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The most widespread response to global warming among alpine treeline ecotones is not an upward shift, but an increase in tree density. However, the impact of increasing density on interactions among trees at treeline is not well understood. Here, we test if treeline densification induced by climatic warming leads to increasing intraspecific competition. We mapped and measured the size and age of Smith fir trees growing in two treelines located in the southeastern Tibetan Plateau. We used spatial point-pattern and codispersion analyses to describe the spatial association and covariation among seedlings, juveniles, and adults grouped in 30-yr age classes from the 1860s to the present. Effects of competition on tree height and regeneration were inferred from bivariate mark-correlations. Since the 1950s, a rapid densification occurred at both sites in response to climatic warming. Competition between adults and juveniles or seedlings at small scales intensified as density increased. Encroachment negatively affected height growth and further reduced recruitment around mature trees. We infer that tree recruitment at the studied treelines was more cold-limited prior to 1950 and shifted to a less temperature-constrained regime in response to climatic warming. Therefore, the ongoing densification and encroachment of alpine treelines could alter the way climate drives their transitions toward subalpine forests.

Within communities, organisms potentially self-organize through endogenous processes that create nonrandom spatial structure as they interact with one another or modify the abiotic environment. In contrast, exogenous processes such as environmental heterogeneity or variable immigration are thought to be dominant processes controlling these spatial patterns. Although both endogenous and exogenous processes likely occur, their relative importance is still largely unknown because of limited analytical tools and the lack of experimental evidence, particularly those that address exogenous sources of environmental heterogeneity. Here, we used a soil heterogeneity experiment to examine the relative effect of endogenous and exogenous processes on plant spatial structure after five years of community assembly. Soil heterogeneity was manipulated by splitting the vertical soil profile into three soil-types that were randomly assigned to 40 × 40 cm patches within 2.4 × 2.4 m plots. Homogeneous plots were created by mixing all soils before filling each patch. Thirty-four grassland species were then sown into all plots and allowed to grow for five years after which the location of all plants was mapped using a 5 × 5 cm grid. Results from point-pattern spatial analysis indicated that, even in the absence of soil heterogeneity and with initial seed arrival, spatial structure was primarily generated by endogenous processes. Although soil heterogeneity increased species aggregation at certain scales, most of the spatial structure was created by endogenous processes. These results suggest that endogenous processes may be more important than expected for generating spatial structure and can develop much faster than anticipated.

Questions: How do the dominant species in a Mediterranean community (Juniperus sabina, Juniperus communis and Pinus sylvestris) colonize abandoned fields? At what rates? Does dispersal limitation shape species colonization patterns? Does J. sabina act as nurse plant for the other two species? If so, in which stages of development: seedlings and saplings or older individuals? Location: Abandoned crop fields in the Alto Tajo Natural Park, central-eastern Spain. Methods: We mapped all individuals of the three species in three 4–14-ha plots, and aged them using dendrochronology. Spatial patterns in 2000, 1980 and 1960 were reconstructed according to estimated ages in 2014. We used a battery of spatial point-pattern analyses to evaluate dispersal in junipers, dispersal in pines, and the role of J. sabina as nurse plant for the other two species. Results: Both junipers colonized earlier than pines, probably due to their more effective endozoochorous dispersal. Late-coming pines, once established, expanded faster due to their higher seed productivity. Recent recruits of J. communis and P. sylvestris showed a random relationship with J. sabina canopies, whereas spatial patterns of older individuals in relation to J. sabina canopies ranged from attraction (plot 2 and marginally plot 1), suggesting facilitation, to repulsion in plot 3. These differences in spatial patterns between plots could be related to a shift in dominant herbivores, from sheep (plots 1 and 2) to red deer (plot 3). Conclusions: Dispersal and plant–plant interactions drove colonization in Mediterranean old fields. The inclusion of a temporal perspective in the analysis of spatial patterns allowed the detection of shifting interactions between J. sabina and the other two species, depending on their life stage. This is a clear advance compared with the usual static analyses, as it provides additional clues to interpret the mechanisms and processes underlying their origin.

