Tanguy Daufresne INRA-CEFS (dept. of wildlife behavior and ecology)Toulouse, France
Biogeochemical signature of herbivores in terrestrial ecosystems
T. Daufresne and J. Merlet
US-France Young Engineering Scientists SymposiumWashington, DC, October 22-24, 2007
The interaction between deer and forest biogeochemistry
General research interests
Influence of biogeochemistry on deer physiologyConsequences for deer demography
Influence of deer on forest biogeochemistryConsequences for plant community dynamics
how chemical constraints influence strategies, interactions between species, and ecosystem functioning
(“Ecological stoichiometry”)
Research topic at CEFS
Biogeochemistry is critical for our understanding of ecosystem functioning (Odum 1969) and
community dynamics (Tilman 1982)
Herbivores can play a major role in biogeochemical cycles
Ungulates can accelerate N cycling in savana(e. g., McNaughton 1992)
N
litière
bactéries
CO2
CO2
plantes
Zooplankton regulate N vs P availability (e. g., Andersen 1997)
Nutrient ratios matter
The deer issue: a recent increase in ranges and densities
Europe North America
Capreolus Cervus Odoileus
Understory of Pacific rainforest (BC)browsed by black-tailed deer
Large-scale impact on biogeochemistry?
Major impacts on understory structure and biodiversity, tree regeneration
Red deer doe, Pyrénées, France
Virtually no forest in Europe and North america free from deer impact
Gardouch Field StationSub Mediterranean downy oak forest
clayish limestone soil (Daufresne et al., in prep)
Looking for patterns: an experimental approach
Creag Meagaidh Nature ReserveNorthern atlantic birch forest, Peaty soil
(Carline et al. 2005)
Sp
Fr
Ge
UK
It
00,050,1
0,150,2
0,250,3
0,350,4
Arum Euphorbia Ruscus Viburnum Quercus
**
* *
P
0
5
10
15
20
Arum Euphorbia Ruscus Viburnum Quercus
**
*
N:P
P N:P
Foliar N and P as a proxy for N and P availability
Deer decrease N to P ratio
0.01 0.02 0.03 0.04 0.05 0.06
0.1
0.2
0.3
0.4
0.5
0.6
0.01 0.02 0.03 0.04 0.05 0.06
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Deer density increases
foliar P
foliar N
As vegetation decreases due to browsing there is more available resource (N and P) for the remaining plants
0.01 0.02 0.03 0.04 0.05 0.06
0.2
0.4
0.6
rc= 0
rc= 0.9
rc= 1
Foliar N:P
- vegetation has less control over soil N
-more leaching of soil N
-decrease of total N
-foliar N increases less dramatically than foliar P, hence, foliar N/P decreases
) (
)1(
)1(
)()1(
BQPP
hrmrBQBNvNaIN
QPvQ
QNvQ
BhmQ
QB
PT
cLNNN
PN
mpP
NN
mNN
N
m
Looking for generic mechanisms:a minimalist
Deer-vegetation-soil model
vegetationbiomass
foliar N
foliar P
Soil N
Soil P
Deer density increases
00,050,1
0,150,2
0,250,3
0,350,4
Arum Euphorbia Ruscus Viburnum Quercus
0
5
10
15
20
Arum Euphorbia Ruscus Viburnum Quercus
The Renecofor Network ONF exclosures -deciduous -broadleaf evergreen -coniferous evergreen
Large scale
Pilot site (Gardouch, France)
Controlled deer density
N, P, … monitoring in plants
N,P, … in soil solution
N, P inputs monitoring
Inorg. / org. N in leachates
North America
?
Europe
Collaboration with soil scientists
Collaboration with forest ecologists and managers