PASTURE, TILLAGE AND CANOPY EFFECTS ON CARBON DIOXIDE FLUXES IN A
SPANISH DEHESA
Uribe, C.a, Hernando, L.b, Román, M.c, Clavero, M.A.a, S. Roig b, Van Miegroet, H.c, Inclán, R.a
aDepartamento
de Medio Ambiente, CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain
Silvopascicultura, Universidad Politécnica, Madrid, Spain
cDept.of Wildland Resources, Utah State Univ. Logan, UT 84322-5230
bDepartamento
1. Introduction
One of the more recent areas of interest in agroforestry system studies concerns the C
sequestering capacity, especially under the afforestation and reforestation activities approved in
the Kyoto Protocol as mitigating strategies for climate change. Agroforestry systems are believed
to have a higher potential for sequestering C than pastures or field crops (Sanchez 2000;
Ramachandran Nair et al. 2009). The use of appropriate silvopastoral practices in dehesa systems
may contribute to their sustainability, by improving soil quality and soil productivity while reducing
the CO2 flux from the soil to the atmosphere.
The objectives of this study were (1) to quantify the effects of pasture and tillage practices on soil
respiration (Rs); (2) to determine the influence of management practices on soil carbon (C) and
nitrogen (N) stocks and the response of Rs to soil microclimatic conditions, and (3) to determine
the influence of tree canopy (Quercus ilex specie) on Rs, soil C and N stocks in a dehesa
ecosystem situated in central Spain (Toledo).
2. Material and methods
Four different treatments were established: non grazed-non tilled (NGNT); non grazed-tilled (NGT);
grazed-non tilled (GNT); grazed and tilled (GT). Rs, soil temperature (Ts), soil moisture (Ms), soil C
and N stocks were measured in all treatments. Rs were conducted from July 2008 to February
2010 at nine different moments using a closed dynamics system LI-6400 coupled to an LI-6400-9
soil chamber (LI-COR inc., Lincoln, NE, USA). Soil samples were taken at the Rs measurement
locations at the end of the experiment. The soil C and N concentration was determined using a
LECO TruSpec CHN elemental analyzer (LECO Corp., St. Joseph, USA).
3. Results and Discussion
Grazing reduced Rs by 26%, 48%, and 22% on three occasions in the course of the experiment.
However, increases of 6 Mg/ha in C stocks and 0.6 Mg/ha in N stocks were measured in grazed
soils. No clear effects of tilling either on soil respiration, soil C or N stocks were detected. Small
changes in surface soil temperature and water content following management operations were
found to influence the response of Rs. Tree canopy induced increases in soil respiration, soil C and
N stocks; and decreases in Ts were observed. The influence of tree canopy on annual Rs carbon
losses decreased by 4 % at grazed sites compared to non- grazed sites.
Grazing and tree canopy had an important influence on the storage ability for soil C and N stocks
in this study, while traditional tilling was not found to have a negative effect on soil C storage
capacity. Maintaining the management practices currently applied in this area is potentially
beneficial to C sequestration, especially in Mediterranean dehesa soils.
4. Conclusions
The results of this study indicate that grazing and tilling had a slight, albeit variable effect on Rs
and soil microclimate during the study period, and that the effect of grazing and tilling on the Rs
sensitivity to Ts and Ms depends on the climatic period considered. Tree canopy cover influenced
soil microclimate, Rs and soil C and N stocks, highlighting the importance of conserving woodland
and forestation in order to maintain the sustainability of dehesa systems and enhance their C
sequestration potential. Future research should be aimed towards improving our understanding of
C exchange with the atmosphere in agroforestry systems in order to better predict the influence of
agroforestry management on the potential C sequestration capacity of dehesa ecosystems.
Acknowledgments
This research was conducted in the framework of the Spanish SUM2006-00034; CGL2006-02922
and CGL2009-07031. The authors would like to express their gratitude to the agricultural research
center team “Dehesón del encinar” and especially Celia López Carrasco for her support. We also
appreciate the assistance of Dr. Agustín Rubio and Dr. Eugenio Diaz-Pines.
References
Ramachandran Nair P K, Mohan Kumar B and Nair V D (2009) Agroforestry as a strategy for
carbon sequestration. Journal of Plant Nutrition and Soil Science 172, 10-23.
Sanchez P A (2000) Linking climate change research with food security and poverty reduction in
the tropics. Agriculture, Ecosystems & Environment 82, 371-383.