Cassandra van Altena

Protected areas are the cornerstone of nature conservation, although this approach has not prevented the current biodiversity crisis. In addition, the approach leads to the suggestion that only organisms living within these areas constitute nature. Nature, however, cannot be spatially constrained, and the same holds for human influence on nature. In this essay we develop an area-wide and human-inclusive vision of nature conservation into a new approach for national parks that we call National Park 3.0 (NP 3.0). The concept is rooted in a re-evaluation of human-nature relations sensu the Nature Futures Framework developed under IPBES. Moreover, we note that ‘landscape’ has always been a social-ecological concept since the term was coined by 17th century Dutch painters. Finally, we note that nature and human infrastructure are deeply entangled at multiple spatial scales in modern landscapes. We define NP 3.0 spatially by the contours of a landscape that is recognizable by people and has geomorphological and ecological coherence. We relate NP 3.0 to other initiatives for restoring biodiversity and provide a conceptual design for NP 3.0. Throughout this essay we use Nationaal Park Hollandse Duinen as a case study where NP 3.0 is worked out in practice.

Shallow lakes have the potential to switch between two alternative stable states: a clear macrophyte-dominated and a turbid phytoplankton-dominated state. Observational and experimental studies show that in some lakes herbivory by birds may severely decrease macrophyte biomass, while in other lakes, the removed biomass by herbivory is compensated by regrowth. These contradictory outcomes might arise because of interplay between top-down control by bird herbivory and bottom-up effects by nutrient loading on macrophytes. Here, we use the ecosystem model PCLake to study top-down and bottom-up control of macrophytes by coots and nutrient loading. Our model predicted that (1) herbivory by birds lowers the critical nutrient loading at which the regime shift occurs; (2) bird impact on macrophyte biomass through herbivory increases with nutrient loading; and (3) improved food quality enhances the impact of birds on macrophytes, thus decreasing the resilience of the clear-water state even further. The fact that bird herbivory can have a large impact on macrophyte biomass and can facilitate a regime shift implies that the presence of waterfowl should be taken into account in the estimation of critical nutrient loadings to be used in water quality management.

A principal aim of ecologists is to identify critical levels of environmental change beyond which ecosystems undergo radical shifts in their functioning. Both food-web theory and alternative stable states theory provide fundamental clues to mechanisms conferring stability to natural systems. Yet, it is unclear how the concept of food-web stability is associated with the resilience of ecosystems susceptible to regime change. Here, we use a combination of food web and ecosystem modelling to show that impending catastrophic shifts in shallow lakes are preceded by a destabilizing reorganization of interaction strengths in the aquatic food web. Analysis of the intricate web of trophic interactions reveals that only few key interactions, involving zooplankton, diatoms and detritus, dictate the deterioration of food-web stability. Our study exposes a tight link between food-web dynamics and the dynamics of the whole ecosystem, implying that trophic organization may serve as an empirical indicator of ecosystem resilience.