Tree Reproduction Research Articles

The impact of fig wasps (Chalcidoidea), new to the Mediterranean, on reproduction of an invasive fig tree Ficus microcarpa (Moraceae) and their potential for its biological control

Natural enemies that reduce plant reproductive success are often utilized for biological control of invasive species. Reproduction in fig trees depends on host-specific fig wasp pollinators that develop in galled ovules, but there are also many species of non-pollinating fig wasps (NPFWs) that reduce seed and pollinator numbers. Fig wasps associated with an invasive Asian fig tree, Ficus microcarpa (Moraceae), were surveyed around the Mediterranean. Eight NPFW species are now known from the area, three of which are newly-recorded. The impacts of the two most prevalent ovule galling NPFW species (both Pteromalidae, Epichrysomallinae) on the tree’s reproduction were compared: Odontofroggatia galili Wiebes is widely-introduced, whereas Meselatus bicolor Chen has not been recorded previously outside its native range. Both gall-forming NPFWs significantly reduce seed and pollinator production, but M. bicolor has a far greater impact, entirely preventing seeds and pollinators from developing in the figs it occupies. M.bicolor has only been recorded from F. microcarpa and has the potential to be a valuable biological control agent in other countries outside the Mediterranean where F. microcarpa has become invasive.

How many seeds does it take to make a sapling?

Tall canopy trees produce many more seeds than do understory treelets, yet, on average, both classes of trees achieve the same lifetime fitness. Using concurrent data on seedfall (8 years) and sapling recruitment (12 years) from a long-established tree plot at the Cocha Cashu Biological Station in Peru, we show that a 40-m canopy tree must produce roughly 13 times the mass of seeds to generate a sapling as a 5-m understory treelet. Mature tree height accounted for 41% of the variance in seed mass per sapling recruit in a simple univariate regression, whereas a multivariate model that included both intrinsic (seed mass, tree height, and dispersal mode) and extrinsic factors (sapling mortality as a surrogate for microsite quality) explained only 31% of the variance in number of seeds per sapling recruit. The multivariate model accounted for less variance because tall trees produce heavier seeds, on average, than treelets. We used "intact" (mostly dispersed) seeds to parameterize the response variable so as to reduce, if not eliminate, any contribution of conspecific crowding to the difference in reproductive efficiency between canopy trees and treelets. Accordingly, a test for negative density dependence failed to expose a relationship between density of reproductive trees in the population and reproductive efficiency (seed mass per recruit). We conclude that understory treelets, some of which produce only a dozen seeds a year, gain their per-seed advantage by failing to attract enemies à la Janzen-Connell, either in ecological or evolutionary time.

Estructura de una población del árbol Peltogyne purpurea (Cesalpinaceae) en un bosque intervenido de la Península de Osa, Costa Rica

The regeneration of the rain forest tree Peltogyne purpururea Pittier after selective logging was studied in Mogos, Osa Peninsula, Costa Rica. The distribution of all adult trees of P. purpurea according to diameter at breath height (dbh) categories revealed that the distribution of the adult trees followed a bell-shaped curve. The largest number of individuals was found in the 70 to 80 cm dbh category. We did not find any significant differences in the distribution of saplings around seed-producing trees. There were similar numbers of saplings in the four transects established around each reproductive tree following the four cardinal directions. Overall, the majority of the saplings were found in the first meters around each seed-producing tree. There was another peak in the number of saplings at the distance where the crown of the tree ended. Logging can negatively affect the regeneration of P. purpurea.

Mechanic defences and reproduction in desert trees under different habitat management

Herbivory can have deleterious effects on plant reproduction by limitation of photosynthates that are either lost by consumption, used to re-growth or invested in defences. In addition, herbivores can also exert direct impact on plant reproduction by consuming flowers. Spine length can act as an inducible defence in plants, because it tends to increase with increasing herbivore pressure. I hypothesized that almost 40 years of different habitat management (cattle exclusion within a protected area vs. cattle grazing in adjacent areas) could affect inflorescence abundance, spine length and fruit production in Prosopis flexuosa trees. The study area was located in the Central Monte desert of Argentina. I estimated differences in spine length, number of inflorescences and fruit production in trees inside the Man and Biosphere Reserve of Ñacuñán and in the adjacent cattle ranches surrounding the protected area. Inflorescence abundance in the tree canopy was similar in cattle grazed and protected sites, but the presence of large herbivores was associated with limited fruit production. Spines were 37% shorter and fruit production three times higher in trees inside the reserve than in trees in cattle ranches. A negative exponential model was used to describe the relationship between reproduction and spine length in trees. The results indicate that after almost four decades of cattle exclusion, trees inside the protected area show higher reproduction and shorter spines than cattle-browsed trees in surrounding areas. The negative association between defence and reproduction may be due to competition for photosynthates. The present results could be useful and relevant in conservation because they provide evidence on how anthropogenic habitat use can affect plant phenotypes and fitness, which in turn can affect the long-term ecological and evolutionary dynamics of plant populations.

