Assu Gil-Tena

Changes in biodiversity indicators in managed and unmanaged forests in NE Spain

Major changes in Mediterranean forests have occurred in recent decades, mainly as a result of the abandonment of traditional activities and population decline in rural areas. In this study, we analyzed the short-term (11-year) evolution of forests in the region of Catalonia (NE Spain) and the role of management, by comparing seven biodiversity indicators estimated from 7,664 plots from the Second and Third Spanish National Forest Inventory. We evaluated the changes in unmanaged and managed stands with different silvicultural treatments, and considered the effect of stand density and land ownership on these dynamics. We found a general naturalization and maturation of forests and an increase in all of the biodiversity indicators investigated during the study period, with the increments being greater in unmanaged than in managed plots. Some types of silvicultural treatments, such as selection cutting or thinning, were shown to be compatible with an increase in the analyzed indicators, and thus were more adequate for a multifunctional management that considers forest production together with the maintenance or improvement of the diversity of forest communities. The increases in shrub species richness and in the number of large-diameter trees after silvicultural treatments were more prominent in dense stands. Private lands presented greater short-term increases than public forests in all biodiversity indicators, except for large-diameter trees. From these results, we concluded that the application of silvicultural treatments can be a key tool to shape and maintain diverse and healthy forest structures in the context of socioeconomic and environmental changes in the Mediterranean region, which may induce potentially excessive densification and homogenization of some forest stands and landscapes.

Mediterranean fire regime effects on pine-oak forest landscape mosaics under global change in NE Spain

Abstract Afforestation after land abandonment and the occurrence of large fires have significantly altered the composition of pine-oak ecosystems in the Mediterranean since 1950s, the latter favouring the prevalence of oak forests and shrublands to that of pine forests. Nevertheless, our ability to integrate the processes driving these changes in modelling tools and to project them under future global change scenarios is scarce. This study aims at investigating how Mediterranean forest landscape composition and seral stages may be affected by mid-term changes in fire regime and climate. Taking Catalonia (NE Spain) as study area, we predicted yearly changes in forest landscape composition using the MEDFIRE model which allows assessing the effects of different fire regimes on landscape dynamics such as post-fire regeneration and afforestation. We considered three climatic treatments based on observed and projected climate, two fire regimes largely differing in the amount of area burnt and the number of large fires, and two fire suppression strategies. While projected afforestation continued to increase forest cover in the 2050 horizon, a climate-related harsher fire regime (higher amounts of area burnt) accelerated a shift towards landscapes progressively dominated by oaks and shrublands, thus precluding general forest maturation. Fire-sensitive pine species contributed to net forest cover loss in the worst scenarios. An active fire suppression strategy partially compensated the effects of a climate-related harsher fire regime on pine forest loss and rejuvenation, whereas variability in climate projections weakly affected spatial fire allocation and afforestation. Our results highlight the need to explicitly incorporate fire suppression strategies in forest landscape composition forecasts in the Mediterranean. At mid-term, large-scale afforestation, post-fire forest rejuvenation and landscape composition changes may alter forest ecosystem functioning and potentially interact with fire suppression planning.

Shape Irregularity as an Indicator of Forest Biodiversity and Guidelines for Metric Selection

The development of quantitative methods in landscape ecology has provided new perspectives for analysing the distribution of forest biodiversity. The shape of landscape patterns may be linked to the imprint of the factors that have configured the boundaries and affected the diversity of forest patches. There is now available a large number of spatial metrics for characterising the shape of landscape patterns. However, the properties, behaviour and adequacy of these shape metrics for landscape pattern analysis have not been sufficiently evaluated, and there is a risk of potential misuse and arbitrary metric selection. We review the main characteristics and limitations of existing landscape shape metrics, and explore the relationships between shape irregularity metrics and forest landscape biodiversity in the regions of Galicia and Asturias (NW Spain). We analysed data from the Spanish Forest Map, the Third Spanish National Forest Inventory and the Spanish Atlas of Vertebrates at two different levels: forest types with homogenous composition and different total areas, and equally-sized heterogeneous UTM 10 × 10 km cells. We found that shape irregularity metrics were significantly correlated with forest vegetation diversity and with the richness of forest birds, mammals and total vertebrate species. Shape metrics correlated more with forest biodiversity variables than fragmentation metrics. We conclude that shape irregularity metrics may serve as valuable spatial indicators of forest biodiversity at the landscape scale, and suggest that more attention should be paid to shape as a key characteristic of landscape patterns.

Integrating fire spread patterns in fire modelling at landscape scale

Fire spread modelling in landscape fire succession models needs to improve to handle uncertainty under global change processes and the resulting impact on forest systems. Linking fire spread patterns to synoptic-scale weather situations are a promising approach to simulating fire spread without fine-grained weather data. Here we present MedSpreada model that evaluates the weights of five landscape factors in fire spread performance. We readjusted the factor weights for convective, topography-driven and wind-driven fires (n=123) and re-assessed each fire spread groups performance against seven other control simulations. Results show that for each of the three fire spread patterns, some landscape factors exert a higher influence on fire spread simulation than others. We also found strong evidence that separating fires by fire spread pattern improves model performances. This study shows a promising link between relevant fire weather information, fire spread and fire regime simulation under global change processes. We used fire spread patterns to simulate fire spread in landscape succession models.Modelling fire spread patterns improved simulations of fire propagation.Factors governing fire spread differed among topographic, convective and wind fires.Synoptic weather situations can populate fire spread modelling at large spatial scales.

Forest Avian Species Richness Distribution and Management Guidelines under Global Change in Mediterranean Landscapes

Determining forest bird responses to environmental factors may represent a keystone to disentangle how forest management could mitigate the current and expected impacts of global change in Mediterranean biodiversity. We analyzed the spatial variation of the relationships between bird species richness (specialist and generalist birds) and forest landscape features, fires and climate in order to provide specific forest management guidelines in the Mediterranean region of Catalonia (NE Spain). We performed Geographically Weighted Regression (GWR) models, an extension of the standard regression approach that accounts for non-stationary processes in the analyzed relationships. Climate warming would negatively affect forest bird diversity, particularly in the southern part of Catalonia where the higher temperatures and lower precipitations occur. However, the key role of forest landscape characteristics to explain the distribution of bird species richness suggests that forest management could buffer the negative impacts of climate change. Management should also avoid landscape homogenization and an excessive fuel accumulation that can boost the increasing wildfire occurrence, which has been here shown to negatively impact forest bird species richness in the region.