Pyrus Bourgaeana Research Articles

Circadian fruit phenology: An overlooked crucial aspect of plant‐frugivore interactions

Abstract The intrinsic ability of plants to face environmental diel changes is paramount for flowering and interactions with pollinators and herbivores. Surprisingly, despite the commendable research efforts on the ecology and evolution of fruit‐frugivore interactions, very little is known about how fruit ripening and dropping vary throughout 24‐h cycle. Even less is known about the potential consequences of circadian fruit phenology on plant interactions with mutualistic and antagonistic frugivores. We illustrate for the first time how the circadian pattern of fleshy fruit dropping and its matching/mismatching with the diel activity of functionally diverse frugivores (fruit/seed predators, seed dispersers, pulp feeders) can drive the outcome of complex multispecies plant‐frugivore interactions. To that end, we used camera trapping to quantify the circadian fruit dropping of a mammal‐dispersed tree, Pyrus bourgaeana, and the diel activity patterns of its functionally diverse vertebrate frugivores during two fruiting seasons in two tree populations of Mediterranean Spain. Using a large data set (20,878 frugivore visits and 701 fruit‐dropping records), we evaluate the adaptive hypothesis that the circadian pattern of fruit dropping will match the diel activity of seed dispersers rather than that of fruit/seed predators. Fruit dropping during daytime doubled that at night‐time, being considerably consistent across and within seasons, study sites and individual trees. Specifically, overlaps between circadian patterns of fruit dropping across and within seasons (0.83 and 0.84 ± 0.02, respectively), study sites (0.95) and individual trees (0.68 ± 0.01) were always high. Whereas seed dispersers (mammalian carnivores) were mostly nocturnal, the most frequent fruit/seed predators (cervids) were mostly diurnal. Consequently, and contrary to our expectations, circadian fruit dropping was more aligned with the diel activity of overabundant fruit/seed predators than with that of carnivore seed dispersers. Our study illustrates how quantifying the circadian patterns of fruit dropping, the diel activity of functionally diverse frugivores, and the matching/mismatching between both patterns can contribute to a better understanding of multispecies plant‐frugivore interactions. Circadian fruiting phenology is an overlooked key attribute for most tropical and temperate fruiting plants, which patterns, mechanisms and outcomes must be fully investigated. Read the free Plain Language Summary for this article on the Journal blog.

The seed dispersal syndrome hypothesis in ungulate-dominated landscapes

The Seed Dispersal Syndrome Hypothesis (SDSH) posits that fruit traits predict the main dispersers interacting with plant species. Mammalian dispersers, relying heavily on olfactory cues, are expected to select dull-colored, scented, and larger fruits compared to birds. However, challenges like overabundant seed predators and context-dependency of frugivore-plant interactions complicate SDSH expectations. We studied the Iberian pear, Pyrus bourgaeana, an expected mammal-dispersed tree based on its fruit traits. Extensive camera-trapping data (over 35,000 records) from several tree populations and years revealed visits from seven frugivore groups, with ungulate fruit predators (59–97%) and carnivore seed dispersers (1–20%) most frequent, while birds, lagomorphs, and rodents were infrequent (0–10%). Red deer and wild boar were also the main fruit removers in all sites and years but acted as fruit and seed predators, and thus likely exert conflicting selection pressures to those exerted by seed dispersers. Although, as predicted by the SDSH, most Iberian pear fruits were consumed by large and medium-sized mammals, the traits of Iberian pear fruits likely reflect selection pressures from dispersal vectors in past times. Our results do not challenge the SDHS but do reveal the importance of considering frugivore functional roles for its adequate evaluation.

