Seed Dispersal Research Articles

Artificial perches for the supply of seeds in a fragmented landscape in southwest Brazilian Amazon

Artificial perches can provide an important supply of seeds and contribute to ecological restoration. In the present study, we verified the effectiveness of artificial perches for the dispersal of seeds in an area of the southwest Brazilian Amazon. We conducted the study on the Catuaba Experimental Farm in State of Acre, Brazil, from March 2016 to March 2017. We installed seed traps with artificial perches and control traps at different distances from the adjacent forest. We collected 19,865 seeds in boxes under the artificial perches and 1300 in the control traps. There was greater richness of plant species and abundance of seeds in the boxes under the artificial perches when compared with the control traps. The artificial perches at a distance of 40 m from the adjacent forest presented a greater species richness and distinct composition of plants. The quantity of dispersed seeds did not correlate with precipitation, although there was a correlation between rainfall and the fresh seed mass. The artificial perches were efficient at dispersing seeds and are a low-cost technique that can be used as a strategy for the regeneration of forests in degraded areas.

Ultrasound as a tool for polymorph control and high yield in flow crystallization

Ortho-aminobenzoic acid (o-ABA) has three polymorphs from which form-I is the most stable and forms-II and III are meta–stable ones at 25 °C. In flow crystallization, the meta-stable form-II is quite persistent and prevents nucleation of the stable form-I. This is contrary to batch crystallization and possibly a result of high local supersaturation. In this work, seeded, anti-solvent crystallization of o-ABA was conducted to overcome nucleation of the meta-stable form and obtain a high yield of form-I. Experiments were conducted in a tubular flow crystallizer under silent and sonicated conditions. Seeding was effective in producing pure form-I only when ultrasound was applied. Under silent conditions, poor dispersion of seeds and heterogeneous wall nucleation led to the growth of form - II. Ultrasound improved dispersion and reduced nucleation on walls and thus a pure form-I product was obtained. Particle sizes and SEM images showed evidence of secondary nucleation as the mechanism for form-I occurring in seeded, sonicated experiments rather than seed growth. A high yield, 48% by mass and 85% of maximum crystallizable mass, could be achieved. Ultrasound increased the potential of the flow crystallization system by combining high yield with polymorph control.

Endozoochorous seed dispersal by golden snub-nosed monkeys in a temperate forest.

Seed dispersal is essential for plant recruitment and the maintenance of biodiversity. Colobine monkeys are primarily folivorous, but they also consume fruits and are often assumed to be seed predators. Although they are known to be epizoochorous seed dispersers, their role as endozoochorous seed dispersers needs reassessment. We examined potential endozoochory in golden snub-nosed monkeys (Rhinopithecus roxellana) at Dalongtan in Shennongjia National Park, central China, by assessing potential germination of ingested seeds (n = 1806, 9 species) from fecal samples. Intact seeds were in almost all fecal samples (ranging from 5-130 seeds), and ingested seeds were from small seeded species (seed width <4.5 mm). The 2 most abundant species were Actinidia arguta (73%) and Rosa caudata (15%). The fruits of A. arguta were unripe when ingested (i.e. effective seed predation) and the ingested seeds did not germinate in the trials. Therefore, ingestion of unripe seeds does not lead to effective seed dispersal. However, germination rates of defecated R. caudata (9%) were greater than control seeds (6% and 0%), demonstrating potential endozoochorous seed dispersal. Thus, colobine monkeys do indeed disperse mainly small-seeded from multi-seeded fruits through potential endozoochory and this process enhances the recruitment of seedlings.

