The invasive species

By Félix García Pereira, Rodolfo Pozuelo, Cristina Vegas, Jesús Fidel González-Rouco.
GuMNet, Universidad Complutense, IGEO UCM-CSIC.

On the second week of December 2020 has been mostly holidays for people from Madrid city in Spain (the madrileños). The national celebration of the Spanish Constitution and a local religious event made up for a long bank holiday. Some of us saw the occasion to escape the Covid-atmosphere in town and have a few days off in the Parque Nacional Sierra de Guadarrama, less than one hour drive from the capital of Spain and still within the Community of Madrid, and thus still complying with the official regional confinement.

Invasive species Sierra de Guadarrama, Madrid, Spain
People from the city of Madrid (Spain) arelikely the most important invasive species in the Sierra de Guadarrama. Image: Parque Nacional Sierra de Guadarrama

No chance, it seems that everybody silently had the same idea. After struggling to get some accommodation we gave up, the Sierra was fully booked: no available rooms during weekends until January. We, the madrileños, are likely the most important invasive species in the Sierra. Possibly we gave her a brake during the first wave of Covid-19 before the summer, but now, as ever and more than ever, the Sierra is the destination to scape everyday confinement and a heal from the limitations of social contact.

Our two cents of touristic read: the Sierra de Guadarrama streches southwest to northeast for more than 80 km within the Spanish Central System and sits between the Communities of Madrid and Castilla y León, with altitudes ranging between 1200 and 2400 m a.s.l.

Figure 1 - Position of Sierra de Guadarrama in Central Spain
Figure 1 – Position of Sierra de Guadarrama in Central Spain (orange square in inset), and zoom in the area including the position of the monitoring stations of the GuMNet ( facility (red labels). The position of the town of Segovia is also shown. Altitude is given in masl. Image: GuMNet

Climate is Mediterranean mild summer Köppen Csb type for most areas and at higher altitudes develops on Bwk cold semiarid type. Landscape changes between forestry and pastures for the most part, but also holds scrub areas, mountain lagoons, streams and a variety of ecological and geological high value systems, some of glacial and periglacial origin. Pyrenian oak (Quercus pyrenaica) and holm oak (Quercus ilex) are present, although coniferous forest (Pinus sylvestris) is predominant.

Figure 2 - View of the Monastery of San Lorenzo de El Escorial
Figure 2 – View of the Monastery of San Lorenzo de El Escorial (1032 masl) near the Herrería site in Figure 1. Image: GuMNet
Figure 3 - Views near Cercedilla, Juan Moya Idígoras (1890)
Figure 3 – Views near Cercedilla, Juan Moya Idígoras (1890). Source: Archivo General de la Comunidad de Madrid.


The area hosts also some of the most emblematic species of Iberian fauna, such as the Iberian imperial eagle (Aquila adalberti), black vultures (Aegypius monachus) and an overpopulation of Iberian wild goat (Capra pyrenaica), together with a variety of endemic amphibian highlights that often get their profiles shared in the public media. All together, this view is punctuated with small villages and has been a route of communication between the northern and southern plateaus since pre-roman times, often also a natural borderline between kingdoms and religions; yes, and sometimes also war frontline.

The Sierra is also regarded as strategic and valuable from a socioeconomic point of view, as a provider of raw materials and essential goods for people not only those living in the mountains, but also in cities located downhill in the plateau, like Madrid and Segovia. It holds water sources and acts as winter storehouse of snow that is later on released during thawing. Pinewood has been harvested for centuries and used for timber while Pyrenian oaks are handled and chopped in autumn to provide the dwellers of the region with firewood for winter. The oldest relict group of Pinus nigra near El Escorial actually dates back to the 16th century, when Madrid became the capital and intensive harvesting of wood for construction and heating developed. The quality of the soil has made them more suitable for livestock. Extensive pastures located both at the range foothills and high altitude prairies have made it possible to raise beef cattle, which holds the Appellation of origin of ‘Carne de la Sierra de Guadarrama’. Moreover, construction activities lean on the extended granite and gneiss formations that shape the distinctive landscape and architecture of the region.

In the last decades, the economic dimension of the Sierra de Guadarrama has progressively incorporated activities linked to the service sector, among which tourism has become the most profitable one. Its closeness to Madrid as well as its abundant natural and cultural heritage has attracted thousands of tourists every weekend for decades at the risk of jeopardizing very sensitive ecosystems. Even if the higher altitude third of the area is protected as a National Park, as in the case of other mountain environments in Europe, preservation constitutes a challenge in the absence of a clear unaltered past state that can serve as a reference for future planning, and also given the coexistence of many intertwined interests and activities: from fishing and hunting, to construction, wood harvesting, sports and leisure activities. Considering all this, it is not an exaggeration to think of the madrileños as the largest invasive species in the Sierra, but surely not the only one.