Decomposing recruitment limitation for an avian‐dispersed rain forest tree in an anciently fragmented landscape

SummaryForest fragmentation may intensify recruitment limitation through impacts on seed production, dissemination and seedling establishment processes. In an ancient mosaic of fog‐dependent rain forest patches on coastal hilltops of semi‐aridChile (30 °S), we investigated how aridity‐driven habitat fragmentation affected the recruitment of the fleshy‐fruited, dioecious treeAextoxicon punctatum(Aextoxicaceae) and the role of birds in seed dispersal across patches.We hypothesized that reduced fragment size enhanced recruitment limitation due to constraints on tree fecundity, avian disperser activity and seedling recruitment, caused primarily by strong edge effects in small fragments.We mapped adultAextoxicontrees and placed 686 seed traps distributed in 3 small (<0.3 ha) and 3 large patches ( > 0.9 ha) in the forest patch mosaic. To identify seed sources, endocarps of 282 dispersed seeds from seed traps were genotyped and compared with 155 genotyped females using nine microsatellite markers. Seed dispersal curves for different forest patches were constructed using maximum likelihood methods. Further, seed addition experiments were conducted in the six fragments to assess recruitment probabilities.Lower density and basal areas of reproductive female trees, in addition to shorter fruiting periods and lower seed yields, led to strong source limitation in small patches. Three bird species accounted for the bulk of visits to fruiting trees, but were less active in smaller patches. Dispersal curves were strongly leptokurtic with maximum dispersal distances related to the shape of patches. Important proportions (5–40%) of genotyped seeds in all patches were immigrants. However, seeds arrived mainly at patch edges or below reproductive trees where germination and survival are reduced. Fewer seedlings originated from experimentally added seeds in small patches subjected to greater edge effects.Synthesis. In summary, we provide evidence for source, dispersal and establishment limitation of this dioecious tree in an aridity‐driven fragmented landscape. Small fragment size and edge effects had negative impacts on fecundity and seedling establishment. Although bird‐mediated seed dispersal favoured immigration between patches, recruitment from such seeds will be unlikely because of low quality of deposition sites.

Forest edge effects on Quercus reproduction within naturally regenerated mixed broadleaf stands

This paper explores the influence of forest edge on the development of tree reproduction and the use of edge as a silvicultural tool for manipulating regeneration outcomes. Oak (Quercus spp.) reproduction was sampled 9 years following edge establishment along transects extending from 8 m into clearcut openings to 40 m into the adjacent intact forest. Trends showed that oak reproduction height in the intact forest was inversely related to distance from edge up to 20 m into the intact forest. Observed oak reproduction densities were greater within 20 m of edge than in distance intervals further into the intact forest. Tree-ring analysis of 106 seedlings was used to evaluate temporal responses associated with edge development. Cross-sectional analysis indicated a mean age of 13 years, 3 years prior to edge establishment. Increased growth was associated with edge establishment, and 10-year radial growth following edge creation showed a similar spatial pattern as height with oak seedlings within 20 m of the edge exhibiting significantly greater growth than those occurring furthest into the intact forest. This study suggests that forest edge can be used to provide environments useful in building reproductive capacity for species like oaks that require advance reproduction.

Anthropogenic edges, isolation and the flowering time and fruit set of Anadenanthera peregrina, a cerrado savanna tree

