Seed Dispersal Research Articles

LIMITING LIFE HISTORY STAGES IN THE ENDANGERED WETLAND PLANT CIRSIUM HYDROPHILUM VAR. HYDROPHILUM (ASTERACEAE)

In addition to its high biodiversity, the California Floristic Province contains over 1600 rare taxa, including many endemics restricted to specific soil types and habitats. In the highly urbanized San Francisco Estuary, these narrow endemics face additional limitations from habitat destruction and modification, prompting an interest in their conservation and management. One such taxon, the Federally listed Cirsium hydrophilum (Greene) Jeps. var. hydrophilum (Suisun thistle), is restricted to two or three populations, and may face limitations beyond past habitat loss. In this study, we investigated life history limitations that may contribute to rarity in C. hydrophilum var. hydrophilum. We documented low seed set, high seed predation by beetle larvae, low localized wind dispersal of seeds, and possible inbreeding in smaller patches. Because seeds did not have a stringent germination requirement in the lab, however, restoration or introduction of new populations from seed is possible. Using seeds from larger source populations could increase success of reseeding, as could adding seeds to augment potentially low genetic diversity in existing smaller subpopulations. Further study is needed to understand the ecology of seed predators, the relative importance of seed set and seed germination in the field, and to confirm our potential finding of reduced genetic diversity and inbreeding. Though the causes and consequences of rarity may differ for each species, this study explores several research directions that could be productive for understanding other California endemic Cirsium and rare wetland endemics.

Simplified Communities of Seed-Dispersers Limit the Composition and Flow of Seeds in Edge Habitats

Edge effects, driven by human modification of landscapes, can have critical impacts on ecological processes such as species interactions, with cascading impacts on biodiversity as a whole. Characterizing how edges affect vital biotic interactions such as seed dispersal by frugivores is important for better understanding potential mechanisms that drive species coexistence and diversity within a plant community. Here, we investigated how differences between frugivore communities at the forest edge and interior habitats of a diverse tropical rainforest relate to patterns of animal-mediated seed dispersal and early seedling recruitment. We found that the lemur communities across the forest edge-interior gradient in this system showed the highest species richness and variability in body sizes at intermediate distances; the community of birds showed the opposite pattern for species richness. Three large-bodied frugivores, known to be effective dispersers of large seeds, tended to avoid the forest edge. As result, the forest edges received a lower rate of animal-mediated seed dispersal compared to the interior habitats. In addition, we also found that the seeds that were actively dispersed by animals in forest edge habitats were smaller in size than seeds dispersed in the forest interior. This pattern was found despite a similarity in seed size of seasonally fruiting adult trees and shrubs between the two habitats. Despite these differences in dispersal patterns, we did not observe any differences in the rates of seedling recruitment or seed-size distribution of successful recruit species. Our results suggest that a small number of frugivores may act as a potential biotic filter, acting on seed size, for the arrival of certain plant species to edge habitats, but other factors may be more important for driving recruitment patterns, at least in the short term. Further research is needed to better understand the potential long-term impacts of altered dispersal regimes relative to other environmental factors on the successional dynamics of edge communities. Our findings are important for understanding potential ecological drivers of tree community changes in forest edges and have implications for conservation management and restoration of large-seeded tree species in disturbed habitats.

The upsizing of the São Tomé seed dispersal network by introduced animals

Biological invasions are a major threat to global biodiversity with particularly deleterious consequences on oceanic islands. The introduction of large terrestrial animals – generally absent on islands – can disrupt important ecosystem functions, such as the dispersal of native seeds. However, while the consequences of plant invasions received much attention, the potential of introduced animals to change insular seed dispersal networks remains largely unknown. Here, we collated evidence from five sampling methods to assemble qualitative and quantitative, multi‐guild seed dispersal network for the island of São Tomé (Gulf of Guinea) and explore whether native and introduced seed dispersers consistently differ in their topological roles, in their gape width and in the size of the dispersed seeds. Our network included 428 interactions between 23 dispersers (14 birds, 2 bats, 1 snake and 6 non‐flying mammals) and 133 plant species. Each method (direct observations, identification of seeds in droppings and stomachs, questionnaires and literature review) was particularly informative for a small group of dispersers, thus rendering largely complementary information. Native and introduced dispersers did not differ in their topological position in either qualitative or quantitative networks (linkage level, specialization d' and species strength). However, introduced dispersers tend to have much larger gape widths and to disperse significantly larger seeds. Our results point to a general upsizing of the seed dispersal network in the island of São Tomé driven by the recent arrival of large, introduced animals. We argue that this pattern is likely common on other oceanic islands where introduced dispersers might counteract the general pattern of seed dispersal downsizing resulting from the selective extinction of larger animals.

