A meta-analytic dataset of plant facilitation in coastal dune systems: responses, regions, and research gaps

Empirical studies in salt marshes, arid, and alpine systems support the hypothe-<br>sis that facilitation between plants is an important ecological process in severe or ‘stressful’ environments. Coastal dunes are both abiotically stressful and frequently disturbed systems. Facilitation has been documented, but the evidence to date has not been synthesized. We did a systematic review with meta-analysis to highlight general research gaps in the study of plant interactions in coastal dunes and examine if regional and local factors influence the magnitude of facilitation in these systems. The 32 studies included in the systematic review were done in coastal dunes located in 13 countries around the world but the majority was in the temperate zone (63%). Most of the studies adopt only an observational approach to make inferences about facilitative interactions, whereas only 28% of the studies used both observational and experimental approaches. Among the factors we tested, only geographic region mediates the occurrence of facilitation more broadly in coastal dune systems. The presence of a neighbor positively influenced growth and survival in the tropics, whereas in temperate and subartic regions the effect was neutral for both response variables. We found no evidence that climatic and local factors, such as life-form and life stage of interacting plants, affect the magnitude of facilitation in coastal dunes. Overall, conclusions about plant facilitation in coastal dunes depend on the response variable measured and, more broadly, on the geographic region examined. However, the high variability and the limited number of studies, especially in tropical region, indicate we need to be cautious in the generalization of the conclusions. Anyway, coastal dunes provide an important means to explore topical issues in facilitation research including context dependency, local versus regional drivers of community structure, and the importance of gradients in shaping the outcome of net interac- tions.

盐沼、干旱及高山生态系统中的野外实证研究支持了植物间促进作用（plant facilitation）是严酷或‘胁迫’环境中重要生态过程这一假说。海岸沙丘属于兼具非生物胁迫与频繁扰动的生态系统。尽管已有文献记录了该系统中的植物促进作用，但迄今尚未有研究对相关证据进行综合整合。
本研究开展了一项结合元分析（meta-analysis）的系统综述（systematic review），旨在明确海岸沙丘植物相互作用研究中的普遍研究空白，并检验区域与局地因子是否会调控此类系统中植物促进作用的强度。
本次系统综述纳入的32项研究均开展于全球13个国家的海岸沙丘区域，其中多数研究位于温带区域（占比63%）。大部分研究仅采用观测方法来推断植物促进相互作用，仅28%的研究同时采用观测与实验两种方法。
在本研究检验的各类因子中，仅地理区域能够在更大尺度上介导海岸沙丘系统中植物促进作用的发生。在热带区域，邻体植物的存在对目标植物的生长与存活具有显著正向影响；而在温带与亚北极区域，邻体对这两类响应变量的效应均为中性。
本研究未发现气候因子与局地因子（如相互作用植物的生活型与生活史阶段）会对海岸沙丘中植物促进作用的强度产生显著影响。总体而言，关于海岸沙丘植物促进作用的研究结论，既取决于所选取的响应变量，更广泛地也取决于所考察的地理区域。
不过，现有研究的高异质性与样本量有限的问题（尤其是热带区域的研究样本极少）提示，在对研究结论进行外推推广时需保持谨慎。尽管如此，海岸沙丘仍是探索植物促进作用研究前沿议题的重要载体，这些议题包括情境依赖性、群落结构的局地与区域驱动因子，以及环境梯度在塑造净相互作用（net interactions）结果中的重要性。