SEED DISPERSAL, SEEDBANK, SEEDLING SURVIVAL, AND INITIAL GROWTH OF THREE CAATINGA TREES

ABSTRACT Myracrodruon urundeuva, Handroanthus impetiginosus and Amburana cearensis are Caatinga tree species that produce valuable timber, but little is known about their ecology. The objective of this study was to evaluate the seed distribution of these species on the forest floor before and after seed dispersal; and seedling emergence, survival, and growth during the rainy season after dispersal of seeds. There were no remaining viable seeds of these species in the seedbank before seed dispersal. The average numbers of seeds after seed dispersal were 188 seed m-2 in a 30 m radius around M. urundeuva, 9 seed m-2 in a 10 m radius around H. impetiginosus, and 5 seed m-2 in a 20 m radius around A. cearensis. The distance of seed dispersal reached 30, 20, and 10 m for M. urundeuva, H. impetiginosus, and A. cearensis trees, respectively, due to differences in tree height, seed weight, forest density, and wind intensity. Seedling emergence was observed during 4 (M. urundeuva) and 9 (H. impetiginosus and A. cearensis) weeks. High mortality predominated at the beginning and end of the rainy season for M. urundeuva and A. cearensis, respectively, while practically all H. impetiginosus seedlings survived. M. urundeuva showed the highest mortality but had higher number of established seedlings than the other species. Seedling survival peaked around 5 m from the tree base. Seedling recruitment and natural regeneration of these trees are assured in the Caatinga site evaluated.

Frugivores vary in their response to neighborhood effects in a novel ecosystem

Seed dispersal is critical for maintaining ecosystem structure and over half of plant species worldwide rely on animals for dispersal. Animal-mediated seed dispersal requires tight links between animals and plants. The introduction of invasive species threatens this mutualism by potentially creating competition between native and invasive plants for dispersers and by altering the consumption of native fruits by introduced dispersers. Although the first critical step in seed dispersal is fruit consumption, we have limited knowledge of the characteristics that attract dispersers to a given plant. In particular, characteristics of the neighborhood surrounding a plant may alter frugivory and frugivores may vary in their responses to these characteristics. Identification of key neighborhood characteristics would help to identify the mechanisms which facilitate or limit seed dispersal, aiding in the management of species in novel ecosystems. We deployed camera traps on Oʻahu, Hawaiʻi to quantify how the total fruit abundance, percent invasive fruit, percent conspecific fruit, canopy cover, and ground vegetation density of the neighborhood influence visitation and fruit removal by introduced avian frugivores. Results showed that neighborhood effects had little influence on frugivory overall, but did influence avian foraging groups in disparate ways. In particular, visitation by arboreal foragers increased with canopy cover and the amount of fruit on the focal plant but decreased with higher neighborhood fruit abundance and more conspecific fruit. Ground forager visitation decreased with higher ground vegetation density and increased with more conspecific fruit. These findings suggest the neighborhood can be modified to facilitate arboreal foragers, which are higher quality dispersers on Oʻahu, and to limit ground foragers, which are primarily seed predators. We argue studies should consider differences among dispersers to adequately address the role of the neighborhood on frugivory in environments with multiple disperser species.

Do regeneration traits vary according to vegetation structure? A case study for savannas

AbstractAimRegeneration traits are crucial for understanding patterns and processes in plant communities. However, regeneration traits are not reported much in community ecology, preventing a better assessment of trait‐based community assembly. Here we assessed habitat‐related regeneration traits by comparing species from open (grassland and shrubland) and closed (woodland) Brazilian savannas (cerrado).LocationOur study site comprised two cerrado areas in southeastern Brazil that range from open to closed vegetation types, as examples of an ecological gradient of resources and environmental conditions.MethodsWe classified 82 species according to dormancy (non‐dormant, physiological, physical, physiophysical, morphological, and morphophysiological dormancy), dispersal syndrome (autochory, anemochory, exozoochory, endozoochory), and dispersal season (rainy, dry, rainy‐to‐dry and dry‐to‐rainy transitions). We determined seed mass, germination percentage, mean germination time and coefficient of variation of germination time in conditions of optimal temperatures. Principal coordinates Analysis (PCoA) was used to explore the relationships between regeneration traits and vegetation types.ResultsThe two main axes of the PCoA explained 38% of the total variance. The first axis was related to germination traits (germination percentage, mean gemination time, and coefficient of variation of gemination time) and separated dormant from non‐dormant species, whereas the second axis was related to seed mass, growth form, and dispersal syndromes which sharply separated open‐ and closed‐savanna species. Unexpectedly, seed germination and dormancy traits did not differ among open‐ and closed‐savanna species.ConclusionsSeasonality is a strong filter for both germination and seedling establishment that shapes germination strategies regardless of vegetation type. The dominant strategy was dispersal of non‐dormant seeds in the rainy season, while the least common strategy was dispersal of dormant seeds during the rainy‐to‐dry season transition. Habitat‐related germination strategies were related to growth form and seed mass, improving our understanding of community assembly in species‐rich Brazilian savannas.

