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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 maybe 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. Key words: Odocoileus virginianus, Thuja occidentalis, browsing, regeneration, disturbance interactions La dynamique des trouees joue un role crucial dans la regeneration des forets en creant des niches de regeneration et de survie favorables pour certaines especes vegetales. Neanmoins, des facteurs potentiellement preponderants, tels que le broutement par les ongules, pourraient limiter ou eliminer cette regeneration liee a la dynamique des trouees. Les effets deleteres du broutement peuvent etre exacerbes pour les especes a croissance lente telles que le thuya de l'est (Thuja occidentalis L.), un arbre grandement selectionne par le cerf de Virginie (Odocoileus virginianus Zimmerman). Nous avons donc cherche a comprendre comment le broutement par le cerf et la dynamique des trouees interagissent pour affecter la regeneration du thuya et avons emis l'hypothese que la regeneration du thuya beneficie des trouees naturelles, mais que le broutement par le cerf pourrait annuler cet effet. Nous avons dresse l'inventaire des trouees naturelles de la canopee le long d'un gradient spatio-temporel d'utilisation de l'habitat par le cerf. Nous avons evalue l'abondance de la regeneration de thuya, la hauteur des arbres et divers parametres relatifs aux trouees, aux peuplements et a la concurrence. Nous avons constate que la pression exercee par le broutement des cerfs limitait considerablement la regeneration des thuyas; cependant, lorsque les populations de cerfs diminuaient, l'abondance de la regeneration des thuyas augmentait en l'espace d'une decennie, meme apres une pression de broutement prolongee, et augmentait encore avec le temps. Notre etude montre que la regeneration des thuyas peut etre favorisee par la creation de trouees et le controle des populations de cerfs. [Traduit par la Redaction] Mots-cles : Odocoileus virginianus, Thuja occidentalis, broutement, regeneration, interactions entre les perturbations, Introduction Gaps can play an essential role in forest dynamics (White and Pickett 1985; Lof et al. 2018), notably in the eastern mixed boreal forests of North America, where small-scale [...]

The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature-trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.

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Gap dynamics facilitate recruitment of late-successional species such as northern white-cedar (Thuja occidentalis L.). For this reason, harvests that result in partial rather than complete canopy removal have been suggested for cedar. However, success of regenerating cedar following partial harvests is uncertain, especially where there is heavy browsing by white-tailed deer (Odocoileus virginianus Zimmerman) or snowshoe hare (Lepus americanus). Efforts to understand how partial harvests and browsing interact to affect natural regeneration of cedar have been limited. We inventoried partially harvested stands along a gradient of 1–11 years since harvest in New Brunswick, Canada, in an area where deer frequently overwinter. Cedar regeneration was negatively influenced by browsing, but positively influenced by years since harvest and sapling basal area. Cedar seedling survival was assessed over a 2-year period and found to be primarily a function of height at initial measurement, with little influence of browsing. Annual vertical gain of cedar seedlings (a surrogate for height growth) decreased with increasing years since harvest and was influenced by distance from gap edge. In gaps, vertical gain increased with distance to gap edge, while distance to gap edge had a negative influence on vertical gain of seedlings in the matrix (between-gap areas). Many tagged cedar seedlings disappeared prior to remeasurement. These were likely completely consumed by browsers, limiting our ability to determine relative influences of partial harvest and browsing on cedar regeneration. We conclude that partial harvests, as applied in this study, increase cedar abundance and vertical gain, but browsing may necessitate seedling protection. We suggest monitoring to confirm sufficient cedar regeneration in partially harvested stands, using exclosures where browsing is a concern, and retaining or at least delaying removal of seed-bearing cedar overstory trees until regeneration has reached heights safe from browsing. [ABSTRACT FROM AUTHOR]

Overabundant populations of large herbivores have strong persistent effects on forest composition, structure, and function. However, the mechanism through which plant communities recover their original composition and function after herbivore management remains poorly understood. We assessed the temporal trajectories of the herbaceous communities in Abies balsamea (L.) Mill. and Picea glauca (Moench) Voss stands on Anticosti Island (Quebec, Canada) over 8 years following clear-cutting and deer management. The impact of deer exclusion or reduction to 7.5 and 15 deer x [km.sup.-2] was compared with benchmark in situ deer densities (27 and 56 deer x [km.sup.-2]). Effects of deer management treatments on plant species and functional trait assemblages over time were assessed using principal response curves. Although complete deer exclusion seemed necessary to modify species composition from that occurring under intense browsing, a reduced density of 7.5 deer x [km.sup.-2] was sufficient to induce significant changes in functional trait assemblages of regenerating stands. For instance, reduced deer densities favored plants with brightly colored flowers and compound inflorescences pollinated by animals and producing large seeds and fleshy fruits dispersed by animals. We conclude that the boreal forest's herbaceous communities are resilient to chronic browsing when deer population reduction and forest clearcutting are applied in synergy. Key words: resilience, species composition, functional traits, plant-herbivore interactions, deer. Les populations surabondantes de grands herbivores ont des effets majeurs et persistants sur la composition, la structure et le fonctionnement de la foret. Toutefois, le mecanisme par lequel les communautes vegetales retrouvent leur composition et leur fonctionnement originels en reponse au controle des herbivores demeure mal compris. Nous avons evalue les trajectoires temporelles des communautes herbacees dans des peuplements d'Abies balsamea (L.) Mill. et de Picea glauca (Moench) Voss a l'ile d'Anticosti (Quebec, Canada) pendant 8 annees apres avoir effectue une coupe a blanc et controle les populations de cerfs. L'impact de l'exclusion du cerf ou d'une reduction de la densite a 7,5 ou 15 cerfs x [km.sup.-2] a ete compare a des densites temoins in situ (27 et 56 cerfs x [km.sup.-2]). Les effets des traitements de gestion du cerf sur les especes vegetales et les assemblages de traits fonctionnels ont ete evalues en fonction du temps au moyen de la methode des courbes de reponses principales. Bien que l'exclusion complete du cerf ait semble necessaire pour modifier la composition specifique par rapport a celle observee en conditions de broutage intense, une densite reduite a 7,5 cerfs x [km.sup.-2] etait suffisante pour induire des changements significatifs dans les assemblages de traits fonctionnels des peuplements en regeneration. A titre d'exemple, des densites reduites de cerfs ont favorise les plantes a fleurs de couleur vive et les plantes a fleurs composees pollinisees par les animaux et produisant de grosses graines et des fruits charnus disperses par les animaux. Nous concluons que les communautes herbacees de la foret boreale sont resilientes au broutage chronique quand une reduction des populations de cerfs et une coupe forestiere a blanc sont appliquees en synergie. [Traduit par la Redaction] Mots-cles: resilience, composition specifique, traits fonctionnels, interactions plantes-herbivores, cerf., Introduction Overabundant populations of large herbivores represent a threat to forest ecosystems around the world, overexploiting their habitat to the point of compromising forest regeneration and composition (Cote et al. [...]