Alpine Ecology in the Iberian Peninsula: What Do We Know, and What Do We Need to Learn?

Abstract The 11th Conference of the Spanish Association of Terrestrial Ecology, held in Pamplona, Spain, on 6–10 May 2013, included a symposium on alpine ecological research in the Iberian Peninsula. This session offered an excellent opportunity to assess the state and progress of alpine ecology in this region, identify knowledge gaps, and discuss further directions for research. Iberian alpine ecosystems are biodiversity hotspots and have traditionally contributed to sustaining rural livelihoods. Today, these ecosystems are subjected to large changes in land uses, including land abandonment, and are affected by climate change. This article reviews the current state of Iberian alpine ecology and proposes a research agenda. Alpine ecology in the Iberian Peninsula is a growing field of research. The need for larger spatial and temporal scales in research and monitoring, along with the integration of socioecological aspects, is a critical issue for understanding the major drivers of change in the alpine ecosystems of the Iberian Peninsula. The implementation of effective mitigation strategies aimed at reducing the impact of the pressing environmental and socioeconomic problems of Iberian mountain areas can only be accomplished through a multidisciplinary and integrative approach.


Introduction
The Iberian Peninsula has one of the most rugged landscapes in Europe, and its mountains host alpine ecosystems (understood broadly as ecosystems occurring above the tree line) of Euro-Siberian (Pyrenees and Cantabrian Range) and Mediterranean (Central and Iberian Ranges, as well as Sierra Nevada) biogeographic origin ( Figure 1). Alpine ecosystems across the Iberian Peninsula are geographically isolated islands, which increases their scientific and conservation interest (Kö rner 2003). Like most mountains worldwide, they provide important ecosystem services that sustain rural livelihoods and are exposed to a range of stressors, including climatic, political, economic, and sociocultural forces (IPCC 2012).
Rural abandonment since the 1960s, as a consequence of the collapse of European rural economies (MacDonald et al 2000), has led to land use changes that have driven profound changes in Iberian mountains. Historically, traditional grazing activities and associated management practices have contributed to the diversity of Iberian alpine grasslands (Sebastià et al 2008), and tree lines have been locally lowered in elevation by pastoral use (Ninot et al 2008). However, the abandonment of traditional land uses has led to densification of the tree lines, recolonization of deforested areas (Batllori and Gutié rrez 2008;Amé ztegui et al 2010;García-Romero et al 2010), and shrub encroachment. This, coupled with intensive afforestation policies, has resulted in a drastic reduction in the extent of grasslands, an increase in large-scale fire hazards, and the loss of important ecosystem services such as water availability and landscape diversity (García-Ruíz and Lana-Renault 2011; WWF/Adena 2013).
Climatic warming is also expected to have a large impact on alpine habitats, and there is clear evidence of  (Wilson et al 2007), and vertebrates (Lurgi et al 2012). In the case of plants, changes in Iberian and other Mediterranean high mountains seem to be faster and more dramatic than in boreal-temperate European mountain ranges, because upslope shifts tend to decrease species richness (Pauli et al 2012). Mediterranean summer droughts pose an additional constraint to plant growth even in the alpine belt (García-Cervigó n et al 2012), and altitudinal migration may not be a straightforward response to climate change as in other European mountains (Olano et al 2013).
Alpine areas represent challenges to researchers, conservationists, and land managers. Some alpine ecosystems, such as snow beds, can serve as early indicators of change due to their marked sensitivity to external drivers (Nagy 2006). In turn, the rugged alpine terrain provides an opportunity for natural experiments, because sharp environmental gradients occur over relatively short distances (Scherrer and Kö rner 2011). Understanding the processes, mechanisms, and responses to external drivers can greatly expand our ability to preserve these ecosystems and promote the sustainable use of the services they provide. The 11th Conference of the Spanish Association of Terrestrial Ecology (AEET) represented a timely opportunity to chart the current state of alpine ecological research in the Iberian Peninsula. Based on the conclusions of the symposium, this article reviews pivotal issues and proposes a research agenda. Abstracts of the symposium are available at the AEET website (AEET 2013). Discrepancies among geographical locations may partly reflect the different extents (and importance) of alpine habitats in each range, with those in the Pyrenees being the largest. Alternatively, they may indicate the positive impact of having a dedicated local research Some such studies may have gone undetected in our search because they did not use the word ''alpine.'' For instance, the term ''mountain'' might be more common in other disciplines (Kö rner 2009), but it would also encompass nonalpine habitats that are outside the scope of this paper. Our search did not cover the gray literature; nonetheless, we acknowledge that nonacademic publications make up an important body of work that often contains relevant development-oriented research on mountains and mountain communities. Current research on alpine ecology in the Iberian Peninsula was presented at the AEET symposium in 17 talks, including 2 by invited speakers. Topics ranged from an overview of Iberian alpine research to the main drivers of vegetation change in Iberian mountains ( Figure 1C). Global change was a hot topic, with emphasis on shrub encroachment. One of the central issues debated was the role of humans in the management and ''preservation''

The way forward
The main directions for future research that emerged from the symposium fell into 4 broad areas.

