|Authors:||Alejandro Valdecantos and Ramón Vallejo (CEAM) with input from study sites
|Source document:||Valdecantos & Vallejo. (2015) Report on structural and functional changes associated to regime shifts in Mediterranean dryland ecosystems. CASCADE Project Deliverable 5.1.|
Landscapes of the Mediterranean Basin have been subjected to different human pressures since millennia in addition to the natural ones derived from climate features. These pressures have increased in number and/or intensity during the past century, with severe impacts on the wildland. Current ecosystems reflect this history of disturbances on plant community structure and composition, and environmental services provided. Pristine undisturbed ecosystems are difficult or impossible to find, instead different degraded ecosystems and landscapes can be identified along disturbance gradients.
Ecosystem services are the benefits societies get from the ecosystems. These are classified in four main groups:
- cultural and
- provisioning services,
with biodiversity as structural feature of ecosystems with direct influence in all other services. Following the Millennium Ecosystem Assessment, supporting services are those that are necessary for the production of all other ecosystem services (e.g. primary production, production of oxygen, soil formation, nutrient cycling) while regulating services are the benefits people obtain from the regulation of ecosystem processes (e.g. air quality, climate regulation, erosion control, regulation of diseases, water purification). There are also services that provide both regulating and supporting services such as water and soil conservation. Biodiversity has intrinsic value independent to any human concern.
In general terms, ecosystems have the ability to withstand some level of stress without showing signs of major changes, or to recover at the short- or medium term after disturbances by themselves. However, when pressures act for very long time and/or high intensity, ecosystem functions might overcome degradation thresholds (tipping points) and show abrupt changes in key ecological properties and ecosystem services (Scheffer et al. 2001, Daliakopoulos and Tsanis, 2013). Beyond these points, natural recovery is very unlikely to occur or very slow (Whisenant 1999) and degradation might also generate new ecosystems very dissimilar to the original reference one (Hobbs et al. 2006). Fire and grazing are the two major disturbances in CASCADE field sites. These two stresses differ significantly in the way they affect ecosystems and, as a consequence, in their short-, medium- and long term impacts. Wildfires represent discrete but very strong events of disturbance while grazing usually occurs in a continuous way with smoother effects on affected ecosystems. Therefore, the assessment of impacts and ecosystem services of sites impacted by grazing can be done at any time, but the same assessment in fire-affected ecosystems will largely depend on the time passed since the last fire because soil properties and plant communities change as secondary succession progresses (Baeza et al. 2007).
Restoring biodiversity and maximizing ecosystem services are priorities in the EU Biodiversity Strategy (Lammerant et al. 2014). Biodiversity can be assessed at different scales, from gene to ecosystems and it underlies all ecosystem processes (Mace et al. 2005). Water cycle regulation is a central ecosystem service for maintaining fresh water resources, controlling floods and, hence, protecting people living downstream (Vörösmarty et al. 2005). This ecosystem service is especially important in densely populated drylands due to the combination of high water demand, low availability and, in many places, low water quality derived from the absence of dilution potential. Transitions and movements of nutrients between and within components of the ecosystems is summarized by nutrient cycling which is regulated by a great variety of organisms and its alterations have deep impacts on ecosystem functioning, other ecosystem services and, finally, human well-being (Lavelle et al. 2005). Soil loss could be an irreversible process at the human and ecological scale. Soil retention provides very important ecosystem service to maintain primary productivity and prevent harmful effects because of soil erosion (de Groot et al. 2002). Ecosystems represent a sink for the removal and storage of carbon from the atmosphere in different biotic and abiotic components. In addition to the evident accumulation in plant aboveground biomass, soils of healthy systems can also store large amounts of C mainly in soil organic matter, roots of vegetation and microbial biomass. Furthermore, there are carbon credit markets where C sequestered in ecosystems can be sold (Jose 2009).
The main objective of this section of CASCADiS is to assess whether there are any losses of important environmental ecosystem services associated to the pressures acting in all six CASCADE study sites, and to quantify these losses if they occur. Knowing and understanding the structure, function and provision of services of degraded and reference (not necessarily pristine) ecosystems at present is a very useful tool to define restoration and conservation management practices.