How Bovine Livestock Affects Seed Rain in Subtropical Climate Forest

Seed rainfall may be one of the mechanisms most impacted by livestock production in forest remnants. The trampling and cattle grazing alter dynamics, structure and floristic composition of the forest. The present work characterized the seed rainin forest remnants and the possible impacts of the presence and the management regime with different cattle stocks in the Pampa biome, southern region of Brazil. We compared three areas in Seasonal Forest remnants with a management history of 43 years: cattle exclusion area (A1); area with a cattle stock of 0.5 ua ha (A2); and area with cattle stock of 1.0 ua ha (A3). The seed rain was collected quarterly in 16 collectors (1 × 1 m2) per area for 24 months. The seeds were counted and identified according to external morphological characteristics, habit and dispersion syndrome. Shannon diversity index, submitted to the Hutcheson test, Pielou evenness, expected diversity and floristic similarity were determined. The results indicated that the impacts caused by livestock to seed rain were more significant in A3 where a quantitative reduction in the number of seeds was observed, probably due to the low number of plant individuals that make up the community.


Introduction
The horizontal distribution of a particular species of the forest community depends on its colonization success, determined by the establishment and dispersion of its propagules (Chazdon, 2014). In this way, the relationships that plant individuals establish with the environment and with anthropic interventions can compromise the colonization and establishment of species (Hutchings, 1989;Begon et al., 2006). foresta is fundamental for understanding recruitment processes, abundance, spatial distribution, density and species richness (Vieira & Gandolfi, 2006).
The southern region of Brazil differs from the rest of the territory because of its subtropical climate. Its paleoclimatic history generated peculiar characteristics of phytophysiognomies in the two biomes of its range: Atlantic Forest and Pampa. There are mosaics of well-defined country and forest vegetation in both biomes. The presence of country vegetation enabled the development of cattle raising activity, especially in the Pampa biome. Its importance is not only economic, but also sociocultural.
The Pampa biome is currently the second most threatened in Brazil and there is a lack of scientific studies that can support restoration and sustainable management plans (Roesch et al., 2009).
The forest remnants are impacted by the advancing commodity productive area, mainly soybean crops, with a reduction in remnant size and connectivity between habitats (Silveira et al., 2017). In spite of this, they present fundamental ecosystem services; most of the springs and water courses of the biome are found in the forest remnants, in addition to serving as refuges for wild fauna and being maintainers of the floristic diversity, its products and services (Rovedder et al., 2016).
In view of the above, the present work aimed to characterize the seed rain in forest remnants in the Pampa biome of southern Brazil, verifying the possible impacts caused by the presence of cattle inside this forest.

Material and Methods
The study was carried out in a Seasonal Forest remnant in the Pampa biome, Rio Grande do Sul state, in the southern region of Brazil. The region presents Oxisols in association with Regosols and Gleisols (Streck et al., 2018;EMBRAPA, 2013). The altitudes range between 50 and 200 masl. The climate is "Cfa" according to the Köppen classification, subtropical humid, without a dry season, with an average annual temperature of 22 °C. The average annual precipitation varies between 1300 and 1800 mm year -1 , with higher values recorded in winter (Alvares et al., 2013).
The vegetation cover is composed of fields and seasonal forests (Marchiori, 2004). The socioeconomic profile is predominantly characterized by small and medium-sized rural properties, based on the commercial cultivation of soybean, corn and extensive livestock farming (Instituto Brasileiro de Geografia e Estatística [IBGE], 2014).

Characterization and Usage History of the Study Area
The property has belonged to the same family for 49 years, which enabled gathering the management history of the place. The remnant forest is located at the coordinates 28°16′42.14″ S; 55°13′14.14″ W and has 57 ha, with eight springs and water courses that flow into the Piratini River, a tributary of the Uruguay River. In 1975, the remainder was divided into three areas (Figure 1), which in the present study configured into the following treatments: Area 1 (A1): part of the forest remnant surrounded and isolated from the entrance of cattle 43 years ago to preserve springs. In the present study we have considered it as a reference area.
Area 2 (A2): part of the forest remnant managed with an animal stock of 0.5 ua ha -1 for 43 years.
Area 3 (A3): part of the forest remnant managed with an animal stock of 1 ua ha -1 for 43 years. jas.ccsenet.

