Ecological restoration of ecosystems degraded by invasive alien plants in South African Fynbos: Is spontaneous succession a viable strategy?

Abstract

Ecological restoration is a global imperative to reverse widespread habitat loss and degradation, including by invasive alien plants. In South Africa's Core Cape Subregion, alien tree invasions are widespread and their control continues to be a major undertaking. As funding is limited, active restoration interventions are rarely implemented and the focus is on invader removalthe assumption being that ecosystems will self-repair. This paper reviews research findings from the past three decades to assess in which situations spontaneous succession is a viable strategy for restoring alien-invaded ecosystems. We found that ecosystems can self-repair, provided that key biotic and/or abiotic thresholds have not yet been crossed. Self-repair has been observed in many cases where dense invader stands with short residence times have been cleared and where diverse native plant growth forms survive, either in the aboveground vegetation or in soil seed banks. However, several factors influence this generalisation, including the identity of the invader, the ecosystem type, and the efficacy of alien control. Thresholds are crossed sooner with invasions of alien Acacia and Eucalyptus species than those of Hakea and Pinus species, resulting in lower potential for spontaneous recovery. Lowland fynbos ecosystems are less resilient to invasion, and have a lower capacity for self-repair, than mountain fynbos ecosystems. Poorly implemented alien plant control measures can result in a resurgence of the invader to the detriment of native species recovery. We outline some management principles for optimising spontaneous succession potential and integrating alien control and restoration interventions.

Predicting the potential global distribution of Ageratina adenophora under current and future climate change scenarios

“…Nonetheless, is spontaneous succession a viable strategy? (Holmes et al., 2020 ) pointed out that the ecosystems can accomplish self‐repair under the conditions which key biotic and/or abiotic thresholds have not yet been crossed. Specifically, the identity of the invader, the ecosystem type, and the efficacy of alien control would influence this process.…”

Benefits of water-related ecological infrastructure investments to support sustainable land-use: a review of evidence from critically water-stressed catchments in South Africa

“…in terms of seedbank dynamics, native species re-establishment and biotic and abiotic thresholds) means that holistic approaches (e.g. also considering ecological or restoration burns and active restoration) are critically important for successful ecological infrastructure interventions [ 40 , 41 ]. One ecological infrastructure intervention (e.g.…”

“…clearing alien trees) applied without considering a more holistic approach (e.g. considering fire dynamics or the potential need for an active restoration) has often exacerbated problems [ 40 ]. For instance, it has been shown that within a single intervention (i.e.…”

Active seed sowing can overcome constraints to passive restoration of a critically endangered vegetation type

“…Vegetation recovery will require fire where native cover is depleted, but a long duration of invasion may deplete native soil seed banks (Le Maitre et al 2011). In such cases active seed sowing is required to reintroduce lost vegetation components (Holmes et al, 2020).…”