Seed dispersal effectiveness in fragmented and defaunated landscapes

AbstractLandscape fragmentation and defaunation have major impacts on plant dispersal and dynamics. However, whether the impact of such perturbations on seed dispersal and recruitment change in sign and strength across habitats and spatial scales, and whether they amplify or buffer each other, remains largely unknown. To evaluate, for the first time, the joint impact of fragmentation and defaunation on seed dispersal effectiveness (SDE) across spatial scales (e.g., short‐ and long‐distance seed dispersal), we utilized the long‐term field data of a mammal‐dispersed tree (Pyrus bourgaeana) in a spatially explicit individual‐based model. By means of simulation experiments, we evaluated the effects of different levels of landscape fragmentation and defaunation on SDE and tree recruitment. Our simulation results revealed that the direction and magnitude of the fragmentation effect on SDE depended on its strength (mild, severe) and the spatial scale considered. Severe fragmentation decreased SDE for short‐ and intermediate‐distance seed dispersal. Interestingly, mild and severe fragmentation increased SDE of long‐distance seed dispersal, suggesting a positive effect of such perturbations (i.e., an increase in the proportion of successful long‐distance dispersal events). Though defaunation had a consistently negative effect on overall SDE, its magnitude was highly species‐ and spatial–scale‐dependent. The impact of defaunation on seed dispersal distance was also species‐specific: the proportion of long‐distance dispersal increased under total badger (Meles meles) defaunation but decreased under total fox (Vulpes vulpes) defaunation. A pervasive integration of seed dispersal distance into the SDE framework is essential to most comprehensively understand the scale‐dependent nature of human activity impacts on plant dynamics. In the long term, strong perturbations (landscape fragmentation and defaunation) could select either for or against long‐distance seed dispersal, altering in different ways the ability of plants to cope with climate change.

Spatial isolation impacts pollinator visitation and reproductive success of a threatened self-incompatible Mediterranean tree

Pollination service is crucial to achieve successful plant sexual reproduction and long-term population persistence. This pollination service can be affected by plant conspecific density and also by intrinsic features of individuals related to their flowering phenology and floral display. However, studies examining intrinsic and extrinsic traits on pollinator visitation and reproductive success of Mediterranean trees with limited reproduction are still scarce. We analyzed the effects of plant isolation, flowering phenology, flower weight and tree size on flower visitation probability, flowering patch visitation probability, fruit set and crop size. To this end, we intensively monitored pollinator visitation and fruit production of 67 (in 2019) and 73 (in 2020) Pyrus bourgaeana Decne trees within a threatened Mediterranean population. Our results revealed that isolated individuals received more pollinators than those on conspecific aggregations, suggesting intraspecific competition for pollinators in dense flowering neighborhoods. However, fruit set was higher in trees close to flowering conspecifics despite having fewer visits from pollinators, suggesting pollen limitation but not pollinator limitation in spatially isolated trees. Interestingly, we found increased crop sizes in spatially isolated trees which could be related to reduced intraspecific competition for resources in low-density neighborhoods (water, nutrients) and/or to higher reproductive investment (i.e. higher flower production). Overall, our results indicated pollen but not pollinator limitation in spatially isolated trees. Under this scenario of sexual reproduction mediated by pollinators, our findings stress the relevance of individuals' spatial distribution for self-incompatible trees exhibiting low individuals’ densities.

Predation risk can modify the foraging behaviour of frugivorous carnivores: Implications of rewilding apex predators for plant-animal mutualisms.

Apex predators play key roles in food webs and their recovery can trigger trophic cascades in some ecosystems. Intra‐guild competition can reduce the abundances of smaller predators and perceived predation risk can alter their foraging behaviour thereby limiting seed dispersal by frugivorous carnivores. However, little is known about how plant–frugivore mutualisms could be disturbed in the presence of larger predators.We evaluated the top‐down effect of the regional superpredator, the Iberian lynx Lynx pardinus, on the number of visits and fruits consumed by medium‐sized frugivorous carnivores, as well as the foraging behaviour of identified individuals, by examining the consumption likelihood and the foraging time.We carried out a field experiment in which we placed Iberian pear Pyrus bourgaeana fruits beneath fruiting trees and monitored pear removal by frugivorous carnivores, both inside and outside lynx ranges. Using camera traps, we recorded the presence of the red fox Vulpes vulpes, the Eurasian badger Meles meles and the stone marten Martes foina, as well as the number of fruits they consumed and their time spent foraging.Red fox was the most frequent fruit consumer carnivore. We found there were fewer visits and less fruit consumed by foxes inside lynx ranges, but lynx presence did not seem to affect badgers. We did not observe any stone marten visits inside lynx territories. The foraging behaviour of red foxes was also altered inside lynx ranges whereby foxes were less efficient, consuming less fruit per unit of time and having shorter visits. Local availability of fruit resources, forest coverage and individual personality also were important variables to understand visitation and foraging in a landscape of fear.Our results show a potential trophic cascade from apex predators to primary producers. The presence of lynx can reduce frugivorous carnivore numbers and induce shifts in their feeding behaviour that may modify the seed dispersal patterns with likely consequences for the demography of many fleshy‐fruited plant species. We conclude that knowledge of the ecological interactions making up trophic webs is an asset to design effective conservation strategies, particularly in rewilding programs.

