Ecosystem services, the benefits that people obtain from ecosystems, are a powerful lens through which to understand human relationships with the environment and to design environmental policy. The explicit inclusion of beneficiaries makes values intrinsic to ecosystem services; whether or not those values are monetized, the ecosystem services framework provides a way to assess trade-offs among alternative scenarios of resource use and land- and seascape change. We provide an overview of the ecosystem functions responsible for producing terrestrial hydrologic services and use this context to lay out a blueprint for a more general ecosystem service assessment. Other ecosystem services are addressed in our discussion of scale and trade-offs. We review valuation and policy tools useful for ecosystem service protection and provide several examples of land management using these tools. Throughout, we highlight avenues for research to advance the ecosystem services framework as an operational basis for policy d...

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The Nature and Value of Ecosystem Services: An Overview Highlighting Hydrologic Services

Global synthesis of the findings from ∼140 recharge study areas in semiarid and arid regions provides important information on recharge rates, controls, and processes, which are critical for sustainable water development. Water resource evaluation, dryland salinity assessment (Australia), and radioactive waste disposal (US) are among the primary goals of many of these recharge studies. The chloride mass balance (CMB) technique is widely used to estimate recharge. Average recharge rates estimated over large areas (40–374 000 km2) range from 0·2 to 35 mm year−1, representing 0·1–5% of long-term average annual precipitation. Extreme local variability in recharge, with rates up to ∼720 m year−1, results from focussed recharge beneath ephemeral streams and lakes and preferential flow mostly in fractured systems. System response to climate variability and land use/land cover (LU/LC) changes is archived in unsaturated zone tracer profiles and in groundwater level fluctuations. Inter-annual climate variability related to El Nino Southern Oscillation (ENSO) results in up to three times higher recharge in regions within the SW US during periods of frequent El Ninos (1977–1998) relative to periods dominated by La Ninas (1941–1957). Enhanced recharge related to ENSO is also documented in Argentina. Climate variability at decadal to century scales recorded in chloride profiles in Africa results in recharge rates of 30 mm year−1 during the Sahel drought (1970–1986) to 150 mm year−1 during non-drought periods. Variations in climate at millennial scales in the SW US changed systems from recharge during the Pleistocene glacial period (≥10 000 years ago) to discharge during the Holocene semiarid period. LU/LC changes such as deforestation in Australia increased recharge up to about 2 orders of magnitude. Changes from natural grassland and shrublands to dryland (rain-fed) agriculture altered systems from discharge (evapotranspiration, ET) to recharge in the SW US. The impact of LU change was much greater than climate variability in Niger (Africa), where replacement of savanna by crops increased recharge by about an order of magnitude even during severe droughts. Sensitivity of recharge to LU/LC changes suggests that recharge may be controlled through management of LU. In irrigated areas, recharge varies from 10 to 485 mm year−1, representing 1–25% of irrigation plus precipitation. However, irrigation pumpage in groundwater-fed irrigated areas greatly exceeds recharge rates, resulting in groundwater mining. Increased recharge related to cultivation has mobilized salts that accumulated in the unsaturated zone over millennia, resulting in widespread groundwater and surface water contamination, particularly in Australia. The synthesis of recharge rates provided in this study contains valuable information for developing sustainable groundwater resource programmes within the context of climate variability and LU/LC change. Copyright © 2006 John Wiley & Sons, Ltd.

Global synthesis of groundwater recharge in semiarid and arid regions

Carbon sequestration programs, including afforestation and reforestation, are gaining attention globally and will alter many ecosystem processes, including water yield Some previous analyses have addressed deforestation and water yield, while the effects of afforestation on water yield have been considered for some regions However, to our knowledge no systematic global analysis of the effects of afforestation on water yield has been undertaken To assess and predict these effects globally, we analyzed 26 catchment data sets with 504 observations, including annual runoff and low flow We examined changes in the context of several variables, including original vegetation type, plantation species, plantation age, and mean annual precipitation (MAP) All of these variables should be useful for understanding and modeling the effects of afforestation on water yield We found that annual runoff was reduced on average by 44% (±3%) and 31% (±2%) when grasslands and shrublands were afforested, respectively Eucalypts had a larger impact than other tree species in afforested grasslands (P=0002), reducing runoff (90) by 75% (±10%), compared with a 40% (±3%) average decrease with pines Runoff losses increased significantly with plantation age for at least 20 years after planting, whether expressed as absolute changes (mm) or as a proportion of predicted runoff (%) (P<0001) For grasslands, absolute reductions in annual runoff were greatest at wetter sites, but proportional reductions were significantly larger in drier sites (P<001 and P<0001, respectively) Afforestation effects on low flow were similar to those on total annual flow, but proportional reductions were even larger for low flow (P<0001) These results clearly demonstrate that reductions in runoff can be expected following afforestation of grasslands and shrublands and may be most severe in drier regions Our results suggest that, in a region where natural runoff is less than 10% of MAP, afforestation should result in a complete loss of runoff; where natural runoff is 30% of precipitation, it will likely be cut by half or more when trees are planted The possibility that afforestation could cause or intensify water shortages in many locations is a tradeoff that should be explicitly addressed in carbon sequestration programs

Effects of afforestation on water yield: a global synthesis with implications for policy

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Mediterranean water resources in a global change scenario

