Reduction in local white-tailed deer abundance allows the positive response of northern white cedar regeneration to gap dynamics

Abstract

Gap dynamics play a crucial role in forest regeneration by creating favourable regeneration and survival niches for some plant species. Nonetheless, potentially overriding factors, such as ungulate browsing, could limit or eliminate this gap dynamic-related regeneration. The deleterious effects of browsing may be exacerbated for slow-growing species such as northern white cedar ( Thuja occidentalis L.), a tree highly selected by white-tailed deer ( Odocoileus virginianus Zimmerman). We therefore aimed to understand how deer browsing and gap dynamics interact to affect cedar regeneration and hypothesized that cedar regeneration benefits from natural gaps but that deer browsing could override this effect. We inventoried natural canopy gaps along a spatiotemporal gradient of deer habitat use. We evaluated cedar regeneration abundance, tree height, and various gap, stand, and competition metrics. We found that deer browsing pressure greatly limited cedar regeneration; however, when deer populations decreased, cedar regeneration abundance increased within a decade, even after prolonged browsing pressure, and increased further over time. Our study illustrates that cedar regeneration can be favoured by gap creation and deer population control.