Fragmentation exposes plants to extreme environmental conditions with implications for species phenology and reproduction.We investigated whether isolation and edge effects influence size, flowering time, fruit set, and seedling establishment of Anadenanthera peregrina var. falcata. We compared trees in the interior (n =85), and on the edge (n =74) of a cerrado savanna fragment as well as in a pasture (n =26) with respect to size, flowering phenology, flower and fruit production, fruit and seed set, predispersal seed predation, and seedling establishment. Trees in the pasture were larger and produced a higher number of flowers and fruits than trees on the edge and interior, yet seed set did not differ across environments. The plant size structure explained the flower and fruit production, and the self-compatibility breeding system caused a similar seed set regardless of the environment. First flowering was later and fruit set higher in the interior. We argue that time of first flower influenced the fruit set of Anadenathera. Edge and isolated trees started to flower earlier as a response to microclimatic conditions--mainly temperature--reducing the fruit set. Predispersal seed predation was lower among pasture trees. Conversely, we found seedlings only on the edge and in the interior of cerrado, suggesting that the pasture was of poor quality habitat for Anadenanthera recruitment. Isolation affected the plant size structure and reproduction of Anadenanthera trees. Studies comparing plant phenology under contrasting environmental conditions may offer clues on how global change may affect plant reproduction in the tropics.

Extending the Time Interval for Applying Herbicide in Cut-Stump Treatments on American Beech

American Beech (Fagus grandifolia Ehrh.) root sprouts often form dense understories that interfere with tree reproduction throughout much of the eastern hardwood region. The cut-stump treatment, whereby herbicide is applied to the stump within a few hours after a larger beech is felled, has been shown to mitigate the interference problem by eliminating beech stems attached to the parent tree's root system. Forest managers are often reluctant to prescribe this treatment because the short time interval between felling the tree and applying herbicide requires the applicator to work in proximity to an active logging operation, raising concerns about safety and efficiency. This study measured the efficacy of the cut-stump treatment on American beech root and stump sprouts for eight time intervals, ranging from 1 to 120 hours, on a 60-acre study site in central West Virginia. Glyphosate as Razor Pro herbicide was diluted to a 65.6% solution with water (26.9% active ingredient) and applied to the outer 2 in. of beech stumps from trees 11-15 in. dbh. The treatments were applied during a cool humid period in September and evaluated 12 months later. Control of root sprouts ranged from 71 to 86%, with no significant differences among the 1- to 96-hour treatments. Efficacy dropped to 50% and 1% for the 120-hour treatment and control treatment, respectively. Stump sprouts were prevented on all stumps treated within 96 hours of tree severing. The results indicated that herbicide can be applied to beech stumps up to four days after severing without reducing control of root and stump sprouts under the conditions in this study. The longer time interval will improve feasibility, safety, and efficiency of the cut-stump treatment. In practice, the effective time interval may vary depending on season of the year and weather conditions.

Consecutive five‐year analysis of paternal and maternal gene flow and contributions of gametic heterogeneities to overall genetic composition of dispersed seeds of Pinus densiflora (Pinaceae)

Genetic variability in monoecious woody plant populations results from the assemblage of individuals issued from asymmetrical male and female reproductive functions, produced during spatially and temporarily heterogeneous reproductive and dispersal events. Here we investigated the dispersal patterns and levels of genetic diversity and differentiation of both paternal and maternal gametes in a natural population of Pinus densiflora at the multiple-year scale as long as five consecutive years. • We analyzed the paternity and maternity for 1576 seeds and 454 candidate adult trees using nuclear DNA polymorphisms of diploid biparental embryos and haploid maternal megagametophytes at eight microsatellite loci. • Despite the low levels of genetic differentiation among gamete groups, a two-way AMOVA analysis showed that the parental origin (paternal vs. maternal gametes), the year of gamete production and their interaction had significant effects on the genetic composition of the seeds. While maternal gamete groups showed a significant FST value across the 5 years, this was not true for their paternal counterparts. Within the population, we found that the relative reproductive contributions of the paternal vs. the maternal parent differed among adult trees, the maternal contributions showing a larger year-to-year fluctuation. • The overall genetic variability of dispersed seeds appeared to result from two sources of heterogeneity: the difference between paternal and maternal patterns of reproduction and gamete dispersal and year-to-year heterogeneity of reproduction of adult trees, especially in their maternal reproduction.

The importance of seed trees in the dioecious coniferPilgerodendron uviferumfor passive restoration of fire disturbed southern bog forests

