If you say this to anyone that “more trees made Europe warmer instead of cooling it“, one might not think twice before concluding that you are insane -at least temporarily and on this occasion , also one would not hesitate to tag you as an illiterate – at least as a climate illiterate.
Even though most of us think that we are climate literate , there are chances that our preconceived notion of certain things , our understanding of certain things might not always be true.The study below does exactly that- it has the capacity to alter our knowledge on climate and trees.
Trees do wonders when it comes to cooling Earth. They suck planet-warming carbon dioxide from the atmosphere, locking it into their trunks, leaves, and roots to the tune of about 2.4 billion metric tons of carbon each year. But a new study has found, somewhat counter-intuitively, that more trees might not always mean a cooler planet. In fact, researchers examining 260 years of changes in European forest management found that—despite a 10% increase in wooded land—the continent’s forests have actually caused a slight increase in regional temperatures since 1750.From 1750 to 2010, the continent added almost 200,000 square kilometers of forest, and created a 0.12°C rise in temperature.
A new study published in the journal Science has shown that forests can function as effective carbon sinks only when sustainable forest management practices are followed. The study has claimed that more than 250 years of wood extraction and other unsustainable practices in European forests had led to the accumulation of 3.1 billion metric tonnes of carbon debt despite considerable afforestation. This afforestation drive, which favoured non-native conifer species over native broad-leaved species, caused these forests to fail at addressing the challenges of climate change.
The study reconstructed the land-use history of Europe from 1750 to examine the effects of these changes on the climate. It says that while deforestation removed nearly 200,000 square kilometres of forest cover in Europe between 1750 and 1850, subsequent reforestation efforts not only made up for the losses, but actually resulted in a net gain in Europe’s overall forest cover during the study period.
But the study also noted that these reforestation efforts mainly favoured conifer trees over broad-leaved species which had dominated the European landscape earlier. This resulted in an increase in the conifer species cover by over 633,000 square kilometres, while broadleaf species cover decreased by 436,000 square kilometres.
Replacing broad-leaved forests with conifers had another unintended warming effect. Since conifer leaves tend to be darker than broad-leaved ones, it resulted in an increase in the absorption of sunlight, adding to global warming. The study adds that conifers are more conservative with water, which leads to less evapotranspiration, and to drier air which further contributed to a warming effect on climate. Overall, air temperature over the forests increased by an average of about 0.12°C during the study period. Another observation made by the study was that in the past 250 years, approximately 85 per cent of Europe’s forests came under human management and have remained under practices such as wood extraction, thinning and litter raking, reducing the climate efficacy of afforestation.
The conifers are worse for the climate because they absorb more light with their dark color, trapping heat that would otherwise be reflected back into space. They also release less cooling water into the atmosphere through evaporation. Together, these two factors were to blame for 0.08°C of the region’s warming. Foresters removing trees for wood products contributed another 0.02°C by releasing carbon that would otherwise be stored in forest debris and soil.
“European forests have failed to realise a net (CO2) removal from the atmosphere, and this is due to the fact that humans extracted wood from unmanaged forests by bringing these forests under management,” Even a well-managed forest today stores less carbon than its natural counterparts in 1750.”
The study concludes that forest management in Europe over the past 250 years has not been climate-friendly. The researchers involved in the study suggest that “the political imperative to mitigate climate change through afforestation and forest management…risks failure, unless it is recognized that not all forestry contributes to climate change mitigation”.
Lessons for India
The findings of this study are relevant to natural forests in India which have been subjected to large-scale species conversion over past several decades. For instance, vast stretches in the Himalayas have been converted to monocultures of conifers such as pines and cedars mainly during the British colonial rule. These species are not only exotic but they also provide fewer non-timber forest products (NTFPs) or other ecosystem services to local people. They have also been found ineffective in soil and moisture conservation when compared to native broad-leaved species such as oak and rhododendron.
But Indian governments and foresters have not yet learned their lessons and continue to promote monocultures and plantation of exotic species in natural forests. Recent guidelines issued by the Ministry of Environment, Forest and Climate Change (MoEF&CC) are also problematic since they propose handing over of open forests and natural scrub areas of the country for captive plantations by wood-based industries. Monoculture plantations over these forestlands will create large-scale ecological, economic and social problems while frequent commercial harvests of unnatural species will further reduce the climate effectiveness of our forests, as suggested by the study.
It’s also tempting to extend these results to other regions. But Europe’s temperature increase was in large part due to the continent’s specific history of forestry, its location, and the kind of tree species that are present there. The tropics, especially, play by different rules—there, slowing deforestation is almost certain to contribute to cooling, because trees in the tropics release comparatively more water into the atmosphere, seeding clouds that reflect light. The European model does indicate, however, that we should be cautious about the promise of forests to solve our climate woes.