The overlooked benefits of synzoochory: rodents rescue seeds from aborted fruits

AbstractLarge‐scale abortion of immature fruits is a pervasive phenomenon across seed plants due to maternal physiological decisions associated with matching resources with fruit crop size. Aborted fruits are usually disqualified from studies of both fruit production and seed dispersal. However, a considerable number of developing seeds occur within immature aborted fruits. We evaluated the untested hypotheses that seeds within aborted fruits are viable and that incomplete predation of seeds within aborted fruits by hoarding rodents provides, in addition to seed movement, increased germination and seedling emergence. To this end, we studied the system composed by the Iberian pear Pyrus bourgaeana and several rodent species in Mediterranean Spain. About a third of aborted fruits found beneath tree canopies (n = 2430) were partially eaten by rodents. Using a seed sowing experiment, we revealed that a considerable fraction of seeds from P. bourgaeana aborted fruits are viable, germinating, and emerging seedlings. Paradoxically, however, these seeds are de facto unviable since they are confined within the extremely hard pericarp of aborted fruits, which prevents any seedling emergence and thus any contribution to tree recruitment. We show that only when rodents partially gnaw the pericarp walls of aborted fruits, seeds that escaped from predation have the prospect of emerging and thus potentially contributing to tree regeneration. Thus, in this and probably in many other similar synzoochore systems, rodents act as rescuers of seeds confined within aborted fruits, conferring the plants a largely overlooked benefit that could shape the reproductive strategy of many plant species.

Interspecific interactions among functionally diverse frugivores and their outcomes for plant reproduction: A new approach based on camera-trap data and tailored null models.

The study of plant-frugivore interactions is essential to understand the ecology and evolution of many plant communities. However, very little is known about how interactions among frugivores indirectly affect plant reproductive success. In this study, we examined direct interactions among vertebrate frugivores sharing the same fruit resources. Then, we inferred how the revealed direct interspecific interactions could lead to indirect (positive or negative) effects on reproductive success of fleshy fruited plants. To do so, we developed a new analytical approach that combines camera trap data (spatial location, visitor species, date and time, activity) and tailored null models that allowed us to infer spatial-temporal interactions (attraction, avoidance or indifference) between pairs of frugivore species. To illustrate our approach, we chose to study the system composed by the Mediterranean dwarf palm, Chamaerops humilis, the Iberian pear tree, Pyrus bourgaeana, and their shared functionally diverse assemblages of vertebrate frugivores in a Mediterranean area of SW Spain. We first assessed the extent to which different pairs of frugivore species tend to visit the same or different fruiting individual plants. Then, for pairs of species that used the same individual plants, we evaluated their spatial-temporal relationship. Our first step showed, for instance, that some prey frugivore species (e.g. lagomorphs) tend to avoid those C. humilis individuals that were most visited by their predators (e.g. red foxes). Also, the second step revealed temporal attraction between large wild and domestic frugivore ungulates (e.g. red deer, cows) and medium-sized frugivores (e.g. red foxes) suggesting that large mammals could facilitate the C. humilis and P. bourgaeana exploitation to other smaller frugivores by making fruits more easily accessible. Finally, our results allowed us to identify direct interaction pathways, that revealed how the mutualistic and antagonistic relations between animal associates derived into indirect effects on both plants seed dispersal success. For instance, we found that large-sized seed predators (e.g. ungulates) had a direct positive effect on the likelihood of visits by legitimate seed dispersers (e.g. red foxes) to both fleshy fruited plants. Then, seed predators showed an indirect positive effect on the plants' reproductive success. Our new analytical approach provides a widely applicable framework for further studies on multispecies interactions in different systems beyond plant-frugivore interactions, including plant-pollinator interactions, the exploitation of plants by herbivores, and the use of carcasses by vertebrate scavengers.