Cottonwood Seed Dispersal Phenology across North America and Worldwide: Tracking ‘Summer Snow’ through an Internet Search

Cottonwoods, Populus trees, provide the foundation for riparian woodlands around the Northern Hemisphere but have declined partly due to river damming and water withdrawal. Cottonwood conservation requires periodic seedling replenishment, which depends upon coordinating river flows with the limited seed dispersal interval. Tracking seed dispersal phenology is laborious and we recognized a complementary approach with photographs and videos of prolific cottonwood seed release on internet websites. We searched the internet for ‘cottonwood seeds’ or ‘summer snow’, and about 800 images were posted since 2004. The 337 reports from North America with dates and/or locations revealed sequential seed dispersal in the American Southwest, the Pacific Northwest, the Great Lakes Region, and finally Alaska. Mean dispersal was June 3, with two-thirds of reports in the flanking four week interval. Dispersal was later at higher latitude and elevation, and a two-factor regression model provided 85% accuracy with reported peak dispersal from nine previous studies across western North America. The 49 Eurasian reports also revealed later seed dispersal with increasing latitude. This study revealed the utility of internet searching for tracking cottonwood seed dispersal, which could facilitate environmental flows for riparian restoration. More broadly, internet reports could reveal spatiotemporal patterns in other natural phenomena.

Quantifying the roles of seed dispersal, filtering, and climate on regional patterns of grassland biodiversity.

Seed dispersal and local filtering interactively govern community membership and scale up to shape regional vegetation patterns, but data revealing how and why particular species are excluded from specific communities in nature are scarce. This lack of data is a missing link between our theoretical understanding of how diversity patterns can form and how they actually form in nature, and it hampers our ability to predict community responses to climate change. Here, we compare seed, seedling, and adult plant communities at 12 grassland sites with different climates in southern Norway to examine how community membership is interactively shaped by seed dispersal and local filtering, and how this process varies with climate across sites. To do this, we divide species at each site into two groups: locally transient species, which occur as seeds but are rare or absent as adults (i.e., they arrive but are filtered out), and locally persistent species, which occur consistently as adults in annual vegetation surveys. We then ask how and why locally transient species are disfavored during community assembly. Our results led to four main conclusions: (1) the total numbers of seeds and species that arrived, but failed to establish locally persistent populations, rose with temperature, indicating an increase in the realized effects of local filtering on community assembly, as well as an increase in the number of species poised to rapidly colonize those warmer sites if local conditions change in their favor, (2) locally transient species were selectively filtered out during seedling emergence, but not during seedling establishment, (3) selective filtering was partly driven by species climate preferences, exemplified by the poor performance of seeds dispersing outside of their realized climate niches into colder and drier foreign climates, and (4) locally transient species had traits that likely made them better dispersers (i.e., smaller seeds) but poorer competitors for light (i.e., shorter statures and less persistent clonal connections) than locally persistent species, potentially explaining why these species arrived to new sites but did not establish locally persistent adult populations. Our study is the first to combine seed, seedling, and adult survey data across sites to rigorously characterize how seed dispersal and local filtering govern community membership and shape climate-associated vegetation patterns.

