Biomass growth and structure of pine plantations and natural forests on dry steppe in Kazakhstan
1993
Usol'tsev, V.A. | Vanclay, J.K.
A study of biomass dynamics was carried out in isolated relict pine ( Pinus silvestris) stands on the dry steppe of Kazakhstan (53-54 N) where potential evaporation is 500-600 mm/ann and the rainfall is 250-260 mm. Samples were taken from 7 plots in natural stands on sandy forest soils (age 13-110 years, site index II-III) and 10 plots in plantations on dark-chestnut-coloured soils (age 5-50 years, site index II-III). Nine or 10 sample trees were taken from each plot, giving a total of 68 and 96 sample trees in natural and plantation stands respectively. Root systems were excavated and fractionated in 11 plots. Analyses of biomass dynamics in plantations and natural forests indicated that ecological stability became critical at 10-20 years when foliage biomass reached its maximum (7-13 t/ha dry weight), both in plantations and natural stands. Selfregulation in natural stands provides stability. At canopy closure, foliage biomass may decrease abruptly, but increases again at 40-50 years. In plantations this critical period may cause dieback and may trigger stand collapse by age 50. Stem and root biomass increases monotonically and does not depend upon stand origin. The total biomass attained is influenced by ground water level and the presence of and depth to the clay layer underlying the sandy sediments
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