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Abstract
Ecosystem management to date largely relies on command-and-control approaches using static target habitat types and species. The dynamic nature of ecosystems, enhanced by climate change and intensification of surrounding landscapes by a growing economy, makes such approaches increasingly ineffective. Ecosystem management and conservation policies are challenged to adopt approaches that build on dynamic views of ecosystems and changing environmental conditions as a central guiding principle towards more adaptive management and conservation strategies. The response of ecosystems to change is contained in the concept of ‘ecological resilience’. Resilience is discussed extensively in the scientific literature, but it needs to be operationalised for application in ecosystem management. In this thesis, I focussed specifically on adaptive capacity, i.e. the capacity of ecosystems to reorganize and maintain ecosystem functioning under changing environmental conditions.
From the ecosystem functioning perspective, the consensus that the loss of an individual species does not necessarily have obvious functional consequences, is growing. Rather, the species composition and the specific ecological roles captured by species traits within it, are central for ecosystem resilience. Following recent insights on the relationship between adaptive capacity and species trait diversity, I analyse how communities, through their trait diversity, respond to environmental conditions both locally and regionally. Plant trait databases are well developed and plant traits are extensively described in different contexts. In Chapter 2, I used response traits associated with resistance to environmental variability, and effect traits that influence plant species recovery, in an effect-and-response framework to study how such resilience mechanisms relate to environmental change. Species trait composition showed a strong resistance to environmental variability and, consequently, a positive effect on resilience.
Of the many factors that affect ecosystem resilience, spatial variation in environmental heterogeneity is commonly identified as one factor that is particularly relevant to managers. In Chapter 3, I tested how species trait selection related to landscape heterogeneity at different spatial extents. The analysis included butterfly and plant species characteristic for wetland ecosystems. Heterogeneity indices and their spatial extent indeed correlated with trait composition for both taxa, but I found no indication that the extent at which heterogeneity affects trait composition differed between the two species groups.
The concept of ecological memory provides a perspective on how the adaptive capacity of ecosystems can be enhanced through management. In Chapter 4, I use this concept to specify how ecological processes at different spatial scales assist in the reorganization of riparian plant communities after disturbances. The variation in ecological processes found suggests that internal and external memory can coexist, enabling ecosystems to adapt to changes in the environment. For ecosystem management to maximise this capacity of ecosystems to reorganise after disturbances, requires to incorporate measures at local, landscape and regional levels.
A central challenge in ecology is to understand the factors affecting ecosystem resilience across spatio-temporal scales. Such knowledge is needed as a basis for management measures and supports the translation of theory into practice. However, field studies are typically short in timespan and small in spatial extent. In Chapter 5, I developed a spatially explicit, demographic model with four plant strategies – avoiders, invaders, resisters and endurers - categorised by their adaptation to river flooding. I used the model to understand how flood regimes and landscape heterogeneity as a management measure to steer flood patterns, impact these different plant strategies. The model illustrates that community reorganization after a flood event is dependent on the relative amount of internal and external memory, which is in turn shaped by the degree of landscape heterogeneity.
I conclude that to maintain ecosystem resilience, site management needs to be embedded in a larger scale adaptive management strategy. In that way ecosystem management can effectively accommodate the dynamics of ecological processes. Guidance towards scaleinclusive management requires further operationalization of the concept of resilience. For this, the multitude and interplay of processes across spatio-temporal scales need to be assessed to understand which processes synergise and which dominate system responses. As the model of nested adaptive cycles indicates, to acknowledge that resilience encompasses multiscale interactions (across time and space), is important. However, to translate this crucial phenomenon in management measures is difficult. Resilience depends on many elements of complexity and perhaps the concept can never be perfectly captured. However, from its original descriptive meaning, resilience is becoming a ‘way of thinking’, a strong concept bridging disciplines, with the capacity to improve the effectiveness of environmental policy and practice – on the condition that the concept is made operational. With this thesis I contribute to this process by outlining and testing a number of dimensions along which resilience may be operationalized. Taken together, these dimensions offer various leads to research, policy and practice alike, to prepare ecosystem management for the challenges an increasingly dynamic world entails.
