Planting trees is often seen as a flagship measure for environmental sustainability. However, it is now clear that simply planting trees is not enough.
The choice of species to be planted and their location play a fundamental role in the effectiveness and ecological benefits of these initiatives. Tree diversity, i.e. the variety and distribution of species within a forest area, is proving to be a crucial factor in ecosystem growth, maintaining biodiversity and building resilience to the effects of climate change.
In this article, we will explore four crucial points supported by studies that demonstrate the importance of prioritizing biodiversity-based reforestation over planting a single tree species, known as monoculture planting.
🦋 Reforesting with biodiversity allows:
→ To increase carbon sequestration capacity
→ To improve soil fertility
→ To increase forest resilience
→ To benefit local populations
Diverse forests have a higher capacity to sequester carbon from the atmosphere
According to IPCC recommendations, some 730 billion tonnes of CO2 need to be removed from the atmosphere by the end of the century in order to limit global warming to 1.5°C. Forests play a crucial role in carbon storage, and a 9% increase in global forest area by 2030 could sequester a quarter of the required atmospheric carbon.
A study entitled "Restoring natural forests is the best way to remove atmospheric carbon" highlights the crucial importance of restoring natural forests for carbon sequestration and the fight against climate change. According to this research, current efforts to restore degraded land through large-scale plantations will not be enough to achieve the desired climate targets.
Current restoration plans mainly favor monocultural industrial plantations, i.e. with a single tree species, which are less effective at storing carbon than biodiverse natural forests. These plantations are often subject to regular harvesting, which does not allow for optimal carbon sequestration, and can instead generate a carbon-emitting forest.
The study published in Nature indicates that, in contrast, naturally regenerated land can sequester carbon for decades, in addition to being in much higher quantities.
A more recent study from the University of Alberta also demonstrates that biodiversity can increase carbon storage in natural forest soils. It shows that the diversity of trees in a forest ecosystem plays an essential role in the carbon cycle, i.e. the balance created by the sequestration of carbon by an ecosystem and its return to the atmosphere through decomposition.
According to Professor Chang of the Department of Renewable Resources, tree diversity in a forest is a term used to describe three specific qualities of the given environment:
- Species richness, measured by the number of trees and species in the area
- Regularity, which Chang describes as the even distribution of species
- The different functions performed by each tree species in a forest
The restoration of biodiverse forests has thus been identified as a more effective solution for sequestering atmospheric carbon, particularly in tropical and subtropical regions.
Restoring forest biodiversity improves soil fertility
This same study, published in Nature last April, highlights the vital importance of tree diversity in preserving soil fertility.
According to Devon Earl, environmental scientist and conservation specialist with the Alberta Wilderness Association, different tree species have distinct physical characteristics that enable them to adapt to different situations. This diversity ensures forest resilience, particularly in the face of rapid environmental changes such as climate change and storms, by promoting carbon storage in natural forest soils. This adaptation is of crucial importance for the populations that depend on these ecosystems.
This research, carried out over almost 20 years and covering numerous forest plots across the country, has tracked changes in soil carbon and nitrogen over time. The results show that increasing species diversity led to increases in soil carbon and nitrogen of the order of 30% and 42% respectively. Similarly, an increase in functional diversity, which encompasses the variety of physical characteristics within the forest, increased soil carbon and nitrogen by 32% and 50% respectively.
Xinli Chen, postdoctoral student and lead author of the study, explains that more diverse trees often have greater biomass production, thanks to factors such as root depth and canopy height, which play a role in forest growth and development.
Increased forest resilience thanks to species diversity
A study published in August 2018 of 40 forest sites analyzed between 1982 and 2016 found that forests composed of diverse tree species are more drought-resistant, more storm-resistant and help reduce the risk of large-scale damage. Promoting the natural restoration of biodiverse ecosystems increases tree survival and the success of the reforestation project.
Each species plays a unique role in the ecosystem, and the loss of just one can have repercussions for the whole ecosystem. A lack of tree species results in fragile biodiversity, making the ecosystem more vulnerable to disease, invasive species and natural disasters. For, if one species is affected, other species will not be present to act as a protective buffer.
The social benefits of restoring diverse forests
In a joint press release, the World Rainforest Movement, Friends of the Earth International and the Global Forest Coalition highlight the considerable environmental and social benefits of restoring diverse forests.
By restoring forests with a rich biodiversity, local communities benefit from a significant improvement in their water sources thanks to the restoration of the natural hydrological cycle and a reduction in air and water pollution.
One of the most important rules when reforesting is to work in direct partnership with local populations, in order to take into account the specific needs of these communities. Forests are a source of subsistence and food sovereignty for their inhabitants and those of the surrounding land. It is important to preserve their traditional and sustainable ways of life, while preserving cultural diversity and encouraging community life to flourish without resorting to generalized violence. Community forest management, for example, creates local employment opportunities and promotes small-scale economic development.
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