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Summary The assessment of biomass and biomass changes due to environmental influences requires not only stem or merchantable mass, but also branches and needles. They have been of relatively lit-tle importance to forest managers to date, but their inclusion in models can make the resulting predictions more precise. A hybrid method is described to derive regressions for site quality, needle and branch biomass for individual Picea abies trees. By using Swiss stand table data on tree density distributions, a traditional yield table for branch and needle biomass is computed, and from these, regressions are derived which use only age and site quality as independent vari-ables. Three tables for typical site qualities are given. The tabulated regressions include pseudo-probability values, coefficients of determination and estimated standard error for the overall models. These biomass fractions comprise a varying fraction of the tree, being important at low ages and much less so at later ages.

Biomass dynamics were studied in isolated relict stands of scots pine (Pinus sylvestris) on the dry steppe of Kazakhstan (53-54°N) where potential evaporation is 500-600 mm yr -1 and the rainfall is 250-260 mm yr -1 . Samples were taken from 7 plots in natural stands on sandy forest soils (age 13-110 years) and 10 plots in plantations on dark-chestnut-coloured soils (age 5-50 years). 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 indicated that the stability of these stands becomes critical at 10-20 years when foliage biomass reaches its maximum (7-13 t ha -1 dry weight), both in plantations and natural stands. Self-regulating mechanisms in natural stands provide stability that may not develop not observed in some plantations. Natural stands may show an abrupt decrease in foliage biomass at the time of canopy closure, but it increases again by age 40-50 years. In plantations this critical period may cause dieback and may trigger stand collapse before maturity. Stem and root biomass increases monotonically and does not depend upon stand origin. The total biomass production is influenced by ground water level and the presence of and depth to the clay layer underlying the sandy sediments.

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1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a

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