Rabbits rule : evaluating livestock grazing in coastal sand dunes of Meijendel, the Netherlands

Abstract

In 1990, livestock grazing was introduced in Meijendel, a 1,800 ha lime-rich coastal dune area, at a density of 0.06-0.07 LLU.ha -1 .year -1 (1:12-18 ha) to counteract encroachment of tall grasses and shrubland on dune grassland and increase the bare sand area. Monitoring was based on four digital orthophotos (1975-1990-2001-2009) with a high spatial resolution (pixel size 25x25 cm). The changes were tested using Generalized Estimating Equations. Habitat changes occurred, but contradicting our hypothesis, there was no significant impact from the grazing on bare sand, grassland or shrubland within 11 and 19 years post livestock introduction. (1) After several decennia of decreasing bare sand, there was a significant increase between 2001 and 2009, irrespective of livestock presence.(2) The changes in grasslands and shrublands are independent of the livestock, but dependent on distance to the coast. (3) Bare sand and shrub cover determine the space left for the dune grasslands. It appears other factors than livestock grazing must have induced the changes. Changes in climate conditions and nitrogen load might have stimulated bare sand. An interaction with the end of Marram planting in 1990 cannot be concluded from available data. The disease-led reduction of rabbit grazing from the mid-1950s led to an expansion of the dominant shrub Hippophae rhamnoides. However, Hippophae shrubland typically regresses to grasslands on its collapse after 25-40 years. Tree species like Crataegus, Betula and Quercus will gradually dominate the landscape for far longer. Active removal of these indigenous species is necessary to prevent future loss of dune grasslands.

The role of livestock grazing in long-term vegetation changes in coastal dunes: a case study from the Netherlands

“…The vegetation of the Meijendel dunes considerably changed after the 1950s (Boerboom 1960;Van der Meulen et al 1985). Shrubland and forest stands have expanded at the expense of grasslands, a development that continued after 1985 (Van der Hagen et al 2020b). Grasslands changed from species-rich into species-poor, monotonous vegetation dominated mainly by Calama-grostis epigejos and other tall grasses and the sedge Carex arenaria, following the general trend in Dutch coastal sand dunes (Kooijman et al 1998).…”

“…Among them are rabbits that predominantly graze in dune grasslands (priority habitat H2130). They dig burrows inducing blowout development (Aggenbach et al 2018) and selectively feed on young sprouts of shrubs and trees (Van der Hagen et al 2020b). However, rabbit disease outbreaks in 1954 and 1989 immediately killed 90-95% of the population, having imminent consequences for the vegetation of the dune ecosystem.…”

“…Three driving factors may explain succession in coastal dune grassland habitats in coastal dunes of North-Western Europe: the almost absence of rabbit grazing and digging, the autonomous return of blowouts after 2001, and the decrease of nitrogen deposition after 1990 (Van der Hagen et al 2020a;2020b;Fig. 3).…”

“…Like livestock, rabbits also feed on grassland vegetation and can significantly reduce above-ground phytomass when occurring in high numbers (Drees 1988). The sharp decline of rabbits due to viral diseases is likely to be the most decisive due to their preference for young nutrient-rich shrub and tree seedlings (Drees and Olff 2001;Van Tongeren 2006;Van der Hagen et al 2020b). Additionally to the grazing patterns, the burrow digging by rabbits also affects the vegetation composition and structure.…”

“…Furthermore, collapsed burrows give way for blowout development (Pluis 1986;Jungerius and Van der Meulen 1988). Both processes create open vegetation structures and facilitate the germination and growth success of annual and low-competitive plants ( Van der Hagen et al 2020b;Aggenbach et al 2018).…”