Genetic rescue by distant trees mitigates qualitative pollen limitation imposed by fine-scale spatial genetic structure.

Restricted seed dispersal frequently leads to fine-scale spatial genetic structure (i.e., FSGS) within plant populations. Depending on its spatial extent and the mobility of pollinators, this inflated kinship at the immediate neighbourhood can critically impoverish pollen quality. Despite the common occurrence of positive FSGS within plant populations, our knowledge regarding the role of long-distance pollination preventing reproductive failure is still limited. Using microsatellite markers, we examined the existence of positive FSGS in two low-density populations of the tree Pyrus bourgaeana. We also designed controlled crosses among trees differing in their kinship to investigate the effects of increased local kinship on plant reproduction. We used six pollination treatments and fully monitored fruit production, fruit and seed weight, proportion of mature seeds per fruit, and seed germination. Our results revealed positive FSGS in both study populations and lower fruit initiation in flowers pollinated with pollen from highly-genetically related individuals within the neighbourhood, with this trend intensifying as the fruit development progressed. Besides, open-pollinated flowers exhibited lower performance compared to those pollinated by distant pollen donors, suggesting intense qualitative pollen limitation in natural populations. We found positive fine-scale spatial genetic structure is translated into impoverished pollen quality from nearby pollen donors which negatively impacts the reproductive success of trees in low-density populations. Under this scenario of intrapopulation genetic rescue by distant pollen donors, the relevance of highly-mobile pollinators for connecting spatially and genetically distant patches of trees may be crucial to safeguarding population recruitment.

The endemic Mediterranean dwarf palm boosts the recolonization of old-fields: Implications for restoration

Understanding the mechanisms underlying the recolonization of old-fields is critical to promote the recovery of the ecosystem functioning, particularly in regions where agricultural abandonment has increased in the last 60 years. Given that seed arrival and seedling survival often limit the recolonization process by woody species in many Mediterranean habitats, the ‘perching’ and ‘nursing’ effects exerted by some pioneer species could be crucial for the restoration of such abandoned lands. We examined the role of an endemic Mediterranean palm (Chamaerops humilis) on the recolonization of old-fields by woody species in southern Iberian Peninsula. We chose three independent old-fields differing in their shrub encroachment levels. To identify potential facilitation by C. humilis, we used a spatially-explicit approach and analyzed its spatial associations with ten common woody species (e.g. Asparagus spp., Daphne gnidium, Olea europaea var. sylvestris, Pyrus bourgaeana). We detected positive spatial associations between C. humilis and woody species at small-scale (1–5 m) in the three plots. Most of such small-scale associations were linked to the bird-dispersal of woody species. Nonetheless, there were marked differences among plots in spatial associations between C. humilis and woody plants, being Asparagus spp. the only species positively associated with C. humilis within the three studied old-fields. These species-specific differences were likely related to variations among old-fields in encroachment level and the legacy of human management. Such small-scales spatial associations between C. humilis and woody species across Iberian old-fields were linked to the perching and nursing effects exerted by the palm. We emphasize the strong potential of this pioneer Mediterranean palm for the restoration of native ecosystems and the recovery of ecosystems services.

Extrinsic factors rather than seed traits mediate strong spatial variation in seed predation

Seed predation is a key demographic process for plant population dynamics and community structure. The strength of seed predation for a given plant species often varies among populations depending on both plant traits (e.g. seed size) and extrinsic factors (e.g. seed predator abundance). Because both types of factors tend to covary spatially, identifying their relative contribution to changes in seed predation through observational approaches is challenging. During two consecutive years, we reciprocally translocated seeds of Iberian pear (Pyrus bourgaeana) from five localities in SW Spain to estimate changes in interaction strength between the tree and its seed-eaters (mostly rodents). We also measured relevant seed traits, the abundance of granivore rodents, and the density of fruiting-shrubs in the same five populations. Both seed traits and extrinsic factors varied among the five studied populations. As predicted, we found significant spatial covariance between some extrinsic factors (i.e. rodent abundance and fruiting-shrub density) as well as between extrinsic factors and plant traits (seed size). Seed removal likelihood varied highly among offering localities, with differences up to 11.6-fold. However, and despite differences in seed traits among populations, no evidence of seed predator preference for seeds from any locality was found in any of the five local experiments. Our study indicated that extrinsic factors (e.g. seed predator abundance) rather than measured seed traits mediated among-population variation in seed predation. Selection pressures exerted by seed predators on seed traits could thus be less pervasive than previously thought. Our experimental approach can help to better understand the potential of different functional animal groups (pollinators, herbivores, granivores, frugivores) to exert selection pressures on plant traits.