Biological legacies are important for ecosystem recovery following disturbance as demonstrated by studies in the northern hemisphere. Southern bog forests dominated by the conifer Pilgerodendron uviferum in Northern Patagonia are a typical case of an ecosystem with low resilience to disturbance by fire, which kills most trees and seeds, on which the species depends for regeneration. In this study, we hypothesize that the natural recovery of P. uviferum populations in burned areas is limited by seed availability and this limitation may be exacerbated by the dioecy of the species. Using a multi-scaled approach, we quantified the seed dissemination potential from P. uviferum seed trees, assessed the suitability of substrates for the germination of seedlings, and finally analysed the spatial distribution of seed trees of the species at the landscape level. Our results indicate that 70 years after a fire on Chiloe Island (43°S), natural regeneration from seed trees can assist the recovery of P. uviferum populations following large-scale fire disturbance, but their effect is limited at a landscape level owing to a low number of reproductive female trees (0.3 trees ha−1) and limited seed dispersal (<20 m). In this context, a mixed passive-active restoration approach that takes into account the spatial pattern and sex of seed trees could be the most effective and efficient option to restore not only P. uviferum forests in North Patagonia, but also other heavily disturbed forests with few remnant seed trees, in particular of dioecious species.

Megaherbivores and cattle alter edge effects around ecosystem hotspots in an African savanna

Wild mammalian herbivores and cattle are fundamental drivers of African savanna ecosystems and have strong impacts on woody vegetation. However, few experimental studies have investigated the separate and combined influences of different large herbivores on spatial vegetation patterning. In East Africa, temporary cattle corrals (bomas) develop after abandonment into productive, treeless ‘glades’ that attract both domestic and wild herbivores. Edges of glades exhibit unusually high densities of large trees. We used a long-term, broad-scale manipulative experiment to test whether megaherbivores (elephants and giraffes), wild meso-herbivores (15–1000 kg), or cattle caused shifts in woody plant abundances in glade edges. We also examined cascading effects of megaherbivore and cattle exclusion on symbiotic Acacia ants and wild meso-herbivores in glade edges. Megaherbivore exclusion resulted in increased densities of tall trees, reproductive trees, and non-aggressive Acacia ant species in glade edges. Cattle presence reduced meso-herbivore use inside and away from glades, but not in glade edges. Our results suggest that megaherbivores and cattle can dampen the magnitude of spatial patterns associated with glades and glade edges. These findings provide insight into the development and maintenance of spatial heterogeneity in savannas, and emphasize that land use change and mammalian extinctions have complex, cascading ecological consequences.

Edge effects enhance selfing and seed harvesting efforts in the insect-pollinated Neotropical tree Copaifera langsdorffii (Fabaceae)

Edge effects may affect the mating system of tropical tree species and reduce the genetic diversity and variance effective size of collected seeds at the boundaries of forest fragments because of a reduction in the density of reproductive trees, neighbour size and changes in the behaviour of pollinators. Here, edge effects on the genetic diversity, mating system and pollen pool of the insect-pollinated Neotropical tree Copaifera langsdorffii were investigated using eight microsatellite loci. Open-pollinated seeds were collected from 17 seed trees within continuous savannah woodland (SW) and were compared with seeds from 11 seed trees at the edge of the savannah remnant. Seeds collected from the SW had significantly higher heterozygosity levels (Ho=0.780; He=0.831) than seeds from the edge (Ho=0.702; He=0.800). The multilocus outcrossing rate was significantly higher in the SW (tm=0.859) than in the edge (tm=0.759). Pollen pool differentiation was significant, however, it did not differ between the SW (=0.105) and the edge (=0.135). The variance effective size within the progenies was significantly higher in the SW (Ne=2.65) than at the edge (Ne=2.30). The number of seed trees to retain the reference variance effective size of 500 was 189 at the SW and 217 at the edge. Therefore, it is preferable that seed harvesting for conservation and environmental restoration strategies be conducted in the SW, where genetic diversity and variance effective size within progenies are higher.

Tradeoffs in basal area growth and reproduction shift over the lifetime of a long-lived tropical species

Understanding of the extent to which reproductive costs drive growth largely derives from reproductively mature temperate trees in masting and non-masting years. We modeled basal area increment (BAI) and explored current growth-reproduction tradeoffs and changes in such allocation over the life span of a long-lived, non-masting tropical tree. We integrated rainfall and soil variables with data from 190 Bertholletia excelsa trees of different diameter at breast height (DBH) sizes, crown characteristics, and liana loads, quantifying BAI and reproductive output over 4 and 6 years, respectively. While rainfall explains BAI in all models, regardless of DBH class or ontogenic stage, light (based on canopy position and crown form) is most critical in the juvenile (5 cm ≤ DBH < 50 cm) phase. Suppressed trees are only present as juveniles and grow ten times slower (1.45 ± 2.73 m(2) year(-1)) than trees in dominant and co-dominant positions (13.25 ± 0.82 and 12.90 ± 1.35 m(2) year(-1), respectively). Additionally, few juvenile trees are reproductive, and those that are, demonstrate reduced growth, as do reproductive trees in the next 50 to 100 cm DBH class, suggesting growth-reproduction tradeoffs. Upon reaching the canopy, however, and attaining a sizeable girth, this pattern gradually shifts to one where BAI and reproduction are influenced independently by variables such as liana load, crown size and soil properties. At this stage, BAI is largely unaffected by fruit production levels. Thus, while growth-reproduction tradeoffs clearly exist during early life stages, effects of reproductive allocation diminish as B. excelsa increases in size and maturity.

