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Vegetation trends in Portugal point to a generalized greening in this territory in the period 1982-2012, in agreement with global greening patterns. Nonetheless, vegetation dynamics may be altered by natural hazards, such as fires and droughts, and also by human activities like land management and land use change. The identification of trend shifts allows to better understand their impacts on vegetation, as well as the recovery after these disturbances.A recently developed a high-resolution (1.1km) spatial dataset of the Normalized Difference Vegetation Index (NDVI) for Portugal spanning the period from 1981 to 2015 is used in the present work. NDVI was derived from the Advanced Very High Resolution Radiometer (AVHRR) sensor on board of the NOAA satellites. Land cover and land cover change are identified using CORINE Land Cover maps. Trends are assessed on seasonally adjusted NDVI time series. Results show at least one breakpoint in the NDVI time series over the study area. Moreover, the majority of the breakpoints separate segments of increasing trend, indicating the recovery of the vegetation after the disturbance. In particular, the extreme drought event of 2005 is pointed out as one main cause of the vegetation shifts occurring, namely in central and southern Portugal, highlighting that water availability plays a major role in vegetation activity in these areas. Additionally, the 2005 fire season presents the second highest value of burned area during the study period, and it is also responsible for a significant number of vegetation shifts. Vegetation behaviour and recovery over the areas affected by drought and/or fires are analysed. Land cover change is also a likely driver of vegetation shifts, since they are both identified on a pixel level on some regions.Acknowledgements: This work was partially supported by national funds through FCT (Fundação para a Ciência e Tecnologia, Portugal) under Project IMDROFLOOD WaterJPI/0004/2014) and the research grant attributed to Ana Russo (SFRH/BPD/99757/2014). [ABSTRACT FROM AUTHOR]

Extreme drought events and plant invasion are concurrently threatening water-limitedecosystems. Especially in the Mediterranean Basin, extreme drought events have increased inthe past years with detrimental effects on many ecosystems. Such events rapidly increase thevulnerability of forest ecosystems by decreasing soil water resources, reducingfitness and growth of trees and finally leading to increased mortality rates. Shrubinvasion can further exaggerate these effects and dangerously decrease tree resilience,eventually turning ecosystems into an alternate state of degraded shrublands. However,experimental evidence on the interaction of recurrent extreme drought and plant invasion isstill scarce and inconclusive, as synergistic effects of different stressors are oftenneglected. Thus, we aim to gain a comprehensive knowledge of the underlying mechanisms ofrecurrent extreme droughts, shrub invasion and their cumulative effects in a Mediterraneanecosystem. To this end, an open savannah-type cork oak (Quercus suber) ecosystem invadedby the native shrub Cistus ladanifer was chosen in South-Eastern Portugal. In threeexperimental blocks, a rainout shelter (30 %) was installed in an uninvaded and invadedcork-oak stand, supplemented by corresponding control plots, in December 2017.Measurements of water and carbon fluxes of trees (n = 36), shrubs (n = 18) and the ecosystemin total will allow to unravel species-specific responses and competition effects underrecurrent extreme droughts. We aim to determine the stress tolerance and critical thresholdsof physiological functioning for both species as well as for the entire ecosystem. Hence, thesedata will help to predict the vulnerability of cork oak ecosystems to progressing climatechange and support future management and conservation decisions for these valuableecosystems. The first year of measurements was dominated by a wet and cold spring, which wasfollowed by a drought period from July to the middle of October. Due to the heavy springrainfall, no significant effects could be observed between treatments. However, aspecies-specific behaviour was evident. Pre-dawn leaf water potentials (ΨPD) of C. ladaniferdecreased from -0.57±0.03 MPa to -3.46±0.05 MPa in the drought period. On the otherhand, ΨPD of Q. suber did not fall below -1.48±0.06 MPa in any treatment. In addition,ecosystem transpiration was clearly dominated by shrubs with maximum sap flow rates (8.8± 0.8 m3 m−2 day−1) over three-fold higher than those of trees. These differences clearlypoint towards two distinctly different drought adaptation strategies of the investigated species. [ABSTRACT FROM AUTHOR]