Frugivore diversity increases evenness in the seed rain on deforested tropical landscapes

The diversity of tropical forests is strongly shaped by mutualistic interactions involving plants and frugivores that disperse their seeds. However, it is little known how decreases in the diversity of frugivores can affect seed dispersal patterns, plant community composition and species' coexistence in tropical forest landscapes. Here, we investigated the effects of bird frugivore diversity on seed dispersal of rare plant species and on the magnitude of equalizing effects on the seed rain in open areas within 12 fragmented landscapes in the Brazilian Atlantic Forest. We monitored the production of bird‐dispersed seeds and bird abundance in forest fragments, and sampled the seed rain and the activity of birds attracted to experimental tree nuclei established in neighboring pastures. The activity of frugivores in tree nuclei was positively correlated with the diversity of birds recorded in nearby forest fragments, and the seed rain diversity increased with frugivore activity. The proportion of seeds dispersed more frequently than expected by chance in tree nuclei increased linearly with the species' richness of birds. The richness and abundance of active frugivores in deforested areas promoted a seed rain with evenness and diversity up to five times greater than the seed pool available in forest fragments due to the proportional increase in the dispersal of rare plant species and a concomitant proportional decrease in the dispersal of dominant fruiting plants. Furthermore, every additional bird species detected in a site was associated with a 10% increase in the equalizing effect on dispersed seeds' relative abundance. Our results show that the aggregated behavior of avian frugivore communities on deforested areas results in higher species richness in the seed rain of plant communities and underscore the urgency to reduce bird species' loss and the simplification of their communities in tropical landscapes.

Cascading Impacts of Seed Disperser Loss on Plant Communities and Ecosystems

Seed dispersal is key to the persistence and spread of plant populations. Because the majority of plant species rely on animals to disperse their seeds, global change drivers that directly affect animals can cause cascading impacts on plant communities. In this review, we synthesize studies assessing how disperser loss alters plant populations, community patterns, multitrophic interactions, and ecosystem functioning. We argue that the magnitude of risk to plants from disperser loss is shaped by the combination of a plant species’ inherent dependence on seed dispersal and the severity of the hazards faced by their dispersers. Because the factors determining a plant species’ risk of decline due to disperser loss can be related to traits of the plants and dispersers, our framework enables a trait-based understanding of change in plant community composition and ecosystem functioning. We discuss how interactions among plants, among dispersers, and across other trophic levels also mediate plant community responses, and we identify areas for future research to understand and mitigate the consequences of disperser loss on plants globally.

Ovule-bearing structures of Karkenia Archangelsky, associated dispersed seeds and Sphenobaiera leaves from the Middle Jurassic of East Siberia, Russia

Ovule-bearing structures of Karkenia are recorded from the Middle Jurassic of East Siberia for the first time. A new species, Karkenia irkutensis sp. nov., described from the lower part of the Prisayan Formation (Aalenian) of the Irkutsk Coal Basin, is a compact, ellipsoidal to spherical structure consisting of numerous ovules. The entire structure is borne on a thin stalk. The pedicels of individual ovules are also thin and most likely recurved. Four membranes are preserved in the ovules: outer and inner cuticles of the integument, the nucellar cuticle, and the megaspore membrane. Additionally, numerous large resin bodies occur in the sarcotesta. Among the ovules of the same ovule-bearing structure, two types of the megaspore membrane with different ultrastructure were obtained, which may indicate different stages of ovule development. Ovule-bearing structures of K. irkutensis were found in association with leaves of Sphenobaiera vigentis and their co-occurrence in the same samples from the Irkutsk Basin suggests that these remains were most likely produced by the same plant. Numerous dispersed seeds described as Allicospermum sp. were also found in the same locality. These seeds are similar to the attached ovules of K. irkutensis in form and size, but differ in having a thicker sarcotesta, smaller resin bodies. There are also differences in some features of the outer epidermis of the integument. Allicospermum sp. may represent more mature seeds/ovules of K. irkutensis. The morphology and epidermal features of the genus Karkenia are discussed.

