Temporal changes in Mediterranean forest ecosystem services are driven by stand development, rather than by climate-related disturbances

https://doi.org/10.1016/j.foreco.2020.118623Get rights and content

Highlights

  • We explored recent changes of ecosystem services (ES) in Mediterranean forests.

  • Timber volume increment, water provision, and carbon sequestration showed a decline since 1990.

  • Recent changes in ES were largely driven by the structure of the forest stands.

  • Temporal analyses revealed more potential trade-offs between ES than purely static assessments.

Abstract

The Mediterranean Region constitutes a biodiversity hotspot and its forests have provided multiple ecosystem services (ES) to human societies for millennia. In the last decades, many Mediterranean forests have undergone a decreasing level of direct human pressure and a growing exposure to environmental stress factors (e.g. wildfires and droughts). However, the degree to which these processes have affected the provision of ES remains largely unexplored. We used an extensive database of 3417 permanent plots (period 1990–2015, 25 years) from the Spanish National Forest Inventory in Catalonia (North-Eastern Spain) and a range of four ecological models to measure and estimate changes in five different ES: wild mushrooms production, timber volume increment, water provision, carbon sequestration and erosion mitigation. We then assessed general trends in ES, their spatial–temporal patterns and searched for potential trade-offs in their delivery. Using mixed-effects models, we explored the differences among three biogeographical regions, as well as the effect of different environmental and site level drivers, including descriptors of stand structure and development, the legacies of management practices and disturbances, as well as the influence of historical climate conditions and their recent anomalies. Our results show a general decline of timber volume increment, water provision and carbon sequestration, along with an increase in erosion mitigation across inland and montane regions. Fitted model parameters suggest a predominant role of stand structure in driving changes in forest ES supply in the study area. In particular, stands with high basal areas were associated with steeper declines in most ES, whereas high mean tree diameter generally contributed to ES increases. Finally, our results showed a series of potential trade-offs among temporal changes in ES that were not reflected in exclusively static analyses, highlighting the relevance of including the temporal dimension in regional assessments of ES. Future forest management and planning could better account for overall ES value as well as expected changes in their future provision, paving the way to landscape planning that balances these two essential components of forest ES.

Introduction

Forests are key terrestrial ecosystems because of their extension (Crowther et al., 2015), their role in sustaining biodiversity (Butchart et al., 2010), and the multiple ecosystem services (ES) they provide to humanity (Ninan and Inoue 2013). However, in the last decades they have been subjected to an increasing amount of pressures related to global change, including changes in land-use and management, and climate-related stress factors (e.g. Smith et al., 2016, Li et al., 2018). For example, climate anomalies and extreme events, such as droughts, are driving episodes of forest decline in many areas (Allen et al., 2015), affecting multiple ES (Anderegg et al., 2013). Other disturbances and natural hazards, such as wildfires, pests and diseases, are also increasingly important for forest dynamics, impacting the provision of different ES (Seidl et al., 2014, Thom and Seidl, 2016). It is hence necessary for the future development of management and conservation policies to quantify forests vulnerability to global change-related factors, and the capacity of forests to maintain the provision of essential ES (Mori et al., 2017). The development of adaptive guiding approaches for decision-making within the ES framework also require the integration of spatially explicit assessments of ES temporal dynamics that account for multiple environmental and site-related drivers (Rau et al., 2018).

Climate has been identified as a relevant driver for the supply of forest ES at multiple scales (Runting et al., 2017). From the regional to the global level, climatic conditions drive the geographic distribution and functioning of forest ecosystems, and control ES provision (Yu et al., 2008, Roces-Díaz et al., 2018). European forests have doubled their canopy mortality in the last decades (Senf et al., 2018) due to the combined effect of natural disturbances and forest-use. The same study reported that higher biomass was associated to higher levels of canopy mortality (Senf et al., 2018).

Forest ES are largely influenced by aspects related with the type and intensity of use, which affects their tree species composition but also ecosystem structure (Baeten et al., 2019, Mina et al., 2017). For example, multiple studies have analysed the complex relationship between forest diversity and its ecological functioning and services (e.g. Gamfeldt et al., 2013, Felipe-Lucia et al., 2018), including e.g. the link between biomass productivity (and derived ES) and tree species richness (e.g., Zhang et al., 2012, Liang et al., 2016). In addition, the spatial structure of forest stands is also relevant for determining the provision of ES such as climate regulation, habitat quality or resistance against disturbances (McGarvey et al., 2015, Yuan et al., 2018). Recent findings revealed that a high intensity in management can negatively impact multiple ES (Sing et al., 2017), while other studies found that common management practices enhance forest productivity in our study area (Garcia-Valdes et al., under review). In fact, the specific role of different management practices on forest community dynamics and derived ES is still unknown for most forest biomes (Pohjanmies et al., 2017).

Mediterranean forests and their derived ecosystem services have been influenced by human activities for millennia (Blondel, 2006), and more recently they have been increasingly affected by multiple global change factors (Doblas-Miranda et al., 2017, Peñuelas et al., 2017). In the last decades, these forests have showed lower levels of human pressure, i.e. less intensive forest management, with lower levels of timber extraction and firewood harvesting. In addition, Mediterranean landscapes are affected by the abandonment of traditional agricultural and livestock uses (Améztegui et al., 2010, Gauquelin et al., 2018). These processes combined with the change in the climatic conditions, have led to forest and tree species expansion (García-Valdés et al., 2013, Cervera et al., 2019, LCMC, 1993-2009), and to changes in forests structure, growth and productivity (Ruiz-Benito et al., 2014, MAPA, 1990-2015). These changes have generally resulted in increasing carbon stocks (Vayreda et al., 2012a), which could strongly impact the provision of ES. A recent analysis based on forest inventory data showed general increases in stand basal areas as well as reductions in ingrowth and growth, and increases in tree mortality in Spanish forests over the past 25 years (Astigarraga et al., 2020). According to some studies, these changes have made Mediterranean forests more vulnerable to hazards such as drought stress (De Cáceres et al., 2015). However, other studies found that changes in forest composition are also increasing the local diversity of drought-tolerance traits, which is buffering negative impacts on productivity (Garcia-Valdes et al., under review).

