Selective logging of trees in Western Ghats impacts epiphyte community

New study finds increase in abundance and diversity in areas that were selectively logged 40 years ago

Forest canopies, dubbed as the last biological frontier, house vascular epiphytes, which form a rich assemblage of plants within the forest canopy. Described as plants that grow on other plants and are devoid of any connection to the soil, epiphytes are said to sustain diverse taxa apart from fulfilling critical ecological functions.

Vascular epiphytes are particularly sensitive to perturbations of microclimate and microhabitat within the canopy, especially from changes such as logging. Selective logging of trees in the Western Ghats profoundly impacts the epiphyte community and the effects continue to persist even 40 years after logging activities were stopped, finds a new study published recently in the journal Frontiers for Forests and Global Change.

Though epiphytes are well studied in parts of Central and South America and parts of Europe, in India, this was the first assessment made, said lead author K.S. Seshadri, a DST-INSPIRE Faculty Fellow at the Centre for Ecological Sciences, Indian Institute of Science.

“We found over 2,000 individuals of 20 epiphyte species growing on 177 of the 200 trees sampled. We compared the diversity of epiphyte species and abundance between an area where trees were selectively logged 40 years ago and another area that was unlogged. We found an increase in abundance and diversity in the logged forest compared to unlogged,” he said.

When the researchers compared the sharing of host trees among epiphytes, a greater number of them were growing on the same tree in selectively logged compared to unlogged.

“This suggests an overcrowding effect, either because of suitable conditions such as light availability or lack of substrates due to logging,” he explained, adding that one of the reasons so few studies exist is because they are difficult to be observed from the ground.

The other authors of the study, ‘Persistent Effects of Historical Selective Logging on a Vascular Epiphyte Assemblage in the Forest Canopy of the Western Ghats, India’ are R. Ganesan and Soubadra M. Devy from the Ashoka Trust for Research in Ecology and the Environment.

Researchers used a ‘Single-Rope Technique’ to gain access to the canopy and study epiphyte ecology in the remote forests of the Kalakad Mundanthurai Tiger Reserve in Tamil Nadu. Mr. Seshadri said they had to climb trees to study the epiphytes because they would not be visible from the ground.

According to the study, vascular epiphytes are diverse, comprising over 31,100 species distributed globally and accounting for nearly 10% of all extant plants. According to Dr. Seshadri, epiphytic plants are structurally dependent on the host tree.

“These plant communities on branches serve as a microcosm for other forms of biodiversity such as insects, either by providing food resources or by serving as refuge in the harsh climate in the canopy. Many epiphytic orchids attract pollinators such as bees and a myriad diversity of insects. Apart from supporting other forms of biodiversity, they are an important component of the forest which stores carbon by absorbing CO2. Because they are disconnected from the ground, they complete their entire life cycle in the canopy and constitute a great proportion of nutrients in the form of canopy soil-organic matter, comprising dead and decaying litter nearly equal to those from trees,” he explained.

Climate change has been termed as a major emerging threat as changes such as excess warming or excess, erratic rainfall will stress the epiphyte community because they are on average 40 ft above ground, and unlike species distribution ranges shifting upwards as it gets cooler, canopy epiphytes, have nowhere higher to go.

“The other major threat to epiphytes, especially orchids, is the illegal harvesting of plants for trade. One only has to go to a nursery to find all kinds of exotic orchids being sold. While many are cultivars, there is really no way to know if a plant was harvested from the wild. Not all epiphytic orchids grow at 40 ft high but are found to grow vertically on a tree. People may sometimes even collect fallen epiphytes, which should belong to the forest and not our homes,” Dr. Seshadri said.

The researchers hope that their findings contribute to the knowledge of vascular epiphytes from South and Southeast Asia and set the stage for future research and conservation.

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