Roller dung beetles of dung piles suggest habitats are alike, but that of guarding pitfall traps suggest habitats are different

AbstractRoller dung beetles play a pivotal role in the nutrient distribution in soil and secondary dispersal of seeds. Dung beetles are sampled either using a dung-baited pitfall trap or an exposed dung pile on the ground. While the former method is useful for a rapid survey of dung beetles, information on the ecology and behaviour of dung beetles can be lost, which the latter method provides, but underestimates species diversity due to its inefficiency in trapping rollers. Efficiency of a new method for sampling rollers—installing guarding pitfall traps around dung piles—is assessed in three habitats—contiguous tropical rainforests, fragmented forests, and disturbed used home gardens—and two diel periods—day and night. Five guarding pitfall traps were installed at 50 cm radius around dung piles. About 98% of the total rollers were sampled in pitfall traps. The habitats were similar when the roller catches of only dung piles—conventional approach—were analyzed, but were different when the rollers of guarding pitfall traps were considered. The roller abundance was negatively affected by forest fragmentation and land-use change. About 98% of the rollers were collected at daytime. Using guarding pitfall traps around dung piles is highly recommended for dung beetle diversity studies.

Evidence of Alectoris chukar (Aves, Galliformes) as seed dispersal and germinating agent for Pistacia khinjuk in Balochistan, Pakistan

Seed dispersal is a key process for the distribution of wild fruit plants in forests and/or rangeland. The ecological role of Alectoris chukar as a seed dispersal agent was hardly known to date, though its diet consists of herbs, shrubs, and fleshy fruits of wild plants. Here we report the first evidence of seed dispersal and germination of wild pistachio plant (Pistacia khinjuk Stocks) favored by Alectoris chukar from the district Killa Saifullah and Pishin in Balochistan, Pakistan. Fecal droppings of Alectoris chukar were collected by a suitable sampling method from August to September 2020. Fecal droppings were kept in plastic bags, and later washed thoroughly, identified, and counted for Pistacia khinjuk seeds, which have a characteristic rounded and tough seed coat easily distinguishable from other seeds. Out of a total of 840 fecal samples collected, 557 were identified as Pistacia khinjuk seeds. A comparative germination trial was carried out for pistachio seeds both from Alectoris chukar fecal droppings and manually collected from mother trees in the forest. After passing through the chukar gut, the seeds were still viable and showed a faster germination rate as compared with seeds collected from mother trees and directly sown in the soil. The results revealed that Alectoris chukar is an important spreading and germinating agent for seeds of pistachio plants in suitable habitats and could contribute in the long term to modify the ground vegetation of (sub)arid regions depending on its dietary preferences.

Germination response of black nightshade (Solanum nigrum) to temperature and the establishment of a thermal time model

AbstractBlack nightshade (Solanum nigrum L.) is one of the worst weeds in crop fields, and it spreads mainly by the dispersal of seeds. Temperature is one of the key environmental factors affecting seed germination. We investigated the seed germination response to temperature in six populations of S. nigrum from mid- to northern China and derived mathematical models from germination data. The results showed that S. nigrum seeds exhibit distinct germination responses to temperature within the range of 15 to 35 C. The optimum temperature for populations XJ1600, JL1697, and HLJ2134 was 30 C, and those for populations NMG1704, HN2160, and LN2209 were 25, 20, and 15 C, respectively. Based on the nonlinear fitting and thermal time models, the predicted base temperatures of the six populations ranged from 2.3 to 6.4 C, and the required accumulated growing degree days (GDD) ranged from 50.3 to 106.0 C·d. The base temperatures and the accumulated GDD for germination differed among populations, and there was a significant negative correlation. HLJ2134 population required a high base temperature and accumulated GDD for germination, indicating that it might be highly adapted to a warmer and moister environment. Based on the different germination responses of S. nigrum populations to temperature, the thermal time model reflects an innate relationship between base temperature and accumulated GDD required for initiation of seed germination, which provides a better basis for predicting seedling emergence and the timing for optimal control of S. nigrum under field conditions.

