Spatial indices of tree diversity have often been proposed as surrogates of direct measures of biodiversity. They are comparatively straightforward to measure as part of forest ecosystem monitoring designed to alert to potentially negative effects of ongoing climate change. The loss of biodiversity, which is thought to be related to a decline in tree diversity, is perceived as a substantial threat, since biodiversity is also crucial to ecosystem resilience. We studied the correlation between community species mingling and size inequality of Knysna Forest, a well-known Afromontane forest ecosystem in South Africa, to better understand the principles of how nature maintains tree diversity. This is an important prerequisite for active conservation. The aforementioned correlation is indicative of the predicting that large trees are surrounded by significantly more heterospecific trees than smaller trees. The mingling-size hypothesis helps understand natural principles of tree diversity maintenance and is motivated by the well-known Janzen-Connell and herd-immunity hypotheses. Our results revealed that the correlation between spatial species mingling and size inequality is mostly negative at Knysna Forest, which is comparatively rare. This implies that the mingling-size hypothesis does not hold in this forest ecosystem. This has implications for conservation, because spatial size-inequality is no longer a by-product of high species mingling and potentially requires additional conservation effort. We could also show that the aforementioned negative correlation can be inferred from the mark cross correlation function when applying this spatial summary characteristic to the mingling and size inequality indices of individual trees.

中文翻译：

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多样化的非洲山地森林中同种物种混合和大小不平等之间罕见的时空相互作用

树木多样性的空间指数经常被提议作为生物多样性直接测量的替代品。作为森林生态系统监测的一部分，它们的测量相对简单，旨在警惕持续气候变化的潜在负面影响。生物多样性的丧失被认为与树木多样性下降有关，被认为是一个重大威胁，因为生物多样性对于生态系统的复原力也至关重要。我们研究了南非著名的阿弗罗山森林生态系统克尼斯纳森林的群落物种混合与规模不平等之间的相关性，以更好地理解大自然如何维持树木多样性的原理。这是积极保护的重要前提。上述相关性表明，预测大树周围的异种树明显多于小树。混合规模假说有助于理解树木多样性维持的自然原理，并受到著名的 Janzen-Connell 假说和群体免疫假说的启发。我们的结果显示，在克尼斯纳森林，空间物种混合与大小不平等之间的相关性大多为负相关，这相对罕见。这意味着混合规模假设在这个森林生态系统中不成立。这对保护具有影响，因为空间大小不平等不再是物种高度混合的副产品，并且可能需要额外的保护工作。我们还可以证明，当将这种空间汇总特征应用于单棵树的混合和大小不平等指数时，可以从标记互相关函数推断出上述负相关性。