In the mountains of west-central Himalayas, India, mixed Oak forests and conifer Pine forests are most abundant. Anecdotes and studies suggest that the monotonous conifer pine forest is replacing the water-retaining oak forests. We wanted to understand how this change affects water and energy partitioning and regulation in these forests. We measured the use of water by oak and pine forests closely at multiple scales (tree, stand, catchment), using towers with sensors, flumes, and special equipment.

We found that the pine forests use more water than the oak forests, especially during and after the rainy season. Oak trees catch back by water when the weather dries, which helps keep moisture in the soil. We also saw that water in streams comes out quickly in dominated areas of pine, which may mean less water is available in dry times.

Overall, this transition from oak to pine shows the water availability in the forest soil and streamflow and their seasonality. It also shows the impact of this transition on the regional atmosphere. This means that shifting from oak to pine trees could seriously affect water availability for both people and the environment in the Himalayan region.