Himalayan treelines might be climbing higher in response to climate change

Subject: Schemes

Section: Education

Context:

Alpine treelines in the Himalayas and Hengduan regions are ascending towards mountaintops in response to climate change.

Details:

The treeline, marking the highest altitude where trees grow, forms a transition from forests to treeless alpine vegetation.
This environment, typically harsh and characterized by low temperatures, is sensitive to climate changes.
Recent studies reveal that these treelines are affected by temperature and moisture, with varying impacts across different species.
For example, in the Himalayas, treelines are primarily moisture-sensitive, while in the Hengduan region, they are affected by both temperature and moisture.
The study also reports differences in seedling recruitment and treeline shifting rates between Nepal and the Hengduan Mountains.
- The Hengduan Mountains are a group of mountain ranges in southwest China that connect the southeast portions of the Tibetan Plateau with the Yunnan–Guizhou Plateau.
- The Hengduan Mountains are primarily large north-south mountain ranges that effectively separate lowlands in northern Myanmar from the lowlands of the Sichuan Basin.
Global studies show that mountain treelines are generally rising, with the rate of ascent accelerating, especially in tropical regions.
This phenomenon underlines the importance of factors like precipitation and temperature in determining treeline distribution and dynamics.

Alpine Forests:

Altitudes ranging between 2,900 to 3,500.
These forests can be divided into: (1) sub-alpine; (2) moist alpine scrub and (3) dry alpine scrub.
The sub-alpine forests occur lower alpine scrub and grasslands.
It is a mixture of coniferous and broad-leaved trees in which the coniferous trees attain a height of about 30 m while the broad leaved trees reach only 10 m.
Fir, spruce, rhododendron, etc. are important species.
The moist alpine scrub is a low evergreen dense growth of rhododendron, birch etc. which occurs from 3,000 metres and extends upto snowline.
The dry alpine scrub is the uppermost limit of scrub xerophytic, dwarf shrubs, over 3,500 metres above sea level and found in dry zone. Juniper, honeysuckle, artemesia etc. are important species.

Understanding treeline dynamics:

Dendrochronology, the study of tree rings, plays a vital role in understanding historical mountain ecosystems.
It helps determine the age of trees and analyze the relationship between climate factors and tree growth.
This method reveals whether a treeline is static or shifting; older trees at the upper boundary suggest a static treeline, while younger trees at higher elevations indicate a moving treeline.
The correlation of annual tree ring widths with climatic data from nearby stations enables researchers to identify limiting climatic factors for tree growth, such as low rainfall leading to smaller rings.
However, treeline shifts are not solely due to climate change. Microbes, fungi, and symbiotes are crucial in supporting alpine tree growth, impacting hydrogen acquisition and seed growth.
The shift in treelines raises concerns about the availability of these biotic conditions. Understanding treelines, particularly in the Himalayas, requires long-term studies from permanent plots to identify the key driving factors.

Consequences:

The upward movement of treelines in the Himalayas, driven by climate change, significantly impacts the region’s mountain ecosystems.
This shift can lead to habitat displacement and loss, affecting plant and animal species adapted to specific elevations and potentially causing local extinctions.
The changing landscape disrupts the intricate relationships between flora and fauna, altering biodiversity patterns, with some species thriving and others declining. Non-vascular plants like bryophytes and lichens, which exist beyond the treeline, face increased competition from advancing sub-alpine forest trees for resources like light.
This upward movement of trees also alters soil properties, such as nutrient content and moisture, impacting understorey plant communities.
Additionally, the growth of sub-alpine forests in previously treeless areas can significantly affect hydrology, potentially reducing stream flow and runoff downstream, particularly in areas where water is already scarce.

Conservation measures:

Understanding the shifting alpine treelines in the Himalayas requires addressing the research gap in treeline dynamics, particularly using precise and updated data like remote sensing rather than outdated toposheets.
Experts emphasize a comprehensive conservation approach, involving habitat preservation, reforestation, effective water management, community engagement, and policy support.
Continuous research, monitoring, and international collaboration are essential for understanding and managing the shifts in treeline and ecosystem dynamics.
Additionally, generating and monitoring baseline data on plant species populations is crucial, considering treelines as part of a broader ecological context, including adjacent eco-regions.