English

Brassica is the second-largest oilseed crop after Soybean. The total production of Brassica in the overall world is 71 million tons. In Pakistan, its total production per unit area is very low. Biotic and abiotic stresses mainly affect the brassica crop. In agriculture, shattering is the dispersal of crops seeds before their ripening. The pod wall shatters and breaks apart when it loses its hydration and cells split in a dehiscence zone organized at a suture between the edge of the lignified pod and the vascular tissue replum. The degeneration of middle lamella and loss of cellular cohesion in the dehiscence zone are the main reasons for pod shattering and seed losses. Grain yield losses in Brassica vary from 10 to 25 percent due to shattering. More than 400 kg has-1 or 12% seed losses can be occurred due to pod shattering under unfavorable conditions. Insect pest and disease damage also accelerate ripening and pod shattering. The main breeding techniques for developing rapeseed grain yield potential are a good knowledge and application of the morphological, physiological, and genetic basis of grain yield. Modern technologies, such as embryo rescue, marker-assisted breeding, and novel variation (mutation), may make it much simpler to introduce new rapeseed types having shattering tolerance than traditional methods. Thus, an overview of anatomical and physiological aspects and genetics of shattering is presented in the context of recent advances in molecular genetics and several agronomic managements to avoid shattering in Brassica.

Effects of mast seeding and insect infestation on predation and dispersal of Castanea mollissima nuts by rodents in the Qinling Mountains of China

Seed predation and dispersal by rodents plays an important role in woodland regeneration. To understand the impact of insect-infestation under different food abundance conditions on rodent predation and dispersal preferences, it is necessary to determine whether rodents have the ability to distinguish between infested and non-infested seeds and whether feeding strategies are affected by food abundance. Here, we compared the predation and dispersal fates of infested and non-infested nuts of Castanea mollissima in mast and non-mast years in a subtropical forest in the Qinling Mountains, central China. We found that rodents could discriminate between infested and non-infested nuts of C. mollissima. Harvest rates of non-infested nuts were relatively faster than those of infested nuts, and rodents preferred to consume infested nuts (typically in situ), while non-infested nuts were cached more often and dispersed farther. Mast seeding had a significant effect on seed predation and dispersal by rodents. When per capita food availability was low (i.e., in non-mast years), harvest rates and dispersal distances (including eaten and cached distances) were obviously accelerated and increased irrespective of insect-infestation. While in mast seed years rodents chose to cache more nuts, and selectively caching a higher proportion of non-infested seeds. This indicated that mast seeding could promote seed caching and result in more seeds escaping predation, which would enhance seed germination and forest regeneration.

Connecting regional-scale tree distribution models with seed dispersal kernels

Regional scale forest distribution models are important tools for biogeography and understanding the structure of forest communities in space. These models take climate and geographic variables as input and are therefore helpful for long-term decision support and climate adaptation planning. Generally, local processes of tree germination and seedling survival are resolved probabilistically with explanatory variables such as elevation, latitude, exposure, soil type, moisture availability, climate and weather inputs and `trained’ using landscape and regional presence-absence data and machine learning techniques. How seeds are distributed in these models, that is, determining the dispersal kernel, is far more problematic. The challenge is that variables conditioning vertebrate seed dispersal (motility and probability of utilization or caching in response to cover type) are not represented in large scale distribution models, and in fact vary on scales (10-100 meters) that are much smaller than the smallest pixel size for the distribution model (1-10 kilometers). We present a homogenized seed digestion kernel (HSDK) which incorporates this scale separation. Homogenization naturally links highly variable small-scale processes (like seed foraging and caching by birds and rodents) with large scale effects (like dispersal of seeds over tens of kilometers). We develop a homogenization strategy to predict seed dispersal on landscape scales, analytically linking small-scale variables (landscape fraction cover by tree type, gut residence times and cover type utilization by frugivorous birds) with large scale behaviors. Closed form approximations are developed in two dimensions for two limiting cases of seed handling behavior, and the approach is illustrated using landscape data and piñon-pine dispersal in a 630,000 square kilometer region in the southwestern US.

