From deer abundance to soil properties : a case study in the forests of Haida Gwaii

The past century witnessed a dramatic increase in deer abundance in North America and Western Europe. Deer overabundance prevented temperate forest regeneration, dramatically reduced their understory vegetation cover and composition, with negative consequences for other trophic layers such as birds and insects. While impacts of abundant deer aboveground have been well documented, effects on the soil of temperate forests remain unclear. Deer interact with the soil through waste deposition, trampling, and reduction of litter quantity and quality through selective foraging. The multiplicity of these pathways makes it difficult to predict the net effect deer will have on soil communities and processes. As a result, current studies in temperate forests have found inconsistent results within, and across, systems. In an attempt to resolve these inconsistencies, we used the unique configuration of the Canadian archipelago of Haida Gwaii which offers a quasi-experimental situation with the presence of islands without and with deer, the latter varying in deer colonisation history. This unique context is complemented by the knowledge gathered in the course of 30 years of studies on the effect of abundant deer aboveground. We measured the effect of deer presence on litter decomposition, soil properties, soil prokaryotic communities and nitrogen cycling rates. We compared three complementary study systems varying in time of deer presence and exclusion. We found that the response of the soil to deer presence was time dependant. Short-term and intermediate effects of deer belowground were the results of the direct interactions deer have with the soil, i.e. waste deposition and trampling. Long-term effects of deer belowground appeared to be the results of both direct interactions, due to trampling, and indirect interactions, due to vegetation shifts. Through the reduction in litter quality by selective browsing, long term deer presence significantly reduced the rate of carbon and nitrogen lost by litter during decomposition. Under long-term deer presence, soil prokaryotic community diversity decreased, and composition was shifted, by trampling. In the absence of deer it had a better ability in decomposing carbon. A preliminary analyse on the nitrogen cycle suggest no effect of deer on the kinetics of nitrogen rates in the forest floor.Forestry, Faculty ofGraduat

De l’abondance des cerfs aux propriétés du sol : Une étude de cas dans les forêts d’Haïda Gwaii

L’augmentation récente et spectaculaire de l'abondance des cerfs en Amérique du Nord et en Europe occidentale a entraîné de profonds changements dans la structure des forêts tempérées. Si ces changements sont aujourd'hui bien caractérisés, les effets de cette forte abondance sur le sol restent cependant mal compris. Les cerfs peuvent interagir avec le sol par le rejet de fèces et d’urine, le piétinement et la réduction de la quantité et de la qualité de la litière par le broutage préférentiel des plantes appétantes. Quelles sont les conséquences de ces interactions pour le sol ? Pour répondre à cette question, nous avons étudié la réponse des sols à la colonisation et à l'élimination du cerf de Sitka (Odocoileus hemionus sitkensis) dans les forêts d’Haïda Gwaii. Nous avons constaté que les cerfs ralentissaient la décomposition en réduisant la qualité de la litière. La structure de la communauté microbienne et sa capacité à décomposer le carbone était impactée par la compaction du sol dû au piétinement. Nous avons également constaté que les effets des cerfs à court et moyen termes n’avaient que peu ou pas d'effet sur le sol, remettant en question les conclusions des études actuelles basées sur de plus court terme.The past century witnessed a dramatic increase in deer abundance in North America and Western Europe that triggered profound changes in the structure of temperate forests. If these changes are today well characterised, the effects of abundant deer belowground in these forests remain unclear. Deer can interfere with the soil through waste deposition, trampling, and reduction of litter quantity and quality by preferential browsing of palatable plants. What are the consequences of these interactions for the soil? To answer this question, we studied the soil response to the colonisation and culling of Sitka black-tailed deer (Odocoileus hemionus sitkensis) in the forests of Haida Gwaii. We found that deer slowed-down litter decomposition by reducing litter quality. They also modified microbial community structure and ability in decomposing carbon via soil trampling. Most of these effects became only apparent in the long term, hence questioning the results obtained through short term studies

Deer exclusion unveils abiotic filtering in forest understory plant assemblages

International audienceBACKGROUND AND AIMS: The role of deer (family Cervidae) in ecosystem functioning has traditionally been neglected by forest ecologists due to the animal’s scarcity in most parts of the northern hemisphere. However, the dramatic rebound in deer populations throughout the 20 th century has brought deer browsing to the forefront of forest ecological questioning. Today there is ample evidence that deer affect tree regeneration, understory plant and animal diversity and even litter decomposition. However, the mechanisms underlying the effects of deer on forest ecosystems remain unclear. Among others, the relative role of abiotic factors versus biotic interactions (e.g. herbivory) in shaping plant assemblages remains largely unknown. METHODS: We used a large-scale experiment with exclosures distributed along abiotic gradients to understand the role of black-tailed deer (Odocoileus hemionus sitchensis) on forest understory on the Haida Gwaii archipelago (western Canada), a unique context where most of the key ecological effects of deer presence had already been intensively studied. KEY RESULTS: Our results demonstrate that 20 years of deer exclusion resulted in a clear increase in vascular plant richness, diversity and cover, and caused a decline in bryophyte cover. Exclusion also unveiled abiotic (i.e. soil water availability and fertility) filtering of plant assemblages that would otherwise have been masked by the impact of abundant deer populations. However, deer exclusion did not lead to an increase in beta diversity, probably because some remnant species had a competitive edge to regrow after decades of over-browsing. CONCLUSIONS: We demonstrated that long-term herbivory by deer can be a dominant factor structuring understory plant communities that overwhelms abiotic factors. However, while exclosures prove useful to assess overall effects of large herbivores, the results from our studies at broader scales on the archipelago, suggest that exclosure experiments should be used cautiously when inferring the mechanisms at work

Deer slow down litter decomposition by reducing litter quality in a temperate forest

International audienceLitter decomposition is a key process that allows the recycling of nutrients within ecosystems. In temperate forests the role of large herbivores in litter decomposition remains a subject of debate. To address this question, we used two litterbag experiments in a quasi-experimental situation resulting from the introduction of Sitka black-tailed deer Odocoileus hemionus sitkensis on forested islands of Haida Gwaii (Canada). We investigated the two main pathways by which deer could modify litter decomposition: change in litter quality and modification of decomposer communities. We found that deer presence significantly reduced litter mass loss after one year, mainly through a reduction in litter quality. This mass loss reflected a 30 and 28 % lower loss of carbon (C) and nitrogen (N), respectively. The presence of deer also reduced the ability of decomposers to breakdown carbon, but not nitrogen. Indeed, litter placed on an island with deer lost 5% less carbon after one year of decomposition than did litter decomposing on an island without deer. This loss in ability to decompose litter in presence of deer was outweighed by the differences in mass loss associated with the effect of deer on litter quality. Additional effects of feces deposition by deer on the decomposition process were also significant but minor. These results suggest that the effects continental-scale dramatic increases in deer populations may have on broad-scale patterns of C and N cycling deserve closer attention

Deer slow down litter decomposition by reducing litter quality in a temperate forest

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Deer slow down litter decomposition by reducing litter quality in a temperate forest

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Obstructive sleep apnea and malnutrition: a preliminary study

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High-throughput phenotyping : characterizing physiological and genetic determinants of key traits of the root system

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High-throughput phenotyping of key legumes (and others) root traits

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