Abandoned Croplands: Drivers and Secondary Succession Trajectories under Livestock Grazing in Communal Areas of South Africa

Bridging the gap between ecological succession of fleshy-fruited shrubs and restoration frameworks in semiarid oldfields

Abandoned agricultural areas (i.e. oldfields) represent an opportunity for natural vegetation recovery, increasing soil carbon sequestration and lessening the impacts of climate change and desertification. Ecological succession in oldfields can be hampered by the harsh conditions of semiarid and arid ecosystems, and hence, restoration actions may be needed in some contexts to reactivate the ecosystem functioning. Fleshy-fruited shrubs are indicators of progression in the ecological succession, which can shift notably across environmental gradients, making difficult to obtain robust conclusions at regional scales. Other poorly studied aspects at such scales (agricultural legacy, structural features and local landscape effects) add to this knowledge gap. Here, we study the species-specific natural colonization patterns of fleshy-fruited shrubs in semiarid oldfields across environmental gradients in the Southeast of the Iberian Peninsula taking into account specific traits of plants. We used Hierarchical Modelling of Species Communities (HMSC) to test the influence of the time since the abandonment and the past land-use history of the oldfields, and the effect of local structural factors, such as the presence of remnant trees and natural patches of vegetation, on the shrub recolonization patterns. We found that altitude and lithology conditioned the structure of shrub communities, allowing the selection of different focal species for making recommendations for restoration. Time since abandonment was not relevant for the colonization process. The persistence of remnant trees in the oldfields showed a positive effect on the occurrence of several shrub species. Close sources of propagules (terrace edges and/or natural vegetation patches) benefited the occurrence of certain species mainly at lower altitudes. Traits of species (growth form, root depth, dispersal mode, fruit length and water content) helped to explain the performance of species along the environmental gradients. We identified the main drivers of natural colonization of fleshy-fruited shrubs in semiarid oldfields across environmental gradients, providing ecological knowledge to guide scientists and practitioners to develop nature-based restoration frameworks. Different management actions are recommended according to the environmental gradient.

Exploring main soil drivers of vegetation succession in abandoned croplands of Minqin Oasis, China

Background

The Minqin Oasis, which is located in Wuwei City, Gansu Province, China, faces a very serious land desertification problem, with about 94.5% of its total area desertified. Accordingly, it is crucial to implement ecological restoration policies such as cropland abandonment in this region. In abandoned croplands, abiotic factors such as soil properties may become more important than biotic factors in driving vegetation succession. However, the connections between soil properties and vegetation succession remain unclear. To fill this knowledge gap, this study investigated these connections to explore major factors that affected vegetation succession, which is meaningful to designing management measures to restore these degraded ecosystems.

Methods

This study investigated seven 1-29-year-old abandoned croplands using the "space for time" method in Minqin Oasis. Vegetation succession was classified into different stages using a canonical correlation analysis (CCA) and two-way indicator species analysis (Twinspan). The link between soil properties and vegetation succession was analyzed using CCA. The primary factors shaping community patterns of vegetation succession were chosen by the "Forward selection" in CCA. The responses of dominant species to soil properties were analyzed using generalized additive models (GAMs).

Results

Dominant species turnover occurred obviously after cropland abandonment. Vegetation succession can be classified into three stages (i.e., early, intermediate, and late successional stages) with markedly different community composition and diversity. The main drivers of vegetation succession among soil properties were soil salinity and saturated soil water content and they had led to different responses of the dominant species in early and late successional stages. During the development of vegetation succession, community composition became simpler, and species diversity decreased significantly, which was a type of regressive succession. Therefore, measures should be adopted to manage these degraded, abandoned croplands.

Extreme weather events and farmer adaptation in Zeeland, the Netherlands: A European climate change case study from the Rhine delta

Global climate change is manifest by local-scale changes in precipitation and temperature patterns, including the frequency of extreme weather events (EWEs). EWEs are associated with a myriad range of adverse environmental and societal consequences, including negative impacts to agriculture and food production. This study focuses on EWEs and their effect on adaptation strategies by potato and onion farmers in Zeeland, a Dutch coastal province in the Rhine delta that can serve as a model for other intensive agricultural landscapes in industrialized nations impacted by extreme weather events. The research approach combines quantitative trend analysis of long-term climatic data (temperature, precipitation) with a formal survey of Zeelandic farmers to statistically test four specific hypotheses regarding the frequency of EWEs in the Netherlands and farmer awareness and adaptation. Trend analyses reveal a strong (statistically significant) increase in extreme heat, a small increase in extreme rainfall and drought, and a strong decrease in frost occurrence. Survey results indicate Zeelandic farmers perceive high risk and awareness of changes to the frequency of EWEs. Many farmers have experienced financial losses from EWEs, particularly between 2017 and 2020. For extreme heat, droughts, and frost, the proportion of farmers that incurred financial damages annually is statistically correlated to the actual occurrence of EWEs. Farmers who incurred more financial losses between 2000 and 2020 due to heat and lack of frost had a higher risk perception of these extremes. Further, almost all farmers have already implemented one or more adaptation strategies. A third of surveyed farmers reduced or stopped with potato and onion cultivation in response to climate change and EWEs. Awareness, exposure to, and risk perception of EWEs contribute to adaptation support by farmers. The high perceived risk of climate change and EWEs among respondents and the high incidence of financial losses from extremes in the past two decades highlights the importance of adaptation in the agricultural sector, including in temperate regions where growing seasons are expanding. Study results support the current 'Rural Development Program' and future 'National Strategic Plan' policies in the Netherlands, both part of the European Union's Common Agricultural Policy (CAP), that provides accessibility to adaptation measures for farmers to avoid financial loss.