An integrodifference model for vegetation patterns in semi-arid environments with seasonality

Vegetation patterns are a characteristic feature of semi-deserts occurring on all continents except Antarctica. In some semi-arid regions, the climate is characterised by seasonality, which yields a synchronisation of seed dispersal with the dry season or the beginning of the wet season. We reformulate the Klausmeier model, a reaction–advection–diffusion system that describes the plant–water dynamics in semi-arid environments, as an integrodifference model to account for the temporal separation of plant growth processes during the wet season and seed dispersal processes during the dry season. The model further accounts for nonlocal processes involved in the dispersal of seeds. Our analysis focusses on the onset of spatial patterns. The Klausmeier partial differential equations (PDE) model is linked to the integrodifference model in an appropriate limit, which yields a control parameter for the temporal separation of seed dispersal events. We find that the conditions for pattern onset in the integrodifference model are equivalent to those for the continuous PDE model and hence independent of the time between seed dispersal events. We thus conclude that in the context of seed dispersal, a PDE model provides a sufficiently accurate description, even if the environment is seasonal. This emphasises the validity of results that have previously been obtained for the PDE model. Further, we numerically investigate the effects of changes to seed dispersal behaviour on the onset of patterns. We find that long-range seed dispersal inhibits the formation of spatial patterns and that the seed dispersal kernel’s decay at infinity is a significant regulator of patterning.

Bird-plant interactions on the edge of a forest fragment in southwestern Brazilian Amazonia

Seed dispersal is one of the principal ecological processes that determine the richness and distribution of plants in tropical forests. Birds play an important role in the zoochoric dispersal of seeds in these forests. The present study investigated the bird-plant interactions involving the ingestion and dispersal of seeds by the birds found in the edge habitat of an isolated forest fragment on the Catuaba Experimental Farm in eastern Acre, in southwestern Brazilian Amazonia. The birds were captured using mist nets, and the seeds were collected from fecal samples obtained during the handling of the animals. These seeds were sorted and identified. The bird and the plant species identified during the study were used to calculate the connectivity and nestedness of the bird-plant interactions. We captured 82 species of birds, with a total sampling effort of 203,180 h.m². Fecal samples obtained from 19 of the bird species contained a total of 2,086 seeds, representing 23 plant species. The interaction network had an intermediate connectance, and significant nestedness. Ramphocelus carbo had the highest importance index and was the bird with the largest number of plant interactions, while Cecropia latiloba was the plant with the highest importance index, followed by Schefflera morototoni. Most of the seed-dispersing birds identified in the present study are generalists found in both the forest core and its edge. The results of the study indicated that the community of generalist-frugivore birds interacts extensively with the plant community of the fragment, providing seed dispersal services that include the deforested areas adjacent to the fragment.

Inducing seed dispersal by generalist frugivores: A new technique to overcome dispersal limitation in restoration

Abstract Dispersal limitation severely impairs the trajectory of restoration, mainly due to the lack of seed vectors bringing seeds from nearby habitats; a role played by many frugivorous vertebrates that can be absent or reduced in restored or degraded sites. Here we propose a new technique named Induced Seed Dispersal, that amplifies the role that many generalist frugivores have in seed dispersal. It consists in the offering of seeds embedded in the pulp of commercial fruits or whole native fleshy fruits in feeders to generalist frugivores, which ingest the seeds and defecate them elsewhere. We set feeders in a restored site and monitored the visiting pattern of these frugivores with cameras‐traps. We also set seed traps to retrieve seeds dispersed by frugivores and offered around 1,500 seeds of Cecropia hololeuca (Urticaceae) per week for 1 year. We recorded at least 24 generalist frugivore species of terrestrial mammals, bats and birds, which ingested/removed the seeds/fruits from the feeders. Seeds of C. hololeuca dispersed by marmosets were retrieved in the seed traps and germinated. We estimated a potential seed rain of more than 600 C. hololeuca seeds ha−1 mo−1. Synthesis and applications. Our study demonstrates that this new technique can make use of generalist frugivores to assist restoration or regeneration into sites where seed dispersal is compromised by the lack of dispersers or limited seed arrival. Inducing seed dispersal by generalist frugivores is a low‐cost and easy‐managed technique that can be applied year‐round in restoration and forest enrichments at all scales.

