Compositional and functional trajectories of herbaceous communities after deer density control in clearcut boreal forests (original) (raw)
Related papers
Canadian Journal of Zoology, 2012
Intense browsing by abundant large herbivores can threaten the ecological integrity of ecosystems by inducing modifications in the structure and composition of vegetation that trigger trophic cascades affecting plant and animal communities. We investigated the relationships between density of white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)), forest succession after clear-cut, and songbird communities on Anticosti Island, Quebec, Canada. We hypothesized that lower deer densities would alter the trajectory of forest succession after clear-cutting and lead to a rapid recovery of habitat attributes favorable to songbirds associated with a dense complex shrub layer. Six years after establishing a controlled browsing experiment (0, 7.5, 15, and >27 deer·km -2 ) in recent clearcuts, reducing deer densities ≤7.5 deer·km -2 initiated the restoration of balsam fir (Abies balsamea (L.) Mill.) forests and increased the regeneration of paper birch (Betula papyrifera Marshall). Increasing birch ground cover from 10% to 20% increased songbird total abundance, species richness, and diversity by 17%, 39%, and 31%, respectively. Alder Flycatcher (Empidonax alnorum Brewster, 1895) was only present at ≤7.5 deer·km -2 and strongly associated with birch regeneration. The regeneration of browse-resistant plants such as white spruce (Picea glauca (Moench) Voss) in some areas at high deer density favored the maintenance of many shrub-dependent songbirds but also species usually associated with forest canopy. Active management of deer populations in Canadian harvested boreal forests will mitigate losses in vegetation and songbirds caused by over-browsing.
Canadian Journal of Forest Research, 2015
Understanding how forests respond to multiple disturbances is becoming increasingly important under global change. We examined the simultaneous influence of canopy decline and deer browsing on regeneration in an old-growth reserve and surrounding managed forest dominated by Fagus sylvatica L. and Abies alba Mill. in Slovenia. We quantified both disturbance processes by measuring characteristics of canopy gaps and reconstructing historical deer densities. Forest response was assessed with repeated measurements of tree regeneration and regeneration patterns within deer exclosures. Most gaps were formed by mortality of A. alba (71%), and gapmaker characteristics suggest that gaps formed slowly and often expanded, resulting in a mosaic of openings covering 17% of the old-growth reserve. Fagus sylvatica dominated the regeneration layer throughout the reserve and recruited to taller height classes over the past 26 years. The recruitment failure of preferred browse species (A. alba and Acer pseudoplatanus L.) in the reserve and the successful recruitment of these species within exclosures indicate that selective browsing by deer has altered the successional response to A. alba decline, facilitating the dominance of F. sylvatica. Given that global change may increase forest decline worldwide and the ubiquitous nature of deer browsing in many temperate forests, understanding their combined effects on forests will become increasingly important.
Comparative Effects on Plants of Caribou/Reindeer, Moose and White-tailed Deer Herbivory
ARCTIC, 2001
We reviewed the literature reporting negative or positive effects on vegetation of herbivory by caribou/reindeer, moose, and white-tailed deer in light of the hypothesis of exploitation ecosystems (EEH), which predicts that most of the negative impacts will occur in areas where wolves were extirpated. We were able to list 197 plant taxa negatively affected by the three cervid species, as opposed to 24 that benefited from their herbivory. The plant taxa negatively affected by caribou/reindeer (19), moose (37), and white-tailed deer (141) comprised 5%, 9%, and 11% of vascular plants present in their respective ranges. Each cervid affected mostly species eaten during the growing season: lichens and woody species for caribou/reindeer, woody species and aquatics for moose, and herbs and woody species for white-tailed deer. White-tailed deer were the only deer reported to feed on threatened or endangered plants. Studies related to damage caused by caribou/reindeer were scarce and often concerned lichens. Most reports for moose and white-tailed deer came from areas where wolves were absent or rare. Among the three cervids, whitetailed deer might damage the most vegetation because of its smaller size and preference for herbs. RÉSUMÉ. À la lumière de l'hypothèse de l'exploitation des écosystèmes (EEH), nous avons examiné les publications qui mentionnent les effets négatifs ou positifs, sur la végétation, du broutement du caribou/renne, de l'orignal et du cerf de Virginie. Cette hypothèse prédit que les impacts négatifs se concentrent dans des endroits où le loup a été éliminé. Nous avons pu énumérer 197 taxons végétaux affectés négativement par les trois cervidés, contre 24 qui profitaient du broutement. Le nombre de taxons végétaux affectés négativement par le broutement du caribou/renne (19), de l'orignal (37) et du cerf de Virginie (141) représentait respectivement 5, 9 et 11 p. cent des plantes vasculaires situées dans les aires de répartition spécifiques des animaux. Chaque cervidé affectait surtout les espèces consommées durant la saison de croissance végétale: lichens et plantes ligneuses pour le caribou/renne, plantes ligneuses et aquatiques pour l'orignal, et plantes herbacées et ligneuses pour le cerf de Virginie. Selon les rapports, ce dernier était le seul cerf qui broutait des plantes menacées ou en voie de disparition. Les études rapportant des dommages causés par le caribou/renne étaient rares et traitaient souvent des lichens. La plupart des rapports sur l'orignal et le cerf de Virginie couvraient des zones où le loup était rare ou absent. Des trois cervidés, celui qui causerait le plus de dommages à la végétation est le cerf de Virginie, en raison de sa taille plus petite et de sa préférence pour les plantes herbacées.