Diploendozoochory in Neotropical fish makes seed germination unlikely

AbstractDiploendozoochory is the seeds’ dispersion ingested by two or more animal species in sequence. This mechanism does not occur among the fish species we studied relative to dispersal of seeds because they were destroyed when passing through the predator fish. Our study is the first about diploendozoochory among tropical fishes.Abstract in Spanish is available with online material.

Within-Species Trait Variation Can Lead to Size Limitations in Seed Dispersal of Small-Fruited Plants

The inability of small-gaped animals to consume very large fruits may limit seed dispersal of the respective plants. This has often been shown for large-fruited plant species that remain poorly dispersed when large-gaped animal species are lost due to anthropogenic pressure. Little is known about whether gape-size limitations similarly influence seed dispersal of small-fruited plant species that can show a large variation in fruit size within species. In this study, fruit sizes of 15 plant species were compared with the gape sizes of their 41 animal dispersers in the temperate, old-growth Białowieża Forest, Poland. The effect of gape-size limitations on fruit consumption was assessed at the plant species level, and for a subset of nine plant species, also at the individual level, and subindividual level (i.e., fruits of the same plant individual). In addition, for the species subset, fruit-seed trait relationships were investigated to determine whether a restricted access of small-gaped animals to large fruits results in the dispersal of fewer or smaller seeds per fruit. Fruit sizes widely varied among plant species (74.2%), considerably at the subindividual level (17.1%), and to the smallest extent among plant individuals (8.7%). Key disperser species should be able to consume fruits of all plant species and all individuals (except those of the largest-fruited plant species), even if they are able to consume only 28-55% of available fruits. Fruit and seed traits were positively correlated in eight out of nine plant species, indicating that gape size limitations will result in 49% fewer (in one) or 16–21% smaller seeds (in three plant species) dispersed per fruit by small-gaped than by large-gaped main dispersers, respectively. Our results show that a large subindividual variation in fruit size is characteristic for small-fruited plant species, and increases their connectedness with frugivores at the level of plants species and individuals. Simultaneously, however, the large variation in fruit size leads to gape-size limitations that may induce selective pressures on fruit size if large-gaped dispersers become extinct. This study emphasizes the mechanisms by which gape-size limitation at the species, individual and subindividual level shape plant-frugivore interactions and the co-evolution of small-fruited plants.

Fine-scale spatiotemporal variation in seed-rodent interactions: A potential contribution to species coexistence

Seed predation and dispersal by rodents plays an important role in seedling establishment and forest regeneration. Spatiotemporal variation in seed availability at fine scales is ubiquitous in the forest because of the different spatial locations and fruiting phenology among tree species, which may further lead to spatiotemporal variation in seed-rodent interactions. However, previous research has generally treated such variation as random effects among experimental replicates and provides few relevant explanations. Therefore, in this study, we directly tested the spatiotemporal variation in seed predation and dispersal at a fine-scale by manipulating a dynamic pattern of seed availability, releasing different species of seeds into the forest at 10 m intervals in space and 6 day intervals in time. In total, we tracked the dispersal and predation of 40,500 seeds belonging to 45 tree species in a subtropical forest in southwest China for three consecutive years. Our results provide strong evidence that fine-scale spatiotemporal variation in seed dispersal and predation by rodents always exists, although the overall intensity of seed harvest and removal significantly differs among experimental years and plots. Furthermore, the fine-scale spatiotemporal effect differs among plant species, indicating that the spatiotemporal effect may be species specific. Consequently, any specific seed may have the probability to survive or be dispersed as long as it appears at a specific site and time. Our findings further suggest that the fine-scale spatiotemporal variation in seed-rodent interactions may contribute to species coexistence in the forest, at least at the seed stage. Generally, we expect that similar fine-scale spatiotemporal variations occur in other plant-animal interactions, such as herbivory and pollination. Incorporating fine-scale spatiotemporal variation into future plant-animal studies may help us to gain a better understanding of species coexistence and biodiversity maintenance.

