Afforestation

Afforestation is a land-based carbon dioxide removal (CDR) technology focused on the conversion of non-forest areas into permanent forest ecosystems through systematic tree planting. It involves multidisciplinary approaches from forestry, ecology, soil science, and remote sensing to restore ecological function while enhancing terrestrial carbon sinks. Trees sequester atmospheric CO₂ via photosynthesis, storing carbon in both aboveground biomass (trunks, branches, leaves) and belowground biomass (roots), as well as through the incorporation of organic matter into soils. The process is enhanced by forest management practices that prioritize long-term carbon permanence and ecological resilience.

The success of afforestation depends on various factors including species selection, site conditions, climate, and management regime. Fast-growing species may offer high short-term sequestration potential, while native species contribute to greater ecological integration and soil stability. Carbon is stored not only in biomass but also in soil organic matter and mineral-associated carbon, which may persist for centuries. The measurement of sequestered carbon relies on direct forest inventories (height, DBH, canopy structure, and density), remote sensing technologies (LiDAR, multispectral UAVs), and soil sampling protocols to track changes in soil organic carbon content.

To ensure scientific robustness, carbon accounting follows the IPCC 2006 Guidelines (AFOLU, Volume 4), offering three methodological tiers. Tier 1 uses default IPCC values, Tier 2 applies regionally calibrated coefficients, and Tier 3 relies on site-specific data and dynamic carbon models. These methods allow for the quantification of carbon stocks across five key pools: aboveground biomass, belowground biomass, dead organic matter, litter, and soil organic carbon.

The technological process of afforestation includes land preparation and for some tree species also growing of seedlings. For example, the growing of seedlings of Norway spruce (Picea abies) starts with sowing and growing spruce seedlings in a greenhouse as illustrated in Photo 1. One-year-old seedlings will be planted in the open field to continue growing for two more years until they are mature for planting in the forest as illustrated in Photo 2. After that, trees will be planted in the forest. However, there are several variations to the process. Sometimes the seedlings from the greenhouse can be planted directly in the forests (spruce, birch, pine), or seeds are sown on prepared soil in the forest (birch, pine).

Photos 1 and 2. One possible technology for sowing and growing of Norway spruce (Picea abies) prior to the planting to the forest. The seeds are sown into the cassettes in the greenhouse (left) and later planted in an open field for two years (right) before planting them to the actual destination in the forest.

In Estonia, seven pilot sites have been established to evaluate afforestation under varying ecological and historical land-use conditions. In Maardu-Jõelähtme, a 30.5 ha site #1 within a former phosphorite mine active until 1991, 20 ha have been reforested primarily with larch (Larix spp.) (Photo3). Long-term monitoring (up to 40 years post-planting) includes tree growth parameters, canopy metrics, vegetation composition, and soil properties (moisture, pH, temperature). Measurement tools include traditional field instruments (e.g., diameter tapes, clinometers) and UAV-based remote sensing.

Photo 3. View of the Maardu–Jõelähtme pilot site showing reforested plots with larch (Larix spp.) trees. Monitoring focuses on the long-term impact of afforestation on former mining land.

Photo 4. Photograph of the Grandas de Salime pilot site, reforested with native species after a wildfire. Focus is on forest regrowth, biodiversity recovery, and post-disturbance carbon sequestration.

All pilot sites will be monitored from April to September 2025. Across all sites, no operational problems have been reported. This integrated platform offers comparative insights across different forest types, land-use histories, and ecological contexts, supporting the advancement of afforestation as a scalable, scientifically validated CDR strategy.