A large herbivore triggers alternative successional trajectories in the boreal forest
2013
Alternative successional trajectories (AST) may result in multiple climax states within an ecosystem when disturbances affect colonization history. In the boreal forest, ungulates have been proposed to drive AST because, under herbivore pressure, preferred species may go extinct and apparent competition may benefit browsing-resistant species. Over a 15-year period following logging, we tested whether deer herbivory altered plant species composition and whether the competitive advantage of resistant species was maintained following herbivore removal. We compared exclosures built immediately after logging with delayed exclosures built eight years later on Anticosti Island, Quebec, Canada. Although the palatable tree Betula papyrifera (paper birch) and some palatable herbs recovered in delayed exclosures, we observed legacies in both tree and herb cover. Woody regeneration in delayed exclosures was dominated by Picea glauca (white spruce), and Poaceae (grasses) were abundant in the field layer. Given that only early-successional species recovered, whereas latesuccessional broadleaf species and Abies balsamea (balsam fir) remained rare, succession may follow an AST after a limited browsing period during early succession.
Functional Responses and Resilience of Boreal Forest Ecosystem after Reduction of Deer Density
PLoS ONE, 2014
The functional trait-based approach is increasingly used to predict responses of ecological communities to disturbances, but most studies target a single taxonomic group. Here, we assessed the resilience of a forest ecosystem to an overabundant herbivore population by assessing changes in 19 functional traits for plant, 13 traits for ground beetle and 16 traits for songbird communities after six years of controlled browsing on Anticosti Island (Quebec, Canada). Our results indicated that plants were more responsive to 6 years of reduced browsing pressure than ground beetles and songbirds. However, co-inertia analysis revealed that ground beetle communities responded in a similar way than plant communities with stronger relationships between plant and ground beetle traits at reduced deer density, a pattern not detected between plant and songbird. High deer density favored plants species that reproduce vegetatively and with abiotic pollination and seed dispersal, traits implying little interaction with animal. On the other hand, traits found at reduced deer density mostly involved trophic interaction. For example, plants in this treatment had fleshy fruits and large seeds dispersed by birds or other animals whereas ground beetle species were carnivorous. Overall, our results suggest that plant communities recovered some functional components to overabundant herbivore populations, since most traits associated with undisturbed forests were reestablished after six years of deer reduction. The re-establishment of functional plant communities with traits involving trophic interaction induces changes in the ground-beetle trait community, but forest structure remains likely insufficiently heterogeneous to shift the songbird trait community within six years.
Ecoscience, 2013
During the twentieth century, populations of several deer species (Cervidae) increased dramatically in temperate and boreal forests worldwide, leading to major changes in forest plant and animal communities. The effect of deer overabundance on understory vegetation has been documented repeatedly. In situations of severe browsing pressure, even the least palatable vascular plants were negatively affected. However, deer impact on bryophytes has been greatly under-investigated despite their key role in ecosystem functioning and their high conservation profile. Taking advantage of a unique situation involving adjacent islands with and without deer that resulted from the introduction of black-tailed deer (Odocoileus hemionus) to the Haida Gwaii archipelago (British Columbia, Canada) we explored the response of the bryophyte community to unregulated browsing. We compared species density, cover, and diversity between small islands never colonized by deer and small islands with prolonged deer presence. We took a novel approach that combined direct observations of deer foraging with sampling of their impact on the vegetation. We show that even in situations of severe browsing pressure deer totally avoided bryophytes. Contrary to what is observed for vascular plants (even for tolerant species such as graminoids), species density, cover, and diversity of bryophytes were higher on the islands with deer. We attribute this pattern of higher bryophyte prevalence to reduced competition with vascular plants, especially for light.