Weighing lysimeters, large-tree potometers, ventilated chambers, radioisotopes, stable isotopes and an array of heat balance/heat dissipation methods have been used to provide quantitative estimates of whole-tree water use. A survey of 52 studies conducted since 1970 indicated that rates of water use ranged from 10 kg day(-1) for trees in a 32-year-old plantation of Quercus petraea L. ex Liebl. in eastern France to 1,180 kg day(-1) for an overstory Euperua purpurea Bth. tree growing in the Amazonian rainforest. The studies included in this survey reported whole-tree estimates of water use for 67 species in over 35 genera. Almost 90% of the observations indicated maximum rates of daily water use between 10 and 200 kg day(-1) for trees that averaged 21 m in height. The thermal techniques that made many of these estimates possible have gained widespread acceptance, and energy-balance, heat dissipation and heat-pulse systems are now routinely used with leaf-level measurements to investigate the relative importance of stomatal and boundary layer conductances in controlling canopy transpiration, whole-tree hydraulic conductance, coordinated control of whole-plant water transport, movement of water to and from sapwood storage, and whole-plant vulnerability of water transport to xylem cavitation. Techniques for estimating whole-tree water use complement existing approaches to calculating catchment water balance and provide the forest hydrologist with another tool for managing water resources. Energy-balance, heat dissipation and heat-pulse methods can be used to compare transpiration in different parts of a watershed or between adjacent trees, or to assess the contribution of transpiration from overstory and understory trees. Such studies often require that rates of water use be extrapolated from individual trees to that of stands and plantations. The ultimate success of this extrapolation depends in part on whether data covering short time sequences can be applied to longer periods of time. We conclude that techniques for estimating whole-tree water use have provided valuable tools for conducting basic and applied research. Future studies that emphasize the use of these techniques by both tree physiologists and forest hydrologists should be encouraged.

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A review of whole-plant water use studies in tree.

The impact of land use change on water resources in sub-Saharan Africa: a modelling study of Lake Malawi

The modification of the drop size spectra of natural and simulated rainfall by the canopies of three tropical plantation tree species was measured using a disdrometer. Contrary to previously published results, large differences were found between species in the degrees of modification. The median-volume drop diameters measured were 2.3, 2.8, and 4,2 mm for Pinus caribaea, Eucalyptus camaldulensis, and Tectona grandis, respectively. The characteristic drip spectra for the different species are equivalent to the corresponding drop size spectra for rainfall with approximate intensities of 50, 100, and 3000 mm h−1 (essentially infinite) for P. caribaea, E. camaldulensis, and T. grandis, respectively. These results have implications for the choice of the best tree species for areas susceptible to soil erosion.

Drop size modification by forest canopies: Measurements using a disdrometer

Transpiration from coppiced poplar and willow measured using sap-flow methods

Part 1 Social, economic and scientific background: developmental forestry in Kamataka - an overview, S. Parameswarappa land use policy and forests, S. Shyam Sunder eucalypts in industrial and social plantations in Karnataka, P.J. Dilip Kumar social or industrial forestry - an NGO's views, D.R. Prafulla Chandra and D.P. Savi Sachi social implications of Eucalyptus propagation, G.N.N. Prasad and S.R. Ramaswamy social or industrial forestry, N.S. Adkoli. Part 2 Forest growth: research strategy for monitoring tree growth and site change, P.G. Adlard observed growth patterns of euclayps in Karnataka, P.G. Adlard fast growing species and sustainability, A.N. Yellappa Reddy and G.V. Sugur the influence of site factors on eucalypt growth in Karnataka, S.J. Dury and B.E. Manjunath spacing at planting of short-rotation Eucalyptus in Karnantaka, P.G. Adlard, et al results from intercropping fast-growing trees and food crops at Morogorro, Tanzania, J.F. Redhead growth and spacing in eucalypts - a case study from Punjab, S.K. Kapur and A.S. Dogra organic productivity, nutrient cycling and small watershed hydrology of natural forests and monoculture plantations in Chikmagalur District, H. Ramachandra Swamy application of root bioassays to detect nutrient deficiencies in fast-growing trees and agoforestry crops, A.F. Harrison, et al. Part 3 Water use of eucalypts - a review, I.R. Calder development of the deuterium tracing method for estimation of transpiration rates of trees, I.R. Calder measurements of transpiration from Ecalyptus plantation, India, using deuterium tracing, I.R. Calder, et al heat pulse observations of eucalptus grandis transpiration in South Africa, P.J. Dye and B.W. Olbrich physiological studies in young eucalyptus stands in southern India and their use in estimating forest transpiration, J.M. Roberts, et al the soil moisture regimes beneath forest and an agricultural crop, R.J. Harding, et al measurements and modelling of interception loss from eucalyptus plantation in sothern India, R.L. Hall water use of eucalypts in Kerala, J. Kallarackal. Part 4 Growth and water use: water use by eucalypts, measurement and implications for Australia and India, E.A.N. Greenwood a water use and growth model for eucalyptus plantation in water limited conditions, I.R. Calder comparative growth rates of eucalyptus in native forest and plantation monoculture, C.L. Beadle and C.R.A. Turnbull modification of climate by forests, R.J. Harding water use of agroforestry systems in semi-arid India, C.K. Ong, et al comparative studies of the associated soil moisture regimes and productivity of different agroforestry systems, V. Bhaskar, et al.

Growth and water use of forest plantations

Dependence of rainfall interception on drop size: 2. Experimental determination of the wetting functions and two-layer stochastic model parameters for five tropical tree species

Robin L. Hall

Papers

The impact of land use change on water resources in sub-Saharan Africa: a modelling study of Lake Malawi

Drop size modification by forest canopies: Measurements using a disdrometer

Transpiration from coppiced poplar and willow measured using sap-flow methods

Growth and water use of forest plantations

Dependence of rainfall interception on drop size: 2. Experimental determination of the wetting functions and two-layer stochastic model parameters for five tropical tree species