Microgeographic variation in recruitment under adult trees: arrival of new genotypes or perpetuation of the existing ones?

Investigating spatial variation in the relative importance of sexual reproduction and clonal propagation is critical to obtain more accurate estimates of future effective population sizes and genetic diversity, as well as to identify ecological correlates of clonality. We combined a stratified sampling scheme with microsatellite genetic analyses to estimate variation in the proportion of sexual versus clonal recruits among saplings in five populations of the tree Pyrus bourgaeana. Using a likelihood framework, we identified clones among the genotypes analysed and examined variation among populations regarding the proportion of saplings coming from clonal propagation. We also examined the relationship between the relative abundance of clonal shoots across the studied populations and their herbivory levels. Our results revealed that one third of the saplings examined (N=225 saplings) had a probability above 0.9 of being clones of nearby (<10m) trees, with the ratio between clonal propagation and sexual recruitment varying up to eight-fold among populations. A small portion of these putative clonal shoots reached sexual maturity. Relative abundance of clonal shoots did not significantly relate to the herbivory by ungulates. Our results call into question optimistic expectations of previous studies reporting sufficient levels of recruitment under parental trees without animal seed dispersal services. Nevertheless, given that some of these clonal shoots reach sexual maturity, clonal propagation can ultimately facilitate the long-term persistence of populations during adverse periods (e.g. environmental stress, impoverished pollinator communities, seed dispersal limitation).

Combined effects of seed provenance, plant facilitation and restoration site on revegetation success

Abstract Plant provenance, plant facilitation and the characteristics of restoration sites are critical determinants of revegetation success. Surprisingly, however, very little is known about how these key factors interact, both with each other and to complex patterns of recruitment in target plant species. We investigated, for the first time, the potential of combining seed provenance, plant facilitation and restoration site characteristics to guide revegetation efforts. As a model system, we used the Iberian pear (Pyrus bourgaeana) and three potential nurse shrub species. To this end, we completed a comprehensive reciprocal transplant experiment in five P. bourgaeana populations within a fragmented landscape at the Doñana Biosphere Reserve (SW Spain). There were marked differences among provenances for seedling emergence and growth, as well as for recruitment, but no evidence of local adaptation was found. Shrubs generally had a positive or neutral effect on P. bourgaeana seedling performance with, for example survival underneath shrubs being, on average, twice as high as in open microhabitats. Interestingly, however, the magnitude and even the sign of such plant–plant interactions changed with both sowing locality and seed provenance. For instance, shrubs enhanced seedling survival and recruitment at the end of the study in four of the five sowing localities, whereas it decreased it in the remaining locality. Also, although nurse shrubs lessened seedling size of two provenances, it did not have a significant effect on the other three. Synthesis and applications. We show how revegetation success can be maximized, not only by selecting the most appropriate plant material, taking advantage of plant facilitative interactions and selecting the right restoration site, but also by using these factors in an integrated fashion. We propose local managers efficiently undertake future revegetation campaigns by mixing seeds from several genetically adequate source populations in numbers weighted according to previously estimated provenance‐specific recruitment successes. Our novel approach can help to guide revegetation of many tree and plant species living in stressful conditions, such as arid, semi‐arid and high mountain habitats.

Strong among population variation in frugivory strength by functional diverse frugivores: a 'reciprocal translocation' experiment.

