Planting Trees as a Nature-Based Solution to Mitigate Climate Change. Opportunities, Limits and Trade-Offs

Trees and forests are of strategic importance for climate change mitigation, but limits and trade-offs are often underestimated. Trees interact with climatic factors with different mechanisms: carbon storage, albedo, transpiration, emission of organic volatile compounds (VOCs) with cooling or warming effects depending on species-specific characteristics and the environmental context. Planting trees poses problems concerning the correct choice of species and genotypes, the suitability of the planting sites, and the management after planting. Such limitations result in a series of potentially negative effects on the persistence (longevity) of plantation, the consumption of water, the depletion of nutrients from soil, the loss of biodiversity and possible warming effects connected to albedo and VOCs. Existing forests offer a large chance for a consistent increase of the biomass and soil carbon stock, and priority efforts should be devoted to the defense and restoration of damaged forests. Old forests assure a great efficiency in carbon retention and accumulation, whereas the role of managed forests is variable in relation to the kind and intensity of management. Considering the different factors involved, planting trees can have both a beneficial and detrimental effect on climate mitigation, and each situation should be considered in its own specificity, avoiding generalizations.