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Ecological Importance of the Himalayan Rhododendron Forests

By Shweta Basnett

Alpine rhododendron habitat © Shweta Basnett

Rhododendron is one of the largest flowering plantgenera of the Himalayan region, exhibiting excellentdiversity in their life forms. In temperate forests,tall rhododendron trees co-occur with castanopsis and conifers. While in the higher subalpine forests, rhododendrons are found as an understory of conifer trees. Furthermore, in the alpine region, rhododendron occurs as dwarf shrubs along with other alpine flowering herbs. The high diversity in its life forms may be one reason why rhododendrons form a dominant plant community of temperate, subalpine, and alpine forests in the Himalayan region.

Tall trees of R falconeri in the Temperate forest © Shweta Basnett

Subalpine Rhododendron forests © Shweta Basnett

Globally, they are recognised as important ornamental plants due to their beautiful and vibrant inflorescence. However, in the Himalayan forests, rhododendrons offer much more than its ornamental value. Rhododendrons flowering in the Himalayan foothills are recognised as spring's onset since it is one of the first flowering plants to bloom immediately after the harsh winters. Therefore, its nectar, pollen, and flower form essential food resources for many birds and insects. In return, these insects and birds serve as the potential pollinators of rhododendron species. The flowering season of rhododendron attracts diverse obligatory and facultative nectarivorous birds, and its sequential flowering along the elevation gradient facilitates the movement of these birds from the lower to the higher elevation. Firetail sunbird, yuhina, warbler,

laughing thrush, hoary-throated barwing are some of the dominant pollinators of rhododendrons.

R.campylocarpum pure stand in the subalpine forest Sikkim © Shweta Basnett

Flowering of R. wightii first species to flower in the higher elevation © Shweta Basnett

Firetail Sunbird female visiting R campylocarpum © Shweta Basnett

Tickells leaf warbler visiting R hodgsonii © Shweta Basnett

Hoary throated barwing visiting R arboreum © Shweta Basnett

Besides birds, rhododendrons are also pollinated by diverse bees, including bumblebee, Apis dorsata and Apis cerana. These bees are also commonly known as the crop pollinators; however, their high dependence on the wildflowers such as rhododendrons also highlights the importance of conserving wild plants to maintain the proper functioning of the native pollinators. Other important insects supported by rhododendrons are flies. Flies are the dominant pollinators of higher elevation flowering plants; however, in the Himalayan region, their roles as pollinators are highly unexplored.

A bumblebee visiting R aeruginosum © Shweta Basnett

A bumblebee visiting R anthopogon© Shweta Basnett

Flies visiting R aeruginosum © Shweta Basnett

Hover fly visiting R campylocarpum © Shweta Basnett

Besides serving as an essential food resource for birds and insects, rhododendron thickets in the temperate and subalpine Himalayan regions provide a perfect habitat for Himalayan black bear, red panda, musk deer, tragopan,blood pheasants, monal, etc. In the higher elevation, during late winters and early spring, the heavy snowfall creates food scarcity for grazers. That's when ungulates such as musk deer feed on the evergreen rhododendron leaves. Similarly, the understory of conifer-rhododendron forests supports the growth of wild tuber plants-Aresima, a typical food preferred by pheasants and monal.

A musk deer © Shweta Basnett

A musk deer © Shweta Basnett

A blood pheasant © Shweta Basnett

A blood pheasant © Shweta Basnett

A Himalayan monal © Shweta Basnett

The conservation of rhododendron forests in theHimalayan region is crucial as it is one of the dominantand highly connected species in the food web's trophicinteractions. There is a clear linkage betweenrhododendrons forests and the biodiversity of birds,insects, and animals. So any loss of rhododendrons may trigger high numbers of secondary extinctions with severe consequences on the ecosystem.

Dr. Shweta Basnett completed her Ph.D. in 2019 on Evolutionary Ecology of Himalayan Rhododendrons from Ashoka Trust for Research in Ecology and the Environment (ATREE) Bengaluru. Her doctoral work contributed to understanding Rhododendrons' plant pollinator interactions and reproductive phenology in the Sikkim Himalayan region. Her study identified the temperature, evolutionary history, and pollinators as the critical driver determining the budding, flowering, and fruiting of high elevation Himalayan Rhododendrons. She has published multiple papers in reputed international journals, and her findings were covered in the Hindu and highly estemmeed nature and conservation magazines in India. In 2018, her work on Rhododendron Phenology won the best oral presentation award from the Bio Meteorology Society in International Phenology Conference held in Melbourne. In 2020, she received a research award from the American Rhododendron Society to further study Himalayan Rhododendrons' biochemical and morphological traits. Under the Full bright-Nehru postdoctoral program at Maryland University, Dr. Shweta will seek to understand the effect of changes in the biotic and abiotic environment on the evolutionary history of mountain endemic plant- pollinator interactions. This work also involves estimating the survival/evolution of endemic plant-pollinator interactions under future climatic scenarios. The outcome of the work will contribute to detect global conservation priorities for one of the largest flowering plant genus, Rhododendron, and its associated pollinators in the face of climate change.


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