Coupling deer and forest models in capsis: why and how?

Tanguy DaufresneINRA ToulouseLaboratoire de Comportement et Ecologie de la Faune Sauvage(Behaviour and Ecology of Wildlife)

Roe deer Capreolus capreolusmedium size ungulate (20-30 kg)Low sexual dimorphismgeneralist selective browser Territorial

Red deer Cervus elaphusLarge size ungulate (80-300kg)High sexual dimorphismGeneralist selective browser/grazerSocial

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

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

seedling small sapling large sapling

deer

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+ +

-Predictions are model and site specificex: 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

seedling small sapling large sapling

undersory

lightnutrient

(After Rooney and Waller 2003)

Tax

on a

b un d

ance

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.