Global biodiversity is in decline, and the global climate is warming, jeopardizing the lives and livelihoods of millions worldwide. When discussing the root causes or obstacles to dealing with these crises, tree-cutting and forest clearance come to the forefront, mainly because tree-cutting and forest clearance destroy plant and animal habitats and disrupt the natural carbon sink, whose atmospheric emission contributes to global warming.
Yet, the world is losing its trees and forests at an unprecedented rate. As per the latest estimates of the Food and Agricultural Organization of the United Nations, humans have been cutting trees and clearing forests at about 10 million hectares per year between 2015-2020.
Understandably, halting and reversing the ongoing losses of trees and forests is a top priority for today's environmental sector. For that, ecological restoration of degraded forests and the generation of new forests via tree plantation is the key.
To that end, national and international initiatives, such as the UN's declaration of the year 2021-2030 as the “Decade on Ecosystem Restoration,” the World Economic Forum's initiative to plant 1 trillion trees by 2030, and Bangladesh Forest Department's yearly “National Tree Fair” commencing on the World Environmental Day of June 5, have been taken to make people aware about of the importance of tree planting to tackle the current environmental crises.
However, although tree planting is an old idea, planting trees for biodiversity and climate is relatively new. While conventional tree planting focuses on getting forest products, the latter seeks to set the building blocks of an ecosystem that can enhance biodiversity and climate resilience.
Planting forest lands with the monoculture of exotic Acacia is an example of a traditional tree plantation that yields forest products but carries minimal biodiversity or climate value.
Similarly, although we usually appreciate tree planting on natural grasslands, such an action could affect grassland biodiversity and release soil carbon into the atmosphere. That means selecting the wrong trees or planting them in the wrong places could harm biodiversity and climate.
So, what should be our strategy for tree planting to combat the climate and biodiversity crises? Although the specifics would depend on the target planting site, I suggest the following strategies for designing a biodiversity-friendly and climate-resilient plantation.
First, plant multiple native species and avoid exotics.
Many could argue that alien species such as Acacia and Eucalyptus have a market demand, and it's not easy to replace them with natives. I counterargue that the market demand for alien species did not arise independently; instead, we put tremendous effort into popularizing them, only now realizing that they harm native biodiversity.
We must rectify this mistake and start popularizing native species. Importantly, the chosen species mixture should include common and rare species instead of only commercially important ones. This approach will ensure consistency with our shifting policy focus from production to conservation forestry and set up a much-needed biologically diverse starting condition for the plantation.
Second, plant species from diverse functional traits.
Choosing species based on their functional attributes can clarify whether the selected species would benefit biodiversity and contribute to climate change adaptation and mitigation.
For instance, a species with high wood density sequestrate more carbon than a species with lower wood density; a species with dense roots can hold soils tightly and prevent soil erosion; species with bushy physical structures can attenuate tidal surges; nectar-producing plants can be attractive to insect pollinators; and species with dense foliage can support nesting format for birds.
Hence, tree planting for climate mitigation should include species with high wood density, while selecting species with dense roots and bushy physical structures can be vital for adaptation against coastal disasters.
Third, tree planting should be prioritized in habitats where trees occurred in the past.
It is commonly believed that planting trees anywhere is probably good for the environment. However, planting trees in the wrong places, such as natural grasslands, wetlands, or seagrass beds, can harm habitat diversity.
Except for the newly accreted chars in coastal areas or built-in ecosystems, we must exercise caution before putting tree seedlings in non-forested natural ecosystems. We should remember that every natural ecosystem has value, and destroying habitat diversity through tree plantation is unexpected.
Fourth, properly consider the land tenure and benefit-sharing mechanisms before launching tree plantations.
Nowadays, most conservation or adaptation projects include a tree-planting component, and it is not uncommon for semi-government and non-governmental organizations to set up community-based short-term tree-planting programs in areas with complex and unsettled land tenure issues.
Such a program could lead to forest encroachment or socio-political conflicts. Many tree planting programs on the Unclassed State Forests (USFs) in the Chittagong Hill Tracts are examples of that scenario. Launching community-based tree-planting programs with Rohingya refugees is also a legally debated case.
In contrast, Bangladesh Forest Department's social forestry program on forest land with a proper benefit-sharing mechanism exemplifies a successful case. Since tree planting is a long-term program, attention must be given to whether the planting agency or community has legal authority over the land.
Fifth, the management focus for a biodiversity-friendly and climate-resilient plantation must go beyond the planted trees and facilitate the natural regeneration of planted and unplanted species.
Innovative approaches, such as aerial seeding or seed broadcasting over the plantation, can also help generate biotic heterogeneity in the plantation.
To conclude, although tree planting can compensate for the loss of trees and forests, not all tree plantations can effectively combat biodiversity and climate crises. We must choose species wisely and plant them in the right places. We also need to remember that the benefits of a tree plantation can only be derived in the long run.
Therefore, modern tree planting programs must consider what benefits the environment today and, at the same time, consider what might be helpful for the environment 40-50 years from now.
Only a well-thought-out and carefully designed tree-planting program can help develop a biodiversity-rich and climate-resilient green Bangladesh where we can live and prosper harmoniously with nature.
Shekhar R Biswas is a professor of ecology at East China Normal University in Shanghai. Earlier, Program Officer at IUCN Bangladesh and consultant at UNDP.