Six years of plant community development after clearcut harvesting in western Washington
Canadian Journal of Forest Research, 2009
What roles do ruderals and residuals play in early forest succession and how does repeated disturbance affect them? We examined this question by monitoring plant cover and composition on a productive site for 6 years after clearcutting and planting Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). The replicated experiment included three treatments: vegetation control with five annual herbicide applications superimposed over two levels of slash removal (bole only or total tree plus most other wood) and an untreated control. Three species groups were analyzed: native forest, native ruderals, and exotic ruderals. Without vegetation control, the understory was rapidly invaded by exotic ruderals but was codominated by native and exotic ruderals by year 6. Douglas-fir cover surpassed covers in the three species group covers at least 3 years sooner with herbicide treatments than without. Species richness and coverage were lower for all species groups with vegetation control than without vegetation control. The effects of organic matter removal were much less than that of vegetation control. As predicted by the Intermediate Disturbance Hypothesis, repeated vegetation control resulted in declining cover and richness; however, native forest species were surprisingly resilient, maintaining as much or more cover and richness as the ruderal groups.
Canadian Journal of Zoology, 2005
Selective browsing by cervids has persistent impacts on forest ecosystems. On Anticosti Island, Quebec, Canada, introduced white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) have caused massive changes to the native boreal forest. Despite the apparent stability of the deer population over recent decades, we suspected that they were not at equilibrium with their browse supply and that further degradation of the habitat had occurred. A comparison of two browse surveys conducted 25 years apart showed a strong decline in browse availability. Although balsam fir (Abies balsamea (L.) P. Mill.) remained the most available browse species, it declined or disappeared from most stands (n = 13). Preferred deciduous species that were still available 25 years ago have almost disappeared. The continuous decline of the browse supply confirmed our hypothesis. This situation may be exacerbated by a subsidy from the winter litterfall, a significant and stable alternative food source. The abundance of litterfall from mature trees is independent of browsing over a long time period, which introduces a temporal uncoupling between the impact of deer browsing on balsam fir seedlings and the negative feedback from recruitment failure of mature balsam fir on the deer population. This means that the system is susceptible to being forced into an alternative regime.
Increased Herbivory in Forest Isolates: Implications for Plant Community Structure and Composition
Conservation Biology, 2001
Abstract: Understanding processes driving population declines and, ultimately, species loss in forest isolates has significant implications for the long-term maintenance of species diversity. We investigated a potential mechanism driving loss of plant species in small, medium, and large land-bridge islands in Lago Guri, a 4300-km2 hydroelectric impoundment in the State of Bolivar, Venezuela. Our hypothesis was that elevated Atta ( leaf-cutter ants) herbivory on small Guri islands, attributable to release from predation, could result in reduced sapling densities, with potentially negative effects on preferred plant species. We experimentally established Atta preferences among 43 common tree species. Vegetation plots on small, medium, and large land masses were examined for variation in density, size-class distribution, and representation of preferred and less preferred species of small stems. Densities of adult trees of preferred and less preferred species were compared between Atta colony foraging zones and control plots without active Atta colonies, and between foraging zones on the small islands and the large island. Small stem densities were significantly reduced on the small islands, especially in the sapling category (≥1 m tall, <1 cm dbh). On medium and large land masses, preferred species were underrepresented in both sapling (≥1 m tall, <1 cm dbh) and juvenile (≥1 cm dbh, <10 cm dbh) size classes. On small islands, however, both preferred and less preferred species showed reduced representation in the sapling size class. Adults of preferred species were significantly reduced within Atta foraging zones compared with control plots without Atta colonies. Small stem densities were independent of adult tree densities for preferred species on small islands and for both preferred and less preferred species on large land masses. High levels of Atta herbivory could be a potentially important cause of reduced plant recruitment