QUESTION: In fragmented forests, edge effects lead to changes in the distribution of plant species. In particular, tropical forest edges are increasingly dominated by lianas. Will this increase in lianas lead to changes in their interactions with other plant morphological groups? If so, will this alter the local distributions and abundance of other species? LOCATION: Plots located at increasing distances from the nearest forest edge and in remnant fragments of rain forest in the Atherton Tablelands, far northeast Queensland, Australia. METHODS: We mapped the distribution of trees, lianas and epiphytic ferns to better understand the role of forest disturbance in shaping their competitive and facilitative interactions. We then used specific spatial point‐process analyses to examine the effects of the spatial distribution of trees on the presence and abundance of lianas and epiphytic ferns. RESULTS: Tree aggregation near forest edges was lower than that in the interior. The higher abundance of lianas near edges was associated with increased spatial segregation between lianas and epiphytic ferns. This segregation suggests there is competition between these two functional groups, and that lianas, being much more abundant, probably outcompete epiphytic ferns. CONCLUSIONS: The ability of lianas to thrive in disturbed tropical rain forests appears to reduce the abundance of epiphytic ferns, probably via direct competition for space. Epiphytic ferns provide unique microclimates and harbour much biodiversity, and their decline could negatively affect many animals and plants that rely upon them.

1. Seed dispersers play a key role in shaping the spatial patterns of plant populations. After their disappearance, we expect a substantial increase in plant aggregation, which can ultimately cascade into high plant competition. 2. We used data of fully mapped distribution of four populations of the shrub Daphne rodriguezii from Menorca Island (Balearic Islands, W Mediterranean Sea), one in which D. rodriguezii coexists with its only disperser, the lizard Podarcis lilfordi, and three populations where this lizard went extinct long ago. 3. We used spatial point-pattern analysis to better understand the lizard's role on the spatial distribution of D. rodriguezii. To this end, we used specific point-process models that represented our main hypotheses on the impact of (i) habitat suitability, (ii) disperser activity, (iii) proximity of adults on the distribution of juvenile and adult shrubs and (iv) the impact of adult proximity on juvenile survival. 4. Plants were aggregated in all populations, and aggregation at short distances was stronger in populations without lizards. The observed spatial pattern of juveniles was better explained by a combination of hypotheses (ii) and (iii). The density of juveniles below adults was similar in all populations, but density far from adults was higher in the population with dispersers. In populations without dispersers, juveniles suffered higher mortality below adults. 5. Overall, our results suggest that the effects of lizard extinction were subtle. In the absence of lizards' dispersal, plants self-replace in favourable locations, but a decline in density, is evidenced near adults attributed to higher competition. Lizards, which often defecate under fruiting plants, create also a tight juvenile—adult association, but allow juveniles to escape from the immediate proximity of adults attributed to longer-distance movements. Our study shows how the analysis of the spatial pattern of plants can leads to detailed hypotheses on the underlying mechanisms structuring plant populations.

Human settlement establishment and reproduction of the baobab tree (Adansonia digitata) appear spatially and temporally dependent because baobabs are abundant in many settlement sites in Africa. This paper tests the spatiotemporal relationship between baobab and settlement distribution. South-western Mali. In an area of 183 km², 1240 baobabs were located and mapped, their diameters measured, and habitat characteristics recorded for each individual. All occupied (n = 9) and abandoned (n = 84) settlements were located and mapped, and occupation dates were determined through interviews. Chi-squared analysis indicated baobab habitat preferences, and bivariate point-pattern analysis tested baobab-settlement spatiotemporal independence. Baobabs and human settlements are positively spatially associated at most distances and for all baobab size-class-settlement age-class pairs. However, positive spatial association is significant only at distances < 500 m, and young settlements and large baobabs are not significantly associated. Positive association between small and large baobabs is marginally significant at <300 m, but observed significance is less than that for baobab-settlement positive association. Baobab abundance is not evenly distributed across the range of habitats it occupies; recruitment is strongest in settlements and fields, and on cliffs, while mortality is highest on cliffs. Ethnographic observations suggest that human settlement practices and fruit use are the main human factors contributing to baobab-settlement positive spatial association. There are three main conclusions: (1) Human settlement and baobab recruitment are spatially dependant because settlement leads directly and indirectly to the development of baobab groves at settlement sites. (2) The lower than expected abundance of mature individuals in natural habitats, and the habitat preferences of the observed population, suggest that baobabs were introduced to south-western Mali, probably centuries ago. (3) Human mobility over decadal time-scales is necessary to maintain baobab population structure in landscapes dominated by shifting land use, where baobabs are not purposefully planted. Baobab population processes in such landscapes occur at the scale of human settlement.

