Natural regeneration triggers compositional and functional shifts in soil seed banks

Drivers and mechanisms of spontaneous plant community succession in abandoned PbZn mining areas in Yunnan, China

The drivers and mechanisms underlying succession and the spontaneous formation of plant communities in mining wasteland remain largely unknown. This study investigated the use of nature-based restoration to facilitate the recovery of viable plant communities in mining wasteland. It was found that scientific analyses of spontaneously formed plant communities in abandoned mining areas can provide insights for nature-based restoration. A chronosequence ("space for time") approach was used to establish sites representing three successional periods with six successional stages, and 90 quadrats were constructed to investigate changes in plant species and functional diversity during succession in abandoned PbZn mining areas. A total of 140 soil samples were collected to identify changes in soil properties, including plant nutrient and heavy metal concentrations. Then, this paper used structural equation models to analyze the mechanisms that drive succession. It was found that the functional diversity of plant communities fluctuated substantially during succession. Species had similar functional traits in early and mid-succession, but traits tended to diverge during late succession. Soil bulk density and soil organic matter gradually increased during succession. Total nitrogen (N), pH, and soil Zn concentrations first increased and then decreased during succession. Concentrations of Mn and Cd gradually decreased during succession. During early succession, soil organic matter was the key factor driving plant colonization and succession. During mid-succession, soil Zn functioned as an environmental filter factor limiting the rates of succession in mining wasteland communities. During late succession, soil bulk density and competition for nutrient resources contributed to more balanced differentiation among plant species. This thesis proposed that a nature-based strategy for the stabilization of abandoned mining lands could facilitate effective plant community restoration that promotes ecosystem services and functioning.

Soil seed bank responses to edge effects in temperate European forests

AIM

The amount of forest edges is increasing globally due to forest fragmentation and land-use changes. However, edge effects on the soil seed bank of temperate forests are still poorly understood. Here, we assessed edge effects at contrasting spatial scales across Europe and quantified the extent to which edges can preserve the seeds of forest specialist plants.

LOCATION

Temperate European deciduous forests along a 2,300-km latitudinal gradient.

TIME PERIOD

2018-2021.

MAJOR TAXA STUDIED

Vascular plants.

METHODS

Through a greenhouse germination experiment, we studied how edge effects alter the density, diversity, composition and functionality of forest soil seed banks in 90 plots along different latitudes, elevations and forest management types. We also assessed which environmental conditions drive the seed bank responses at the forest edge versus interior and looked at the relationship between the seed bank and the herb layer species richness.

RESULTS

Overall, 10,108 seedlings of 250 species emerged from the soil seed bank. Seed density and species richness of generalists (species not only associated with forests) were higher at edges compared to interiors, with a negative influence of C : N ratio and litter quality. Conversely, forest specialist species richness did not decline from the interior to the edge. Also, edges were compositionally, but not functionally, different from interiors. The correlation between the seed bank and the herb layer species richness was positive and affected by microclimate.

MAIN CONCLUSIONS

Our results underpin how edge effects shape species diversity and composition of soil seed banks in ancient forests, especially increasing the proportion of generalist species and thus potentially favouring a shift in community composition. However, the presence of many forest specialists suggests that soil seed banks still play a key role in understorey species persistence and could support the resilience of our fragmented forests.

Seed bank bias: Differential tracking of functional traits in the seed bank and vegetation across a gradient

A goal in trait-based ecology is to understand and predict plant community responses to environmental change; however, diversity stored within seed banks that may expand or limit these responses is typically overlooked. If seed banks store attributes that are more advantageous or vulnerable under future conditions, they could impact community adaptability to change and disturbance. We explored compositional differences between seed banks and vegetation (i.e. seed bank bias) across a twelve-site gradient of increasingly higher and older soil terraces, asking: How do seed banks contribute to taxonomic and functional composition, and what do shifts in seed bank biases along the gradient (i.e. tracking) reveal about the processes driving seed bank variation and its implications for community adaptability? Across the gradient, seed banks stored distinct pools of species that added to species richness but not functional dispersion. Seed banks were generally biased towards short-life histories and 'fast' species with small seeds, thinner and more acquisitive roots, and lower root biomass allocation; however, trait means in the seed bank and vegetation sometimes shifted along the gradient, amplifying or reversing these biases. For example, species with higher specific leaf area (tied to rapid resource acquisition) tended to dominate vegetation on lower soil terraces but were more common in the seed bank on higher terraces - at least when patterns were weighted by species' relative abundances. Although seed banks were generally characterized by 'fast' attributes, observed shifts in seed bank biases across the gradient - particularly in leaf traits - demonstrate that environment can impact stored diversity, and consequently, our expectations for future vegetative turnover. The seed bank bias patterns that we characterized could be the result of many potential processes, including environment- or trait-driven variation in seed bank inputs (seed production, dispersal) or losses (seed desiccation, germination), and may have important implications for a system's adaptive capacity. Only by integrating seed banks into the functional ecology agenda will we be able to unpack these processes and use seed banks more effectively in both prediction and ecosystem management.

Land use intensity determines soil properties and biomass recovery after abandonment of agricultural land in an Amazonian biodiversity hotspot

There has been widespread clearance of tropical forests for agriculture, but in many cases the cultivation phase is only transient. The secondary forests recovering on these abandoned sites may contribute to mitigation of greenhouse gas emissions and protection of biodiversity, but the rates of recovery may be dependent on land-use intensity and changes in soil properties during cultivation. However fine-scale details on these changes are poorly known for many tropical forest locations. We quantified soil properties and recovery of woody biomass in 42 tropical forest fragments representing a chronosequence following two types of agricultural land-uses, and in 15 comparable reference old growth forests, between the Andes and the Amazon in Peru. Soil fertility, particularly base cation concentrations, responded negatively to increasing intensity of agricultural land-use, and either decreased or increased with time after abandonment dependent on prior land-use. The predicted mean recovery rate of woody biomass over the first 20 years following abandonment matched that predicted by a general model for the Neotropics, but recovery was three-fold higher on sites abandoned following traditional agriculture than on sites recovering from intensive agriculture. Estimated total biomass recovered to just above half that of reference old growth forests within 71 years. The inclusion of the biomass of lianas and smaller tree stems did not modify the apparent rate of ecosystem biomass recovery, however the proportion of the total biomass stored in small stems was greater following intensive than traditional agriculture, which suggests that patterns of stand structural development are sensitive to land-use history. We conclude that effects of historic land use on soil nutrient concentrations and their changes through time are required for a more complete interpretation of variation in biomass recovery rates at local scales. These results also highlight the critical importance of contemporary agricultural intensification for carbon storage in tropical forests.