Rewilding with red deer in Het Groene Woud: impact on woody recruitment and vegetation structure

Abstract

In national landscape Het Groene Woud, located in the Dutch province of Noord-Brabant, nature managers reintroduced red deer to increase the ecological value of the area. As intermediate feeders, red deer forage on both woody and grassy vegetation, and can, through top-down interactions, broadly impact their environment. The idea is that red deer, in combination with other herbivores like cattle and roe deer, can increase the graduality of the transitions between grasslands and forests in Het Groene Woud, and can maintain a diverse, half-open landscape. To monitor if these goals are being obtained, the aim of this study was to measure woody recruitment and vegetation structure within the red deer enclosure, and to quantify how these can be linked to area use by red deer. I used camera traps to determine the area use by red deer in 2021, I used GPS data to determine historic area use, and I performed a field survey of eighty 20x20m plots to measure vegetation characteristics. I also used vegetation data from 2019, to measure vegetation change. In an elaborate statistical analysis, I then studied the interaction between red deer and the vegetation, and the influence of various covariates, like tree species, habitat type and coarse woody debris. I found that red deer preferred to stay in oak-hazel-alder forests and grasslands. I also found indications of red deer influencing the growth of saplings, possibly keeping them below a certain height. Interestingly, the results show that this effect differs per tree species. Furthermore, I found little indications of red deer influencing bramble growth, or increasing woody vegetation structure. In fact, grassland plots barely contained any woody structure. Restoring top-down trophic interactions, or trophic rewilding, has received increasing interest. The red deer enclosure of Het Groene Woud, together with this study, provide examples of the effect of rewilding with large herbivores, as well as on how to study these processes.