Aims: Patterns of spatial community dissimilarity have inspired a large body of theory in ecology and biogeography. Yet key gaps remain in our understanding of the local-scale ecological processes underlying species replacement and species nestedness, the two fundamental components of spatial community dissimilarity. Here, we examined the relative influence of dispersal limitation, habitat filtering and interspecific species interactions on local-scale patterns of the replacement and nestedness components in eight stem-mapped temperate forest mega-plots at different ontogenetic stages (large versus small trees). Location: Eight large (20–35 ha), fully mapped temperate forest plots in northern China and northern U.S.A. Time period: 2004–2016. Major taxa studied: Woody plants. Methods: We combined decomposition of community dissimilarity (based on the Ružička index) and spatial point-pattern analysis to compare the spatial (i.e., distance-dependent) replacement and nestedness components of each plot with that expected under five spatially explicit null models representing different hypotheses on community-assembly mechanisms. Results: Our analyses revealed complex results. In all eight forests, spatial community dissimilarity was best explained by species replacement among local tree assemblages and by a null model based on dispersal limitation. In contrast, spatial nestedness for large and small trees was best explained by random placement and habitat filtering, respectively, in addition to dispersal limitation. However, interspecific interactions did not contribute to local replacement and nestedness. Main conclusions: Species replacement is the predominant process accounting for spatial community dissimilarity in these temperate forests and caused largely by local-scale species clustering associated with dispersal limitation. Nestedness, in contrast, is less prevalent and primarily associated with larger variation in local species richness as caused by spatial richness gradients or 'hotspots' of local species richness. The novel use of replacement and nestedness measures in point pattern analysis is a promising approach to assess local-scale biodiversity patterns and to explore their causes.

Spatial processes underlie major species coexistence mechanisms. A range of spatial analysis techniques are increasingly applied to data of fully mapped communities to quantify spatial structures in species and phylogenetic and functional diversity at some given spatial scale with the goal of gaining insights into processes of community assembly and dynamics. We review these techniques, including spatial point pattern analysis, quadrat-based analyses, and individual-based neighborhood models, and provide a practical roadmap for ecologists in the analysis of local spatial structures in species and phylogenetic and functional diversity. We show how scale-dependent metrics of spatial diversity can be used in concert with ecological null models, statistical models, and dynamic community simulation models to detect spatial patterns, reveal the influence of the biotic neighborhood on plant performance, and quantify the relative contribution of species interactions, habitat heterogeneity, and stochastic processes to community assembly across scale. Future works should integrate these approaches into a dynamic spatiotemporal framework.

Canopy gaps and the processes that generate them play an integral role in shaping the structure and dynamics of forests. However, it is only with recent advances in remote sensing technologies such as airborne laser scanning that studying canopy gaps at scale has become a reality. Consequently, we still lack an understanding of how the size distribution and spatial organization of canopy gaps varies among forests ecosystems, nor have we determined whether these emergent properties can be reconciled with existing theories of forest dynamics. Here, I outline a roadmap for integrating remote sensing with field data and individual-based models to build a comprehensive picture of how environmental constraints and disturbance regimes shape the three-dimensional structure of the world’s forests.

Current evidence suggests that tree-fall gaps can influence forest structure and dynamics by enabling certain species guilds to persist over the long term. Here we assessed the development of local size hierarchies and asymmetric competition for light in tree-fall gaps, and the role played by these two processes for the persistence of rare light-demanding species in the Barro Colorado Island Forest Dynamics Plot (Panama). We performed spatial point pattern analysis, considering both the spatial locations (x,y) and the diameter at breast height (DBH) of all the woody plant recruits from the 1985 and 2000 censuses located in tree-fall gaps, and followed their fate up to the 1990–2010 and 2005–2010 censuses, respectively. For these two recruit cohorts, we found that, from the initial census until 5–10 yr later, close neighbors presented a larger DBH than the mean DBH of all individuals within gaps, which points to a positive growth response of recruits to the increased light levels in the gap centers. However, close neighbors of the 1985 cohort also showed larger than expected DBH differences that disappeared in subsequent censuses, indicating an enhancement of size differences between neighbors and the mortality of the smaller individuals. Finally, for both recruit cohorts, we found that 10–15 yr after gap formation, surviving individuals of rare light-demanding species had a negative impact on survival of neighboring individuals of other species. Our results indicate that gaps favor the persistence of rare light-demanding species through the development of local size hierarchies and asymmetric competition for light. The strength of this process, however, apparently depends upon gap size and the role played by the woody plants already existing at the time of gap formation in early colonization. Moreover, our findings suggest that in this forest, gaps may enhance colonization of plant species typical of nearby dry tropical areas, and that, over the coming decades, similar processes could strongly modify the structure and dynamics of moist tropical forests in the region.