the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Jan 2025
Timberline formation and relationship with climatic variables of Indian central Himalaya: role of topography
Abstract. The young and rapidly rising Himalayas, with their diverse landscapes and ecosystems, are highly vulnerable to climate change impacts. This study explores relationship between spatially different timberline altitudes and geological regions of the Indian Himalayan region. First time, geological and topographical influence of mountainous terrain on formation of high-altitude timberline in the Indian Central Himalaya has been described. Total 2,750 km of timberline was mapped using Landsat 8 (30 m) satellite images. Timberline occurs between 2600 m and 4365 m amsl altitude in the Indian Central Himalayan region but predominance (~75 %) was between 3200 m and 3800 m amsl. Geologically different regions have different representations of timberline altitudes. Maximum occurrence was in the Greater Himalaya (77 % of the total timberline, mean timberline altitude 3599 m asl) followed by the Lesser Himalaya (17 %, mean altitude 3424 m asl) and Trans Himalaya (6.3 %, mean altitude 3723 m asl). Timberline around summits which is far away from permanent snowline was not present in the Trans Himalaya, and was mostly present in the Lesser Himalaya (between two major geological faults). It was observed that occurrence of geological faults created habitats in greater number of Island Type Timberline (ITL), and also brought higher segmentation in Continuous Type Timberline (CTL). The average annual temperature was 9.9 °C ± 3.41, ranging from 1.0 °C to 18.3 °C, with average annual rainfall of 1049 ± 183 mm, varying between 609 mm and 1448 mm. CTL areas had high rainfall peaks in July (275 mm) and August (269 mm), with lower winter levels, while ITL areas experienced consistently higher rainfall year-round, peaking in July (325 mm) and August (255 mm). CTL temperatures dropped significantly with elevation, from 3.7 °C in January to below -5.5 °C, whereas ITL temperatures remained milder and more stable, ranging from 1.4 °C to 5.16 °C. In the high ranges of Indian Central Himalaya, geological disturbances accounted for the segmentation in continuity and created habitats for isolated timberlines. These observations indicate that geological factors have a considerable role in giving shape to continuation of high elevation forests and upper limits of timberline. At local scale topography is an obvious way to size up the landscape and influencing distribution of high-altitude tree species.
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RC1: 'Comment on egusphere-2024-3155', Anonymous Referee #1, 29 Jan 2025
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This manuscript focused on description of treeline elevation across Indian central Himalaya. The topic seems to be interesting. I like to see new but this version did not provide new information. It is limited by the descriptions.
Major comments:
The author may have confusing definition on treeline and timberline. In this ms, it should be treeline rather timberline through most part in the text.
For climatic treeline, the elevation in the Himalaya should be much higher than 2600m. Such a wrong description may result from an unclear definition of treeline.
As showed by a cited reference: Körner, C., and Paulsen, J.: A world‐wide study of high altitude treeline temperatures. Journal of Biogeography, 31(5), 713-732, 2004. Treelines tend to have a threshold temperature. The temperature descriptions in this text are very confusing.
The descriptions on treeline elevation and climatic variables are too general. There are no new messages.
The topic is related to treeline dynamics, but it has no deeper analysis. I cannot give more detail comments.
Citation: https://doi.org/10.5194/egusphere-2024-3155-RC1 -
AC1: 'Reply on RC1', Subrat Sharma, 02 Feb 2025
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General:
This manuscript focused on description of treeline elevation across Indian central Himalaya. The topic seems to be interesting. I like to see new but this version did not provide new information. It is limited by the descriptions.
We thank the reviewer for this valuable assessment. In this manuscript we have described on the role of habitat creation for timberline through geological processes, i.e., upliftment of summits along the fault line away from the permanent snowline which pave the way for alpine/treeline/timberline types of vegetation in the Himalayan region. Further, we explored the relationship between distributed timberline altitude and climatic variables at that altitude in the Indian Central Himalayan region. The study is first of its kind to investigate the formation of high-altitude timberlines influenced by geological and topographical terrain of Himalayan mountains.
Specific:
The author may have confusing definition on treeline and timberline. In this ms, it should be treeline rather timberline through most part in the text.
