Abundance Of Soil Seed Bank Research Articles

Quantifying shrub encroachment through soil seed bank analysis in the Ethiopian highlands.

This study aimed to understand the impact of shrub encroachment on native species in the Guassa Community Conservation Area in Ethiopia. We assessed the soil seed bank composition and density across different elevations and aspects, and management systems within the area. The vegetation was stratified and eight blocks were selected across a range of elevation (<3350 m and >3350 m) and aspect (northeast, northwest, southeast, southwest). Within each block we established twenty 5m x 5m plots for a total of 160. We then collected soil samples from five subplots (1 m x 1 m) at three depths (0-3 cm, 3-6 cm and 6-9 cm) for a total of 480 samples, which were established in pots in greenhouse. We calculated species abundance by totaling the number of seedlings that emerged from each sample. To determine the variability in the abundance of Festuca macrophylla and Helichrysum splendidum in the soil seed bank along altitudinal gradient, we used two-way ANOVA using SAS statistical software version 9.0.1. Shannon diversity index was used to determine species diversity in the soil seedbank. After counting all the seeds, we identified 74 plant species represented in the soil seedbank which belong to 55 genera and 23 families. Eleven species are endemic to Ethiopia. At the lower elevation range, the effects of aspect (P <0.0088) and soil depth (P <0.005) are not significant to determine the abundance of seeds of H. splendidum and F. macrophylla. But when the factors are segregated, both aspect and soil depth play a significant role (p<0.0001) regarding the abundance of the seeds of the competing species at lower elevation. At higher elevation, only the effect of soil depth is significant (P<0.0001) for determining the abundance of H. splendidum. Soil depth and aspect have no significant effects on soil seed bank abundance at this elevation.

A global synthesis of fire effects on soil seed banks

Fire is a major disturbance affecting plant communities in terrestrial ecosystems. Understanding fire effects on soil seed banks is critical in the context of altered global fire regimes. Through a systematic and quantitative review of the literature, we provide the first global assessment of how soil seed banks respond to fire based on 539 paired comparisons. The overall effects of fire on soil seed bank richness ( i.e. , the species richness in soil seed bank) and abundance were negative and neutral, respectively. Wildfires and high-intensity fires led to greater decreases in the richness and abundance of the seed bank than prescribed burns and low-severity fires, respectively. As an important fire cue, the presence of simulated smoke increased seed bank richness and abundance, but simulated heat shock had no effect on both two metrics, in contrast to the findings of previous empirical studies. Strong, positive fire effects on soil seed bank abundance were found in Mediterranean ecosystems, but fire effects were negative for forest ecosystems, especially tropical forests. Both the richness and abundance of tree species in the seed bank decreased after fire. Burning only had a negative effect on the soil seed bank in habitats with no previous fire history or a short fire history. As time elapsed post-fire, the soil seed bank abundance also increased. Overall, fire tended to decrease soil seed bank richness globally, and this was especially the case for high-severity fires in non-fire-prone ecosystems. Our findings enhance our understanding of the spatiotemporal variability in fire effects on soil seed banks, and highlight the importance of monitoring post-fire seed bank composition across ecosystems, with crucial implications for vegetation regeneration and ecosystem recovery.

A global meta‐analysis of grazing effects on soil seed banks

AbstractLivestock grazing is a major disturbance affecting plant diversity and abundance in terrestrial ecosystems. The intermediate disturbance hypothesis (IDH) predicts that moderate‐intensity grazing should produce the highest species diversity, while the Milchunas‐Sala‐Lauenroth (MSL) model posits that the IDH is valid only for mesic areas. However, it remains unclear how grazing affects soil seed bank and whether or not the IDH or MSL models are valid for soil seed bank communities. Here, we presented a global meta‐analysis synthesizing 483 observations: we found that grazing had a negative effect on soil seed bank abundance, but did not alter seed bank richness or the compositional similarity between the soil seed bank and the aboveground vegetation. Further refining the analysis, light‐intensity grazing was found to increase seed bank richness, while moderate‐intensity grazing had no effect, and heavy‐intensity grazing had a negative effect. Additionally, for both arid and mesic areas, soil seed bank richness declined with grazing intensity increased. Overall, grazing effects on soil seed banks differed from expectations set by studies of aboveground vegetation. Our study provides key insights for policy‐makers managing livestock grazing and grassland conservation.

Are all patches worth exploring? Foraging desert birds do not rely on environmental indicators of seed abundance at small scales

BackgroundConsumers should show strong spatial preferences when foraging in environments where food availability is highly heterogeneous and predictable. Postdispersal granivores face this scenario in most arid areas, where soil seed bank abundance and composition associates persistently with vegetation structure at small scales (decimetres to metres). Those environmental features should be exploited as useful pre-harvest information, at least to avoid patches predicted to be poor. However, we did not find the expected spatial association in the algarrobal of the central Monte desert by observing foraging seed-eating birds, a field technique influenced by how much they exploit visited patches. In this work we tested if the first stage of foraging by granivorous birds (patch visit, encounter or exploration) is positively associated with environmental indicators of patch quality by recording the removal of single seeds from 300 scattered experimental devices during seasonal trials. Spatial selectivity was analysed by comparing the structural characteristics of used vs. available microhabitats, and evaluated against bottom-up and top-down hypotheses based on our previous knowledge on local seed bank abundance, composition and dynamics. Their foraging activity was also explored for spatial autocorrelation and environmental correlates at bigger scales.ResultsPostdispersal granivorous birds were less selective in their use of foraging space than expected if microhabitat appearance were providing them relevant information to guide their search for profitable foraging patches. No microhabitat type, as defined by their vegetation structure and soil cover, remained safe from bird exploration. Analyses at bigger temporal and spatial scales proved more important to describe heterogeneity in seed removal.ConclusionsCloseness to tall trees, probably related to bird territoriality and reproduction or to their perception of predation risk, seemed to determine a first level of habitat selection, constraining explorable space. Then, microhabitat openness (rather than seed abundance) exerted some positive influence on which patches were more frequently visited among those accessible. Selective patterns by birds at small scales were closer to our predictions of a top-down spatial effect, with seed consumption creating or strengthening (and not responding to) the spatial pattern and dynamics of the seed bank.