Trees Outside Forests of Kathmandu Valley

Abstract

Trees Outside Forests (hereafter TOFs) are one or more trees and or shrubs found in an area of <0.5 ha. These are found in all strata such as urban, suburban and rural. These are important for biodiversity conservation and carbon storage. Some TOFs serve as Tree Related Micro Habitats (hereafter TreMs) while some TOFs are important for timber production. All TOFs are important for firewood production. The broad objective of this research is to increase our knowledge in the field of TOFs by understanding biodiversity, carbon stock and ecosystem services provided by TOFs in urban-rural gradient in Kathmandu Valley. The specific objectives of the study are: to assess the species diversity of TOFs; to estimate the phytomass carbon stock and SOC of TOFs; to assess the ecosystem services (TreMs) provided by the TOFs and to assess the economic valuation (Timber and firewood) of TOFs. This research was carried out in Kathmandu Valley. Data were collected from May 2015 to February 2017. Inventory was performed in 209 randomly selected points by MS Excel using circular plots of 20 m radius in all three strata. Tree level characteristics of TOFs (height > 1.37 m and DBH ≥ 5 cm) in the plots were recorded along with quality class. Other organisms making one or more habitats or support on the TOFs species were also enumerated. Nests and cavities if present were noted along with the organism types. Sap or resin if present were also recorded. Soil samples were also collected from five cordial pits in each plot. A comparative analysis of species richness, similarity index, species diversity index, evenness, maturity index, species richness index, species importance value index (IVI), family importance value (FIV), tree density, phytomass carbon stock, Soil Organic Carbon (hereafter SOC), Tree related Microhabitats (TreMs) along with quality class, wood production potential and timber and firewood values were done in TOFs along the urban–rural gradient in Kathmandu Valley. A total of 6,210 individuals of 150 plant species [trees (n=121) and shrubs (n=29)] belonging to 111 genera and 57 families were recorded. These species came under 80 natives and 70 exotics. The average values of species number, species richness, Shannon-Weiner diversity index, evenness and Menhinick's species richness index were 6.32, 50.24 ha-1, 1.33, 0.61, and 1.24 respectively in the study area. The average species richness was higher in the urban stratum (55.95 ha-1). Similarity index was higher in urban-suburban (SI= 0.66) strata. The average Shannon Weiner diversity index was higher in the urban stratum (1.46). Average evenness was significantly higher in the urban stratum (0.67). The average Menhenick’s species richness index was higher in the rural stratum (1.28). Maturity index of the study area was 4.39. It was higher in rural stratum (6.74). The average values of tree density, phytomass carbon stock and SOC in the study area were 236.35 ha-1, 32.40 t ha-1 and 42.32 t ha-1. Average tree density was found higher in the suburban stratum (248.44 ha-1). Average species richness was found higher in the urban stratum (55.95 ha-1). The suburban stratum was richer in native species (53.33 %). Similarly, average phytomass carbon stock was significantly higher in urban stratum (39.41 t ha-1). But average SOC was higher in rural stratum (44.78 t ha-1). One thousand and thirty-eight individuals of 64 species were found to serve as TreMs. Four forms, 5 groups and 14 types of TreMs were recorded in the study area. All types were found in urban stratum. Similarly, 53 tree species were recorded with merchantable timber in the study area. The average tree density of quality class A was significantly higher and that of quality class B was higher in the urban stratum. The average tree density of quality class C was higher in the suburban stratum. Cinnamonum camphora and Pinus roxburghii were found to have more market values for total timber and firewood respectively. TOFs have diverged species diversity in the study area. C. camphora was found to be the important TOFs species for carbon storage, TreMs along with higher merchantable value of total wood. The study provides the baseline data useful for biodiversity conservation through TOFs, urban green enhancement, green urban planning and development, carbon sink management, TreMs along with the useful timber species suggesting a need for appropriate species selection for TOFs plantations. Gravillea robusta, C. camphora & P. roxburghii with highest IVI values and carbon storing capacities should be planted on urban areas for greenery and to enhance the air quality & manage carbon in the atmosphere. More tree plantations in TOFs areas are recommended for timber availability which would upgrade the local livelihoods, to lessen the import of wood & wooden materials, increase the urban greenery and create better environment. More researches on TOFs that is kept under forestry should be done.