Droughts and heat stress may also cause infestation in trees, research notes
Climate change and increased greenhouse gas emissions are likely to trigger forest losses in Himalayan Cedar (Cedrus deodara), commonly known as deodar, pointed out a recent study.
Researchers from India conducted studies at 17 sites from low, middle and high-latitude areas under two climate regimes of the Himalayas. The two climates are dominated by monsoon rainfall and westerly disturbances.
Deodar has a high demand in the market owing to its fine-grade timber, medicinal qualities and sacred use.
The growing climate crisis will result in up to 38 per cent decline in deodar growth for plantations in low- and mid-latitude regions, noted the study, Is survival of Himalayan Cedar (Cedrus deodara) threatened? An evaluation based on predicted scenarios of its growth trend under future climate change.
However, a moderate increase in growth is predicted for deodar trees located in high-latitude sites, noted the analysis published in journal Elsevier.
The scientists predicted possible greenhouse gas and aerosol emissions scenarios under representative concentration pathways (RCP) 4.5 and 8.5.
RCP 4.5 is a moderate scenario where global emissions peak around 2040 and then decline, as defined by the Intergovernmental Panel on Climate Change. RCP 8.5 is a climate scenario where business is as usual and emissions will continue to rise for the entire 21st century.
Hence, the projections due to climate change owing to RCP 8.5 will typically have more impact compared to the former.
“The predicted growth trends show forest loss between 34 per cent and 38 per cent under RCP 4.5 scenario while the decline is predicted to be for 29 per cent and 32 per cent for RCP 8.5 scenario,” JC Kuniyal, one of the authors, said in the study.
Deodar located in inner dry and outer moist ranges receives precipitation due to western disturbances from December to February and summer monsoon between June and September.
The tree is also known for its capacity to sequester a significant amount of carbon. However, climate change combined with anthropogenic activities such as deforestation and competition with other species has shrunk its distributional range.
Deodar faces threats from chir pine species, which shows more tolerance towards drought and fire and is also outcompeted at higher elevations by silver fir in moist areas and blue pine in dry regions.
Moreover, deodars also face insect attacks, causing heavy losses. Kuniyal said the deodar species was chosen due to its longevity and climate sensitivity, which facilitates tree ring studies. The species is widely used for studies concerning the Hindu Kush Himalayas (HKH).
While temperatures from March to May have a negative impact on tree growth, the spring precipitation leads to positive tree ring growth, analysis by researchers pointed out.
Heavy snowfall in the previous year’s winter is another factor favouring deodar growth, followed by pre-monsoon spring. The snowmelt in spring offers soil moisture and further helps the growth of deodar, enhancing photosynthesis.
The process increases food production and cambial (a tissue layer that helps plant growth) activity in March, April and May. However, dry conditions due to increased temperature during the growing season stunts tree ring growth. The high temperatures cause quick evaporation of snow-pack water that reduces moisture in the soil, suppressing photosynthetic activity and slowing the cambium activity.
“The chronology of high-latitude sites shows a significant positive relationship with November temperature, which prolongs the growing season,” the report noted.
Earlier analysis in the western Himalayas as per ecological modelling raised concerns about a decline in the potential habitat of this species owing to climate change.
However, the new findings revealed that deodar trees located at low and mid-latitudes may be unable to keep up with the increasing temperatures at RCP 4.5 and RCP 8.5 conditions.
Kuniyal said the decline in the growth of deodar is primarily due to temperature increase and precipitation decline during pre-monsoon months between March and May.
The researcher added that trees hypersensitive to drought and heat stress become vulnerable to pathogens and insect infestation.
“Insects causing epidemics in deodar are prevalent in the mesic site in this region. It has been known for a long time that Ectropisdeodarae, a defoliator (an insect that consumes leaves or needles) causes an epidemic of deodar in many parts of the HKH mountain region,” the study noted.
These findings may be used to take suitable migratory steps for the conservation of deodar in the HKH region, it added.
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