Fruit-frugivore interactions are critical for the dynamics and evolution of many plant communities. The strength of the interactions between a given plant species and different frugivore guilds (e.g., seed dispersers, seed predators) often vary in space due to changes in plant extrinsic factors (e.g., frugivore abundances) and plant traits (e.g., fruit size and reward). By reciprocally translocating Pyrus bourgaeana ripe fruits representative of five Mediterranean localities during 2 consecutive years, we experimentally quantified guild-specific variations among populations in frugivory strength, while accounted for plant-intrinsic and- extrinsic factors. Though overall fruit removal did not differ among localities, there were strong guild-specific differences in fruit removal strength. Fruit removal by pulp feeders, seed dispersers, and fruit predators varied among populations up to 8.5-, 5.6-, and 4.0-folds, respectively. These strong variations seemed mediated by changes in frugivore relative abundances rather than on availability of alternative fruits. As expected, all fruit traits considered (e.g., fruit size, pulp amount) markedly varied among tree populations. However, no frugivore guild showed preference for fruits from any locality, suggesting that fruit traits did not contribute much to differences in frugivory strength among populations. Since the functional diverse frugivore guilds played contrasting roles in P. bourgaeana dynamics (e.g., seed dispersal vs. seed predation), our study highlights the importance of accounting for functional diversity in frugivore guilds when estimating spatial variations in the strenght of seed dispersal. This investigation also illustrates a neglected but widely applicable experimental approach to identify the relative importance of extrinsic factors and fruit traits in mediating fruit-frugivore interactions.

Assisting seed dispersers to restore oldfields: An individual‐based model of the interactions among badgers, foxes and Iberian pear trees

Abstract Increasing land abandonment in many areas of the world presents an opportunity for ecosystem recovery, which is often driven by seed dispersal by vertebrate frugivores. However, we are far from understanding the most effective way of using common management actions (i.e. planting fruiting trees) to stimulate animal seed dispersal and thus the restoration of human‐altered abandoned habitats. To investigate how to stimulate animal seed dispersal, we combined long‐term field data with individual‐based, spatially explicit simulation models. We used our approach to assess the effectiveness of contrasting Iberian pear Pyrus bourgaeana planting strategies in enhancing restoration of abandoned lands through seed dispersal by red foxes Vulpes vulpes and Eurasian badgers Meles meles in the Doñana World Biosphere Reserve (South West Spain). Our simulation results indicate that planting trees in an aggregated fashion is less efficient in terms of seed arrival than planting them regularly or randomly. For aggregated planted trees, the increase in the area of the oldfield that received seeds was only 7%–9% compared to the baseline scenario of no intervention, whereas for regularly distributed planted trees the increment was up to 40%. Doubling the number of planted P. bourgaeana trees appeared cost‐effective for regular and random tree distributions, but not for the aggregated one. For example, while doubling the number of trees planted regularly leads up to 12% increase in the number of seeds arriving into the oldfield, no increment on the number of arrived seeds was detected when trees were planted aggregately. Synthesis and applications. Choosing the spatial distribution and density of planted trees in abandoned lands depends on a number of ecological and socio‐economical factors. Given our results, the strong seed dispersal limitation of the target tree population and that our study site was fully protected for conservation, planting Pyrus bourgaeana trees regularly appeared to be the most efficient strategy to enhance seed arrival into the target oldfield. Combining long‐term field data with individual‐based, spatially explicit simulation models have the potential to guide local restoration efforts in diverse human‐altered habitats and thus bridge the existing gap between basic and applied research on animal seed dispersal.

Long-term effect of temperature and precipitation on radial growth in a threatened thermo-Mediterranean tree population

Key messageBased on the first dendroclimatological analyses of the thermo-Mediterranean treePyrus bourgaeana, the positive relationship between the growth and climate (i.e., precipitation) has strengthened in recent decades.The combined effect of climate change and habitat destruction and fragmentation threatens many plant populations and even entire communities in Mediterranean ecosystems. The Iberian pear, Pyrus bourgaeana Decne, a characteristic species of Mediterranean ecosystems, is threatened by both habitat and climate changes. We ask whether and how the growth of mature P. bourgaeana in the thermo-Mediterranean zone (i.e., altitude <700 m) has been affected by long-term climate changes during the last century in a fragmented landscape. Dendrochronological methods were used to find growth–climate relationships. We made the first dendroclimatological analyses and constructed a first 103-year tree-ring chronology (1905–2007) of this species. The tree-ring series revealed large growth variability. We found a clear, strong relationship between tree growth and climate, with annual precipitation being the most important climate factor enhancing radial growth. Our results also showed that warm autumns and winters positively affect growth. There was no temporal stability in the relationship between tree growth and climate. The most general trend was in the relationship between annual precipitation and tree growth: the decrease of rainfall in the last decades of the twentieth century was associated with a constant increase of the correlation coefficient. Water accumulated in the soil in autumn and winter proved to be a key factor augmenting tree growth in the following vegetation period. The climate–growth relationship in P. bourgaeana has strengthened in recent decades apparently due to decreased precipitation levels.

