Temporal changes in species composition, diversity, and woody vegetation structure of savannas in the Cerrado-Amazon transition zone

ABSTRACT Vegetation in the transition between tropical forest and savanna is hyperdynamic and there is evidence that in the absence of fire, forest advances over savanna. Between 2008 and 2013 we evaluated changes in species composition and diversity and in the structure of the woody vegetation of savanna physiognomies in the transition between the Cerrado and Amazon biomes that were fire free for 11 years. The physiognomies form a gradient from savanna woodland (Typical Cerrado - TC), to low woodland (Dense Cerrado - DC), to woodland (locally called Cerradão - CO). We hypothesise that: 1) the more open physiognomies (TC and DC) are more dynamic compared to the closed physiognomy (CO); and 2) in the absence of fire vegetation tends to become more forested. We found that: 1) TC was more dynamic (e.g. greater increases in richness, diversity, and abundance of plants and basal area) than CO and DC; 2) The three physiognomies experienced an increase in basal area and abundance of individuals, but only certain key species contributed to these increases. These results indicate that the open physiognomies were more dynamic than the closed physiognomies, and in the absence of fire the savanna physiognomies became more forested and accumulated biomass.

摘要：热带森林与稀树草原过渡带的植被具有极高的动态性，且有研究证据表明，在无火干扰的条件下，森林群落会向稀树草原区域扩张。2008年至2013年间，我们针对塞拉多（Cerrado）与亚马逊（Amazon）生物群系过渡带的稀树草原植被外貌类型，开展了为期11年无火干扰下的物种组成、多样性及木本植被结构变化的评估工作。该类植被外貌类型形成了连续梯度：从稀树灌丛（典型塞拉多（Typical Cerrado，TC））、矮灌丛（密灌塞拉多（Dense Cerrado，DC））到灌丛（当地称塞拉多恩（Cerradão，CO））。我们提出如下研究假说：1）相较于封闭型植被外貌类型（CO），开放型植被外貌类型（TC与DC）具有更高的动态性；2）在无火干扰的条件下，植被群落会愈发趋向森林化方向发展。研究结果显示：1）TC的动态性显著高于CO与DC（例如，植物丰富度、多样性、个体丰度及基面积的提升幅度更大）；2）三种植被外貌类型的基面积与个体丰度均有所提升，但仅部分关键物种推动了此类增长。上述结果表明，开放型植被外貌类型的动态性高于封闭型植被外貌类型，且在无火干扰的情况下，稀树草原植被类型会愈发趋向森林化，并积累更多生物量。