The African Savanna Cyclone Experiment (CyclEx)

CyclEx将通过研究飓风Idai的长期影响来测试稀树草原和干燥森林是替代稳定状态的理论。生态系统具有替代稳定状态的概念对于我们如何管理和预测生物圈的未来至关重要。热带大草原是热带地区最大的土地覆盖，支撑着世界上数以亿计的最贫穷人口的生计。它们还拥有一种古老、独特、富有魅力的动植物--“狩猎”景观。然而，世界上发现最多热带草原的地区被广泛认为是双稳定的--也就是说，它们可以支持热带草原(一种稳定的状态，几乎没有树木，经常燃烧，可以养活许多放牧动物)，或者森林(另一种稳定的状态，有封闭的树冠，高碳储存，更少的草和很少的火)。许多科学家认为，在相同的环境条件下，这两种状态都可能存在，例如，干燥的森林可能会因为系统受到冲击(如气旋)而“翻转”成为稀树草原。这些想法被广泛用于指导稀树草原的管理和预测稀树草原将如何应对气候和其他全球变化。然而，尽管干燥热带地区的双稳概念很容易被假设，但它很难被证明，而且一直存在争议。它的证据来自数学模型，以及对树木覆盖率和树高的静态空间模式的观察，这些模式在频率分布上显示出明显的“峰值”，许多人将其解释为不同的稳定状态。然而，最近的建模工作表明，这些峰值并不是双稳的可靠证据--它们与这一想法是一致的，但与非双稳生态系统相关的其他机制可以产生这些观察结果。飓风艾达为检验这些理论提供了一个独特的机会。据报道，龙卷风在理论上可能出现其他稳定状态的地区倾倒或损坏了大量树木。我们的现场，戈龙戈萨国家公园，在龙卷风期间遭遇了一些最高的风速，为长期观察影响和恢复提供了绝佳的场所。我们相信，如果确实存在其他稳定状态，我们很可能在这里观察到它们。CyclEx将首先使用雷达遥感绘制气旋影响的地图，以检查热带草原和干旱森林在气旋前后的结构。然后，我们将建立长期的地块，在那里我们可以了解飓风过后植被是如何恢复的，并看看许多树木被掀翻或损坏的地区是否会陷入稳定的开阔草原状态，或者林区是否最终恢复到飓风前的结构和物种组合。这将告诉我们稀树草原和森林之间的转换是否可能，以及替代稳定状态的理论是否得到支持。CyclEx的结果无论是作为对替代稳定状态的关键生态学理论的测试，还是在更实际的水平上都是重要的。由于气候变化，预计强烈气旋将在东非变得更加常见，并将影响比目前更广泛的地区。我们需要知道它们将对对生物多样性和当地生计重要的生态系统产生什么影响，CyclEx将是有史以来第一次分析非洲大草原上气旋的影响。

CyclEx will test the theory that savannas and dry forests are alternative stable states by examining the long term impacts of Cyclone Idai.The concept of ecosystems having alternative stable states is crucial to how we manage and predict the future of the biosphere. Savannas are the largest land cover in the tropics and support the livelihoods of 100s of millions of the world's poorest people. They also harbour an ancient, unique, charismatic flora and fauna - the "safari" landscape. However, the regions of the world where most savannas are found are widely considered to be bistable - that is they can support either savannas (a stable state with few trees that burns regularly and can support many grazing animals), or forests (another stable state with a closed tree canopy, high carbon storage, less grass and few fires). Many scientists believe that these two states can both exist given the same environmental conditions, and that for example dry forests may "flip" to become savannas due to shocks to the system, such as cyclones. These ideas are widely used to guide savanna management and to predict how savannas will respond to climate and other global change.However, whilst the concept of bistability in the dry tropics is easy to hypothesise, it is very hard to prove and has remained controversial. The evidence for it comes from mathematical models, and observations of static spatial patterns of tree cover and tree height, which show distinct "peaks" in their frequency distributions, which many have interpreted as the different stable states. Recent modelling work suggests however that these peaks are not reliable evidence of bistability - they are consistent with the idea, but other mechanisms associated with non-bistable ecosystems can generate these observations. Cyclone Idai provides a unique opportunity to test these theories. The cyclone is reported to have toppled or damaged large numbers of trees, in areas where theory suggests alternative stable states are likely. Our field site, Gorongosa National Park, was subjected to some of the highest windspeeds during the cyclone and provides an excellent place to carry out long term observations of the impacts and recovery. We believe that, if alternative stable states do exist, we are very likely to observe them here.CyclEx will first map the impact of the cyclone using radar remote sensing to examine the structure of the savannas and dry forest pre- and post-cyclone. We will then establish long term plots where we can understand how the vegetation recovers after the cyclone and see if areas where lots of trees were knocked over or damaged get "stuck" in a stable open savanna state, or if forest areas eventually recover their pre-cyclone structure and mix of species. This will tell us if switches between savanna and forests are possible, and whether the theory of alternative stable states is supported.The results of CyclEx are important both as a test of the key ecological theory of alternative stable states, and on a more practical level. Intense cyclones are predicted to become more common in East Africa due to climate change, and to affect a wider area than at present. We need to know what their impacts will be on an ecosystem that is important for biodiversity and for local livelihoods, and CyclEx will be the first ever analysis of the impacts of cyclones in African savannas.