Population structure and fruit production of Pyrus bourgaeana D. are affected by land-use

The Iberian wild pear (Pyrus bourgaeana D.) is a rare, fleshy-fruited tree restricted to dehesas and evergreen sclerophyllous Mediterranean forests in the southwestern Iberian Peninsula. It produces palatable fruits and leaves attractive to different species groups, playing an important trophic role in the ecological networks of Mediterranean ecosystems. However, the intensification in the traditional land-use linked to these areas could threaten the stability of the wild pear populations in the short/medium-term. In order to determine the population dynamics of this relevant species in relation to the land-use history, we selected two populations (southern Spain) subjected to different land-use management, dehesa (D) and abandoned olive grove (AOG). An analysis of 122 adult trees reported an overall density of 0.6 trees ha−1. The tree age was estimated by tree-rings analysis in all adult trees. Dendrometric parameters, reproductive features, and germination rates were also measured. Regeneration was clearly biased, as evidenced by the truncated age structure. A low correlation (R2 = 34%) between age and DBH (diameter at breast height) (244 cores analysed) showed that diameter seems not to be a reliable predictor of tree age. Trees from AOG populations had significantly-higher values of DBH, height and crown diameter, but were less productive in terms of fruits and seeds. Nested analysis of variance showed significant variation in fruit production, fruit size, dry mass, water content and seed viability. There were also significant differences in masting. No evidence was found to demonstrate that fruit production, seed viability, or germination rate influence the low natural recruitment of this species. These findings indicate that the traditional agrosilvopastoral practices carried out in the study area for decades, and its subsequent intensification, have strongly influenced the ecological structure of the Iberian wild pear populations at the local scale, which could compromise its stability in the near future.

Estructura de edades, tamaños y crecimiento en una población local de piruétano (Córdoba, España)

Arenas-Castro, S., Fernandez-Haeger, J., Jordano-Barbudo, D. 2015. Structure of ages, sizes and growth in a local population of the Iberian wild pear (Cordoba, Spain). Ecosistemas 24(2): 7-14. Doi.: 10.7818/ECOS.2015.24-2.02 In recent decades, the remarkable proliferation of dendrochronological studies in Spain has contributed significantly to advancing knowledge of the structure and dynamics of forests. However, researches have focused mainly on forest species of greatest interest, to the detriment of other species which have a greater ecological interest. A paradigmatic case is the Iberian wild pear ( Pyrus bourgaeana , D), a virtually unknown species from the ecological point of view, although classified as characteristic species of Mediterranean ecosystems. In order to describe the population structure of this species, through the tree-rings analysis we obtained the age and size of 122 individuals with DBH > 5 cm, located in two adjacent areas (abandoned olive grove and meadows of Oaks or dehesa) in Sierra Morena (Cordoba, Spain). The mean age of trees was ≈ 37±12 years, the oldest was 80, and the tree sizes were highly different, between 10 and 35 cm. Trunk diameter was not a good predictor of the tree-age, because even we found very striking differences in the age and trunk diameter relationship between closely spaced trees. Both age and growth-rates of trees in the abandoned olive grove were significantly higher than in the trees of the Dehesa. These differences could be related to the management history conducted in the study area during the last 50 years, because there are no negative density-dependent effects on growth-rates.

