values. For the same months, the highest heat stroke values were recorded. These results show that these two variables are directly linked.
The water content in soil showed no statistical difference between the average in both experimental periods (Table 2). In period I, the highest recorded soil water content was in the month of March/2016 and the lowest in the month of November/2015, with 13.40% and 0.67%, respectively. In period II, the month of February/2017 registered higher value with 12.68% and the month of November/2016 the lowest value with 0.62%. It is possible to observe that the water content in the soil increased from January/2016 (Period I) and February/2017 (Period II), due to the higher rainfall indexes that occurred in the region. In period I, the first rains were recorded in December/2015 with 6.2 mm and higher volume in January/2016 with 193.3 mm. In period II, it began to occur in the first rains in January/2017 and recorded a greater amount of rain in March/2017, with 5.6 mm and 205.6 mm, respectively.

Deposition of Litter
The total litter production deposited in period I was 2.356.89 kg ha -1 (Figure 3a). ith the first rai s its energies to itter for the pe ods ( Figure 5) formation, at t a) and Period ar -1 (Figure 3b) o the reduction m and, conseq dant, contribut arks contribut 16.57 kg ha -1 er during the tw kg ha -1 in peri the highest ave the highest rec g ha -1 , respectiv in the RPPN F od II (August/2 however, a gr ins, the canopy o produce flow eriod I and 354 .  According to the data obtained in Table 3, it can be observed that for period I the average time for renewal of the litter is approximately 427 days, so that 50% of this material is decomposed it takes an average of 295 days and, to decompose 95% of the accumulated litter on the soil surface it takes 1.285 days. In period II, the average time for renewal of the litter is around 573 days, however, it takes approximately 398 days to decompose 50% and to decompose 95% of the accumulated litter, it takes 1,723 days.

Discussion
In the Brazilian semiarid region, the characteristics presented by the climate reflect directly on the way in which the vegetation behaves locally as well as on the seasonality of litter produced monthly (Brasil et al., 2017). The low rainfall in tropical forests directly influences leaf fall (Wagner et al., 2016), in addition, the species present in these formations present grater reproductive effort than in humid forests (Lohbeck et al., 2015).
The rainfall in these regions presents great variability, so it is important to monitor the atmospheric conditions and the soil water content, thus evaluating the litter decomposition process present in these local (Souto et al., 2013).
Different studies carried out in areas of caatinga confirm the dynamics that occur in relation to the production of litter. The values of total deposition were similar to those obtained by Brasil et al. (2017) A study by Toscan et al. (2017), in the RPPN Fazenda Santa Maria, in Santa Terezinha de Itaipu-PR, observed that annual litter production was 11.886 kg ha -1 , however, it should be noted that this high result is generally reported for seasonal semideciduous forests, not occurring in dry tropical forests such as the Caatinga.
According to Henriques (2016), studying the seasonality of the leaves fraction allows greater knowledge about how the vegetation behaves in relation to climatic variations, the distribution and stock of the nutrients present in the litter disposed on the forest floor, providing a better understanding of the strategies that the vegetation uses in the process of ecosystem maintenance. Nascimento et al. (2013), emphasize that the production of the leaves fraction is directly linked to the reduction of precipitation along with the reduction of the photoperiod, contributing to the water stress that leads to higher deposition of this material in the most critical periods of the year. Holanda et al. (2017), studying the Sítio Riachão in Pombal-PB, found that the month of April/2010 presented higher deposition of the fraction of twigs + bark, being able to be associated with high rainfall indexes that caused strong winds, allowing the dry branches in the treetops to be soaked. Thus, increasing their weight and making them more vulnerable to the action of the winds.
However, Maciel et al. (2012) in Serra Talhada-PE, obtained results superior to 50% for fraction of twigs + bark, due to the absence of rainfall and the non-sprouting of vegetation, resulting in the loss of lignified structures.
The production of reproductive material in the dry period may be related to the high rainfall that occurred previously, thus contributing to the maintenance of soil moisture for a longer period and supplying the water needs of the plants (Souza et al., 2016).
There are indications that the contribution of the reproductive material fraction throughout the year is directly related to the maturation stage of the fruits and, consequently, their dispersion, common characteristics for species present in the Caatinga (Ferreira, 2011).
The diversity of species present in fragments of preserved Caatinga allows greater phenological variability, providing that these ecosystems are in equilibrium even if a low water availability occurs in these regions (Araújo et al., 2018).
In the miscellaneous fraction, it is possible to observe variability in its composition and deposition, presenting a smaller participation in the constitution of the litter, however, it presents considerable importance as it is easy to decompose and releases nutrients to the soil faster (Alves, 2014). In the dry period, much of this fraction is composed of bird excreta, feathers and insect carcasses. Deposition generally increases in the middle of the rainy season and extends to the dry season (Moura et al., 2016).
In any biome or study site differences can be found in relation to the litter decomposition time, this fact is related to the amount and quality of litter disposed on the forest floor, because there are variations from one period to another, especially those that refer to climatic variations (Ferreira, 2011).

Conclusions
The total deposition of litter during the two study periods is in line with the average yield for the Caatinga biome; The increase in precipitation provided higher deposition of litter after the rainy season; In both periods in the dry season there was greater litter production due to the intensification of the deciduous species of most caatinga species;