Identify the drivers of change
Understanding ongoing changes is critical to predicting future impacts. To identify the main causes of change, and distinguish their effects from natural variation, it is essential to establish baseline monitoring programs (discussed later) focusing on the main functional ecosystem processes. New, promising tools can help this goal; for example, herb chronology (  responses at the population level or studying changes in the diversity and productivity of areas with a long grazing history after cattle exclusion.

Analyze the responses of individuals, populations, and ecosystems to external drivers
Responses at different organizational levels can determine how ecosystems react to impacts. For example, both local adaptation processes and dispersal or migration capacity might be relevant to the response of populations at their range limits. Knowledge on this adaptive potential would inform strategies that minimize the impact of global change on biodiversity. Investigating how external drivers can affect the delivery of ecosystem services is paramount. The relationship between social and ecological systems is reciprocal (Collins et al 2011; Figure 3); decision-making by humans affects ecosystem processes, which in turn feed back to human well-being by determining the quality and quantity of ecosystem services. For example, humanrelated changes in the Pyrenees (eg demographic changes leading to rural abandonment and forest regeneration) are driving increases in populations of certain forest animals, like wild boars (Sus scrofa). In turn, wild boars root up extensive areas while foraging in alpine grasslands (Bueno et al 2010); this is perceived by farmers as a reduction of the surface available to livestock grazing (one of the ecosystem services provided), and this drives further decision-making.

Develop larger-scale monitoring programs
While some initiatives have long been in place for specific taxonomic groups, such as the Global Observation Research Initiative in Alpine Environments for plants (Pauli et al 2012), efforts should also target multidisciplinary assessments in which socioecological aspects are considered. Ideally, these monitoring networks could build on ongoing initiatives and learn from experiences at other sites. A solid monitoring program should be aware of the past to understand the present and try to adapt to the future; this is particularly important in Mediterranean mountain ecosystems, which have been managed by humans for centuries.
Comparisons across mountain ranges and long-term data collection networks can provide useful insights into processes and responses to changes and can inform management practices (McDougall et al 2011). On a global scale, comparative long-term data and research can be achieved by forming a coordinated alpine environmental observatory network, such as the one within the Global Mountain Biodiversity Assessment (2013), which includes long-term ecosystem research (LTER) sites from areas with different climates and land use histories. The LTER-Spain network (2012) contains 3 important mountain nodes (Ordesa and Monte Perdido, Sierra Nevada, and Aigü estortes National Parks), where a basic collaboration is being developed to share protocols for data collection on land use changes, plant and animal population trends, and running-water analyses. Comparative research across time and space can validate the impacts of environmental factors on the functioning, vulnerability, and sustainability of natural and anthropogenic systems in alpine environments globally.

Implement adaptive management
Monitoring should guide management to reduce uncertainty, through an iterative process of robust decision-making, by accruing information that improves further management (Lindenmayer and Likens 2009). Mountain protected areas are invaluable as natural

Concluding remarks
Alpine ecology is a dynamic field of research in the Iberian Peninsula. Current and predicted changes, primarily in land use and, to a lesser extent, in climate and biotic exchanges, pose challenges to researchers, conservationists, and managers. Improving our understanding of the responses of individuals, populations, and ecosystems to global change will facilitate decision-making to mitigate ecological and socioeconomic impacts. However, this can only be achieved under a new conceptual framework, in which socioeconomic aspects are analyzed together with ecological processes, following adaptive management guidelines based on and developed from solid scientific knowledge. Due to Iberian mountains' long history of human use, their ecology cannot be isolated from past and present socioeconomic forces. Hence, it is time to build bridges across disciplines and to encourage researchers, stakeholders, practitioners, and policymakers to work together toward sustainable development of Iberian mountains that provides for the conservation of their natural resources, the provisioning of their ecosystem services, and their socioeconomic profitability.

ACKNOWLEDGMENTS
This article builds on ideas discussed in the 11th AEET Conference; we are grateful to the conference organizers, and to all participants in the symposium-especially A. Escudero, T. Sebastià, and X. de Lamo-for interesting discussions. Special thanks are due to J.M. Iriondo for helpful comments on an earlier version of the manuscript.