Unravelling conflicting density‐ and distance‐dependent effects on plant reproduction using a spatially explicit approach

Summary Density‐ and distance‐dependent (DDD) mechanisms are important determinants of plant reproductive success (PRS). Different components of sequential PRS can operate either in the same or in different directions and thus reinforce or neutralize each other, and they may also operate at different spatial scales. Thus, spatially explicit approaches are needed to detect such complex DDD effects across multiple PRS components and spatial scales. To reveal DDD effects of different components of early PRS of the Iberian pear (Pyrus bourgaeana) sampled over three consecutive years, we used marked point pattern analysis. Our special interest is to identify conflicting processes that regulate populations at different spatial scales, for example whether DDD on fruit initiation and on fruit development acted in opposite directions. To evaluate the significance of observed mark correlation functions based on empirical data (e.g. fruiting success), we compared them to expectations given by spatially explicit null models. Diverse DDD processes affected several aspects of PRS in a variable extent over the three seasons. First, fruit initiation was higher for individuals with more neighbours at small distances (i.e. up to 40 m). However, P. bourgaeana fruit development decreased with increasing number of nearby neighbours, but these effects cancelled for overall fruit set that did not show DDD effects. Secondly, the absolute number of fruits produced (crop sizes) by trees showed positive density dependence in 2011 and 2012 but not in 2013. Finally, the total number of seeds produced did not show DDD effects, indicating that conflicting demographic processes can disrupt the initial spatial pattern of tree investment in reproduction. Synthesis. Understanding complex spatial effects of DDD processes requires dissection of component processes to attain the complete picture since contrasting DDD processes may be hidden behind a single cumulative measure of reproductive success. The combination of novel and classic mark correlation functions used here constitutes a powerful spatially explicit tool that can be broadly applied to unravel conflicting mechanisms of DDD regulating the persistence of sessile organisms at a range of spatial scales. Our findings help to explain why some authors failed to find expected DDD of PRS and highlight the importance of detailed multiyear field studies on plant reproductive success.

A Method For Tree-Ring Analysis UsingDiva-GisFreeware On Scanned Core Images

Tree-ring analysis is a basic technique of paramount importance in forest management, yet it may prove difficult and time-consuming for many slow-growth hardwood tree species. Moreover, it requires the use of specialized tools and proprietary software, which may hinder researchers working with limited budgets. We describe an innovative and inexpensive method using DIVA-GIS freeware software to analyze true color high-resolution scanned images of cores previously enhanced with ImageJ freeware (GIS-SDI), and test its accuracy against the widely-used LINTAB-TSAPWin™ and WinDENDRO™ methods. For this purpose, Abies pinsapo and Pyrus bourgaeana increment cores were processed independently using each of the three methods and the results were statistically compared. Dating results were consistent across all three methods, although identifying rings was easier and quicker to perform on the digital images. Using a modern but affordable flatbed scanner to digitize tree cores and the free DIVA-GIS software to analyze the scanned digital images proved to be an inexpensive but highly accurate and efficient approach to tree-ring analysis. Furthermore, this method greatly facilitates tree-ring analysis in species with inconspicuous rings, and enables a complete digital record of every core analyzed to be stored.

Evaluation and Comparison of QuickBird and ADS40-SH52 Multispectral Imagery for Mapping Iberian Wild Pear Trees (Pyrus bourgaeana, Decne) in a Mediterranean Mixed Forest

The availability of images with very high spatial and spectral resolution from airborne sensors or those aboard satellites is opening new possibilities for the analysis of fine-scale vegetation, such as the identification and classification of individual tree species. To evaluate the potential of these images, a study was carried out to compare the spatial, spectral and temporal resolution between QuickBird and ADS40-SH52 imagery, in order to discriminate and identify, within the mixed Mediterranean forest, individuals of the Iberian wild pear (Pyrus bourgaeana). This is a typical species of the Mediterranean forest, but its biology and ecology are still poorly known. The images were subjected to different correction processes and data were homogenized. Vegetation classes and individual trees were identified on the images, which were classified from two types of supervised classification (Maximum Likelihood and Support Vector Machines) on a pixel-by-pixel basis. The classification values were satisfactory. The classifiers were compared, and Support Vector Machines was the algorithm that provided the best results in terms of overall accuracy. The QuickBird image showed higher overall accuracy (86.16%) when the Support Vector Machines algorithm was applied. In addition, individuals of Iberian wild pear were discriminated with probability of over 55%, when the Maximum Likelihood algorithm was applied. From the perspective of improving the sampling effort, these results are a starting point for facilitating research on the abundance, distribution and spatial structure of P. bourgaeana at different scales, in order to quantify the conservation status of this species.