Differences among species in seed dispersal and conspecific neighbor effects can interact to influence coexistence

Seed dispersal is a critical mechanism for escaping specialist natural enemies. Despite this, mean dispersal distances can vary by an order of magnitude among plant species in the same community. Here, we develop a theoretical model to explore how interspecific differences in seed dispersal alter the impact of specialist natural enemies, both on their own and though a trade-off between seed dispersal and enemy susceptibility. Our model suggests that species are more able to recover from rarity if they have high dispersal because (1) seedlings are more likely to escape their parent’s natural enemies, (2) adults are more spread out, reducing the chance that a seed will disperse near conspecifics, and (3) seedlings compete less with kin for open gaps. Differences in dispersal do not produce stabilizing mechanisms—species with low dispersal are purely at a disadvantage and do not gain a novel niche opportunity. However, dispersal-susceptibility trade-offs will be equalizing, as species disadvantaged by low dispersal will benefit from being less susceptible to specialist natural enemies. This mechanism, unlike most mechanisms of dispersal-mediated coexistence, does not require that there is an abundance of empty space: high-dispersers gain an advantage by escaping from their enemies, not by colonizing empty habitat. Our study therefore suggests that differences in dispersal are unlikely to promote diversity on their own, but may strengthen other coexistence mechanisms.

Soil applied boron (B) improves growth, yield and fiberquality traits of cotton grown on calcareous saline soil.

Boron (B) is required during all growth stages of cotton crop, especially during boll formation. However, Typic Haplocambid soils of cotton growing belt in Pakistan are B-deficient, which results in low yield and economic returns. Foliar application of B improves cotton productivity; however, information is limited on the role of soil applied B in improving cotton growth and yield. The current study investigated the role of soil applied B in improving growth, yield and fiber quality of cotton crop. Five different B doses (i.e., 0.00, 2.60, 5.52, 7.78 and 10.04 mg kg-1 of soil) and two cotton cultivars (i.e., CIM-600 and CIM-616) were included in the study. Soil applied B (2.60 mg kg-1) significantly improved growth, yield, physiological parameters and fiber quality, while 10.04 mg kg-1 application improved B distribution in roots, seeds, leaves and stalks. Significant improvement was noted in plant height (12%), leaf area (3%), number of bolls (48%), boll size (59%), boll weight (52%), seed cotton yield (52%), photosynthesis (50%), transpiration rate (10%), stomatal conductance (37%) and water use efficiency (44%) of CIM-600 with 2.60 mg kg-1 compared to control treatment of CIM-616. Similarly, B accumulation in roots, seeds, leaves and stalk of CIM-600 was improved by 76, 41, 86 and 70%, respectively compared to control treatment. The application of 2.60 mg kg-1 significantly improved ginning out turn (6%), staple length (3.5%), fiber fineness (17%) and fiber strength (5%) than no B application. The results indicated that cultivar CIM-600 had higher ginning out turn (1.5%), staple length (5.4%), fiber fineness (15.5%) and fiber strength (1.8%) than CIM-616. In crux, 2.60 mg kg-1 soil B application improved growth, yield, physiological and fiber quality traits of cotton cultivar CIM-600. Therefore, cultivar CIM-600 and 2.60 mg kg-1 soil B application is recommended for higher yield and productivity.

Do Pubescent Seeds Encourage Secondary Dispersal by Dung Beetles?