Gene flow in an overexploited population of Swietenia macrophylla King (Meliaceae) in the Bolivian Amazon

Abstract Pollen and seed movement among and within populations connect individuals and populations, and therefore are among the most important evolutionary processes determining the genetic structure of populations. Seven microsatellite loci were used to investigate the realized pollen dispersal and intra-population spatial genetic structure (SGS) in four permanent plots located in an overexploited big-leaf mahogany (Swietenia macrophylla King) population in the Bolivian Amazon. All adult trees found in the plots were mapped, sampled and genotyped. Seedlings were sampled below the canopy of reproductive trees. Private alleles in the sub-population of the adults and the seedlings were observed. The observed heterozygosity was significantly lower and fixation index was significantly higher for the seedlings (Ho=0.697, F=0.068) compared to the adults (Ho=0.761, F=-0.023). In one plot, seed immigration was observed (18%). Realized pollen immigration ranged among the plots from zero to 41% and selfing ranged from zero to 5.8%. We observed an average pollen dispersal distance from 75 to 255 m, with the maximum reaching 576 m. We found a significant SGS up to 150 m, showing that near neighbour individuals are relatives. The observed data on pollen- and seed dispersal provides important information for the sustainable management of the endangered mahogany species.

Structure and genetic diversity of Ixora margaretae an endangered species

The dry forests of New Caledonia are an excep- tional ecosystem because of their numerous endemic botan- ical species and their highly diversified fauna of insects, mollusks, reptiles and birds. Unfortunately, the area of the dry forests has been significantly reduced, mainly by human activities. Ecological, phenological and genetic analysis of Ixora margaretae, a symbolic species of the sclerophyll forest, has revealed contrasting traits among natural stands. The division of the natural range and then the separation of forest islands has greatly reduced the existing genetic vari- ability of this species. The genetic diversity is strongly structured in genetic clusters which correspond well to spe- cific ecotypes according to the environmental conditions and the forest types. Furthermore, genetic analysis of the reproductive and non-reproductive trees as well the half- sib families obtained by complete protection of mother trees has revealed substantial genetic drift which has resulted in increased loss of allelic variability. The total consumption of seeds by mainly rats confirms the ob- served absence of natural regeneration. All these results show that measures taken to protect the stands of dry forests will not be enough to maintain sufficient genetic variability of I. margaretae populations in the long term. Assisted regeneration with control of the increase in var- iability will be necessary to maintain the biodiversity of the species. The results obtained for I. margaretae must be confirmed with other symbolic species in order to take the necessary measures for the effective preservation of the dry forests in New Caledonia.

Morph-specific mating patterns in a low-density population of a heterodichogamous tree, Juglans ailantifolia

Heterodichogamy, including protandrous (PA) and protogynous (PG) morphs, is considered a mechanism to avoid selfing and promote disassortative mating. Although morphotypes are usually present in a population at a 1:1 ratio, this ratio may be biased in a low-density population by demographic stochasticity, resulting in a deficiency of mating partners in a neighbourhood dominated by a single morph. In this study, we determined morph ratio of the heterodichogamous tree species, Juglans ailantifolia by observing flowering in a low-density population during 2 years. The morph ratio (PG: PA) of 2.56:1 deviated significantly deviated from 1:1. We genotyped 59 reproductive trees and 405 offspring derived from eight PG-mother and three PA-mother trees with 11 microsatellite markers. Paternity analysis was conducted to clarify the effects of mother morph on the proportion of intra-morph mating. Then, we applied the Bayesian mixed effect mating model (MEMM) to clarify mating system, pollen dispersal, and individual fecundity of PG- and PA-mother trees. We found that the selfing rate and the distance of pollen dispersal were not clearly different between PG- and PA-mother trees. In contrast, the proportion of intra-morph mating was higher in the majority-morph (PG) mother trees than in the minor-morph (PA) mother trees. The MEMM indicated that mean dispersal distance of PG-mother trees was larger than that of PA-mother trees with large variance. Furthermore, we observed individuals with unusually high intra-morph fecundity for majority-morph (PG) trees. These findings indicate that intra-morph mating may occur when majority-morph mothers suffer a deficiency of potential inter-morph mates.

