Water for forest & people in the Mediterranean Region: a challenging balance

Transcription

1 Water for forest & people in the Mediterranean Region: a challenging balance

2 The water cycle links ecosystems and human societies Water: foundation for all biological life on Earth; equally fundamental for humans and nature Basic link between biosphere and atmosphere Med. Region: area with marked interactions between MaB Interactions & co-evolution between MaB over millenaries; over the last 150 years, contrasted evolutions in land use between the N & the S Water the main limiting factor for life; more constraints due to CC and demographic expansion The need for water: Blue and Green, but what trade-off?

3 In a scarcity context, understanding the interactions water x forest x society is crucial Med. Region is mountainous, with forests located in upper part of watershed, acting as water tower, and influencing water resources and ecosystems (incl. aquatic) downstream A complex issue, characterized by clichés and commonly accepted opinions; «no one size fits all» Hydrological patterns specific to the Mediterranean call for specific approaches; soil and water are linked Balancing water between man and nature trough socio-eco-hydrological approach, based on integrated water/ecosystem/land/territories management: a necessity, but on which background?

4 Water-related ecosystem processes & services Considering water in all processes underlying the functioning of Forest (& adjacent Ecos. and the supply of goods and services Support functions nutrients cycle soil formation primary production functional biodiversity Provision food fresh water wood & fibres fuel Regulation climate erosion peak flows & floods water purification Changing the paradigm of looking only at blue water Source : Millenium Ecosystem Assessment (2005) Cultural aspects aesthetical spiritual education recreation Athens, 12/05/

5 Climate change (temp. & rain) and water resources Projection of changes in runoff by based on 12 models Source: IPCC, AR4,

6 The need for a collective scientific expert review reconciling science s findings and public perception assembling available knowledge scattered among disciplines (forestry, hydrology, soil science, climatology, ecology, economics) proposing ways to cope with future challenges EFIMED initiative 40 authors Yves Birot, Carlos Gracia and Marc Palahi (editors)

7 A glance at the book Outline 1.Green & blue water: what trade-offs? 2.New approaches to assess the impact of land-use & forest management on waterrelated ecosystem services Supply of blue water to the Roman city of Nimes: the Gard Aqueduct 2000 years BP - Photo: C. Birot

8 Rainfall Rainfall mm mm Water use in a Mediterranean forest AET 504 mm AET 504 mm Up to 90 per cent of rainfall goes back to the atmosphere!. Throughfall 476 mm Runoff 28 mm Stemflow 50 mm Source: Gracia, 2011 Data from PRADES: Quercus ilex forest

9 A tree transpires 500 g H 2 O to fix 1 g of C Source: Gracia, g of C 500 g of H 2 O The tree respires and releases CO 2 ; to fix 1 g of C (net) in tissues (wood, etc.), 1-1,5 l. H 2 O are needed

10 Can canopy manipulation increase water yield? Study on 94 watersheds (Bosch, 1982) Source : Lavabre

11 Water foot print of wood (m 3 of water/m 3 of wood) depends on: a) Tree species b) Management options (P. sylvestris) Tree species Water footprint Tree species Water footprint Quercus ilex 2,842 Pinus halepensis 2,073 Quercus suber 2,981 Pinus pinea 1,642 Castanea sativa 675 Pinus pinaster 698 Pinus radiata 332 * * Source: Gracia, 2011 It is crucial to understand the responses of forests not just in terms of C and biomass, but in terms of water

12 New approaches to assess the impact of land-use & forest management on water-related ecosystem services Blue water and green water are needed to sustain the benefits from the ecosystem services that we need Source: Muys & Mavsar, 2011

13 Integrated water use Source: Maes et al, 2009 Integrated impact of land use & management on terrestrial and aquatic E.S. in a catchment is function of the actual E.Tr. Impact is minimal at the E.Tr. level of the potential natural vegetation and increases both sides reaching a maximum at complete soil denudation and at an increased transpiration level above the environmental water requirement of the aquatic ecosystem

14 Tools for integrated water use Improving the conservation of forest ecosystems as water providers, is possible through the payment by downstream users of clean water to upstream land users, and can allow internalizing what would otherwise be an externality Source: Croitoru & Young, 2011

15 The artificial lake of La Môle in a fully forested watershed dominated by cork oak, supplying water to the tourist town of Saint- Tropez, Var, France. Photo by C. Birot. The water company is paying annual fees to the local forest owners (public & private) for maintaining the fuel break network, and thus limiting the risk of wildfires, whose impact on dam siltation and water quality can be huge.

16 Take home messages The huge global flux of water vapour from terrestrial vegetation is a fundamental ecosystem service: Forests sustain the hydrological cycle through evapotranspiration, which cools climate through feedbacks with clouds and precipitation We should improve the understanding and modelling of the climatic responses incl. precipitation patterns, to land cover change In the Med., forests are mostly water limited in summer period and energy limited in winter period Several factors influencing water use by tree plantations can be controlled by management Water footprint of forest products depends on tree species & growth conditions

17 Take home messages There is room to optimize the water oriented forest management In the Med., water and soil go together Integrating ecological, socio-economic and hydrological management is a key approach towards sustainability The Green water paradigm -in addition to the blue water paradigmshould receive increased attention, as green water flows sustain main ecosystem functions With regard to integration of water with other ecosystem services, a myriad of new tools for trade-off analysis and land management optimization has become available

18 Thank you! Acknowledgements a) For this presentation Giorgio Matteucci Jerry Vanclay Javier Martin Vide Carlos Gracia Bart Muys Robert Mavsar b) For the book The 40 authors Book available in pdf (French and English) on