High Grazing Pressure of Geese Threatens Conservation and Restoration of Reed Belts

Abstract

Reed (Phragmites australis (Cav.) Trin. ex Steud.) beds are important habitat for marsh birds, but are declining throughout Europe. Increasing numbers of the native marsh bird, the Greylag goose (Anser anser L.), are hypothesized to cause reed bed decline and inhibit restoration of reed beds, but data are largely lacking. In this study, we experimentally tested the effect of grazing by Greylag geese on the growth and expansion of reed growing in belts along lake shorelines. After 5 years of protecting reed from grazing with exclosures, reed stems were over 4-fold denser and taller than in the grazed plots. Grazing pressure was intense with 50–100% of the stems being grazed among years in the control plots open to grazing. After 5 years of protection we opened half of the exclosures and the geese immediately grazed almost 100% of the reed stems. Whereas this did not affect the reed stem density, the stem height was strongly reduced and similar to permanently grazed reed. The next year geese were actively chased away by management from mid-March to mid-June, which changed the maximum amount of geese from over 2300 to less than 50. As a result, reed stem density and height increased and the reed belt had recovered over the full 6 m length of the experimental plots. Lastly, we introduced reed plants in an adjacent lake where no reed was growing and geese did visit this area. After two years, the density of the planted reed was six to nine-fold higher and significantly taller in exclosures compared to control plots where geese had access to the reed plants. We conclude that there is a conservation dilemma regarding how to preserve and restore reed belts in the presence of high densities of Greylag geese as conservation of both reed belts and high goose numbers seems infeasible. We suggest that there are three possible solutions for this dilemma: (1) effects of the geese can be mediated by goose population management, (2) the robustness of the reed marshes can be increased, and (3) at the landscape level, spatial planning can be used to configure landscapes with large reed bed reserves surrounded by unmown, unfertilized meadows.

The public and geese: a conflict on the rise?

“…Geese provide various benefits to humans (i.e., ecosystem services) such as nutrient cycling and stimulation of plant productivity, recreational hunting, meat, esthetic experience, and ecotourism (Green & Elmberg, 2014). However, the super-abundance of some geese has also led to over-grazing and impacts on ecosystems, and it is associated with several "ecosystem disservices," such as crop damage, fouling on beaches and in parks, compromised air safety, contamination of freshwater, degradation of natural vegetation, and concern about spread of disease (Bakker et al, 2018;Buij et al, 2017;. Notably, what constitute a service or disservice partially depends on who makes the evaluation leading to different assessments by stakeholder groups (Buij et al, 2017).…”

Disentangling causes of the dieback of littoral stands in an overloaded water-bird reserve: roles of eutrophication, fish and geese

“…On the other hand, some species can destroy the stands if they occur there in high densities. This has been documented both for birds (Bakker et al 2018) and sh (Crivelli 1983). In addition, the size and stability of the littoral stands can be reduced by many other factors such as oods, high and stabilized water levels (Ostendorp 1989), eutrophication (van der Putten 1997(van der Putten , Čížková et al 1999, toxic substances in the sediment (Armstrong et al 1996, Armstrong andArmstrong 2001) and, nally, mechanical damage caused by human activities.…”

“…Generally, either sh (Hroudová et al 2010;Francová et al 2019a) and/or water birds (Chaichana et al 2011;Bakker et al 2018) can destroy the littoral stands when they occur in high densities.…”

“…As Bakker et al (2018) point out, the conservation of both the littoral stands and high geese numbers seems infeasible. There are two possible solutions for this dilemma: (1) negative effects of geese can be limited by the restriction of their populations, (2) or it can be compensated by supporting the recovery of the littoral stands.…”

Does intensive goose grazing affect breeding waders?

“…However, the increases have caused socioeconomic conflicts with farming interests due to damage to agricultural crops (Fox, Elmberg, Tombre, & Hessel, 2017) and flight safety (Bradbeer, Rosenquist, Christensen, & Fox, 2017), as well as concerns for impacts on vulnerable ecosystems and biodiversity. Ecosystem impacts may be due to overgrazing of natural habitats (Bakker, Veen, Heerdt, Huig, & Sarneel, 2018;Jano, Jefferies, & Rockwell, 2002;Pedersen, Speed, & Tombre, 2013;Srivastava & Jefferies, 1996) and nutrient input via defecation to aquatic environments used as roost sites (Dessborn, Hessel, & Elmberg, 2016;Jensen et al, 2019). The increasing socioeconomic and ecological conflicts have resulted in calls for the management of populations at national and international levels.…”