Using gradient Forest to predict climate response and adaptation in Cork oak.

Climate change is impacting locally adapted species such as the keystone tree species cork oak (Quercus suber L.). Quantifying the importance of environmental variables in explaining the species distribution can help build resilient populations in restoration projects and design forest management strategies. Using landscape genomics, we investigated the population structure and ecological adaptation of this tree species across the Mediterranean Basin. We applied genotyping by sequencing and derived 2,583 single nucleotide polymorphism markers genotyped from 81 individuals across 17 sites in the studied region. We implemented an approach based on the nearest neighbour haplotype 'coancestry' and uncovered a weak population structure along an east-west climatic gradient across the Mediterranean region. We identified genomic regions potentially involved in local adaptation and predicted differences in the genetic composition across the landscape under current and future climates. Variants associated with temperature and precipitation variables were detected, and we applied a nonlinear multivariate association method, gradient forest, to project these gene-environment relationships across space. The model allowed the identification of geographic areas within the western Mediterranean region most sensitive to climate change: south-western Iberia and northern Morocco. Our findings provide a preliminary assessment towards a potential management strategy for the conservation of cork oak in the Mediterranean Basin.

Ecosystem services: Urban parks under a magnifying glass.

Urban areas' population has grown during the last century and it is expected that over 60% of the world population will live in cities by 2050. Urban parks provide several ecosystem services that are valuable to the well-being of city-dwellers and they are also considered a nature-based solution to tackle multiple environmental problems in cities. However, the type and amount of ecosystem services provided will vary with each park vegetation type, even within same the park. Our main goal was to quantify the trade-offs in ecosystem services associated to different vegetation types, using a spatially detailed approach. Rather than relying solely on general vegetation typologies, we took a more ecologically oriented approach, by explicitly considering different units of vegetation structure and composition. This was demonstrated in a large park (44ha) located in the city of Almada (Lisbon metropolitan area, Portugal), where six vegetation units were mapped in detail and six ecosystem services were evaluated: carbon sequestration, seed dispersal, erosion prevention, water purification, air purification and habitat quality. The results showed that, when looking at the park in detail, some ecosystem services varied greatly with vegetation type. Carbon sequestration was positively influenced by tree density, independently of species composition. Seed dispersal potential was higher in lawns, and mixed forest provided the highest amount of habitat quality. Air purification service was slightly higher in mixed forest, but was high in all vegetation types, probably due to low background pollution, and both water purification and erosion prevention were high in all vegetation types. Knowing the type, location, and amount of ecosystem services provided by each vegetation type can help to improve management options based on ecosystem services trade-offs and looking for win-win situations. The trade-offs are, for example, very clear for carbon: tree planting will boost carbon sequestration regardless of species, but may not be enough to increase habitat quality. Moreover, it may also negatively influence seed dispersal service. Informed practitioners can use this ecological knowledge to promote the role of urban parks as a nature-based solution to provide multiple ecosystem services, and ultimately improve the design and management of the green infrastructure. This will also improve the science of Ecosystem Services, acknowledging that the type of vegetation matters for the provision of ecosystem services and trade-offs analysis.

More than trees: Stand management can be used to improve ecosystem diversity, structure and functioning 20 years after forest restoration in drylands.

In Mediterranean drylands, extensive areas have been restored by reforestation over the past decades to improve diversity, soil fertility, and tree natural regeneration, contributing to halting desertification and land degradation. However, evaluating reforestation success usually relies on tree survival, while holistic and long-term evaluations of reforestation success based on ecosystem diversity, structure and functioning are scarce. In this work, we provide the first assessment that combines the evaluation of planted trees and indicators of ecosystem diversity, structure, and functioning in established reforestations with three native Mediterranean species along a climatic gradient. We sampled 43 20-year-old stands with umbrella pine, holm oak and cork oak in Portugal, and tested the effects of tree species composition, stand management (i.e., differences in tree density and shrub cover), and edaphoclimatic conditions, on the size of planted trees, species diversity, structural complexity and indicators of ecosystem functioning related to productivity, soil nutrients and tree natural regeneration. Our results show that, after 20 years of reforestation, stand management was an essential driver of plant diversity and ecosystem functioning. Higher tree density, particularly of oaks, and higher shrub cover improved plant diversity, ecosystem productivity, and oak regeneration. The latter was also improved by structural complexity. Tree composition effects highlighted the importance of pine management to avoid competition. Since we evaluated these reforestations along a climatic gradient, we also conclude that climate influenced pine and holm oak size, ecosystem productivity, and soil C/N. Our research, by being based on assessing the long-term reforestation success in a more holistic way, highlighted the importance of stand management for improving ecosystem diversity and functioning in these restored systems. Practices such as increasing tree density up to ~800 trees/ha and allowing a shrub cover of ca. 30 %, may improve the ecological condition of future and currently reforested areas across the Mediterranean region.

