Periodic Reporting for period 1 - PERS-RELICT-CLIM (The persistence of relict populations under climate change)
Reporting period: 2016-02-01 to 2018-01-31
Forests provide essential ecosystem functions and services, including regulation of nutrient and water cycling, atmospheric composition and climate, as well as the maintenance of biodiversity and human well-being. However, climate change is expected to alter forest functioning, with profound consequences that range from genes to ecosystems. Rear-edge populations occur along the transition between biomes and contribute to the impressive diversity of ecosystems and species found in these regions. Furthermore, rear-edge populations hold a singularity that makes them very relevant for the maintenance of ecosystem services and biodiversity, as well as very attractive for the uses and profits by human societies. In this context, the progress that this project provides is essential to refine and advance our ability to predict, monitor and manage the impacts of climate change on the function and fate of rear range-edge populations.
Here we aim to propose a framework for research design and analysis at species' rear range-edges, and we then aim to demonstrate how the framework improves our understanding of marginality and rear-edge population dynamics. In order to put into practise the framework we have established our study system at the rear range-edge of the European beech tree (Fagus sylvatica L.), a species with a high ecological importance yet highly drought sensitive. The species occurs along the transition between the Mediterranean and temperate biomes, where beech populations are distributed across a fragmented landscape and along highly heterogeneous ecological conditions. In this region, relict beech populations persist out of the species' physiological tolerances. The main objectives of this project are:
1) To propose a conceptual and methodological framework for a better understanding and assessment of marginality in order to refine predictions of rear-edge population decline.
2) To test if populations inhabiting the most drought-prone habitats show higher levels of mortality and canopy decline, and altered tree growth and limited physiological performance to increased drought stress.
3) To monitor and characterize the microclimate of rear-edge populations, and to test if microclimates contribute to the local persistence of populations under unfavourable regional climates.
4) To study the amount genetic variation of rear-edge populations across ecological and habitat fragmentation gradients, and to test if geographical isolation is associated to the loss of genetic diversity.
5) To model tree growth dynamics and predict population loss under different scenarios of climate change.
The framework is applied to field-based studies across 40 populations distributed across the species rear range-edge. Preliminary results suggest that adult mortality and canopy decline (i.e. defoliation and early leaf yellowing and browning) is concentrated in drought prone areas within the core-range, while relict populations show signs of high persistence (low mortality and canopy decline). Dendroecological data and physiological parameters are measured, while population microclimatic conditions monitored. All this information complements in-deep the preliminary results found and provides key data to understand population performance in terms of tree growth and water-use efficiency in response to drought stress.
At the same time, leaf tissue is sampled and its DNA sequenced across multiple rear-edge populations distributed along gradients of fragmentation and climatic drought stress. This data allows to (1) evaluate the role of geographical isolation determining the amount of genetic diversity across populations and its temporal trends by comparing the genetic characteristics among tree age classes; (2) to contribute on the production of a reference genome sequence for the European beech tree; and (3) to contribute to identify patterns of local adaptation of rear-edge populations inhabiting the more drought-prone areas of the species range.
Finally, an extensive network of dendroecological data collected across the entire species distribution including rear-edge, range-core and leading-edge populations is used to project future growth trends under different climate change scenarios. The outputs of the models will help to predict which populations are the most vulnerable to increased aridity, as well as where population loss will occur under future climatic conditions.