查看更多>>摘要：Despite noticeable concern about the deforestation rate worldwide, the forest surface in Europe has considerably expanded over the past centuries as a consequence of the rural exodus and abandonment of agrarian practices. Tree recruitment associated with forest regrowth is a multi-stage process influenced by several biotic and abiotic factors. Yet, it is uncertain whether their influence on recruitment patterns and dynamics varies along a gradient of forest expansion. Similarly, for dioceious species, the influence of tree sex in recruitment is not entirely un-derstood. Here, we aim to elucidate what drives Spanish juniper recruitment in expanding forests. Specifically, we hypothesized that facilitation by conspecifics and heterospecific woody species would occur at the expanding front, where environmental conditions are harsher and that recruitment would be preferably associated to female trees because of the likelihood of mature cones produced by them germinating in the nearby area. The study was conducted in Mediterranean forests of Juniperus thurifera in central Spain. A total of 17 plots were delimited along a gradient of forest expansion including three stages: i) old forests, ii) an intermediate zone and iii) novel forests at the expanding front. Within each plot all J. thurifera individuals (saplings and adults) were mapped. We also recorded bio-volumetric characteristics and tree sex for all adult trees and estimated the percentage of cover of heterospecific woody species within the area of influence of each adult individual. We analysed the spatial pattern of J. thurifera individuals for each stand (plot). Using a novel spatial approach, we evaluated how conspecific (female and male tree sizes) and heterospecific (woody cover) vegetation influenced sapling density along a forest expansion gradient. We also studied the effects of the stage of the forest expansion gradient and the sex of adult trees on the spatial association between adults and saplings. Our results showed that sapling recruitment was negatively influenced by conspecific adult size along the whole gradient, while the effect of heterospecific woody vegetation was always positive. Conspecific facilitation of recruitment in J. thurifera forests occurred at their expanding front where saplings were associated to male adult trees. Despite having been overlooked in conservation policies, recently colonised areas in extreme environments are key targets to implement management measures aimed at achieving forest restoration, which aligns with the Aichi targets and the biodiversity policies of the European Union.
McKendrick, Scott AlexanderEde, Fiona JeanMiller, Rebecca ElizabethGreet, Joe...
10页
查看更多>>摘要：The use of direct seeding for revegetation often results in poor recruitment outcomes. For many species, it is unclear where recruitment bottlenecks occur in the transitions between early life-history stages and how soil moisture conditions affect these bottlenecks. Thus, we asked: (1) which life-history stage transitions are most limiting to seedling recruitment? and (2) how do soil moisture levels affect recruitment? Using a field-based trial, we quantified the recruitment process from a seed to seedling for two woody Acacia species. Using a novel technique, in which seeds were confined to germination caches (small baskets), along with the use of germination bags, we assessed pre-emergence processes at regular intervals. Seeds sown directly into the soil in adjacent rows were intensively monitored to assess post-emergence processes. To investigate the effects of soil moisture on seedling recruitment, a glasshouse experiment assessed transitions between life-history stages under three different soil moisture treatments. In the field, the transition between a seed and germinated seed limited recruitment more than all other life-history stage transitions combined, with 32%-50% of seeds not germinating for the two species. Approximately one third of seeds of both species died prior to germinating, with few seeds remaining dormant. In the glasshouse trial, seed germination increased with increasing soil moisture, however, so did the extent of seed death. Our results suggest that the transition from a seed to germinated seed was the most limiting bottleneck to recruitment, mostly due to seed mortality rather than dormancy processes, with pathogen attack the most likely cause. As increased soil moisture both promoted germination but also seed mortality, understanding the optimal soil moisture thresholds that maximise germination and the transition to an established plant is essential in maximising direct seeding outcomes. Identifying the life-history stage transitions most limiting to plant recruitment may allow management to target specific bottlenecks in order to improve direct seeding outcomes.
NSTL
Elsevier