title: Performance of an age series of alnus-cardamom plantations in the Sikkim Himalaya: productivity, energetics and efficiencies.
abstract: Biomass, net primary productivity, energetics and energy efficiencies were estimated in an age series of Alnus-cardamom plantations in the eastern Himalaya. The impact of stand age (5, 10, 15, 20, 30 and 40 years) on the performance of mixtures of N2-fixing (Alnus nepalensis) and non-N2-fixing (large cardamom) plants was studied. Large cardamom (Amomum subulatum) is the most important perennial cash crop in the region and is cultivated predominantly under Alnus trees. Net primary productivity was lowest (7 t ha(-1) per year) in the 40-year-old stand and was more than three times higher (22 t ha(-1) per year) in the 15-year-old stand. Agronomic yield of large cardamom peaked between 15 and 20 years of age. Cardamom productivity doubled from the 5- to the 15-year-old stand, and then decreased with plantation age to reach a minimum in the 40-year-old stand. Performance of cardamom in association of N2-fixing Alnus remained beneficial until 20 years of age. Annual net energy fixation was highest (444 x 10(6) kJ ha(-1) per year) in the 15-year-old stand, being 1.4 times that of the 5-year-old stand and 2.9-times that of the 40-year-old stand. Inverse relationships of production efficiency, energy conversion efficiency and energy utilized in N2-fixation against stand age, and a positive relationship between production efficiency and energy conversion efficiency suggest that the younger plantations are more productive. The Alnus-cardamom plantation system will be sustainable by adopting a rotational cycle of 15 to 20 years.
authors.affiliation: G. B. Pant Institute of Himalayan Environment and Development, Gangtok, Sikkim, India.
authors.forename: G
authors.initials: G
authors.lastname: Sharma
authors.forename: E
authors.initials: E
authors.lastname: Sharma
authors.forename: R
authors.initials: R
authors.lastname: Sharma
authors.forename: K K
authors.initials: KK
authors.lastname: Singh
mesh_terms: D000465:Algorithms; D029661:Alnus / Q000254:growth & development* / Q000378:metabolism; D018533:Biomass; D003246:Conservation of Energy Resources / Q000379:methods; D017753:Ecosystem; D028523:Elettaria / Q000254:growth & development* / Q000378:metabolism; D016468:Forestry / Q000379:methods; D007194:India; D016014:Linear Models; D009586:Nitrogen Fixation / Q000502:physiology; D018514:Plant Structures / Q000254:growth & development / Q000378:metabolism; D013997:Time Factors