Local-scale factors matter for tree cover modelling in Mediterranean drylands.

Forests contribute directly to ecosystem structure and functioning, maintaining biodiversity, acting as a climate regulator and reducing desertification. To better manage forests, it is essential to have high-resolution forest models and appropriate spatial-explicit variables able to explain tree cover at different scales, including the management scale. Most tree cover models rely only on broad-scale variables (>500 m), such as macroclimate, while only few studies include also local-scale variables (<500 m). This study aimed to identify the importance of local-scale factors relative to broad-scale factors and identify the environmental variables at different scales that explain tree cover in oak woodlands in Mediterranean drylands. Sixty sites previously identified as being covered with Holm oak or Cork oak were stratified by precipitation. Normalized Difference Vegetation Index, used here as a surrogate of tree cover, was modelled using simultaneously broad-scale factors (macroclimate) and local-scale factors (microclimatic and edaphic conditions). The percentage of variance explained by local- and broad-scale factors and the effect size of each environmental variable on tree cover was determined for the study site. It was found that local-scale factors and their interaction with broad-scale factors explained more variance than broad-scale factors alone. The most important local-scale factors explaining tree cover were elevation, potential solar radiation, used as a surrogate of microclimatic conditions, and wetness evaluated terrain used as an indicator of water flow accumulation. The main broad-scale factors were related to temperature and precipitation. The effect of some local-scale variables in tree cover seems to increase in areas where water as a limiting factor is more important. This study demonstrates the critical importance of including local-scale factors in multi-scale modelling of tree cover to obtain better predictions. These models will support well-suited forest management decisions, such as reforestation and afforestation plans to reverse evergreen oaks decline in Mediterranean drylands.

The effect of grazing exclusion over time on structure, biodiversity, and regeneration of high nature value farmland ecosystems in Europe.

Climate change and increasing socio-economic pressure is placing many ecosystems of high ecological and economic value at risk. This is particularly urgent in dryland ecosystems, such as the montado, a multifunctional savannah-like system heavily modeled by grazing. There is still an ongoing debate about the trade-offs between livestock grazing and the potential for ecosystem regeneration. While it is consensual that overgrazing hinders the development of the shrubs and trees in this system, the effects of undergrazing or grazing exclusion are unclear. This study provides the unique opportunity to study the impact of grazing on compositional and structural biodiversity by examining the ecological chronosequence in a long-term ecological research site, located in Portugal, where grazing exclusion was controlled for over 15years. As the threat of intensification persists, even in areas where climate shifts are evident, there is a critical need to understand if and how the montado might recover by removing grazing pressure. We evaluate succession on structural and compositional diversity after grazing pressure is removed from the landscape at 5, 10, and 15years post-cattle exclusion and contrast it with currently grazed plots. A LiDAR-derived structural diversity index (LHDI), a surrogate of ecosystem structure and function first developed for the pine-grassland woodland systems, is used to quantify the impact of grazing exclusion on structure and natural regeneration. The distribution of the vegetation, particularly those of the herbaceous and shrub strata (>10≤150cm), presents statistically significant changes. The LHDI closely mimics the compositional biodiversity of the shrubs, with an increase in diversity with increased years without grazing. Under present climate conditions, both shrub regeneration and the establishment of tree saplings were strongly promoted by grazing exclusion, which has important management implications for the long-term sustainability of montado systems.