Researchers have used different geospatial datasets of land, soil, climate and topography to model, map and identify potentially suitable areas for trees in Nepal.

Farmers in Nepal grow trees in farming landscapes, considering them an integral part of the agricultural system, which is the mainstay of the Nepalese economy and, in addition to forestry, contributes about 27% of total gross domestic product. Agroforestry already plays a signi­ficant role in supporting the diversifi­cation of livelihoods and increasing socio-ecological resilience in various climate-change scenarios. The recently endorsed National Agroforestry Policy of Nepal has one of its goals as the development, expansion and commercialization of agroforestry systems to contribute to national prosperity. Yet, land is a fi­nite resource and its productivity varies geographically, especially, in a small and mountainous country such as Nepal. Government planners, development agencies and scientists did not have enough information about which parts of the country were suitable for agroforestry in order to meet the objectives of the national policy. This was a challenge that researchers set out to meet.

A research team — from the Vindhyan Ecology and Natural History Foundation, Ranchi University, Ministry of Forest and Environment and World Agroforestry (ICRAF) South Asia Regional Program — recognised the need to scienti­fically evaluate the potential for speci­fic land uses while ensuring sustainability. The findings from their subsequent study have been published in the journal, Modeling Earth Systems and Environment.

‘On-farm tree cultivation is potentially crucial for livelihoods’ strategies and forest conservation but varies depending on local contexts in Nepal,’ said Bishwa Nath Oli, secretary, Ministry of Forest and Environment, Government of Nepal, and one of the co-authors. 

Firoz Ahmad from the Vindhyan Ecology and Natural History Foundation in Uttar Pradesh, India and the lead author, emphasizes, ‘To understand the potential areas in the country that might be suitable for growing trees, we investigated the global geospatial datasets of Nepal and integrated them into a GIS platform using a modelling concept.’

The team drew on the Harmonized World Soil Database from the Food and Agriculture Organization of the United Nations. Six parameters were used: nutrient availability, nutrient retention capacity, rooting conditions, oxygen availability to roots, excess salts and toxicity. These help in understanding a soil’s qualities for crop production in agroforestry systems. The parameters were merged into a GIS database of Nepal with equal weight for each layer. Climate factor data, such as mean annual temperature (1970–2000), precipitation and mean annual aridity, were used to create maps (retaining a 1-km spatial resolution). Topographical and land vegetation data, such as Digital Elevation Model, were used to create a slope map and MODIS Normalized Difference Vegetation Index data to create a map for the quanti­fication of vegetation vigour and health as an indicator of degradation, sensitively linked to erosion and water control.

The overall analysis revealed that 18.9%, 12.8% and 68.3% of the total land area of Nepal is considered to be suitable for trees, respectively, with low (less than 30%), medium (30–60%) and high (more than 60%) categories.

Nepal is broadly divided into three ecological zones: Tarai (17%); Hills (68%); and Mountains (15%). Although about 68.6% of the Tarai region has a rating of over 80% suitability for trees, the area features only 40.2% tree cover. Similarly, 67.7% of the Hills region that has greater than 70% suitability has only 49.2% tree cover. The Mountains region retains snow cover most of the year, with undulating terrain, and take up roughly 28.1% of the nation’s land area, featuring greater than 60% tree suitability but with only 22.9% tree cover.

The total agricultural area, including rainfed and irrigated cropland, is approximately 24% of the country’s total geographical landscape. One-third of this total is rainfed cropland, with 83% identified as having greater than 60% suitability for trees. The research team also ranked 862 villages as having more than 80% of land suitable for trees, a fact that could be harnessed for expanding the scale of integrated agroforestry practices.

‘The findings addressed one of the most important research gaps about the potential of land to grow more trees for environmental and social benefits,’ said Javed Rizvi, co-author and director of ICRAF’s South Asia Regional Program. ‘With the new national policy, there is a mandate for expansion of tree-based systems across the nation. But where, exactly? And which trees would be most suitable for which areas? These were questions that until now no-one could answer. This research has gone a long way toward giving us the full set of answers that the nation needs.’

Traditionally, agriculturalists from Nepal have grown trees on their farms and produced diversifi­ed products, such as annual crops, cattle, honey, medicines and aromatic plants. Outstanding examples of agroforestry in Nepal and neighbouring South Asian countries include multifunctional homegardens, which boost food security and heterogeneity; woody perennial agroforestry systems, which contribute to job creation and rural farm-based industrialization; fertilizer trees and shrubs and integrated tree-pasture/crop production, which promotes natural resource conservation; and a tree-dominated environment, which assists agrobiodiversity and climate-change mitigation.

Read the journal article

Ahmad F, MM Uddin, Goparaju L, Dhyani SK, Oli BN, Rizvi J. 2020. Tree suitability modeling and mapping in Nepal: a geospatial approach to scaling agroforestry. Modeling Earth Systems and Environment (2020) DOI 10.1007/s40808-020-00922-7. [Please note the article is not open access]