Shrubland ecosystems across Europe face a range of threats including the potential impacts of climate change. Within the INCREASE project, six shrubland ecosystems along a European climatic gradient were exposed to ecosystem-level year-round experimental nighttime warming and long-term, repeated growing season droughts. We quantified the ecosystem level CO2 fluxes, i.e. gross primary productivity (GPP), ecosystem respiration (Reco) and net ecosystem exchange (NEE), in control and treatment plots and compared the treatment effects along the Gaussen aridity index. In general, GPP exhibited higher sensitivity to drought and warming than Reco and was found to be the dominant contributor to changes in overall NEE. Across the climate gradient, northern sites were more likely to have neutral to positive responses of NEE, i.e. increased CO2 uptake, to drought and warming partly due to seasonal rewetting. While an earlier investigation across the same sites showed a good cross-site relationship between soil respiration responses to climate over the Gaussen aridity index, the responses of GPP, Reco and NEE showed a more complex response pattern suggesting that site-specific ecosystem traits, such as different growing season periods and plant species composition, affected the overall response pattern of the ecosystem-level CO2 fluxes. We found that the observed response patterns of GPP and Reco rates at the six sites could be explained well by the hypothesized position of each site on site-specific soil moisture response curves of GPP/Reco fluxes. Such relatively simple, site-specific analyses could help improve our ability to explain observed CO2 flux patterns in larger meta-analyses as well as in larger-scale model upscaling exercises and thereby help improve our ability to project changes in ecosystem CO2 fluxes in response to future climate change.
Soil profile reconstruction during the reclamation of mine waste dumps and establishment of sustainable vegetative covers are well recognised rehabilitation practices and targets of the modern mining industry. In the central Queensland coalfields, many on-site and laboratory trials have characterised the Tertiary spoil requiring rehabilitation and assessed subsequent vegetation establishment. However, relatively few studies have investigated longer-term development of these ecosystems. In 2003, the re-monitoring of a Tertiary spoil trial at Saraji Mine provided the opportunity to reflect on 12 years of soil and vegetation development. The trial consisted of four media treatments: sodic, alkaline Tertiary clay spoil; saline, acid coal rejects overlying spoil; and two depths (10 cm and 30 cm) of topsoil overlying spoil. These were sown with two vegetation treatments: a native tree/shrub mix (5.16 kg ha) with and without improved pasture grasses (2 kg ha). Twelve years from establishment, preliminary investigation has shown that where poor plant growth resulted from adverse media characteristics, salts have concentrated in the soil surface due to capillary rise. In the most severe case, on Tertiary spoil, mean ground cover (22%) corresponded with an increase in mean electrical conductivity at 0-1 cm soil depth (1.5 to 7.8 dS m, 1991-2003). However, on media where good vegetation cover established (90%), such as on the 30 cm topsoil treatment, the salt concentration at 30-40 cm depth for one site was reduced (1.2 to 0.6 dS m, 1995-2003). Identification and interpretation of these trends and their relationship to initial media characteristics and vegetation treatments will assist site environmental officers with long-term postmining management of the central Queensland Tertiary spoil landscape.