Furthermore, the supply of a specific service is rarely independent from other ES, and positive (synergies) and negative (trade-offs) pairwise relationships between ES are common (e.g., Duncker et al., 2012, Roces-Díaz et al., 2018, Sing et al., 2017, Schwaiger et al., 2019). However, these relationships have been usually assessed from a purely spatial (i.e. static) perspective (e.g., Roces-Díaz et al., 2018), and the temporal dimension of these relationships, which is critical for management and planning, has rarely been tackled (Tomscha and Gergel, 2016, Willemen, 2020).

In this study, we examined the dynamics of five ES (provision of wild mushrooms, timber volume increment, water provision, carbon sequestration and erosion mitigation) in Catalonia’s forests (North-Eastern Spain) along the past 25 years. We explored their spatial and biogeographical patterns, and their relationships with multiple environmental and site factors, including: the historical climatic conditions and their recent anomalies, disturbances, stand structure and management legacies. The specific objectives of this study were to: i) assess the changes in each forest ES values during the 1990–2015 period for the whole study area, and for its different ecological regions; ii) understanding the causal factors that drive observed dynamics of ecosystem services in the study area; and iii) determine the relationships between different ES over space and time (potential synergies and trade-offs). We hypothesize a dominant role of stand structure in driving recent changes in forest ES in the study area, consistent with previous studies assessing changes in forest dynamics and species composition (e.g., Vayreda et al., 2016). Based on recent findings describing lower levels of stand growth of Iberian forests during the last three decades (Astigarraga et al., 2020), we expect declining trends in timber volume increment and carbon sequestration, whereas increased vegetation cover would result in lower levels of water provision but increased erosion mitigation. We do not have specific expectations regarding changes in wild mushroom production. Finally, we also anticipate a negative impact of recent drought events, in agreement with recent episodes of drought-induced mortality in the study area (e.g., Chaparro et al., 2017).

Section snippets

Study area and outline of the experimental approach

This study focuses on forest ecosystems in Catalonia (North-eastern Spain; Fig. 1A), a region that covers 32,114 km2 and has a population of ~7.5 M people (2015). Most of its area belongs to the European Mediterranean Biogeographical Region, although its northern part, the Pyrenees mountain range, belongs to the Alpine bioclimatic zone. Catalonia has a marked altitudinal gradient from the sea level to more than 3000 m above sea level. According to the Eco-regional classification by Dinerstein

General changes in forest ecosystem services

Our results showed different temporal dynamics for the five forest ES analysed, with different levels of spatial heterogeneity (Fig. 2) and a predominantly declining trend in timber volume increment (overall reduction of 7.08%), water provision (−29.73%) and carbon sequestration (−16.52%; Supplementary material Table B1). Wild mushrooms production and erosion mitigation did not show consistent changes and their average values changed <1.5% for the whole study area during the 1990–2015 period.

Discussion

To our knowledge, this study provides one of the first assessments of forest ES change at regional level (32,114 km2) spanning across different ecoregions (sensu Dinerstein et al., 2017). Our results revealed a general temporal decline (from 1990 to 2015) in three of the five studied ES across our study region, which encompasses large topographic and climatic gradients. Our study was based on a large database (n = 3417) with direct field information resampled using standard protocols (Alberdi

Conclusions and implications

This study analyses the spatiotemporal dynamics of five key forest ES during the 1990–2015 period in a Mediterranean region, by combining a series of spatially explicit indicators, ecological models, and information derived from a large network of NFI plots. Our results showed a general decline of three ES, particularly large for water provision and carbon sequestration. Declines in all ES were driven by variables describing the forest structure and management legacies, being particularly

Funding

Funding was obtained from the Catalan Office for Climate Change (OCCC) through project FOREStime, from EU FORESTERRA program (INFORMED project) and from the Spanish government (CGL2013-46808-R, AGL2015-66001-C3-1-R, CGL2014-59742, CGL2017-89149-C2-2-R, CGL2017-89999-C2-1-R and C2-2-R, and RTI2018-099315-A-I00). We also thank the ECOMETAS (CGL2014-53840-REDT) network for support. JVRD was supported by the Government of Asturias and the FP7-Marie Curie-COFUND program of the European Commission

CRediT authorship contribution statement

Jose V. Roces-Díaz: Conceptualization, Writing - original draft, Writing - review & editing. Jordi Vayreda: Conceptualization, Data curation, Writing - review & editing. Miquel De Cáceres: Conceptualization, Data curation, Writing - review & editing. Raúl García-Valdés: Conceptualization, Data curation, Writing - review & editing. Mireia Banqué-Casanovas: Conceptualization, Data curation, Writing - review & editing. Alejandra Morán-Ordóñez: Data curation, Writing - review & editing. Lluís

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank Sergio Vicente-Serrano and Albert Alvarez for providing part of the data used, and Victor Granda for helping us with data processing.

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