Abstract
Shrubs can have a net positive effect on the recruitment of other species, especially relict species in dry-stressful conditions. We tested the effects of nurse shrubs and herbivory defoliation on performance (survival and growth) of nursery-grown seedlings of the largest living palm, the relict wine palm Jubaea chilensis. During an 18-month period, a total of more than 300 seedlings were exposed to of four possible scenarios produced by independently weakening the effects of nurse shrubs and browsers. The experiment followed a two-way fully factorial design. We found consistent differences in survival between protected and unprotected seedlings (27.5% and 0.7%, respectively), and herbivory had a dramatic and overwhelmingly negative effect on seedling survival. The invasive rabbit (Oryctolagus cuniculus) is clearly creating a critical bottleneck in the regeneration process and might, therefore, partially explain the general lack of natural regeneration of wine palms under natural conditions. Apparently biotic filters mediated by ecological interactions are more relevant in the early stages of recruitment than abiotic, at least in invaded sites of central Chile. Our data reveal that plant-plant facilitation relationship may be modulated by plant-animal interactions, specifically by herbivory, a common and widespread ecological interaction in arid and semi-arid environments whose role has been frequently neglected. Treatments that protect young wine palm seedlings are mandatory to enable the seedlings to attain a height at which shoots are no longer vulnerable to browsing. Such protection is an essential first step toward the conservation and reintroduction of this emblematic and threatened species.
Highlights
In arid and semi-arid environments, environmental gradients differ at local scales because shrubs generally improve soil fertility and produce microclimates under their canopies that favor plant-plant interactions [1]
Our results show that for Jubaea chilensis, seedling survival and growth were not affected by seed size (Pearson correlation, P > 0.05 for both comparisons)
Our findings from experimentally decoupling the herbivory and abiotic effects on wine palm seedling performance support the scarce empirical evidence indicating that semi-arid ecosystems have a strong impact on plant-plant interactions [11, 13, 14]
Summary
In arid and semi-arid environments, environmental gradients differ at local scales because shrubs generally improve soil fertility and produce microclimates under their canopies that favor plant-plant interactions [1]. According to the stress-gradient hypothesis (SGH) [2], interactions among plants vary with environmental conditions, shifting from competition to facilitation as environmental stress increases. Such environmental stress comprises stresses from abiotic and biotic (i.e., consumers) sources. The occurrence of facilitation interactions under high abiotic stress conditions has been verified by numerous studies in many ecosystems and has provided a crucial basis for empirical studies and theory governing plant-plant interactions in stress-prone Mediterranean environments (see [1] and references therein, [3]) where tree seedlings benefit from habitat amelioration, especially during summer drought [3,4,5,6,7,8,9]. The role of herbivory, a common and widespread interaction in arid and semiarid environment, has attracted little attention in this context [11,12,13,14]
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