on small Guri islands. Our findings contribute to understanding of the role of altered ecological interactions as deterministic mechanisms driving a process of change in the structure and composition of fragmented communities.Resumen: El entendimiento de los procesos que intervienen en la declinación de poblaciones y, finalmente, la pérdida de especies en fragmentos aislados de bosque tiene implicaciones significativas en el mantenimiento a lo largo de especies. Investigamos un mecanismo potencial de la pérdida de especies vegetales en islas pequeñas, medianas y grandes en el Lago Guri, una presa hidroeléctrica de 4300 km 2 en el estado de Bolívar, Venezuela. Nuestra hipótesis fue que alta herbivoría de Atta ( hormigas arrieras) en islas pequeñas atribuible a la ausencia de depredación podría resultar en bajas densidades de renuevos con efectos potencialmente negativos en las especies preferidas. Experimentalmente establecimos las preferencias de Atta entre 43 especies de árboles comunes. Se examinaron parcelas de vegetación pequeñas, medianas y grandes para ver la variación en la densidad, distribución de clases de tamaño y la representación de especies preferidas y menos preferidas. Comparamos las densidades de árboles adultos de las especies preferidas y menos preferidas en zonas con forrajeo de Atta y en parcelas control (sin colonias activas de Atta) y entre zonas de forrajeo en islas pequeñas y en la isla grande. Las densidades de plántulas fueron significativamente bajas en las islas pequeñas, especialmente en la categoría ≥1 m de altura y <1 cm dap. En parcelas medianas y grandes, las especies preferidas estaban poco representadas en las clases renuevo (≥1 m de altura <1 cm dap) y juvenil (≥1 cm DAP <10 cm dap). Sin embargo en islas pequeñas, tanto las especies preferidas como las no preferidas mostraron baja representación en la clase renuevo. Adultos de las especies preferidas estaban significativamente reducidos dentro de las zonas de forrajeo en comparación con las parcelas control (sin colonias de Atta). Las densidades de renuevos fueron independientes de las densidades de árboles adultos de especies preferidas en islas pequeñas y para especies preferidas y menos preferidas en islas grandes. Niveles altos de herbivoría de Atta pudieran ser un importante factor potencial de reducción del reclutamiento en islas pequeñas de Guri. Nuestros hallazgos contribuyen al entendimiento del papel de interacciones ecológicas alteradas como mecanismos determinísticos que dirigen un proceso de cambio en la estructura y la composición de comunidades fragmentadas.Resumen: El entendimiento de los procesos que intervienen en la declinación de poblaciones y, finalmente, la pérdida de especies en fragmentos aislados de bosque tiene implicaciones significativas en el mantenimiento a lo largo de especies. Investigamos un mecanismo potencial de la pérdida de especies vegetales en islas pequeñas, medianas y grandes en el Lago Guri, una presa hidroeléctrica de 4300 km 2 en el estado de Bolívar, Venezuela. Nuestra hipótesis fue que alta herbivoría de Atta ( hormigas arrieras) en islas pequeñas atribuible a la ausencia de depredación podría resultar en bajas densidades de renuevos con efectos potencialmente negativos en las especies preferidas. Experimentalmente establecimos las preferencias de Atta entre 43 especies de árboles comunes. Se examinaron parcelas de vegetación pequeñas, medianas y grandes para ver la variación en la densidad, distribución de clases de tamaño y la representación de especies preferidas y menos preferidas. Comparamos las densidades de árboles adultos de las especies preferidas y menos preferidas en zonas con forrajeo de Atta y en parcelas control (sin colonias activas de Atta) y entre zonas de forrajeo en islas pequeñas y en la isla grande. Las densidades de plántulas fueron significativamente bajas en las islas pequeñas, especialmente en la categoría ≥1 m de altura y <1 cm dap. En parcelas medianas y grandes, las especies preferidas estaban poco representadas en las clases renuevo (≥1 m de altura <1 cm dap) y juvenil (≥1 cm DAP <10 cm dap). Sin embargo en islas pequeñas, tanto las especies preferidas como las no preferidas mostraron baja representación en la clase renuevo. Adultos de las especies preferidas estaban significativamente reducidos dentro de las zonas de forrajeo en comparación con las parcelas control (sin colonias de Atta). Las densidades de renuevos fueron independientes de las densidades de árboles adultos de especies preferidas en islas pequeñas y para especies preferidas y menos preferidas en islas grandes. Niveles altos de herbivoría de Atta pudieran ser un importante factor potencial de reducción del reclutamiento en islas pequeñas de Guri. Nuestros hallazgos contribuyen al entendimiento del papel de interacciones ecológicas alteradas como mecanismos determinísticos que dirigen un proceso de cambio en la estructura y la composición de comunidades fragmentadas.