Integrating theory into disturbance interaction experiments to better inform ecosystem management

Abstract

Managing multiple, interacting disturbances is a key challenge to biodiversity conservation, and one that will only increase as global change drivers continue to alter disturbance regimes. Theoretical studies have highlighted the importance of a mechanistic understanding of stressor interactions for improving the prediction and management of interactive effects. However, many conservation studies are not designed or interpreted in the context of theory and instead focus on case-specific management questions. This is a problem as it means that few studies test the relationships highlighted in theoretical models as being important for ecological management. We explore the extent of this problem among studies of interacting disturbances by reviewing recent experimental studies of the interaction between fire and grazing in terrestrial ecosystems. Interactions between fire and grazing can occur via a number of pathways; one disturbance can modify the other's likelihood, intensity or spatial distribution, or one disturbance can alter the other's impacts on individual organisms. The strength of such interactions will vary depending on disturbance attributes (e.g. size or intensity), and this variation is likely to be nonlinear. We show that few experiments testing fire-grazing interactions are able to identify the mechanistic pathway driving an observed interaction, and most are unable to detect nonlinear effects. We demonstrate how these limitations compromise the ability of experimental studies to effectively inform ecological management. We propose a series of adjustments to the design of disturbance interaction experiments that would enable tests of key theoretical pathways and provide the deeper ecological understanding necessary for effective management. Such considerations are relevant to studies of a broad range of ecological interactions and are critical to informing the management of disturbance regimes in the context of accelerating global change.

Avoiding ecosystem collapse in managed forest ecosystems

“…; Foster et al . ). As an example, altered (and intensive) herbivore grazing regimes interact with fire regimes in Australian coastal forests and have considerably greater negative effects on vegetation than either of these in isolation (Foster et al .…”

“…Foster et al . () provided a valuable experimental framework for studies to help distinguish the potential impacts of multiple interacting stressors, including how to underpin such studies with relevant ecological theory (Figure ). Notably, many investigations have demonstrated that the demise of individual species stems from multiple interacting factors (eg Woinarski et al .…”

Untitled

“…Given increasing anthropogenic pressures (e.g., land use changes, human population growth, species introductions) and climate change, increased disturbance frequency, as well as interactions among disturbances, are likely consequences in the future (Seidl et al 2014, Buma 2015, Foster et al 2016. Although a relatively small proportion of fires have occurred in beetle-killed fuels in the western US over the last three decades (0.5 % to 1.3 %), there are recent examples of fires burning through forests with high levels of beetle-impacted fuels .…”

Approaches to Landscape Scale Inference and Study Design

“…As outlined above, adequate replication of large experimental units (such as entire landscapes) for true experiments is often difficult, and it is even more of a challenge when the target species for study are wide-ranging, highly mobile taxa, such as birds and bats [27]. In other cases, the strict statistical design constraints that underpin true experiments may limit the kinds of potentially important factors and/or management interventions that can be tested, including complex interactions among factors (but see [28]). For example, the Suitability of Altered Forest Ecosystems Project (SAFE) in Borneo is quantifying a range of drivers of effects of fragmentation, but the effects of matrix conditions surrounding fragments are not being examined despite their importance being increasingly recognised [29].…”