Coupling deer and forest models in capsis: why and how? Tanguy Daufresne INRA Toulouse Laboratoire de Comportement et Ecologie de la Faune Sauvage (Behaviour and Ecology of Wildlife)

Roe deer Capreolus capreolus medium size ungulate (20-30 kg) Low sexual dimorphism generalist selective browser Territorial Red deer Cervus elaphus Large size ungulate (80-300kg) High sexual dimorphism Generalist selective browser/grazer Social

In France overall deer populations (both roe and red) have dramatically increased over the past three decades, due to local density increases and re-colonization. Data are from ONCFS

In 2000 red deer were present on 39 % of the woody areas in continental France (+Corsica). and 50 % of the total red deer population occupied 10 % of the wooded areas. Data are from ONCFS

Deer effects on forest dynamics (Rooney et al. 2003): Direct effects by selective browsing: -understory density and diversity -tree regeneration Indirect effects: -mediation of plant-herbivore interactions -mediation of plant-plant interactions -altered nutrient recycling Forest effects on Deer dynamics: Habitat quality: -transfert of soil fertility to foliage quality -understory density -hedge effect

Impact of black-tailed deer (Odocoileus hemionus) on forest understory in Western British Columbia (Stockton et al 2005) Species richness Biomass density

Impact of black-tailed deer (Odocoileus hemionus) on population structure of an understory shrub, the red huckelberry (Vaccinium parvifolium) in Western British Columbia (Vila et al 2004)

-Deer browsing affects community dynamics of vegetarian insects by reducing host plant densities (Baines et al. 1994). -Deer affect patterns of dominant species in understory and canopy through selective browsing (Rooney and Waller 1994). Indirect effects of deer on vegetation -Deer affect nutrient status of saplings through differential recycling of nitrogen versus phosphorus (Carline et al. 2005), and nutrient transfer from cultivated land to woodland (Seagle 2003).

Feed-back effects of forest structure on deer population dynamics -Reduction of understory biomass due to change in fire regime entailed decline of mule deer in Oregon (Peek et al. 2001). -Soil fertility influences foliage quality, hence body size in roe deer (Petorelli et al. 2001).

Impact of red and roe deer on forest succession in Europe -Gap models with a negative “deer effect” on recruitment seedlingsmall saplinglarge sapling deer Predictions are model and site specific ex: Pine land evolving towards birch-oak stand (Jorritsma et al. 1999) -roe deer eliminate the oak and succession tends to pure birch stand -red deer tends to slow down the succession process and promote pineland over birch-oak forest Spruce evolving towards pine stand (Kienast et al. 1999) -ungulate does not affect succession pattern but affects forest structure by accelerating the maturation cycle and reducing the density of trees.

Caveats : -Models do not detail enough the early stages of the life cycle of trees -Indirect effects of deer on trees are ignored -Feed-backs of forest structure on deer population dynamics are ignored

deer seedlingsmall saplinglarge sapling undersory light nutrient (After Rooney and Waller 2003) Taxon abundance deer density

Perspectives 1- Theoretical “toy models”: - mediation tree-understory: deer population + understory +one species of canopy tree -stoichiometric model of N and P: soil nutrient+ deer population+understory 2- introducing “deer effects” (including indirect effects) in forest models. 3- creating a deer population model in capsis.