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The significant difference between A1 and A3 for the number of seeds in 2016 may be a consequence of an interaction between the climatic atypicality of that year and the intensity of management in A3 (Table 3). In the present study, we observed a decrease in the number of seeds and the number of seeds per hectare, respectively. In addition, the presence of livestock may affect the presence of dispersers due to the diet overlap, modifying floral traits of the existing species (Vázquez, 2002;Eaton et al., 2016). Thus, the higher animal stock for 43 years in A3 contributed to affecting the regeneration mechanisms and altered the vertical structure of the forest, reducing sub-forest strata. This can be verified by the light incidence (Table 1) due to the lower number of plant individuals in the community. The area consequently presents lower resilience and greater susceptibility to environmental variations, such as extreme weather events.
The highest amounts of seeds of arboreal species found in all areas in the two years of evaluation can be considered as a positive indicator. According to Martini and Santos (2007), species of arboreal habitats attract and favor the permanence of pollinating and dispersing animals in the local promoting greater ecological balance in the community.
The number of C. trichotoma seeds in the two years of evaluation may be related to the species phenology, since it presents abundant flowering between February and June (Reitz et al., 1988;Felippi et al., 2012). Nevertheless, the species' number of seeds was affected by the atypicality of the precipitation regime in the year 2016. As C. trichotoma is a species that occupies the upper strata of the forest formations and presents anemochoric dispersion, its flowers, fruits and seeds are subject to the effects of excessive rainfall. According to Felippi et al. (2012), the species flowers show greater sensitivity in the rainy season due to the impact of raindrops which damage the floral buds, in turn damaging the entire reproductive process.
A. leiocarpa is one of the species with the greatest abundance in the seed rain in 2015 and 2016, and in addition to I. paraguariensis did not present expressivity in the development of the natural regeneration of areas with cattle (A2 and A3), according to a floristic survey carried out in the same areas by Stefanello (2016). It is assumed that these species are more susceptible to the impacts of livestock management, since the development of a species in the regenerating stratum is related to seed rain and is determined by the seed rainfall density and of the seedling density (Simpson, 1989).

Scattering Syndrome
The predominance of zoochory in seasonal forest in southern Brazil (Figure 3), has been reported by several authors (Scipioni et al., 2011;Giehl et al., 2007;Scipioni et al., 2013;Sccoti et al., 2016). This also seems to be a typical pattern of forests in tropical Brazil. According to Fenner (1985) and Piña-Rodrigues and Aoki (2014), the high amount of zoochoric species is indicative of plant communities in more advanced succession stages.
However, finding values between 31 and 37% of anemochoria in formations with a more advanced succession stage, as in the case of areas A2 and A3, can be a response to the disturbances caused to the vegetation by the cattle management during the four decades. The presence of anemochoria can be considered as an indication of environmental disturbance in already established forest formations, since wind dispersion benefits these conditions (Piña-Rodrigues & Aoki, 2014). The luminosity values for the respective areas (Table 1) show that the forest cover is more spaced in these places, which would justify the anemochoria values found in this forest formation.

Diversity Indices
There were no significant differences for Shannon diversity in the two years. However, the distribution of morphospecies in A1 for the year 2015 showed to be more heterogeneous in relation to areas with livestock, based on the Pielou evennes index. For the year 2016, A2 showed to be the area with more heterogeneous distribution in relation to the others.
The expected species richness ( Figure 4) demonstrates a curve-stabilizing behavior in all areas (Magurran, 2004;Kageyama & Piña-Rodrigues, 1993;Felfili et al., 2011). In addition, there is an inversion behavior trend of the seed rain from the year 2015 to the year 2016 for the evaluated areas. The seed rain in A2 suffered greater oscillations in relation to the atypical precipitation, probably due to the presence of native field patches in the interior of the sentence fragment ( Figure 1). This discontinuity of the forest area in A2 contributes to the action of wind (Giehl et al., 2007) and rain (Vieira & Gandolfi, 2006;Felippi et al., 2012;Piña-Rodrigues & Aoki, 2014) in the interior of the forest, unlike A1 and A3, which have a continuous forest formation, considering only the external physiognomy.

Floristic Similarity
Changes in floristic similarity between the analyzed areas in a short time may be related to several factors; among them climatic factors, such as the case of the atypical precipitation in 2016. Extreme conditions such as excessive rainfall or prolonged droughts with cleared gaps are disturbances that influence the dynamics of the forest community (Giehl et al., 2007) in terms of quantity and quality of flowering and fruiting of species and seed dispersion (Piña-Rodrigues & Aoki, 2015). These disturbances may directly influence the dissimilarity of areas that may have been closer in floristic terms (Giehl et al., 2007).
In the location under study, we observed that the oscillations in the rainfall regime caused changes in cattle behavior and diet, causing the native field areas surrounding the A2 and A3 areas to decrease their biomass, resulting in a lower supply of food for cattle. This factor may have influenced the animals to look for food inside the forest, intensifying the herbivory and trampling in the local. It also may have contributed to the change in similarity in the evaluation period. The management history and the in loco observations carried out in different years with unequal climatic situations, as in the case of the present study, provide such inferences.

Conclusion
The presence of cattle within the forest remnant acts effectively as a filter for the dynamics and composition of seed rain.