A spatialized assessment of ecosystem service relationships in a multifunctional agroforestry landscape of Senegal.

Agroforestry systems are an integral part of Sub-Saharan agricultural landscapes. Studies conducted at tree or plot scales on the supply of ecosystem services (ES) suggest that agroforestry practices are a promising way to build multifunctional agricultural landscapes. However, the current characterization and understanding of how multiple ES are associated across such heterogeneous agricultural landscapes are still limited. This study provides the first characterization of the multiple ESs supplied by a Sahelian Faidherbia albida agroforestry parkland and their relationships. Relying on field data for 11 ES indicators, recent advances in remote sensing-derived information, and blending different ES mapping approaches, we first assessed the spatial heterogeneity of the supply of each ES. We found that the majority of ES indicators remained below ES potential values over the study area by 25 % to 50 %, revealing that there is a considerable scope for increasing the ES supply in the F. albida parkland. Then, using a scoring approach, we analyzed the supply of multiple ESs. We observed a large number of hotspots and a clear effect of the proximity of F. albida trees fostering the supply of multiple ESs in their vicinity. Finally, we mapped and analyzed the dominant relationships - trade-offs, synergies or losses - between ESs from a cooccurrence spatial approach. We showed that significant trade-offs and losses (58 % of the area) between ESs can exist in the F. albida parkland. Interestingly, we also showed that synergies occurred mainly up to 10 m from the F. albida trees, suggesting that synergies need to be increased beyond this threshold. By adopting an original ES valuation framework, we provided basic insights into ESs and their relationships. The different maps and information generated can support public debates and target new policies fostering the multifunctionality of F. albida parklands as well as in various other parklands of West Africa.

Soil respiration at mean annual temperature predicts annual total across vegetation types and biomes.

Soil respiration (SR) constitutes the largest flux of CO(2) from terrestrial ecosystems to the atmosphere. However, there still exist considerable uncertainties as to its actual magnitude, as well as its spatial and interannual variability. Based on a reanalysis and synthesis of 80 site-years for 57 forests, plantations, savannas, shrublands and grasslands from boreal to tropical climates we present evidence that total annual SR is closely related to SR at mean annual soil temperature (SR(MAT)), irrespective of the type of ecosystem and biome. This is theoretically expected for non water-limited ecosystems within most of the globally occurring range of annual temperature variability and sensitivity (Q(10)). We further show that for seasonally dry sites where annual precipitation (P) is lower than potential evapotranspiration (PET), annual SR can be predicted from wet season SR(MAT) corrected for a factor related to P/PET. Our finding indicates that it can be sufficient to measure SR(MAT) for obtaining a well constrained estimate of its annual total. This should substantially increase our capacity for assessing the spatial distribution of soil CO(2) emissions across ecosystems, landscapes and regions, and thereby contribute to improving the spatial resolution of a major component of the global carbon cycle.

Fruit development, not GPP, drives seasonal variation in NPP in a tropical palm plantation.

We monitored seasonal variations in net primary production (NPP), estimated by allometric equations from organ dimensions, gross primary production (GPP), estimated by the eddy covariance method, autotrophic respiration (R(a)), estimated by a model, and fruit production in a coconut (Cocos nucifera L.) plantation located in the sub-tropical South Pacific archipelago of Vanuatu. Net primary production of the vegetative compartments of the trees accumulated steadily throughout the year. Fruits accounted for 46% of tree NPP and showed large seasonal variations. On an annual basis, the sum of estimated NPP (16.1 Mg C ha(-1) year(-1)) and R(a) (24.0 Mg C ha(-1) year(-1)) for the ecosystem (coconut trees and herbaceous understory) closely matched GPP (39.0 Mg C ha(-1) year(-1)), suggesting adequate cross-validation of annual C budget methods. However, seasonal variations in NPP + R(a) were smaller than the seasonal variations in GPP, and maximum tree NPP occurred 6 months after the midsummer peak in GPP and solar radiation. We propose that this discrepancy reflects seasonal variation in the allocation of dry mass to carbon reserves and new plant tissue, thus affecting the allometric relationships used for estimating NPP.

Whole-plant adjustments in coconut (Cocos nucifera) in response to sink-source imbalance.

Coconut (Cocos nucifera L.) is a perennial tropical monocotyledon that produces fruit continuously. The physiological function of the large amounts of sucrose stored in coconut stems is unknown. To test the hypothesis that reserve storage and mobilization enable the crop to adjust to variable sink-source relationships at the scale of the whole plant, we investigated the dynamics of dry matter production, yield and yield components, and concentrations of nonstructural carbohydrate reserves in a coconut plantation on Vanuatu Island in the South Pacific. Two treatments were implemented continuously over 29 months (April 2002 to August 2004): 50% leaf pruning (to reduce the source) and 100% fruit and inflorescence pruning (to reduce the sink). The pruning treatments had little effect on carbohydrate reserves because they affected only petioles, not the main reserve pool in the stem. Both pruning treatments greatly reduced dry matter production of the reproductive compartment, but vegetative growth and development were negligibly affected by treatment and season. Leaf pruning increased radiation-use efficiency (RUE) initially, and fruit pruning greatly reduced RUE throughout the experiment. Changes in RUE were negatively correlated with leaflet soluble sugar concentration, indicating feedback inhibition of photosynthesis. We conclude that vegetative development and growth of coconut show little phenotypic plasticity, assimilate demand for growth being largely independent of a fluctuating assimilate supply. The resulting sink-source imbalances were partly compensated for by transitory reserves and, more importantly, by variable RUE in the short term, and by adjustment of fruit load in the long term. Possible physiological mechanisms are discussed, as well as modeling concepts that may be applied to coconut and similar tree crops.