Local changes in floristic richness in two ecorregions of the caatinga

AbstractThe caatinga vegetation of northeastern Brazil occurs mainly in Pre-Cambrian, crystalline-derived soils and also on sedimentary-basin-derived sandy soils. Recent evidence has shown variations in the dynamics, structure and floristic composition of the caatinga over these two different edaphic macro-environments, which justifies the need for studies focusing on different substrates. A floristic study of the caatinga ecoregions Depressão Sertaneja Meridionaland Raso da Catarina in the municipality of Tucano, Bahia, Brazil, is of special interest because both substrates occur in a local scale, allowing the opportunity to broaden our knowledge on ecological heterogeneity within the Caatinga biome. In the current study we carried out a floristic survey of 14 sites distributed throughout the ecoregions of caatinga in Tucano. We found high species diversity in the caatingas of Tucano when compared to other areas in northeastern Brazil. A total of 450 species, 288 genera, and 82 families were collected. The most species rich families are Leguminosae and Euphorbiaceae. There occur 226 species in the sites on crystalline basement, whereas 284 species were collected in the sandy areas. The ecoregions were only 13% similar in floristic composition. We found strong differences between the ecoregions with respect to floristic composition and predominant plant habit as proxy for phytophysiognomy. Overall, our results reinforce the hypothesis of two distinct biotas that assembly the caatinga dry woodlands.

摘要：巴西东北部的卡廷加植被（caatinga）主要分布于前寒武纪结晶源土壤，同时也见于沉积盆地衍生的砂质土壤。近期研究显示，在这两类不同的土壤基质大型生境中，卡廷加植被的动态、结构及区系组成均存在差异，这凸显了针对不同基质开展研究的必要性。针对巴西巴伊亚州图卡诺市境内的卡廷加生态区——塞尔坦尼亚南部洼地（Depressão Sertaneja Meridional）和拉索达卡塔里纳（Raso da Catarina）开展的区系研究具有特殊价值，因这两种基质在当地小尺度范围内共存，为深入解析卡廷加生物群区的生态异质性提供了研究契机。本研究对图卡诺市卡廷加生态区内分布的14个样地开展了区系调查。相较于巴西东北部其他区域，图卡诺市卡廷加植被的物种多样性水平显著更高。本次调查共采集到450种植物，隶属于288属、82科。物种丰富度最高的类群为豆科（Leguminosae）与大戟科（Euphorbiaceae）。其中结晶基底样地共记录226种，砂质土壤样地则采集到284种。两个生态区的区系组成相似度仅为13%。研究发现，二者在区系组成及表征植物群落外貌的优势生活型方面均存在显著差异。综上，本研究结果进一步佐证了“卡廷加旱生林由两类截然不同的生物群落构成”这一假说。