Himalayan forests: resource for rural livelihood, massive carbon sink and indicators of changing climate

Abstract

The Himalayan forests are ecologically important for floral and faunal diversity. The forests provide many invaluable ecosystem services that have significant roles in the socio-economic and cultural lives of people living in these high mountains. However, these forests are facing rapid degradation due to economic growth and climate change. Adapting to these emerging challenges require a better understanding of linkages between human-environment and climate variables to manage these forests sustainably. Various aspects related to forest ecology and restoration, ecosystem services, forest growth and their response to climate are at an early stage of investigation in Bhutan Himalayas. Within this thesis, we have studied the aspects of regeneration and restoration, carbon storage and climate impacts on the high-altitude forest to provide more information relevant for forest management and sustainable utilization of resources. We investigated the socio-cultural values of high-altitude forests through the lens of ecosystem services to understand the importance of forests in the livelihood of rural communities. By assessing the priorities and values of stakeholders on a suite of ecosystem services, the research identified various gaps in the preferences of ecosystem services that can potentially lead to competing interests in forest management. The study highlighted several challenges that currently undermine sustainable forest management. This includes inadequate information on oak forest ecology and regeneration, forest biomass-carbon storage potentials, and forest’s growth response to changing climate. A nation-wide study of the old-growth oak forest of Bhutan indicated inadequate forest regeneration, particularly oaks, which is a huge concern for long-term conservation of these forests. Concentrated local experiments using exclosures and canopy gap creation indicated livestock grazing and inadequate canopy gaps as important factors leading to regeneration failure. On the other hand, forests without grazing resulted in undesirable bamboo thickets in the understory. An experiment using tree shelters and planted oak seedlings supported our findings on the adverse effect of grazing on oak regeneration. Tree shelters not only deterred seedling herbivory but also promoted the survival of seedlings and kept bamboo thickets at bay. Based on this study, we recommended tree shelter techniques as a promising avenue to regenerate oaks in the Himalayas and should be considered in the annual forest plantation programs. We quantified forest biomass and carbon storage potentials of two dominant forest types of high-altitude Himalayas––broadleaf forest and an adjacent conifer forest––to understand the role of these forest ecosystems in biomass accumulation and, subsequently, the carbon storage. The study estimated a total carbon stock of 366.7 ± 18.3 (Mean ± SE) Mg ha-1 (megagram per hectare) for broadleaf forest and 303 ± 9.3 Mg ha-1 for conifer forest indicating the importance to conserve these forests for climate change mitigation. The major challenge for the sustainability of these forests, however, lies in trees response to changing climate conditions, particularly to the ever-changing temperature and precipitation patterns in the Himalayas. We investigated this objective through a dendrochronological approach correlating tree growth of the high-altitude Himalayan larch (Larix griffithii) with climate (temperature and precipitation). The growth of trees was positively correlated with summer monsoon rainfall (May-August) and negatively correlated with the summer temperature indicating that summer precipitation and temperature were two crucial factors limiting tree growth. The study resulted in a reconstruction of 639-year (1379-2018) monsoon rainfall patterns over Bhutan Himalayas. The global weather patterns of El Nino-Southern Oscillation and Indian Ocean Dipole demonstrated a strong influence on the rainfall variability and consequently tree growth over Bhutan. With global climate projections predicting high rainfall variability in the future, the response of trees to these variations may significantly impact tree growth and forest distribution, which require further investigation spanning both temporal and spatial scales. The thesis is a comprehensive dive into the ecology of temperate old-growth forests of Bhutan Himalaya and is a significant contribution to the knowledge of these forests, in how they respond to human interference, and, potentially changing climate.