Ficus abutilifolia and Ficus tettensis maturation: location and cracks are crucial factors

Ficus abutilifolia and Ficus tettensis are two species of deciduous rock fig trees commonly found on the vertical faces of Mapungubwe National Park, South Africa. The demographics of the rock figs as well as the habitat features necessary for successful maturation are currently unknown. This study first aims to provide demographic data and determine the points in the fig life cycle where bottlenecks occur. Secondly, it probes the importance to growth of location and usage of cracks. From general observations, we hypothesized that seedlings would be located anywhere on the rock faces, but that larger trees would be more limited to specific areas. We also conjectured that usage of cracks by tree roots would positively correlate with tree height, due to stability and nutrient gathering arguments. Within the sampled population, there was an uneven distribution of seedlings (62.8%), saplings (21.9%) and adults (15.3%). All size classes were contagiously dispersed on the outer edges of the rock faces, despite our expectation about seedling dispersal. Lastly, the number of cracks used by the roots as well as the number of large cracks used showed some degree of positive correlation with tree height. These results suggest that (1) there are growth bottlenecks in the population, (2) the outer edges of rock faces are either popular for dispersal or essential for establishment, and (3) large cracks provide more stability and/or necessary nutrients for trees as they mature.苘叶榕（Ficus abutilifolia）与特滕斯榕（Ficus tettensis）是两种落叶岩生无花果树，广泛分布于南非马蓬古布韦国家公园的垂直岩壁区域。目前学界对该类岩生无花果的种群统计特征，以及其成功成熟所需的生境条件均缺乏了解。本研究首先旨在获取该类无花果的种群统计数据，并明确其生活史周期中存在生长瓶颈的关键环节；其次，探讨岩壁裂隙的空间位置与根系对裂隙的利用情况对植株生长的重要性。基于前期常规观测，我们提出如下研究假说：幼苗可分布于岩壁的任意区域，而较大植株的分布则更局限于特定区域。此外，基于植株稳定性与养分获取的相关理论，我们推测植株根系对裂隙的利用程度与树高呈正相关关系。在本次采样的种群中，幼苗（62.8%）、幼树（21.9%）与成树（15.3%）的个体占比分布不均。尽管我们最初对幼苗的空间分布模式存在预设，但所有大小级的植株均集群分布于岩壁的外缘区域。最后，植株根系所利用的裂隙总数，以及其中大型裂隙的数量，均与树高存在一定程度的正相关关系。上述研究结果表明：（1）该种群存在生长瓶颈；（2）岩壁外缘要么是植物传播的偏好区域，要么是植株定植的必需生境；（3）大型裂隙可为成熟过程中的植株提供更充足的稳定性与/或必需养分。