In tropical forests, primary dispersal by birds and mammals is a disproportionately important form of seed dispersal. Dung beetles are secondary seed dispersers attracted to mammal dung. When they bury dung of fruit-eating mammals they move seeds that are not too large, to new, possibly safer or better microclimates away from conspecifics, and potentially increasing rates of germination. We observed three species of dung beetles (Oxysternon conspicillatum, Canthon angustatus, and Can- thidium sp.), all treating the large (2 cm long) Spondias mombin seeds defecated by a brown-headed spider monkey (Ateles fusciceps fusciceps) as though the seeds were dung, even though S. mombin is approximately 1.6 times longer than the upper size limit of seeds normally included in either O. conspicillatum’s dung logs or Canthon angustatus’s dung balls. The seed’s soft hairs covering its surface hold a thin layer of dung and possibly trick the dung beetles into treating them as a dung ball, moving them away from other conspecific seeds. The dung beetle loses in this situation because they cannot eat the seed. At the genus level large, mammal-dispersed (endozoochorous), seeds are disproportionately pubescent. This may indicate that secondary dispersal by dung beetles can exert some selection pressure on mammal dispersed seeds.

Study on characteristics of biflavanones distribution in Garcinia kola seeds and identification of compounds in gum resin exuded from fresh slices

Garcinia kola seeds play an important role in African traditional medicine, which are widely used to treat stomachache, gastritis, malaria, venereal diseases and laryngitis. The habitats, specification, different parts of seeds and slicing process are important factors that affect the quality of Garcinia kola seeds. Interestingly, brownish yellow or brownish red spots were derived from gum resin exuded during slicing, whose chemical constituents have not been elucidated. A rapid high performance liquid chromatography method was established for quantitative study of four main biflavanones (GB-2, GB-1, kolaflavanone and GB-1a) in Garcinia kola seeds. We found that the content of the tested biflavanones was slightly different in Garcinia kola seeds from different habitats, while the seeds weight showed no obvious influence on the biflavanones content from the same habitat. With the aid of “spider-web” mode, we unveiled that the accumulation of biflavanones mainly occurred in seed kernels. Furthermore, slices thickness (1–2 mm) was optimized by comprehensive evaluation of biflavanones’ content, moisture, cutting-time and drying-time to efficiently dry the slices. By employing of ultra-high performance liquid chromatography coupled with electrospray ionization quadrupole Orbitrap high resolution mass spectrometry (UHPLC/ESI Q-Orbitrap MS), garcinoic acid and its derivatives were successfully identified in gum resin, conducing to the interesting finding about the distribution of biflavanones and derivatives of garcinoic acid in Garcinia kola seeds. Generally, our findings in this research could contribute to standardizing the process of harvesting, processing and quality control for Garcinia kola seeds, and help better development and utilization of this important medicinal plant.

Longitudinal dispersal properties of floating seeds within open-channel flows covered by emergent vegetation

The effect of emergent stems on the transport of downstream floating particles (e.g., buoyant seeds) is explored theoretically and experimentally at moderate to high Reynolds number (Rd=2Ubas/υ>300) in an open channel, where Ub is the bulk velocity, as is stem radius, and ν is the kinematic viscosity. Longitudinal dispersion (Dl) of such seeds is shown to be given by Dl=Up3τ02η(1−η)/2/(S1+ητ0Up) thereby requiring the bulk transport velocity of particles Up, spacing between canopy elements S1, collision efficiency η between a particle and the stem, and a wake trapping time scale τ0. Linkages between Up and Ub, and terms η and τ0 are then derived using inhomogeneous flow characteristics adjacent to the stem with physical properties of particles. A semiempirical model with potential flow theory around the stem is introduced to estimate η whereas τ0 is shown to be related to the bulk drag coefficient and radius of stems. The Dl is experimentally determined across a wide range of Rd and particle sizes and shown to be in good agreement with the proposed model calculations.

