Konza Species Composition: Konza-Kruger Fire-Grazing Project (2006-2010)

The distribution, structure and function of mesic savanna grasslands are strongly driven by fire regimes, grazing by large herbivores, and their interactions. This research addresses a general question about our understanding of savanna grasslands globally: Is our knowledge of fire and grazing sufficiently general to enable us to make accurate predictions of how these ecosystems will respond to changes in these drivers over time? Some evidence suggests that fire and grazing influence savanna grassland structure and function differently in South Africa (SA) compared to North America (NA). These differences have been attributed to the contingent factors of greater biome age, longer evolutionary history with fire and grazing, reduced soil fertility, and greater diversity of plants and large herbivores in SA. An alternative hypothesis is that differences in methods and approaches used to study these systems have led to differing perspectives on the role of these drivers. If the impacts of shared ecosystem drivers truly differ between NA and SA, this calls into question the generality of our understanding of these ecosystems and our ability to forecast how changes in key drivers will affect savanna grasslands globally. Since 2006, an explicitly comparative research program has been conducted to determine the degree of convergence in ecosystem (productivity, N and C cycling) and plant community (composition, diversity, dynamics) responses to fire and grazing in SA and NA. Thus far, initial support has been found for convergence at the ecosystem level and divergence at the community level in response to alterations in both fire regimes and grazing. However, there have also been two unexpected findings (1) the ways in which fire and grazing interact differed between NA and SA, and (2) the rate of change in communities when grazers were removed was much greater in NA than in SA. These unexpected findings raise a number of important new questions: (Q1) Will exclusion of grazing eventually affect community structure and composition across all fire regimes in SA? (Q2) Will these effects differ from those observed in NA? (Q3) What are the determinants of the different rates of community change? (Q4) How will these determinants influence future trajectories of change? (Q5) Will the different rates and trajectories of community change be mirrored by responses in ecosystem function over time? This project is based on a large herbivore exclusion study established within the context of long-term (25-50+ yr) experimental manipulations of fire frequency at the Konza Prairie Biological Station (KPBS) in NA and the Kruger National Park (KNP) in SA. The suite of core studies and measurements include plant community composition, ANPP, and herbivore abundance and distribution at both study sites to answer these research questions.

湿润稀树草原草地（mesic savanna grasslands）的分布、结构与功能，强烈受控于火制度（fire regimes）、大型草食动物放牧及其交互作用。本研究旨在解答一个关乎全球稀树草原草地认知的核心问题：我们对火与放牧的认知是否具备足够的普适性，足以精准预测这些生态系统随上述驱动因子变化的响应轨迹？

已有研究表明，南非（South Africa, SA）与北美（North America, NA）的火与放牧对稀树草原草地结构与功能的影响模式存在差异。这类差异曾被归因于一系列偶然性因素：南非生物群落更古老、火与放牧的演化历史更长、土壤肥力更低，以及植物与大型草食动物多样性更高。另有假说认为，研究方法与路径的差异才是导致两地对驱动因子作用认知分歧的根源。若北美与南非的共享生态系统驱动因子影响确实存在实质性差异，则将动摇我们对这类生态系统认知的普适性，以及我们预测关键驱动因子变化将如何影响全球稀树草原草地的能力。

自2006年起，学界启动了一项明确的比较研究计划，旨在探明北美与南非两地的生态系统（生产力、氮（N）与碳（C）循环）及植物群落（组成、多样性、动态）对火与放牧的响应在多大程度上具有趋同性。截至目前，研究初步发现：在火制度与放牧格局改变的背景下，生态系统层面的响应呈现趋同性，而群落层面的响应则存在分异。

但同时也得到了两项意料之外的结果：其一，火与放牧的交互作用模式在北美与南非存在差异；其二，移除草食动物后，北美群落的变化速率远高于南非。这些意外发现引出了一系列重要的新问题：（Q1）在南非所有火制度下，排除放牧最终是否会影响群落结构与组成？（Q2）这类影响是否会与北美观测到的结果存在差异？（Q3）导致群落变化速率差异的决定因素是什么？（Q4）这些决定因素将如何影响未来的群落变化轨迹？（Q5）群落变化的速率与轨迹差异，是否会随时间推移在生态系统功能的响应中得到体现？

本项目基于一项大型草食动物排除研究，该研究设立于北美康扎草原生物站（Konza Prairie Biological Station, KPBS）与南非克鲁格国家公园（Kruger National Park, KNP）的长期（25~50+年）火频率实验操控框架内。整套核心研究与测量内容涵盖两地的植物群落组成、地上净初级生产力（Aboveground Net Primary Production, ANPP）以及草食动物的丰度与分布，以解答上述研究问题。