Groundwater (GW) drawdown is of obvious importance to vegetation as reduction of water tables may sever the plants from one of their key water sources. GW lowering or surface diversions can produce dramatic changes in stand structure and species composition [1, 2], inevitably affecting GW-dependent ecosystems [e.g 3, 4]. It can induce ecological effects such as the decrease in plant species richness, changes in plant communities, performance or survival of plant species [5, 6, 7]. Sand dune habitats are particularly sensitive to GW stress, as GW is one of their primary water-source, and the stress effects are dependent on GW level variations [8, 9]. Sand dune plant communities encompass a diverse number of species that differ widely in root depth, tolerance to drought and fluctuations of the water table, and capacity to shift between seasonal varying water sources [10, 11]. This high ecological diversity can occur in different climatic regions, such is the case of Tropical, Meso-mediterranen and Mediterranean areas, where future climate change is predicted to reduce water availability, which could exacerbate GW limitation [12]. A large-climatic-scale study, covering Brazil, Portugal and Spain, would provide an excellent experimental condition to study the GW dynamics and community functioning in natural dune Forests of high ecological and economical value.
An important aspect in water resource management is the potential impact of GW abstraction on dependent ecosystems [13]. The additional impact of climatic drought on GW-dependent ecosystems has become of increasing concern since climatic drought aggravates GW abstraction impacts and there are uncertainties about how GWdependent vegetation will respond over the short and long term [14, 15]. Functional groups may be affected by water distribution and availability differently [12, 16]. Analyses of the relative natural abundances of stable isotopes of carbon (13C/12C), oxygen (18O/16O) and deuterium (D/H) have been used across a wide range of scales, contributing to our understanding of plant ecology and interactions [17]. This approach can show important temporal and spatial changes in utilization of GW by vegetation [18, 19, 20]. This approach, together with plant reflectance indices and forest structure, can be a useful tool to assess plant performance and be used as a GW stress indicator.
Questions still remain about the integrated effects of natural and anthropogenic alterations in GW regime on the performance and survival of plants. Successful conservation of coastal dune forests will require knowledge on the dependency of the vegetation on GW and equally on the feedback between plant functional groups and water dynamics. Thus, it is crucial to better understand specific water requirements, in order to minimize future impacts of GW limitation. Estimation of GW limitation impacts on ecosystems is challenging because methods are commonly used with no particular attention to physiological functioning. This lack of data often leads to a difficult interpretation and/or prediction of the effects of GW dynamics under a changing environment. The use of plant functional types ecophysiological responses is essential to study and predict consequences of global change, particularly water availability, on vegetation and ecosystem processes at a global scale.
References