RésuméThe concept of Ecosystem Services (ES) highlights Humanity’s dependence on ecosystems for its survival and well-being in a global context of ecosystems’ degradation. One model that has been widely used represents ES at the centre of a ‘cascade’ (Haines-Young and Potschin, 2010a), flowing from the ecosystems biophysical structures and processes to human well-being. Among research needs regarding ES, there is a crucial one for accurately quantifying every component of the ES ‘cascade’ through suitable indicators. While current policy-driven initiatives of ES assessments and mapping are often based on methods relying on simple land cover proxies, research is needed to propose indicators that can easily be mapped, but better reflect the underlying complexity of processes underpinning ES supply.
Among ES, those related to water are of prime importance. Literature regarding forest cover effect on water related processes is relatively abundant. However, the combined effect of these processes on hydrological ES is less evident given the ecosystems’ complexity and heterogeneity at the landscape scale. Questions related to the integrated effect of mixed land uses and land covers at the landscape scale and regarding the forests’ position in the landscape (i.e. within riparian zone or within the whole catchment) where its effect on hydrological ES is the strongest remain unanswered. Finally, global changes push for renewing the studies of the ecosystems’ effect on hydrological ES.
The main objective addressed in this research is to assess the impact of forest cover on hydrological ES in Wallonia (Belgium). In particular, the effect of forest cover on instream water supply and flood protection is studied in terms of quantity, quality and timing. Along with this thematic objective, transversal methodological objectives are pursued: to ensure replicability of the methods and to broaden the scope of the results, moving towards land planning oriented results.
Our main results show that forest cover effect on instream water supply in terms of quantity is negative when studying water yield, whereas a significant positive effect of forest cover in low flows is demonstrated. Studying baseflow relationship with forest cover lets us assume that local site conditions (soil types, topography, forest management) have a major impact on specific volume. Regarding flood protection, forest cover is negatively linked with the flashy behaviour of the catchment thus a positive effect on the flood protection ES. Climatic factors and rainfall in particular are often significantly linked to hydrological indicators and can be considered as main drivers of instream water supply and flood protection.
Regarding instream water supply in terms of quality, one main result is that forest cover is systematically positively correlated with higher water quality whether when describing it through nine physico-chemical variables or through two biological indices (based on diatoms and macroinvertebrates). In both studies, forest cover explains about one third of the variability of water quality (and around 10% when spatial autocorrelation is controlled) at the regional scale. Results also show that unlike needle-leaved forest cover, broad-leaved forest cover presents an independent effect from ecological variables on physico-chemical water quality. Another important insight of this study is that physico-chemical water quality is one of the main drivers of biological water quality, and that anthropogenic pressures often explain a relatively important part of biological water quality. Results on biological water quality show that the proportion of forest cover in each catchment at the regional scale and across every ecoregions except for the Loam region is more positively correlated with high water quality than the proportion of forest cover in the riparian zone only.
Results regarding forest cover effect on studied hydrological ES in terms of quantity and timing make us question the use of LULC based matrix approach to assess and map hydrological ES at a complex landscape scale. However, the strong link between forest cover in catchment and water quality allows being more confident when using simple land cover proxies to map ecosystem services related to water quality.
Working with “real-life” catchments presents the advantage to fit the spatial scale for drawing land-planning recommendations. Results at the regional scale and across ecoregions lead us to recommend riparian forests protection in the Loam region (where they are left) but the overall forest catchment effect on water quality (whether physico-chemical or biological) suggests that catchment-wide impacts and a fortiori catchment-wide protection measures are the main drivers of rivers’ ecological water quality.
|la date de réponse||28 août 2017|
|Superviseur||Nicolas DENDONCKER (Promoteur), Caroline Vincke (Copromoteur), Catherine Linard (Président), Mathieu Javaux (Jury), Cláudia Carvalho Dos Santos (Jury) & Flavie Cernesson (Jury)|
Attachement à un institut de recherche reconnus à l'UNAMUR