Abstracts of the 1st Webinar of the SFDP (17 November 2020)

Research Highlights: Frugivores able to disperse large seeds over large distances are indispensable for seedling recruitment, colonization and regeneration of tropical forests. Understanding their effectiveness as seed dispersal agents in degraded habitat is becoming a pressing issue because of escalating anthropogenic disturbance. Although of paramount importance in the matter, animal behaviour’s influence on seed shadows (i.e., seed deposition pattern of a plant population) is difficult to evaluate by direct observations. Background and Objectives: We illustrated a modeling approach of seed shadows incorporating field-collected data on a troop of northern pigtailed macaques (Macaca leonina) inhabiting a degraded forest fragment in Thailand, by implementing a mechanistic model of seed deposition with random components. Materials and Methods: We parameterized the mechanistic model of seed deposition with macaque feeding behavior (i.e., consumed fruit species, seed treatments), gut and cheek pouch retention time, location of feeding and sleeping sites, monthly photoperiod and movement patterns based on monthly native fruit availability using Hidden Markov models (HMM). Results: We found that northern pigtailed macaques dispersed at least 5.5% of the seeds into plantation forests, with a majority of medium- to large-seeded species across large distances (mean > 500 m, maximum range of 2300 m), promoting genetic mixing and colonization of plantation forests. Additionally, the macaques produced complementary seed shadows, with a sparse distribution of seeds spat out locally (mean >50 m, maximum range of 870 m) that probably ensures seedling recruitment of the immediate plant populations. Conclusions: Macaques’ large dispersal distance reliability is often underestimated and overlooked; however, their behavioral flexibility places them among the last remaining dispersers of large seeds in disturbed habitats. Our study shows that this taxon is likely to maintain significant seed dispersal services and promote forest regeneration in degraded forest fragments.

Foxes: A Key Mammals in Ecosystem Builders

The foxes are an exceptional adaptor usually prefers mixture of different ecosystems viz., grassland, coniferous, deciduous, tundra ecosphere and agro-ecosphere. Predators provides functional and productive role in the ecosystem mainly through nutrient cycling process and their detrimental impact on maintaining prey-predator system with ecosystem sustainability by hunting of small rodents, insects, rabbits, earthworms which helps in dispersion of seeds of many forest species by the process of endozoochory.

Epidemiological aspects of natural poisoning by Prosopis juliflora in ruminants in semiarid areas of the state of Bahia, Brazil, invaded by the plant

ABSTRACT: Poisoning by Prosopis juliflora (mesquite) leads to neurological signs, cachexia and death, mainly in cattle and goats. Although the uncontrolled spread of mesquite in the Caatinga biome (biological invasion), which alters the epidemiological conditions of intoxication by this plant, has been proved for approximately 20 years, strategies for its control and prophylaxis still remain out of date. These new epidemiological conditions have allowed the uncontrolled consumption of large amounts of in natura mesquite pods by ruminants for long periods in invaded pastures, thus resulting in increased history of poisoning. This study aimed to describe the new epidemiological aspects of P. juliflora poisoning in cattle and goats, 78 years after the introduction of this plant in the country, with emphasis on its degree of invasion, and to update the control and prophylaxis measures of this intoxication and the mapping of areas of outbreak occurrence in the semiarid region of the state of Bahia, Brazil. Seven outbreaks of natural mesquite poisoning, two in goats (OB 1 and OB 2) and five in cattle (OB 3, OB 4, OB 5, OB 6, and OB 7), were studied in loco in the municipalities of Juazeiro, Iaçu, Tucano, Santa Teresinha, Barra do Mendes, Barra and Tabocas do Brejo Velho. In the studied outbreaks, clinical-epidemiological (OB 1 to OB 7) and histopathological (OB 1, OB 2, OB 3, and OB 5) findings were compatible with mesquite poisoning, and this was the first anatomopathological proof of poisoning by this plant in this state. In addition, in the state of Bahia, disease occurs in an area approximately three times larger than previously known. On the farms investigated, mesquite introduction occurred between 1980 and 2005, through the single planting of an average of 33 seedlings. Since then, propagation of this plant has occurred progressively, with gradual invasion of native pastures, which enabled the evaluation of plant spread (biological invasion) on these farms 15 (OB 2), 25 (OB 7), 30 (OB 5 and OB 6), 35 (OB 3) and 40 (OB 1 and OB 4) years after its introduction. Historical information on the introduction and spread of mesquite in the state of Bahia had never been analyzed. In 2020, a degree of mesquite invasion an average 59.57% was verified in the pastures of the seven farms where the outbreaks occurred. The great biological invasion capacity of this plant drew attention, especially in OB 5. The high degree of mesquite invasion observed (new epidemiological conditions) justifies the increased number of cases of poisoning observed in this study. Processing of P. juliflora pods (grinding) was not carried out on any farm (OB 1 to OB 7), and ruminants uncontrollably consumed large amounts of pods in natura for long periods in invaded pastures, which allowed massive dispersal of seeds through feces over decades. The main factors responsible for the gradual invasion of pastures by mesquite over time were absence of crop management plans (silvicultural treatments) and lack of knowledge by producers on disease etiology. Given the new epidemiological conditions, restriction of animal access to in natura pods in pastures and supply of mesquite bran are crucial for the control and prophylaxis of this poisoning, as consumption of in natura pods had a strong correlation with the high degree of invasion in the pastures where the seven outbreaks occurred. Additionally, although the commercialization of pods and exploitation of wood of mesquite trees can provide livestock farmers with extra income - being the correct management for areas invaded by this plant, such practice is either not yet known or not carried out technically or satisfactorily by farmers. In addition to being a threat to the Caatinga’s biodiversity, the increasing invasion of semiarid areas by mesquite 78 years after its introduction in the Northeast region of Brazil, is a risk for herds, since the occurrence of poisoning outbreaks may become more frequent. Therefore, it is highly advisable that effective measures be adopted to control P. juliflora propagation.