Mesopredator frugivory has no effect on seed viability and emergence under experimental conditions

AbstractMembers of the orderCarnivoraare a unique and important seed disperser who consume and deposit undamaged seeds while providing regular long‐distance seed dispersal opportunities. Some members ofCarnivora, such as coyotes (Canis latrans), are undergoing range expansions which may help the plant species they consume colonize new locations or replace dispersal services provided by recently extirpated species. In this study, we evaluated aspects of the seed dispersal effectiveness of coyotes and gut passage time to determine the potential dispersal distances for three commonly consumed and commonly occurring plant species (Amelanchier alnifolia, Celtis ehrenbergiana, andJuniperus osteosperma). We also investigated the potential effects of secondary dispersal of seeds away from scats by comparing seedling emergence from whole scats to those where seeds were first removed from scats. We found that seeds generally took between 4 and 24 h to pass through the digestive tract of coyotes, which could result in regular seed dispersal up to 7 km. Gut passage through coyotes had no effect on seed viability or emergence for any of the three plant species, including that gut passage forA. alnifoliaandJ. osteospermadoes not replace cold stratification for breaking physiological dormancy. By simulating secondary dispersal, we found that 22% (±8.2%) moreC. ehrenbergianaseedlings emerged when seeds were removed from scats and those seedlings emerged 7 d earlier (±5 d) compared to seeds that remained in the coyote scat. Coyotes are effective seed dispersers, with the potential for regular long‐distance dispersal services and for providing opportunities for secondary seed dispersal, which could aid in climate migration or serve to replace extirpated dispersal mutualists.

Spatial Analysis as a Tool for Plant Population Conservation: A Case Study of Tamarix chinensis in the Yellow River Delta, China

Saltcedar (Tamarix chinensis) is undergoing population declination and fragmentation due to climate change and human disturbance. The existing restoration strategies usually focus on improving the environmental conditions based on the environment–saltcedar relationship, while they ignore the role of spatial autocorrelation resulting from biological interaction and ecological processes. This oversight limits the efficiency and sustainability of the restoration. Here, we explored the spatial pattern of the saltcedar population in the Yellow River Delta, China, and its relationship with environmental factors, incorporating spatial autocorrelation. The plant and soil parameters were extracted by an airborne LiDAR system integrated with fixed soil environment measurements. The environment–saltcedar relationship incorporating spatial autocorrelation was evaluated with different regression models. Results showed that saltcedars aggregated at small scales (2–6 m), resulting from intraspecific facilitation and wind dispersal of seeds, while intraspecific competition was responsible for the random distribution at large scales (>10 m). The long-distance dispersal of seeds through water explained the significant positive spatial autocorrelation of saltcedars at distances up to 125 m. Consequently, resulting from intraspecific facilitation and seed dispersal, aggregation distribution and positive spatial autocorrelation within the saltcedar population improved the adaptability of saltcedar to environmental stress and thereby reduced the impact of environmental factors on the abundance of saltcedar.

Programming sequential motion steps in 4D-printed hygromorphs by architected mesostructure and differential hygro-responsiveness