We thank the reviewer for the insightful comment regarding definition of Timberline and Treeline. The term in the manuscript used is Timberline, not Treeline. For clarity, the definitions of both terms are provided:
Timberline- A timberline is upper edge of a forest with at least 30% crown density. A timberline generally took a course of line of many miles in length parallel to permanent snowline (Singh & Rawal 2017, S.P. Singh 2018, Sah & Sharma 2018). In this concept, timberline is an entity (the upper edge of the forested vegetation towards high altitude leading to alpine meadows).
Treeline- A treeline is a transition zone or an ecotone between the upper edge of continuous and closed forests (Timberline) and a tree species line or the beginning of alpine grassland or scrubland (Körner 1998, Singh et al. 2021)
For climatic treeline, the elevation in the Himalaya should be much higher than 2600m. Such a wrong description may result from an unclear definition of treeline.
The term "climatic treeline" refers to the elevation at which climatic conditions, such as temperature, precipitation, and growing season length, limit the ability of trees to survive. The definition of the treeline can vary slightly, with some researchers focusing on the upper limit of tree growth, while others consider the zone where tree growth becomes sparse or discontinuous.
Generalization that the climatic treeline in the Himalayas occurs at an elevation around 2600 meters does not encompasses the complexities of Himalayan arc. Almost 2500 km long Himalayan arc (NW-SE) stretches over nearly 25o longitudes (~72o-~97o E), and takes a latitudinal dip (close to 26o 30’ N) in the central region of Nepal (Inset in Fig. 1. of the manuscript) hence, have a significantly lower latitudes (> 10° difference) than the farthest end in west (above 26o 30’ N). Thus, create diverse high-altitude tree vegetation resulted with interaction of specific location, local climate, and ecological conditions in these latitudinal and longitudinal bands. For example, latitudinal decline in global treeline altitude is known due to decreasing temperature towards north, and in an earlier study (Singh et al. 2019) we analysed Himalayan dataset (145 study sites ranged from 3200 m to 4900 m amsl), and found that treeline elevation decreases with increases in latitude (P < 0.01, global trend, decreasing temperature) but increases from NW to SW of the Himalayan arc (P < 0.001, regional pattern, increasing precipitation), along which the dominance of evergreen species among broad leaved trees increases and that of deciduous decreases (for details please see Singh et al. 2019). In the present study timberline elevation are taken into consideration which is location dependent (further variation in regional pattern) and is distributed considerably over a large landscape of the Indian central Himalayan region. An understanding of the Himalayan timberline requires approach integrating both the physical and ecological factors that influence tree distribution in these high-altitude regions.
As showed by a cited reference: Körner, C., and Paulsen, J.: A world‐wide study of high altitude treeline temperatures. Journal of Biogeography, 31(5), 713-732, 2004. Treelines tend to have a threshold temperature. The temperature descriptions in this text are very confusing.
Analysis of primary data from 21 stations (distributed in Western, Central, and Eastern Himalaya; representing different climate regimes along the Himalayan Arc; Joshi et. al., 2024), for three elevation transects leading to treeline suggest that re-parameterization of the climate models over the Himalayan data-sparse regions, especially for the alpine region of Himalaya where observed data are extremely scarce, and higher growing season temperature (9.2 ± 1.8 °C, 10.0 ± 1.4 °C, and 7.8 ± 1.7 °C for three regions) was more than normally found at treelines. These finding indicate that temperature conditions in high Himalayas are likely to be warmer than generally held out. In Indian central Himalayan study of Joshi et al. (2018), annual mean temperature at timberline altitude (3360 amsl) of NW aspect was 5.6 °C, however, at highest treeline altitude of the same location (3680 amsl) it was 5.8 °C. Comparing the two different aspects of the same altitude of treeline altitudes the annual mean temperature was slightly higher (6.0 °C) than the NW aspect. Such variations describe influence of topographical variability on timberline fomrations, and explain the aspect-related difference in treeline elevation in the Himalaya (Schickhoff 2005).
The descriptions on treeline elevation and climatic variables are too general. There are no new messages.
