Seeing the fruit for the trees in Borneo: responding to an unpredictable community-level fruiting event

由于选择性采伐和广泛清除油棕榈树种植，东南亚热带森林最近承受着巨大的压力。因此，人们对使用自然更新或积极恢复处理恢复退化的森林产生了兴趣。然而，东南亚热带林木的繁殖生物学限制了对这些方法的有效性的研究，因为大多数大型树冠树很少开花和结果。这些零星的大规模繁殖事件是建立新的苗木群体的原因，这些苗木长大后成为下一代成年冠层树，关键是要发现这些时断时续的更新尝试在因采伐而退化的森林中的成功程度是否与在原始森林中一样大，以及在已采取植树和攀援砍伐等处理措施的森林中，导致幼苗招募的过程是否得到有效恢复。然而，由于这些更新事件发生得如此罕见和不可预测，因此很难将其纳入常规规划周期进行研究，尽管在树木生命周期早期发生的事件对未来的森林至关重要。在这个项目中，我们将在马来西亚沙巴州迅速建立采样点，我们知道2019年5月开始了树冠树的大规模开花，这是自2010年以来的首次。我们的目标是比较原始(未受干扰的，未被砍伐的)森林和邻近森林在这一盛事期间产生的果实和幼苗的数量和多样性，这些森林已经被砍伐，要么被留下来自然再生，要么通过种植树苗并通过攀缘砍伐维持五年来恢复。由于砍伐森林的恢复始于20多年前，最初种植的苗木现在是，在某些情况下，可能在今年繁殖活动期间首次贡献种子和幼苗的大棚树。我们还将测量决定植物如何捕捉和利用三种类型森林中最常见物种的资源(如光和养分)的特征的表达，这将确定在恢复的森林中建立的苗木群落的功能是否与未受干扰的原始森林中的苗木群落的功能更相似，而不是在伐木后自然再生的森林中。这项研究的重点将放在主要树冠和新兴乔木家族的物种上，即龙脑香科，这些物种是被砍伐的目标。原木林拥有较低密度的繁殖成熟的大型龙脑果树个体，恢复的一个关键目标是通过种植和维护龙脑树种苗来重建该家族的优势度和多样性。对于热带森林的乔木植物区系来说，龙脑果具有一个不同寻常的特征，那就是它们与根部定植的外生菌根真菌(ECM)形成互惠共生关系，而森林中的大多数其他物种与丛枝菌根(AM)形成不同类型的根联结。我们最近的研究表明，ECM幼苗受益于接近高密度的ECM成虫，可能是因为它们通过共同的地下真菌网络交换资源，而且ECM物种抑制根病原体。相反，AM幼苗在接近同一物种的高密度成虫时存活率较低。我们项目的最终目标是测试高成虫密度对ECM物种的有利影响是否在ECM成虫密度低得多的伐木森林中减少，以及这些影响是否被恢复所抵消。因此，这项研究将有助于了解东南亚森林在采伐活动期间是如何再生的，以及恢复采伐是否可以减轻采伐的负面影响。

Southeast Asian tropical forests have been subjected to recent intense pressure due to selective logging and widespread clearance for Oil Palm cultivation. Consequently there is an emerging interest in restoring degraded forests using either natural regeneration or active restoration treatments. However, the reproductive biology of Southeast Asian tropical forest trees limits research on the effectiveness of these approaches, because most large canopy trees only flower and fruit very rarely. These sporadic mass reproductive events are responsible for establishing new cohorts of seedlings that grow up to become the next generation of adult canopy trees, and it is critical to discover whether the success of these episodic attempts at regeneration is as great in forests that have been degraded by logging as they are in primary forests, and whether the processes leading to seedling recruitment are restored effectively in forests where treatments such as tree planting and climber cutting have been applied. However, because these regeneration events occur so infrequently and unpredictably it is very difficult to incorporate them into the conventional planning cycle for research, despite the critical importance of the events that occur early in the life cycle of trees to future forests. In this project we will rapidly establish sampling sites in Sabah, Malaysia, where we know that a mass flowering of canopy trees was initiated in May 2019, for the first time since 2010. We aim to compare the amount and diversity of fruits and seedlings produced during this masting event in primary (undisturbed, unlogged) forests, and in adjacent forests that have been logged and either left to regenerate naturally or restored by planting tree seedlings and maintaining them for five years by climber cutting. Because the restoration of logged forests began more than 20 years ago, the original cohort of planted seedlings are now, in some cases, large canopy trees that may contribute seeds and seedlings for the first time during the reproductive event this year. We will also measure the expression of traits that determine how plants capture and use resources such as light and nutrients for the most common species that occur in each of the three types of forest, which will determine whether the community of seedlings that establish in the restored forests functions in a more similar way to that in the undisturbed primary forest than in the forests left to regenerate naturally after logging. A key focus on this study will be on species of the dominant family of canopy and emergent trees, the Dipterocarpaceae, which are targeted for logging. Logged forests possess a lower density of large reproductively mature dipterocarp individuals, and a key aim of restoration is to re-establish the dominance and diversity of this family by planting and maintaining dipterocarp seedlings. Dipterocarps possess an unusual trait for the tree flora of tropical forests, which is that they form mutualistic associations with root-colonising ectomycorrhizal fungi (ECM), whereas most other species in the forest form a different type of root association with arbuscular mycorrhizas (AM). Our recent research has shown that ECM seedlings benefit from proximity to a high density of ECM adults, possibly because they exchange resources through a common below-ground fungal network and because ECM species suppress root pathogens. In contrast, AM seedlings have lower survival when located close to a high density of adults of the same species. A final aim of our project is to test whether the beneficial effects of high adult density for ECM species is reduced in logged forests where the density of ECM adults is much lower, and whether these effects are offset by restoration. This research will therefore contribute results that are vital to understanding how Southeast Asian forests regenerate during masting events, and whether the negative effects of logging can be mitigated by restoration.