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

QQ

QPvQ

QQ

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