Ecological services provided by wetlands as a function of vegetation - hydrology co-evolution

[Truncated abstract] Triggered by climate forcing, various feedback mechanisms between physical, chemical and biological processes define the various ecological services that a wetland can provide. These ecological services include habitat provision and carbon cycling and storage. If the climate forcing is within a dynamic equilibrium, these ecological services will emerge in a quasi-steady state. If the climate is non-stationary, the ecological services provided by a wetland can respond in a non-linear way, as the feedback mechanisms that mediate the climate forcing may maintain the system stability or may drive it into a new stable state. This research explores the hypothesis that non-intuitive shifts in the ecological services provided by wetlands occur in response to hydro-climatological changes. The hypothesis was explored through the application of an ecohydrological model designed to evaluate plant habitat allocation and carbon storage, the ecological services of interest. The study was focused on the south-west of Western Australia (SWWA), a semi-arid region that has been experiencing a non-stationary climate forcing and salinisation. As such, the model was parameterized to represent plants typically found in the region, in particular two threatened species, Casuarina obesa and Melaleuca strobophylla, and validated against available data from Lake Toolibin, a Ramsar listed wetland. Firstly, the model was used to evaluate wetland response to different hydrologic management interventions that have been undertaken in Lake Toolibin. The aim was to quantify their effectiveness in controlling the impact of salinisation on the vegetation community. Model results showed that groundwater extraction by pumping was more effective than surface diversion of saline inflows to maintain vegetation abundance. Also, the results revealed that groundwater extractions favoured the establishment of C. obesa over M. strobophylla. It was also shown that the salinity status in Lake Toolibin can only remain below the levels tolerable by vegetation if long term, large scale intervention, such as catchment reforestation to reduce regional groundwater levels, takes place. Model sensitivity analysis showed that a linear change in parameters causes a non-linear response by the system, mainly due to the complexity of the dynamics between the different major controls, namely the water table level, vegetation, soil moisture and salinity. The model was particularly sensitive to soil parameters, suggesting soil as an important control on wetland ecohydrology. Secondly, the model was applied along a gradient of increasing aridity across SWWA to demonstrate the feedback mechanisms that shape the co-evolution between hydrology and vegetation. Model results corroborated the hypothesis that non-intuitive shifts in ecological services occur in response to distinct regimes of climate forcing. In particular, the results showed that higher water availability (i.e. higher mean annual rainfall depth) does not necessarily represent a higher vegetation density, if the wetland experiences high salinities. Results also showed that not only rainfall depth, but also rainfall intra-annual distribution affects environment partitioning, and therefore vegetation...