Skip to main content

Carbon Accumulation over Succession to Enhance mitigation of CO2 emissions

Periodic Reporting for period 1 - CASE-CO2 (Carbon Accumulation over Succession to Enhance mitigation of CO2 emissions)

Periodo di rendicontazione: 2018-06-01 al 2020-05-31

During the last decades, the concentration of greenhouse gases (GHGs) in the atmosphere has risen up to unprecedented levels since the beginning of the industrial revolution, reaching 405.5 ppm in 2018. This increase is expected to continue over the XXI century, causing a large number of environmental as well as socio-economic problems. However, trees are able to capture carbon though the photosynthesis, and therefore, increasing the forest cover might be one of the most effective strategies to offset CO2 emissions across the globe. The area covered by trees can be increased by means of the deliberate planting of trees in areas that were once covered (i.e. reforestation) or not covered (i.e. afforestation) by forests. However, it has also occurred as a consequence of the spontaneous revegetation of formerly cultivated areas that have been abandoned as a consequence of its low productivity and/or the difficulties for the mechanization of the agrarian labour, leading to a low economical profitability. This forest expansion in abandoned agricultural lands has been particularly pervasive in the Northern Hemisphere, where it has apparently contributed to the development of a persistent carbon (C) sink. However, whereas the C stocks developed as a consequence of this process have been quantified in some regions such as Eastern Europe and the former Soviet Republics, in others such as Southern Europe they have not. Moreover, there are still a large number of uncertainties concerning C accumulation in different parts of the forest (i.e. above- and below-ground biomass, woody debris, litter, soil), as well as on the role played by mean annual rainfall and temperature, and soil nutrient concentrations, among other factors, in this process, particularly in Mediterranean environments.

The overall objective of this project is to improve our knowledge on the process of carbon accumulation over forest expansion in abandoned agricultural lands, in a vast region of Central-North Spain (Castilla y León) that has been severely affected by this process. Specifically, we aim to quantify the C stocks developed as a consequence of forest expansion in abandoned agricultural lands, and shed light on the factors responsible for the process. The project has been developed in the Institute for Sustainable Forestry Management (iuFOR), located in Palencia (Spain), but depending on the University of Valladolid, with a two-month secondment in the School of Geosciences of the University of Edinburgh (United Kingdom).
"To attain the aforementioned objectives, first, the researcher selected five study sites in abandoned agricultural lands dominated by the main types of forests occurring in Castilla y León. In each of these sites, he and his collaborators located six permanent plots with differing ages of abandonment (30 plots in total), in which they perform an inventory of the woody vegetation (i.e. trees and shrubs), and they took fine woody debris, litter and soil samples. Second, they calculated plot-level values for the carbon accumulated in the above- and below-ground vegetation by using allometric equations, and by analysing the samples collected in the field in the laboratory. Third, they estimated the above- and below-ground carbon in all forests and other wooded lands developed as a consequence of agricultural land abandonment in Castilla y León. To this end, they analysed the Synthetic Aperture Radar (SAR) scenes of this region and adjusted the best fit models for the regressions between the radar backscatter (i.e. the return pulse of the microwave beam which is sent by the sensor and interacts with the main elements of the vegetation), and the above-ground carbon, in each plot. They used this relationship to estimate the above-ground carbon values in those areas in which there were no plots through interpolation algorithms. Finally, they assessed the main abiotic factors determining carbon (C) accumulation in above- and below-ground biomass, fine woody debris, litter and soil by means of Generalised Linear Mixed Models (GLIMMs).
The researcher and his team have obtained a few interesting preliminary results so far. Their findings suggest that a large carbon pool has developed in the areas affected by forest expansion as a consequence of agricultural land abandonment in Castilla y León, over the last 60-70 years. However, the persistence of this carbon pool over the next decades is threatened as a consequence of the increase in the frequency and intensity of droughts, fires and outbreaks of pest and pathogens driven by climate change, and the and the lack of appropriate management strategies. Moreover, climatic factors (i.e. mean annual rainfall and temperature) are among the most important drivers of C accumulation over the period in which agricultural land abandonment has occurred), which create doubts concerning the capability of these areas to continue sequestering carbon over the next decades.
The researcher could perform some of the Exploitation and Dissemination (ED) activities planned for the project. He developed a Plan for the Exploitation and Communication of Results: Dissemination, Outreach and Public engagement. The results were presented at the V Meeting of the ""Working Group in Forest Modelling of the Spanish Society of Forest Sciences"" (SECF), held at Solsona (Lleida) in November 2019. The researcher and his supervisor planned to attend to a couple of conferences more, and to organize a Workshop within the Congress of the European Chapter of the Society for Ecological Restoration (SERE). The researcher has written the drafts of two manuscripts and he will upload de CASE-CO2 dataset to the Open Access repository of the UVa once the two manuscripts were accepted for publication.
With regard to the Communication and Dissemination activities, the researcher gave a seminar in the University of Valladolid within the master DATAFOREST. He also participated in the European Researcher’s Night 2019 in Palencia, Spain."
To our knowledge, this is the first time that the spontaneous revegetation of abandoned agricultural lands has been studied in Mediterranean continental environments of Southern Europe from an approach related to the study of biogeochemical cycles. Although forest expansion in after agricultural land abandonment has been a common phenomenon in the inland regions of the Iberian Peninsula over the last few decades, this process had not been properly studied focusing on carbon accumulation.

The results of the project could be crucial in order to update the regional carbon balance, as well as to redefine the long-term greenhouse gases emission reduction strategies of countries such as Spain and Portugal up to 2050. They can be used to design appropriate strategies for the restoration, afforestation and management of abandoned agricultural lands in order to enhance CO2 sequestration, enhancing mitigation and adaptation to climate change. Moreover, over the last few years, a strong public debate has risen in Spain about what to do with the largely depopulated regions inland the country. The results of this study will surely contribute to define suitable management strategies for the forests and other wooded lands developed in abandoned farmland do far.