In Spain there are already a significant amount of observational evidences of the biological effects of climate change. The biological spring has been moved forward and the arrival of winter has been delayed, making the vegetative period 5 days longer every decade along the last fifty years, and in the mountains Mediterranean vegetation seems to be moving to higher altitudes. Many other modifications due to climate change have been observed along the last decade: more frequent and severe droughts, increased fire risks, higher emissions of biogenic volatile organic compounds of our ecosystems, etc. If the warming and the decrease of the precipitations foreseen for the next decades finally happen, they will affect the physiology, phenology, growth, reproduction, establishment and, finally, the distribution of living beings, and thus, the structure and functioning of the ecosystems. As a matter of fact, it has already been tested in experimental studies simulating warming and drought that some species will be more affected than others, causing the alteration of their competitive ability, which ultimately produces a modification in the composition of the communities. It has been observed for example that there is a decrease of diversity in our forests and bushes. Together with the structural changes, these studies have observed functional changes, like for example the decrease in CO2 absorption due to droughts, or the loss of nutrients in the leached after rains in response to global warming. Also, it has also been tested how the organisms will attempt to adapt even genetically to the new conditions, but this happens at a slower pace than climate change. The changes affect, and will affect, multiple productive, environmental and social services provided by terrestrial ecosystems. For example, the role of many of our terrestrial ecosystems as carbon sinks will be deeply compromised along the following decades. In the next years, the "a-forestation" policies of the abandoned agricultural spaces and the "reforestation" of disturbed zones should take into consideration the conditions that are projected for the near future.