Effect of the grass Leersia hexandra on the dispersal, seed germination, and establishment of Pachira aquatica seedlings

Abstract In wetlands, hydrochory is one of the main mechanisms of seed dispersal and there is often synchrony between propagule production and the flood season. Different sources of disturbance can prevent seed dispersal to suitable sites, and if environmental conditions are not adequate for germination and seedling establishment, recruitment will be limited, affecting succession. We worked in a disturbed tropical freshwater swamp where the native grass Leersia hexandra has dominated open areas, creating a grass matrix that surrounds patches of swamp forest. Leersia grows vigorously, forming cushions of dry matter that cover the soil, forming a potential obstacle to seed dispersal. We asked whether the vegetative growth of this grass prevents the entry and dispersal of seeds of the tropical swamp tree Pachira aquatica, thwarting seed germination and seedling establishment, and arresting succession. We set up transects in the grass matrix in two zones: close to the river (R) and bordering the tree patches or fragments (F). We quantified tree seed and seedling presence, survival and growth in situ and experimentally introduced seeds and seedlings in the field and monitored seed germination and the survival and growth of their seedlings, as well as that of transplanted seedlings. There was a negative relationship between the number of seeds and established seedlings, and the distance to river or fragment (r = −0.86, p &lt; 0.001 for zone R; and r = −0.77, p &lt; 0.001 for zone F) and with the grass cushion (r = −0.68, p = 0.005 for zone R; and r = −0.66, p = 0.007 for zone F); the grass creating a barrier to dispersal. When seeds were sown after clearing the grass cushion, germination success was high, so this stage is not limited. The transplanted seedlings had better survival and a greater final height than the seedlings of the sown seeds. Grass cover had a negative effect on both types of seedlings. Seedling survival rates were inversely related to grass cover, showing that seedlings overgrown by grass had low survival rates. Flooding is a stress factor for seedlings and produced mortality, in addition to the effects of the grass. Together, the field survey and the experiment show that succession is being arrested in two ways: (1) by limiting seed dispersal because the grass cushion slows the dispersal and penetration of seeds into the vegetation; and (2) by limiting seedling establishment because the grass competes for space and light. Our results show that even where the grass is native, slower growing, seed‐dependent species may struggle to compete and establish. If grass cover is increasing, these swamps are very vulnerable to a decrease in area because it is very difficult for them to regenerate naturally.