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Effect of the local wind reduction zone on seed dispersal from a single shrub element on sparsely vegetated land.

ABSTRACT: Accurate predictions of seed dispersal kernels are crucial for understanding both vegetation communities and landscape dynamics. The influences of many factors, including the physical properties of seeds, the time-averaged wind speed and the wind turbulence, on seed dispersal have been studied. However, the influence of local wind speed reduction around a single shrub element (e.g. a small patch of scrub) on seed dispersal is still not well understood. Here, the spatial distribution of the wind intensity (represented by the wind friction speed u _*) around a single shrub element is described, with an emphasis on the variation in the streamwise direction, and assuming that the time-averaged lateral and vertical speeds are equal to zero. The trajectories of the seeds were numerically simulated using a Lagrangian stochastic model that includes the effects of wind turbulence and particle inertia. The patterns of seed deposition with and without the effect of local wind reduction were compared. The variation in seed deposition with changing wind intensity, release height and shrub porosity were also simulated. The simulation results revealed that the local wind reduction increased seed deposition in nearby regions and therefore decreased seed deposition in the regions farther away. Local wind reduction had a greater impact on short-distance dispersal than on long-distance dispersal. Moreover, the dispersal in the circumferential direction decreased once the motion of a seed moving in the streamwise direction was reduced due to the local wind reduction. As the wind intensity and release height increased, the effect of local wind reduction on seed dispersal weakened. Seed dispersal was both wider and farther as the shrub porosity increased. These results may help explain the disagreement between the mechanistic models and the fitting curves in real cases. In addition, the results of this study may improve the currently used mechanistic models by either increasing their flexibility in case studies or by helping explain the variations in the observed distributions.

SUBMITTER: Fu LT

PROVIDER: S-EPMC8266638 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSeagrasses are clonal marine plants that form important biotic habitats in many tropical and temperate coastal ecosystems. While there is a reasonable understanding of the dynamics of asexual (vegetative) growth in seagrasses, sexual reproduction and the dispersal pathways of the seeds remain poorly studied. Here we address the potential for a predominantly clonal seagrass, P. australis, to disperse over long distances by movement of floating fruit via wind and surface currents within the coastal waters of Perth, Western Australia. We first simulated the dominant atmospheric and ocean forcing conditions that are known to disperse these seagrass seeds using a three-dimensional numerical ocean circulation model. Field observations obtained at 8 sites across the study area were used to validate the model performance over ~2 months in summer when buoyant P. australis fruit are released into the water column. P. australis fruit dispersal trajectories were then quantified throughout the region by incorporating key physical properties of the fruit within the transport model. The time taken for the floating fruit to release their seed (dehiscence) was incorporated into the model based on laboratory measurements, and was used to predict the settlement probability distributions across the model domain.ResultsThe results revealed that high rates of local and regional demographic connectivity among P. australis meadows are achieved via contemporary seed dispersal. Dispersal of seeds via floating fruit has the potential to regularly connect meadows at distances of 10s of kilometres (50% of seeds produced) and infrequently for meadows at distances 100 s km (3% of seeds produced).ConclusionsThe spatial patterns of seed dispersal were heavily influenced by atmospheric and oceanographic conditions, which generally drove a northward pattern of connectivity on a regional scale, but with geographical barriers influencing finer-scale connectivity pathways at some locations. Such levels of seed dispersal infer greater levels of ecological and genetic connectivity and suggest that seagrasses are not just strongly clonal.

Project description:Hydrology is a major environmental factor determining plant fitness, and hydrological niche segregation (HNS) has been widely used to explain species coexistence. Nevertheless, the distribution of plant species along hydrological gradients does not only depend on their hydrological niches but also depend on their seed dispersal, with dispersal either weakening or reinforcing the effects of HNS on coexistence. However, it is poorly understood how seed dispersal responds to hydrological conditions. To close this gap, we conducted a common-garden experiment exposing five wind-dispersed plant species (Bellis perennis, Chenopodium album, Crepis sancta, Hypochaeris glabra, and Hypochaeris radicata) to different hydrological conditions. We quantified the effects of hydrological conditions on seed production and dispersal traits, and simulated seed dispersal distances with a mechanistic dispersal model. We found species-specific responses of seed production, seed dispersal traits, and predicted dispersal distances to hydrological conditions. Despite these species-specific responses, there was a general positive relationship between seed production and dispersal distance: Plants growing in favorable hydrological conditions not only produce more seeds but also disperse them over longer distances. This arises mostly because plants growing in favorable environments grow taller and thus disperse their seeds over longer distances. We postulate that the positive relationship between seed production and dispersal may reduce the concentration of each species to the environments favorable for it, thus counteracting species coexistence. Moreover, the resulting asymmetrical gene flow from favorable to stressful habitats may slow down the microevolution of hydrological niches, causing evolutionary niche conservatism. Accounting for context-dependent seed dispersal should thus improve ecological and evolutionary models for the spatial dynamics of plant populations and communities.

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Effect of the local wind reduction zone on seed dispersal from a single shrub element on sparsely vegetated land.

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