Drought-induced dieback of riparian black alder as revealed by tree rings and oxygen isotopes

ABSTRACT: Progressive death of twigs and branches (i.e. dieback) may happen in response to biotic and abiotic agents
thereby reducing tree growth and eventually death. Drought-induced dieback has been seldom studied in riparian habitats. We used retrospective tree-ring and oxygen isotope analyses to determine whether growth patterns, sensitivity to climate and hydrology, as well as access to deep subsurface water and microhabitat river variables, are related to Alnus glutinosa [L.] Gaertn. decline. Tree-ring sampling was conducted on A. glutinosa individuals showing dieback ‘declining’ (defoliated) and compared with paired ‘non‐declining’ (not defoliated) individuals in one slow-running stream. Radial growth of declining trees responded to the rate of precipitation-evapotranspiration from February to July more than non-declining. In contrast, the growth of non-declining trees positively correlated with the October river discharge of the year preceding tree-ring formation. After the severe 1998 drought, the growth of declining trees decreased in comparison to non‐declining trees, showing, since then, early warning signals of dieback. Since 1998, resilience decreased as drought events accumulate in declining trees, but not in non-declining trees. Also, trees situated near to the active river channel recover better from drought. In the 1998 tree ring, we found differences in δ18O between vigour classes suggesting that nondeclining trees had access to deeper water pools in drought years. Our findings provide new information that could be used to forecast changes in black alder dynamics under the current climate change scenario, especially at the species’ xeric range edges, and assist managers in designing riparian forest adaptation strategies.

Ants as Bioindicators of Riparian Ecological Health in Catalonian Rive

ABSTRACT: In this study, we assess the potential of ants as bioindicators of riparian ecological health in two river types (upland and lowland type) located in the Catalonian region. We proposed to understand to what extent do metrics based on ant responses provide useful information that cannot be presented by traditional biophysical assessments while attempting an approach to creating an ant-based multimetric index (ant-based MMI) of the riparian ecological health. A total of 22 ant species were identified, and 42 metrics related to ant foraging activity, species richness, and functional traits were evaluated as potential core metrics of the index. Riparian features and proximal land use land cover (LULC) were used to distinguish disturbed from less disturbed sites. We found that ant communities strongly responded to human disturbance. When compared with an exclusively physical-based index for the assessment of the riparian health, the ant-based MMI was more sensitive to human disturbance, by also reacting to the effects of the surrounding LULC pressure. This study provides a preliminary approach for an ant-based assessment tool to evaluate the health of riparian corridors although additional research is required to include other river types and a wider stressor gradient before a wider application.

Nature-based solutions in Granollers: From ecosystem restoration to the circular economy

ABSTRACT: The environmental and health impacts that occurred in the city of Granollers (Barcelona, Spain) ultimately led to a public rejection of natural surroundings, which became polluted and neglected places. The regeneration of these degraded spaces required an ambitious and multidimensional revitalisation programme to re-establish their ecological and cultural functions. This paper describes and evaluates the arduous restoration process carried out over more than 20 years, analysing the outcomes, challenges and setbacks involved in achieving a more resilient, green and liveable city. This paper examines innovative projects with nature-based solutions, such as the river restoration project to naturalise and release the Congost River, and the creation of a lagoon-based system in the Can Cabanyes area to foster biodiversity and create a local green economy based on the reuse of water. The paper presents evidence of the contribution of a long-term local restoration programme to the improvement of biodiversity and health in a medium-sized city. Empirical evidence has demonstrated a remarkable ecological improvement of the restored habitats. Social appraisal of the project has notably increased over the years, although some long-standing negative views persist regarding the restored river areas. The overarching strategy implemented in Granollers has transformed and empowered the city, multiplying the local green infrastructure and creating a valuable public corridor between the city and the regenerated spaces.

Ministerio de Agricultura y Pesca, Alimentación y Medio Ambiente