Investigations by field biologists have been described in smaller geographies limited to certain localities. For example, high altitude treeline ecotone in a high-altitude valley of the Indian central Himalaya has been described between 3020–3450 m asl by one field study (Gupta et. al. 2023), however in the present study minimum and maximum elevations of timberline in the entire region were 3043m and 4365m asl, respectively, with a mean timberline elevation of 3723m. Thus, the range of treeline ecotone will certainly change. In other geographies of the world, treeline dynamics were not found uniform in diverse ecologies (Holtmeier and Broil, 2007, Harsch et al., 2009). This study, first time describes a range of timberline altitudes at regional scale having diverse geographies shaping various tree- altitude-climate relationship. Further, first time it tells that past geological processes have created a niche for isolated timberline habitats far away from the permanent snowline (inner ranges) where climate is not similar to inner ranges. At a broader regional level, both climatic conditions and geological factors are pivotal in influencing the occurrence of the timberline. In contrast, on a more localized scale, the landscape's topography plays a vital role. In the inner ranges of the Indian central Himalaya, geological disturbances further contribute to the segmentation of timberline continuity, thus affecting various process of tree species and animal interactions in treeline ecotone above the timberline. The present findings suggest that geological factors play a significant role in shaping the continuity of high-elevation forests and the upper limits of the timberline, however, at local scale, topography serves as a key factor in assessing the landscape and influencing the distribution of high-altitude trees.
The topic is related to treeline dynamics, but it has no deeper analysis. I cannot give more detail comments.
Thank you for the comment. This article presents the findings on the geological influence of mountains on timberline formation in the Indian Central Himalayas. The study specifically focuses on Timberline at a regional level, with detailed analysis of timberline altitude and climatic factors.
We hope these explanations provide more clarity on the scope of present research.
We thank for further improvement of the manuscript.
References:
1- Gupta, R., Garkoti, S. C., Borgaonkar, P.: Composition, age-structure and dendroecology of high altitude treeline forest in the western Himalaya, India. Forest Ecology and Management, Volume 549, 121494, 2023. ISSN 0378-1127, https://doi.org/10.1016/j.foreco.2023.121494.
2- Harsch, M. A., Hulme, P. E., McGlone, M. S., Duncan, R. P.: Are treelines advancing? A global meta‐analysis of treeline response to climate warming. Ecology letters, 12(10), 1040-1049, 2009.
3- Holtmeier, F. K., BroiL, G.: Sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change at landscape and local scales. Global Ecology and Biogeography, 14:395-410, 2005.
4- Joshi, R., Kumar, S., Singh, S. P., Near surface temperature lapse rate for treeline environment in western Himalaya and possible impacts on ecotone vegetation. Trop Ecol 59(2), 197-209, 2018.
5- Joshi, R., Tamang, N.D., Balraju, W., Singh, S. P.: Spatial and seasonal patterns of temperature lapse rate along elevation transects leading to treelines in different climate regimes of the Himalaya. Biodiversity Conservation, 33, 3517–3538, 2024. https://doi.org/10.1007/
6- Körner, C.: A re-assessment of high elevation treeline positions and their explanation. Oecologia, 115: 445-459, 1998.
7- Sah, P., Sharma S.: Topographical Characterisation of high-altitude timberline in the Indian Central Himalayan region. Tropical Ecology 59(2): 187-196, 2018.
8- Sah, P., Sharma, S.: Geospatial Attributes of Western Himalayan Timberline over Himachal Pradesh. In Handbook of Himalayan Ecosystems and Sustainability, Volume 1, 265-280. CRC Press, 2022.
9- Schickhoff, U.: The upper timberline in the Himalayas, Hindu Kush and Karakoram: a review of geographical and ecological aspects, pp. 275-354. In: G. Broll& B. Keplin (eds.) Mountain ecosystems, Springer, Berlin, Heidelberg, 2005.
10- Singh, S. P.: Research on Indian Himalayan treeline ecotone: an overview. 163-176, 2018.
11- Singh, S. P., R. S. Rawal.: Manuals of Field Methods. Central Himalayan Environment Association, Nainital, 2017.
12- - Singh, S. P., Sharma, S., Dhyani, P. P.: Himalayan arc and treeline: distribution, climate change responses and ecosystem properties. Biodiversity and Conservation, 2019. https://doi.org 10.1007s10531-019-01777-w.
13- Singh, S. P., Singh, R. D., Gumber, S.: Interpreting mountain treelines in a changing world. Central Himalayan Environment Association and International Centre for Integrated Mountain Development, 2021.
Citation: https://doi.org/10.5194/egusphere-2024-3155-AC1
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AC1: 'Reply on RC1', Subrat Sharma, 02 Feb 2025
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