Tropical forest refuge in peripheral soils of slags in Caatinga

Abstract

18The influence of environmental factors on the structure and composition of plant 19 communities in the Caatinga is complex and poorly explored. Spatial variation of 20 biodiversity in Caatinga is poorly know and strictly attributed to climatic conditions. 21 We investigated the influence of slags on floristic composition and structure of a 22 shrubby-arboreal community in one of the driest region in Brazil. Chemical and 23 physical analyses of soils were performed in samples of seven plots from savannic 24 formations and from forest formations. Vegetation was characterized floristically and 25 structurally in all plots. Habitats were structurally distinct, and diversity differed 2 26between peripheral and non-peripheral areas of slags. Nine of the ninety-seven species 27 identified are reported to (sub)humid biomes. Soils are dominantly shallow, eutrophic 28 and sandy loam. However, soils in the periphery of slags are more developed once 29 paludization, melanization and bioturbation were verified. Our results suggest that soil 30 fertility did not influence vegetable cover in Caatinga. The cover of plant species 31 considered exclusive of (sub)humid biomes in Brazil extends beyond highlands in the 32 semiarid, associated with high soil organic carbon content and water retention capacity 33 of more developed soils than the typical of the Caatinga. 34 35 36 Dryland biomes cover 41.5 % of the Earth's surface, with seasonally dry tropical 37 forests occupying approximately 1,327 million hectares within this area [1]. The largest 38 area of continuous dry tropical rainforests in Latin America occurs in Brazil, with 39 approximately 800.00 km². Popularly called as Caatinga (Mata Branca), most trees and 40shrubs lose their leaves in the dry season, which can last up to nine months a year in 41 certain regions [2]. 42 Caatinga is a Brazilian exclusive biome composed by different plant formations 43 [3] and its diversity is considered one of the most biodiverse among semiarid biomes 44 [4,5]. Among the several ecosystems that exist in the Caatinga, granitic intrusions in the 45 form of inselbergs, massive, slags (lajedos in portuguese) and bornhardts cover 15 % of 46 the total area of the northern Brazilian Northeast [6]. 47Low developed, shallow and eutrophic soils are dominant in Caatinga due to 48 tropical dry climate. However, high local diversity of soils has been attributed to 49 variance of lithology and, or, relief by recent studies [7]. Understood soil diversity is a 50 relevant task, especially considering that plant distribution is conditionate by soil 3 51 properties [8,9]. Soil influences plant physiognomies in Brazilian Savanna (Cerrado) 52[10], Restinga forest [11], Amazonia rainforest [12,13], Tundra [14] and other biomes 53 around the world [15,16]. However, species diversity in Caatinga is poorly know [17] 54 and strictly attributed to climatic conditions [18][19][20]. 55The purpose of this study was to investigate a vegetation gradient at preserved 56 slabs in Caatinga, and t...