Indeed, it is not difficult to imagine global environmental change as the integral of local pressures like those in the example of our Sierra. However, we know that not all mechanisms impinging on local environment are local in their nature; some obey large-scale processes such as those involved in climate change. Global scale emissions of greenhouse gases and aerosols resulting from attending the energy demand of a continuously growing population modify the radiative balance of the Earth and climate at a global scale, while their consequences reach regional-local scales including mountain regions. The IPCC reports (Hock et al 2019) on a general decline of low elevation snow cover, glaciers and permafrost in mountain areas in recent decades, together with changes in species composition and abundance. Changes in the cryosphere, together with other processes affecting high elevation climates, affect the magnitude and frequency of natural hazards, infrastructures and socioeconomic activities. Current trends in the cryosphere and related mountain ecosystems are expected to continue and intensify their impact; all evolving for worse unless emissions are tamed down in the next decade. Mountains are the home of about 700 million people, and many more if their neighborhood of influence is considered. The local climate of our Sierra, or of any Sierra for that matter, is thus affected now by the global neighborhood. There, the Homo Sapiens becomes actually the offending species, not just the madrileños.

However, in spite of the relevant impacts on mountain regions we are experiencing, we argue that there’s a lack of infrastructures monitoring the response of high altitude climates. Monitoring of the atmosphere, land and the cryosphere as nests for their inner ecosystems, including societies, is crucial for a realistic understanding and awareness of the evolution of climate change in these regions. The value of such facilities increases with time and the long-term character of the information they can provide. However, the sustainability of such observational networks is expensive and institutions need to perceive they are good investments for long term planning and management; the paces of short term programming of institutions and the long term needs of management and maintenance of observational systems do not fit.

We have recently shown from observations and high resolution modeling (Vegas et al 2020) that a significant widespread warming over the Sierra de Guadarrama has taken place over the last decades, likely since the beginning of the 20th century, though no high elevation observations have stood for that long. Warming is evident since the 1950s in the Sierra and the nearby region of Madrid and accelerated through the last decades; warming rates being larger in autumn with values exceeding 1ºC/decade across the southern range side. These values are at the high end of those in Hock et al (2019).

Figure 3 - Views near Cercedilla, Juan Moya Idígoras (1890)
Figure 4 – Spatial distribution of trends in autumn for the period 2000–2018 for both a regional model simulation (shaded) and observational datasets (symbols). Altitude-contour lines are given in masl. Acronyms stand for GuMNet sites and sites provided by the Spanish Meteorological Agency: Cabeza Mediana (CBM), Colmenar Viejo (CLV), Cotos (CTS), Madrid Torrejon (MTJ), Madrid Barajas (MBJ), Madrid Cuatro Vientos (MCV), Madrid Getafe (MGF), Madrid Retiro (MRT), Navacerrada (NVC), San Rafael (SRF), Segovia (SGV), Talamanca del Jarama (TLJ). Source: Vegas et al (2020).

Research studies over the area have shown that the high warming rates are contributing to important environmental changes, one of them being the changes in the distribution of alpine species, which see themselves forced to migrate to higher altitudes, like 16 species of Lepidoptera (butterflies), which are in danger of extinction (Nieto-Sánchez et al., 2015). Climate change is also having an impact on the hydrological cycle, reducing snow cover in winter and shrinking flows of rivers and aquifers all over the year, aggravating the hydric stress these mountains are submitted to, as a distinctive feature of mediterranean climate. Moreover, higher temperatures translate into drier soils and vegetation, which has fueled an increasing number of wildfires in summer, such as the ones occurred in Robledo de Chavela in 2012, and 2020. Loss of soil productivity, and setback of agricultural and farming uses, alteration in biological cycles (carbon and nitrogen), or drop of bee pollination activity due to changes in hatching cycles are cherry picked examples of risks, just to name a few.

In the globalized village we are all neighbors and local stressors are the result long-range climate change influences, a result of the invasive species’ activities. Policy makers should understand that long term planning needs of systematic long term monitoring of climate at high altitude regions. Intensive local climate monitoring is fundamental to understand local environmental changes, and science based arguments seems the only way to have an objective compass that can rule out intertwined interests. If we want to preserve the rich ecological, cultural and social heritage bequeathed by highly sensitive mountain environments like Sierra de Guadarrama from the growing threat of climate change, comprehensive science based action plans must be accomplished. That would already be a good deal of a green deal.

In the meantime, GuMNet wishes you the best for Christmas and 2021!


Hock, R., G. Rasul, C. Adler, B. Cáceres, S. Gruber, Y. Hirabayashi, M. Jackson, A. Kääb, S. Kang, S. Kutuzov, A. Milner, U. Molau, S. Morin, B. Orlove, and H. Steltzer, 2019: High Mountain Areas. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.

Nieto-Sánchez, S., Gutiérrez, D., and Wilson, R.J.: Long-term change and spatial variation in butterfly communities over an elevational gradient: driven by climate, buffered by habitat, Diversity and Distributions, 21, 950-961,, 2015.

Vegas-Cañas, C., González-Rouco, F., Navarro-Montesinos, J., García-Bustamante, E., Lucio-Eceiza, E. E., García-Pereira, F., Rodríguez-Camino, E., Chazarra-Bernabé, A., and Alvárez-Arévalo, I.: An Assessment of Observed and Simulated Temperature Variability in Sierra de Guadarrama, Atmosphere, 11(9), 985,, 2020.