Through their anisotropic cellular mesostructure and differential swelling and shrinking properties, hygroscopic plant structures move in response to changes in the environment without consuming metabolic energy. When the movement is choreographed in sequential time steps, either in individual structures or with a coordinated interplay of various structural elements, complex functionalities such as dispersal and protection of seeds are achieved. Inspired by the multi-phase motion in plant structures, this paper presents a method to physically program the timescale and the sequences of shape-change in 4D-printed hygromorphic structures. Using the FDM 3D-printing method, we have developed multi-layered, multi-material functional bilayers that combine highly hygroscopic active layers (printed with hygroscopic bio-composite materials) with hydrophobic restrictive and blocking layers (printed with PLA and TPC materials). The timescale of motion is programmed through the design of the mesostructured layers and 3D-printing process parameters, including thickness (number of printed active layers), porosity (filling ratio of the active layer), and water permeability (filling ratio of the blocking layer). Through a series of experiments, it is shown that the timescale of motion can be extended by increasing the thickness of the active layer, decreasing the porosity of the active layer, or increasing the filling ratio of the hydrophobic restrictive and blocking layers. Similarly, a lower thickness of the active layer and lower filling ratio of all layers result in a faster motion. As a proof of concept, we demonstrate several prototypes that exhibit sequential motion, including an aperture with overlapping elements where each completes its movement sequentially to avoid collision, and a self-locking mechanism where defined areas of the structure are choreographed to achieve a multi-step self-shaping and locking function. The presented method extends the programmability and the functional capabilities of hygromorphic 4D-printing, allowing for novel applications across fields such as robotics, smart actuators, and adaptive architecture.

Effect of Tree Density on Seed Production and Dispersal of Birch (Betula pendula Roth and Betula pubescens Ehrhs)

Silver and downy birch (Betula pendula Roth and B. pubescens Ehrhs) are pioneer species which play an important role in forest regeneration in disturbed areas. Knowledge of birch seed production and dispersal is key to making good predictions of the persistence and colonization of birch. Both processes can be affected by the density of trees in the neighbourhood. In this study, we studied the seed production and dispersal of birch trees in two plots in Wytham Woods, UK, in 2015, and investigated the potential effect of neighbourhood tree density. We applied inverse modelling to seed trap data, incorporating tree density around the source tree and on the seed path to estimate birch fecundity and the dispersal kernel of the seeds. We show that the pattern of dispersed seeds was best explained by a model that included an effect of tree density on seed dispersal. There was no strong evidence that conspecific or heterospecific tree density had an effect on birch fecundity in Wytham Woods. A birch with diameter at breast height (DBH) of 20 cm is estimated to have produced ~137,000 seeds in 2015. Mean dispersal distance in an open area is estimated to be 65 m but would be reduced to 38 m in a closed stand. Both the mean dispersal distance and the probability of long-distance dispersal of birch decreases in dense environments. Areas with higher tree density also would intercept more seeds. These results highlight the importance of considering tree density in the neighbourhood and in the overall landscape when predicting the colonization and recruitment of birch.

Development and characterization of a Napier grass (Cenchrus purpureus Schumach) mapping population for flowering‐time‐ and biomass‐related traits reveal individuals with exceptional potential and hybrid vigor

AbstractNapier grass is a tropical perennial C4 grass with superior biomass yield and quality. It is an important forage crop and a promising feedstock for lignocellulosic biofuel production. However, precise phenotyping and genotyping data to support the molecular breeding of Napier grass are scarce. A Napier grass F1 mapping population (segregating pseudo‐F2 population) was generated by hybridizing genetically distant parents (N190 × N122) with contrasting flowering‐time‐ and biomass‐related traits. True F1 hybrids were confirmed with a simple sequence repeat marker, vegetatively propagated, and phenotyped in replicate field plots for 2 years (2 harvests per year) in Citra, FL, USA (29.40N). Near‐normal distributions were observed for flowering date, plant height, number of tillers, stem diameter, and leaf width, confirming the quantitative nature of these traits. The annual dry biomass yield of F1 hybrids varied between 21.0 and 41.1 t ha−1. The highest‐yielding F1 hybrids showed remarkable hybrid vigor exceeding the annual biomass production of the highest‐yielding parental accession (26.9 t ha−1) by 52% and the biomass yield of the control “Merkeron” cultivar (29.2 t ha−1) by 41% over 2 years. F1 hybrids with delayed flowering time along with significantly increased biomass yield were also identified. Late‐flowering accessions allowed maximum biomass harvest before formation and dispersal of seeds, reducing invasion risk. The developed mapping population will be an excellent resource for identifying quantitative trait loci and candidate genes for flowering‐ and biomass‐related traits in Napier grass that will accelerate the improvement of this non‐domesticated bioenergy crop.