As rehabilitation areas are established and develop, it is essential to monitor their success. The minerals industry and, for this particular study the coal industry in central Queensland, is facing increasing pressure to show proof of the sustainability of its rehabilitation strategies. Currently, despite much activity in this area, there are no generic recognised criteria in Australia for determining when rehabilitation is complete. Many approaches are being pursued, however, actual demonstration of achievement still provides the most powerful proof of rehabilitation sustainability. Sustainability implies long time-frames and there are relatively few examples of rehabilitation trials in the central Queensland coal fields that have a known establishment history, are well-documented over more than a few years and remain intact. One of the few trials in central Queensland which meets these criteria is the Tertiary Spoil Trial established in 1991 at the Saraji Mine. To investigate the constructed ecosystems at the Saraji Mine trial, it was important to first recognise that long-term rehabilitation monitoring is concerned with trends and that by understanding these ecosystem trends, the rehabilitation decision-making process is assisted. The research undertaken as part of this thesis provided documented evidence of trends through time for the ecosystem types at the Tertiary Spoil Trial at Saraji Mine. In the early stages of ecosystem development, vegetation growth was influenced by the media characteristics and the treatment species mix. Twelve years after establishment, it was evident that the initial surface media characteristics continued to influence both the potential of the system and the rate of system development. However, investigation of infiltration characteristics on the trial treatments after twelve years identified that vegetation cover had become the dominant influencing factor on infiltration, regardless of the media treatment or vegetation treatment. Investigation of the trends within each ecosystem type showed a number of attributes had reached a steady state, such as ground cover on the topsoil treatments, giving an indication of ecosystem sustainability. However, other attributes such as the canopy foliage projective cover, continued to change through time and these require future monitoring to identify when steady state has been achieved. The comparison of the trial monitoring data with reference communities from the surrounding landscape found that although the trial treatments were more alkaline, more saline, and more sodic through the profile, the rehabilitation landscape after 12 years of development had many similarities to those in the surrounding region, indicating a level of sustainability within the trial treatments. One exception to this was identified, where all vegetation attributes on a trial treatment were below the range observed in the reference communities. Overall, these studies highlighted the importance of media characterisation prior to rehabilitation . Given the dominance of the vegetation influence on infiltration characteristics, the rapid establishment of ground cover at these tertiary spoil rehabilitation sites is desirable. Additionally, the low nutrient concentrations identified in one of the trial media at trial establishment may have future detrimental effects. Those spoils requiring rehabilitation that have media characteristics which restrict seedling emergence and vegetation establishment should be avoided or capped with a deeper application of topsoil to restrict accumulation of salts at the soil surface. The study also showed that those media treatments initially slower to establish a vegetative cover can develop over time to produce attributes that approach the more 'rapidly developing' media treatments. However, as these treatments initially provided lower ground cover than the topsoil treatments, landscape stability, decreased infiltration and increased runoff would all be issues requiring consideration in the early stages of rehabilitation. There are many other facets of these rehabilitation ecosystems and reference communities that could be investigated to give an improved understanding of the underlying processes. This series of studies however, provides a valuable tool to those surrounding operations with similar climatic conditions and similar overburden (or spoil) media. In addition, it has reinforced the importance of on-going rehabilitation monitoring and the valuable nature of this long-term data in mapping ecosystem trends and providing indications of sustainability. Inclusion of reference communities within these investigations and comparison of to trial treatment information will continue to provide a valuable tool for evaluation of the rehabilitation and assist in showing sustainable ecosystem development.
Abstract. Soil respiration studies are increasingly undertaken with the aim of quantifying C fluxes and predicting changes for the future. The interpretation of field data into annual C loss predictions requires the use of modeling tools which generally include model variables related to the underlying drivers of soil respiration, such as soil temperature, soil moisture and plant activity. Very few studies have reported using model selection procedures in which structurally different models are calibrated, then validated on separate observation datasets and the outcomes critically compared. This study utilized thorough model selection procedures to determine soil heterotrophic (microbial) and autotrophic (root) respiration for a heathland chronosequence. The model validation process identified that none of the six measured plant variables explained any data variation when included in models with soil temperature, which contradicts many current studies. The best predictive model used a generalized linear mixed effect model format with soil temperature as the only variable. There were no heterotrophic respiration differences between the community ages. In contrast, autotrophic respiration was significantly greater on the youngest vegetation (55 % of total soil respiration in summer) and decreased as the plants aged (oldest vegetation: 37 % of total soil respiration in summer). Total annual soil C loss from the youngest and oldest communities was estimated to be 650 and 435 g C m−2 yr−1 respectively. Heathlands are cultural landscapes which are managed through cyclical cutting, burning or grazing practices. Understanding the C fluxes from these ecosystems provides information on the optimal management cycle-time to maximize C uptake and minimize C output. Inclusion of the predicted soil fluxes into a preliminary ecosystem C balance suggested that the youngest vegetation is a C sink while the oldest vegetation is a C source, indicating that shorter management cycles could reduce C emissions.
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)
