A few months ago we said that Spain was getting greener. We did not refer to renewables, but the spectacular effects of an exceptionally rainy spring that away the ghosts of the past. The problem was what would happen after those rains and if the drought would call the door again. Now we are in a totally different scenario: heat waves that are chained and, as every summer of recent years, the fight against fires. In spite of everything, and to climate change, NASA shows that Andalusia is today more “green” than in the 90s.
And it is not to be too excited.
Short. Spain is a country with drastic microclimal changes on which the flora depends. In the south of the Peninsula, it is the Mediterranean forests that occupy 26% of Andalusia and the conditions of much of the soil have made pines and oaks the dominant species, since they adapt well to areas without plant cover.
Andalusia is a good study scenario because climate change clearly draws its effects, such as upward temperature, decline rains and increased aridity. And, as we see in Phys, a team of researchers has published in Ecological Indicators how these forests have responded during the last 30 years.
Tools. For the analysis, the researchers used more than 5,000 satellite images captured between 1994 and 2021 obtained thanks to Landsat 5 and Landsat 7, from NASA. In total, they analyzed 2,358 plots that compared with Google Earth Engine data and created an “greenery” index measured by NDVI.
They are the acronym of ‘Standardized Difference Vegetation Index ”, a way of quantifying, through satellite images or remote sensors, how much living vegetation there is in an area. In short, it is something that indicates the amount and vigor of the vegetation, being a tool widely used in studies of agriculture, natural resources management or those associated with climate change.
Black squares represent 2,358 farms analyzed. In the most dependent areas of agriculture, the effects are much more limited
What do we see. In general, except red eucalyptus, all species have shown an increase in this NDVI value, something that points to sustained revergeration. In trees such as holm oaks, cork oaks and pines, the maximum moment of activity is concentrated in the soft winter months, falling in the summers. And the chestnut, which is the only deciduous species of the study, operates on the contrary.
The effects of climate change and aridity have a decisive role in these cycles, lengthening the period of activity of the Carrasco pine and the resin in the driest places and shortening that of other pine species, such as the wild, and that of the wild olive tree. Between 1994 and 2005, the growth of these species was evident, and followed its course from 2005 to 2021, although at a more moderate speed.
¿Because? The result is that, the green territory is now greener and the conclusion is that many species have maintained or increased its green coverage. There are several explanations, and very diverse. The Carrasco or Encina pine are designed to withstand heat and drought, which allows them to remain active when other species lower the activity. Here has played a role of natural reforestation and regeneration policies, as well as global factors such as the increase in atmospheric CO₂ that would act as fertilizer.
There are also factors directly related to human activity, such as a progressive abandonment of farmland in certain areas that has favored the natural regeneration of the forest, as well as changes in land use, such as the decrease in livestock pressure that reduces the degradation of the undergrowth.
We have also influenced the contrary, as with a cork oak, which we extract cork periodically, limiting the regeneration of the tree.
Nuances. The study is very useful to see the current situation of the Andalusian Mediterranean forest, but also to observe which are the most resilient species and those that best adapt to changing conditions and a rampant aridity. And the conclusion of the study is that things are not going well, but due to that resilience of some species and, despite the continuous increase in annual average temperatures, most species did not demonstrate a relationship between phenological metrics and that increase in temperature.
And, perhaps, the most important thing is that the greenest does not equals a healthier vegetation, since various factors (natural and human) intervene and we see that this revergence is nothing uniform, with a south and this drier in which the vegetation is hardly growing. But well, as researchers point out, seeing which species are more resistant and adapt better is something that allows you to find the best options for adequate reforestation policies, not as we are doing in many places in Europe.
Before we talked about that rainy spring that moved the ghost of drought and that summer was returning to reality. And the recent restrictions in Galicia are a sad sign of this.
Image | José Sánchez Rodríguez and Rafael Palomo López
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