Aquatic bryophytes in Himalayan streams: testing a distribution model in a highly heterogeneous environment

Area of Science:

• Ecology
• Botany
• Environmental Science

Background:

• Aquatic bryophytes are sensitive indicators of stream health.
• Understanding bryophyte distribution is crucial for stream ecosystem assessment.
• Previous models for bryophyte distribution were developed in New Zealand.

Purpose of the Study:

• To investigate the factors influencing aquatic bryophyte richness, cover, and community composition in Nepal.
• To assess the applicability of a New Zealand-based bryophyte distribution model in the Himalayas.
• To relate bryophyte communities to physicochemical variables and habitat characteristics.

Main Methods:

• Sampling of aquatic bryophytes from 108 streams across varying altitudes in Nepal.
• Analysis of community composition, richness, and cover.
• Statistical analyses including multiple regression, DECORANA ordination, and TWINSPAN.
• Comparison with a hierarchical descriptive model from New Zealand.

Main Results:

• Community composition and cover significantly correlated with altitude, streambed stability, and alkalinity.
• Riparian land use showed evidence of impacting bryophyte cover.
• Maximum cover occurred at low-to-middle altitudes with steep slopes, high stability, and low conductivity.
• Bryophyte richness increased with altitude and moderate stability, but was lowest in unstable, low-altitude streams.

Conclusions:

• Aquatic bryophyte distribution in Nepal is influenced by altitude, streambed stability, and water chemistry.
• The New Zealand model showed similarities but also key differences, with streambed stability being more critical in Nepal.
• Habitat factors like large plant size and vegetative reproduction may explain widespread species distribution in challenging Himalayan streams.