A framework for measuring the effects of disturbance in restoration projects

Abstract

Ecological resilience is widely acknowledged as a vital attribute of successful ecosystem restoration, with potential for restoration practice to contribute to this goal. Hence, defining common metrics of resilience to naturally occurring disturbances is essential for restoration planning, efforts, and monitoring. Here, we reviewed how plant community ecologists have measured resilience of restoration projects to disturbances and propose a framework to guide measurement of restoration projects to disturbance. We found 22 studies that investigated the impact of disturbances on restoration projects, from three continents and for three disturbance types. Over half of the studies were from Australia, with the dataset biased toward fire responses of restored, or partially restored, forest ecosystems. Native plant species richness, cover, and density were common response variables. Studies varied in restoration context, design, response variables, and statistical approaches, limiting generalizations. Nonetheless we have identified several response variables that offer potential as lagging indicators (e.g. species richness) and leading indicators (e.g. recruitment) of resilience in diverse vegetation types exposed to a variety of disturbance regimes. We suggest a third set of variables, proxy measures of resilience (e.g. functional redundancy), to complement lagging and leading indicators. We conclude with a framework to guide decisions about when to use each of the three types of measures to assess resilience of restoration projects to disturbance, providing some clarity to decision-making despite the uncertainty of changing disturbance regimes. Lastly, we invite researchers to understand the impact of disturbance on the resilience of restoration projects, rather than assume resilience.

Soil seed bank development of smoke‐responsive plant species in a 23‐year restoration chronosequence and implications for resilience to fire

“…For example, invasive species may be present in the SSB at higher densities and for longer owing to broad ecological niches and recent disturbances (Leder et al, 2017). In addition, origin is commonly used to evaluate restoration success because exotic species typically are undesirable and contrary to goals (Cowan et al, 2021). Lastly, factors that contribute to varying establishment success in restoration, such as climate, may have legacy effects on seed production in established vegetation (Yang et al, 2021).…”

“…Demonstrating resilience to both historical and changed disturbance regimes is key to long‐term persistence of restoration (Shackelford et al, 2013). However, empirical studies of responses of restored vegetation to disturbances are lacking (Cowan et al, 2021). Fire is a common disturbance globally (Bowman et al, 2009), and many plant species have evolved adaptations promoting regeneration following fire including smoke‐responsive, persistent soil seed banks (SSB; Pausas & Keeley, 2014).…”

Drivers of post‐fire resprouting success in restored Banksia woodlands

“…In contrast, plants in restoration projects will either be even‐aged (all established immediately) or uneven‐aged with a truncated upper limit and often young relative to the species’ lifespan. Restoration age is commonly used to understand ecosystem trajectories and predict plant responses to disturbances also (Cowan et al., 2021). Knowing the maximum plant age of individual resprouting plants provides an opportunity to assess how long resprouting capacity takes to develop, while the drivers of resprouting can be determined without being influenced by effects of previous disturbances.…”

“…Enright et al., 2014; Gallagher et al., 2021; Keeley et al., 2005; Le Stradic et al., 2018). However, we are unsure of the drivers of resprouting success of species with different resprouter organ types (Klimešová et al., 2021) and resprouting responses to fire in restored ecosystems (Cowan et al., 2021).…”

The acceptable range of variation within the desirable stable state as a measure of restoration success

“…There have been limited efforts to explore variability among restoration site outcomes (Brudvig et al 2017; Atkinson et al 2022), but variability among reference sites remains largely ignored. Terrestrial restoration ecology has traditionally focused on average states (Crouzeilles et al 2016; Cowan et al 2021), testing for example, whether on average, restored sites have more or less diversity than reference sites (Brudvig et al 2017; Atkinson et al 2022). Analyses estimating differences among means are clearly appropriate to creating generalizable findings for specific research questions; however, such analyses are generally inappropriate for determining restoration success, especially where individual restoration sites are the focus.…”