ARTICLE Spatiotemporal dynamics of natural tree regeneration in unmanaged subalpine conifer forests with high wild ungulate densities Martin Brüllhardt, Anita C. Risch, Flurin Filli, Rudolf M. Haller, and Martin Schütz Abstract: Increasing wild ungulate populations in the northern hemisphere led to extensive research on their influence on forest regeneration. According to the results of different studies, high ungulate densities may alter forest structure and compo- sition, as well as inhibit forest regeneration. However, little is known about the long-term impact of large herbivores on forest dynamics at the landscape scale. Therefore, we studied forest regeneration in conifer forests of the highly protected Swiss National Park. We assessed sapling densities and apical shoot loss by repeated systematic sampling in 2003 and in 2011–2012 in two valleys featuring exceptionally high densities of wild ungulates of up to 86 individuals per vegetation-covered square kilometre during summer and 28 individuals per vegetation-covered square kilometre during winter. Mean apical shoot loss ranged between 2.9% and 10.6% depending on study site and assessment year. In addition to the increasing sapling densities, these results suggest that ungulates had little impact on tree establishment in the studied subalpine conifer forests. Additionally, sapling diversity was higher on plots repeatedly influenced by ungulates (apical shoot loss), suggesting rather positive effects of ungulates on sapling diversity. Habitat containing a mixture of forest and grassland without livestock or human disturbance provides a high-quality environment for ungulates, which likely explains the low impact of ungulates on forest regeneration in our study area. Key words: mountain forest, sapling density, sapling diversity, herbivory, red deer (Cervus elaphus), chamois (Rupicapra rupicapra), ibex (Capra ibex). Résumé : L'augmentation des populations d'ongulés sauvages dans l'hémisphère nord est a ` l'origine de recherches approfondies visant a ` déterminer leur influence sur la régénération forestière. Selon les résultats de différentes études, de fortes densités d'ongulés peuvent modifier la structure et la composition forestière et inhiber la régénération forestière. Cependant, les impacts a ` long terme des gros herbivores sur la dynamique forestière a ` l'échelle du paysage sont peu documentés. Ainsi, nous avons étudié la régénération de forêts résineuses du Parc national suisse qui est sous haute protection. Nous avons estimé la densité des gaules et la perte de pousses apicales a ` l'aide d'un échantillonnage systématique réalisé en 2003 et répété en 2011–2012 dans deux vallées abritant des densités exceptionnellement élevées d'ongulés sauvages atteignant jusqu'a ` 86 individus par km 2 de territoire couvert de végétation pendant l'été et 28 individus par km 2 pendant l'hiver. La perte moyenne de pousses apicales variait de 2,9 a ` 10,6 % selon la station étudiée et l'année d'inventaire. Nos résultats associés a ` des densités croissantes de gaules indiquent que les ongulés ont eu peu d'impact sur l'établissement des arbres dans les forêts subalpines de conifères a ` l'étude. De plus, la diversité des gaules était plus grande dans les parcelles influencées de façon répétée par les ongulés (perte de pousses apicales), ce qui indique que les ongulés auraient un effet plutôt positif sur la diversité des gaules. Les habitats composés d'un mélange de forêts et de prairies sans bétail ni perturbation humaine offrent un environnement de haute qualité pour les ongulés, ce qui explique probablement le faible impact des ongulés sur la régénération forestière dans notre aire d'étude. [Traduit par la Rédaction] Mots-clés : forêt montagnarde, densité des gaules, diversité des gaules, herbivorisme, cerf élaphe (Cervus elaphus), chamois (Rupicapra rupicapra), bouquetin des Alpes (Capra ibex). Introduction Natural regeneration of temperate and boreal forests is influ- enced by several exogenous abiotic and biotic factors. Among the former, light and water availability, soil temperatures (degree days), and soil substrate quality are most important for tree estab- lishment (Price et al. 2001). The main biotic factors are competi- tion from ground vegetation (Pages et al. 2003; Cunningham et al. 2006) and trampling and herbivory (Gill 1992; Skarpe and Hester 2008). Although the influence of herbivores on tree establishment is a controversial topic of discussion among foresters and re- searchers (Senn and Suter 2003), herbivory by wild ungulates is widely accepted as a major cause of tree mortality during forest regeneration (Tilghman 1989; Motta 1996; Witt and Webster 2010). Moreover, through selective feeding on certain tree species, wild ungulates can influence forest structure and tree species compo- sition (Gill 1992; Ammer 1996; Danell et al. 2003; Didion et al. 2009). Depending on how well tree saplings are adapted to her- bivory, which can depend on the timing and intensity of her- Received 12 August 2014. Accepted 11 January 2015. M. Brüllhardt.* Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Community Ecology, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland; Parc Naziunal Svizzer, Chastè Planta-Wildenberg, CH-7530 Zernez, Switzerland. A.C. Risch and M. Schütz. Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Community Ecology, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland. F. Filli and R.M. Haller. Parc Naziunal Svizzer, Chastè Planta-Wildenberg, CH-7530 Zernez, Switzerland. Corresponding author: Martin Brüllhardt (e-mail: martin.bruellhardt@usys.ethz.ch). *Current affiliation and address: Swiss Federal Institute of Technology ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland. 607 Can. J. For. Res. 45: 607–614 (2015) dx.doi.org/10.1139/cjfr-2014-0358 Published at www.nrcresearchpress.com/cjfr on 31 March 2015. Can. J. For. Res. Downloaded from www.nrcresearchpress.com by Lib4RI - Library of Eawag, Empa, PSI & WSL on 04/28/15 For personal use only.