From protégé to nurse plant: establishment of thorny shrubs in grazed temperate woodlands

Abstract

Question: Thorny shrubs play keystone roles in grazed ecosystems by defending non‐protected plants against herbivores, but their establishment in grazed ecosystems is poorly understood. Which factors control establishment of recruits of thorny nurse shrubs in grazed temperate woodlands? Location: Ancient grazed temperate woodlands (52°32′N, 6°36′E), The Netherlands. Methods: We surveyed biotic and abiotic factors for saplings of thorny nurse shrubs in plots with and without saplings. To disentangle these factors, we performed a transplantation experiment over two growing seasons with nurse shrub saplings (Prunus spinosa and Crataegus monogyna) planted in two dominant vegetation types – tall unpalatable swards and short grazed lawns – half of them protected from herbivory via exclosures. Results: Plots with shrub saplings had taller surrounding vegetation, higher soil pH and higher soil moisture than plots without saplings. These plots predominantly contained unpalatable sward species, while plots without saplings mainly contained palatable lawn species. After transplantation, sapling survival was higher in exclosures than in the open, and higher in sward exclosures than in lawn exclosures. Sapling growth was higher in swards than in lawns, higher inside than outside exclosures, and higher for Prunus than Crataegus, while browsing on saplings was higher in lawns. Conclusion: Unpalatable swards form essential establishment niches for thorny shrubs in grazed temperate woodlands: they protect against herbivores before thorns fully develop in saplings, and sapling growth is better due to improved micro‐environmental conditions. Once established and thorny, shrub saplings grow out of the protective range of the swards and in turn facilitate tree seedlings, which are essential for long‐term persistence of grazed temperate woodlands. This study shows that nurse plants may start as protégés before becoming facilitators for other plants in a later life stage. This may be common for nurse plants in various ecosystems. We argue that improved understanding of establishment of nurse plants and their constraining factors is crucial for effective conservation and restoration in various ecosystems.

Seeing the oakscape beyond the forest: a landscape approach to the oak regeneration in Europe

“…According to F. Vera, sustaining the open character of landscapes through grazing is indispensable for successful oak regeneration (Vera 2000;Vera et al 2006). Under such conditions however, oak saplings require a strong anti-grazing/browsing protection, through either facilitation secured by unpalatable species (such as thorny shrubs, e.g., Watt 1919; Kuiters and Slim 2003;Smit and Ruifrok 2011;Jensen et al 2012), or numeric dilution-an effect of the exuberance of plants more palatable than young oaks (Jensen et al 2012). …”

Grazing and abandonment determine different tree dynamics in wood-pastures

“…Symbol size for grazed sites corresponds to the number of junipers, and for abandoned sites, it corresponds to the openness of the site. The dashed line indicates a hypothetical situation where small and large conspecific trees would be equally abundant numbers of thorny or unpalatable nurse shrubs (Bakker et al 2004;Smit and Ruifrok 2011), in this case junipers: Small birches and pines were more abundant in sites with numerous junipers. The most likely reason for this is that junipers facilitate the survival of palatable tree seedlings by acting as nurse shrubs, i.e., providing shelter from grazers (Lampimäki 1939;Olff et al 1999;Bakker et al 2004).…”

Scrub encroachment into species-rich limestone grassland: recruitment, herbivory and the threat from incipient scrub

“…Today, as shown by this study, incipient scrub has already colonised 20-30 m of grassland adjacent to scrub. The density and composition of the heterogeneous patchwork of developing incipient scrub vary continually in accordance with the differential success of seed dispersal and grazer-induced mortality (Ward 1990; see also Olff et al 1999;Smit and Ruifrok 2011).…”

“…In protected cultural landscapes, managers need to know how and why vegetation boundaries shift, particularly when the preservation of landscape mosaics of woody and grassland vegetation is an explicit goal of the reserve. A better understanding of the process of woody plant regeneration at the scrub-grassland interface in grazed ecosystems is therefore crucial for the preservation of a system where two opposing processes -suppression of woody plant regeneration and succession toward closed woody vegetation -are continually at work (Kollmann and Poschlod 1997;Olff et al 1999;Van Utyvanck et al 2008;Smit and Ruifrok 2011). It is also an essential first step in designing and implementing management practices that will allow for the effective control of scrub.…”