What is left after sex in fragmented habitats? Assessing the quantity and quality of progeny in the endemic tree Prosopis caldenia (Fabaceae)

Prosopis caldenia (caldén) is a commercially valuable tree endemic to Central Argentina, a region that holds one of the highest estimates of deforestation rates worldwide. Caldén woodlands within Córdoba province currently remain as a highly fragmented mosaic with a single continuous area of forest left. Here, we assess reproduction, seed predation, and progeny performance of trees growing in continuous forest, small forest fragments and isolation. By assessing both mutualistic and antagonistic interactions we aim to determine net fragmentation effects on the quantity and quality of the surviving progeny. Contrary to expectations, the probability of setting fruits and seeds as well as the levels of seed predation were similar among trees growing across the three contrasting landscape conditions. However, trees growing in isolation produced significantly larger numbers of flowers than trees growing in continuous forest. Thus, the absolute quantity of progeny left for potential recruitment was higher in isolated trees, despite their lower pollination efficiency. However, progeny generated in continuous forest significantly outperformed the progeny from forest fragments and isolated trees, which also suffered higher levels of mortality. Finally, the cumulative performance across all measured life stages was also significantly greater in continuous forest. Therefore, it is within the last continuous forest tract that progeny produced may successfully grow and survive in natural conditions. Assurance of long-term persistence of remaining caldén populations should involve the incorporation of propagules from the continuous forest together with effective restoration efforts to enable gene flow via pollen and seeds among populations through forest corridors.

Do birds bias measurements of seed rain?

Accurate measurements of seed rain are important for understanding tree reproduction (Greene &amp; Johnson 1994), forest regeneration (Cole et al. 2010, Cubiña &amp; Aide 2001, Howe et al. 2010, Zahawi &amp; Augspurger 2006), forest ecology (Muller-Landau et al. 2008, Terborgh et al. 2011) and maintenance of community diversity (Harms et al. 2000). Seed traps generally consist of a bucket or net of a fixed area suspended 0.3–1 m above the ground, and seeds are typically collected once or twice per month. An implicit assumption of all seed-rain studies is that traps do not influence seed dispersal. Should birds perch on and defecate seeds into seed traps, seed abundance will be overestimated. This behaviour could produce a directional bias if birds perch on seed traps in one habitat more than others. To our knowledge, no study has considered this potential bias.

Microclimatic-induced fluctuations in the flower and pollen production rate of olive trees (Olea europaea L.)

The possible impact of altitude and the related microclimatic conditions on the total production of fruiting branches, inflorescences, flowers and pollen grains of olive trees Olea europaea was analysed. A total of 90 Picual cultivar trees, the most extensive olive cultivar in the Iberian Peninsula, were studied for a three-year period (2007–2009). The study shows that production of flowers and pollen grains in a cultivar of the olive tree varies according to the microclimate. Our study also indicates that the olive trees frequently can have up to half a million flowers per tree. Moreover, the total flower production differs between years and study areas. In the Picual cultivar, the average production of pollen grains per anther is usually more than 60 000 grains. The total production of pollen per tree is around 72 000 million on average. The most favourable microclimatic conditions for reproduction in olive trees are found in years and olive growing areas with low temperature and high precipitation records during the months prior to flowering of the olive trees. We hypothesise that olive trees tend to increase their pollen production rate as altitude increases, which can be interpreted as a reproductive strategy to ensure fertilisation.

Scots pine seed dynamics on a waterlogged site

Scots pine (Pinus sylvestris) grows some 400 km south of its current native limit at Wybunbury Moss, Cheshire, UK, on a peatland around a small floating bog (Schwingmoor). Cone and seed production of trees, which have been growing on the site for just over 100 years, were investigated over 3 years. Cones matured between September and March and seed shedding began in early April. The number of cones produced per reproductive tree ranged between 31 and 2,418, with a total average of 685 cones tree−1 y−1. A strong relationship was found between tree diameter and seed production which allowed the prediction of annual seed production. Scots pine on this peatland produced between 766,874 and 950,000 seeds ha−1 annually with a germination percentage of 64%. The predicted number of seeds reaching the central bog (maximum of 120 m from the trees) every year was c. 16,000.