The importance of ecological memory for trophic rewilding as an ecosystem restoration approach

Abstract

Increasing human pressure on strongly defaunated ecosystems is characteristic of the Anthropocene and calls for proactive restoration approaches that promote self-sustaining, functioning ecosystems. However, the suitability of novel restoration concepts such as trophic rewilding is still under discussion given fragmentary empirical data and limited theory development. Here, we develop a theoretical framework that integrates the concept of 'ecological memory' into trophic rewilding. The ecological memory of an ecosystem is defined as an ecosystem's accumulated abiotic and biotic material and information legacies from past dynamics. By summarising existing knowledge about the ecological effects of megafauna extinction and rewilding across a large range of spatial and temporal scales, we identify two key drivers of ecosystem responses to trophic rewilding: (i) impact potential of (re)introduced megafauna, and (ii) ecological memory characterising the focal ecosystem. The impact potential of (re)introduced megafauna species can be estimated from species properties such as lifetime per capita engineering capacity, population density, home range size and niche overlap with resident species. The importance of ecological memory characterising the focal ecosystem depends on (i) the absolute time since megafauna loss, (ii) the speed of abiotic and biotic turnover, (iii) the strength of species interactions characterising the focal ecosystem, and (iv) the compensatory capacity of surrounding source ecosystems. These properties related to the focal and surrounding ecosystems mediate material and information legacies (its ecological memory) and modulate the net ecosystem impact of (re)introduced megafauna species. We provide practical advice about how to quantify all these properties while highlighting the strong link between ecological memory and historically contingent ecosystem trajectories. With this newly established ecological memory-rewilding framework, we hope to guide future empirical studies that investigate the ecological effects of trophic rewilding and other ecosystem-restoration approaches. The proposed integrated conceptual framework should also assist managers and decision makers to anticipate the possible trajectories of ecosystem dynamics after restoration actions and to weigh plausible alternatives. This will help practitioners to develop adaptive management strategies for trophic rewilding that could facilitate sustainable management of functioning ecosystems in an increasingly human-dominated world.

Restoration potential of threatened ecosystem engineers increases with aridity: broad scale effects on soil nutrients and function

“…However, species loss has a complex and context-dependent relationship with ecosystem functioning (Cadotte et al 2011), whereby the magnitude of change depends on characteristics of the species and the ecosystem (Dobson et al 2006, Coggan et al 2016. Returning locally extinct fauna has recently been recognised as a key component of ecosystem restoration because such species may play trophic or engineering roles important for ecosystem structure (Wilmers and Schmitz 2016, Sobral-Souza et al 2017, Schweiger et al 2018). However, the value of reinstating species for ecosystem function is also likely to be context-dependent (Coggan et al 2016(Coggan et al , 2018.…”

Where to rewild? A conceptual framework to spatially optimize ecological function

“…This priority score, normalized between 0 and 1, should reflect the level of function need and the benefit of functional restoration for each cell. For example, areas with high ecological memory [51], defined as 'an ecosystem's accumulated abiotic and biotic material and information legacies from past dynamics', should be prioritized over areas with lower ecological memory. At the community (or landcover) level, areas with more intact terrain and those that retain remnant populations or propagule sources of native species would be prioritized.…”

Analogous losses of large animals and trees, socio‐ecological consequences, and an integrative framework for rewilding‐based megabiota restoration

“…This includes the consideration of the target landscape's ecological history, which may affect ecological and societal responses to rewilding activities (e.g. Schweiger, Boulangeat, Conradi, Davis, & Svenning, ). The integration of different knowledge systems like modern, scientific knowledge and traditional ecological knowledge of the local population can help to find such creative solutions to account for the ecological history of the rewilding site and at the same time meet the needs of the local community.…”