Abstracts

Irvine, J., Law, B.E., et al. 2004, 'Age-related Changes in Ecosystem Structure and Function and Effects on Water and Carbon Exchange in Ponderosa Pine', Tree Physiology, vol. 24, pp. 753-763.

As forests age, their structure and productivity change, yet in some cases, annual rates of water loss remain unchanged. To identify mechanisms that might explain such observations, and to determine if widely different age classes of forests differ functionally, we examined young (Y, ~25 years), mature (M, ~90 years) and old (O, ~250 years) ponderosa pine (Pinus ponderosa Dougl. ex P. Laws.) stands growing in a drought-prone region of central Oregon. Although the stands differed in tree leaf area index (LAI_T) (Y = 0.9, M = 2.8, O = 2.1), cumulative tree transpiration measured by sap flow did not differ substantially during the growing season (100–112 mm). Yet when water was readily available, transpiration per unit leaf area of the youngest trees was about three times that of M trees and five times that of O trees. These patterns resulted from a nearly sixfold difference in leaf specific conductance (K_L) between the youngest and oldest trees. At the time of maximum transpiration in the Y stand in May–June, gross carbon uptake (gross ecosystem production, GEP) was similar for Y and O stands despite an almost twofold difference in stand leaf area index (LAI_S). However, the higher rate of water use by Y trees was not sustainable in the drought-prone environment, and between spring and late summer, K_L of Y trees declined fivefold compared with a nearly twofold decline for M trees and a < 30% reduction in O trees. Because the Y stand contained a significant shrub understory and more exposed soil, there was no appreciable difference in mean daily latent energy fluxes between the Y stand and the older stands as measured by the eddy-covariance technique. These patterns resulted in 60 to 85% higher seasonal GEP and 55 to 65% higherwater-use efficiency at the M and O stands compared with the Y stand.

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Ježík, M., Blaženec, M., et al. 2007, 'Intraseasonal Stem Circumference Oscilations: their Connection to Weather Course', Oecologia, vol. 34, no. 2, pp. 105-115.

The diameter (circumference, radial) growth of trees is primarily connected with activity of secondary lateral meristematic tissues - cambium and phellogen. Their activity is linked with the basic physiological processes running in trees, the influence of which can be either direct or indirect. This process is also influenced by climate and weather fluctuations. At the same time, the tree stem with its tissues (bark, phloem, xylem) serves as a water reservoir for transpiration, and the short-time oscilations in the stem magnitude reflect the water balance and water potential of these tissues. The study ran in the vegetation period 2006. We measured short-time stem circumference changes on 1 beech and 3 spruce individuals in a primeval spruce forest in locality Predná Pol'ana (1360 m asl). In this contribution we deal mainly with inter-daily circumference changes and their connection to the seasonal weather course. A strong weather signal, affecting the circumference changes, was observed both on spruce and beech.

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Lagergren, F. and Lindroth, A. 2004, 'Variation in Sapflow and Stem Growth in Relation to Tree Size, Competition and Thinning in a Mixed Forest of Pine and Spruce in Sweden', Forest Ecology and Management, vol. 188, pp. 51-63.

The aim of this study was to analyse the relationship between different biometric parameters and sapflow and growth, respectively, in order to assess their potential for use in scaling. The effect of thinning on these relationships was also investigated. The studied stand consisted of Scots pine (ca. 60%), Norway spruce (ca. 35%) and downy birch (ca. 5%). Sapflow was measured by the tissue heat-balance method, and growth in circumference was measured by dendrometer bands, during a 3-year period. The thinning was carried out after 1 year of measurements. Regressions were calculated between sapflow and growth and tree diameter, needle mass estimated by allometry, and a competition index (CI), which depended on the distance and diameter of neighbouring trees. Both sapflow and growth were affected by strip-roads from a thinning ca. 8 years earlier. Before thinning, the variation in sapflow for spruce was best explained by CI when trees close to a strip-road were excluded; for pine, needle mass was equally as good as CI. In 1999 and 2000, needle mass generally explained the variation in sapflow best. Before thinning, the variation in pine growth was explained almost as well by diameter alone, as by CI. For spruce, needle mass explained most of the variation if all trees were included. If trees beside strip-roads were excluded, r² for CI increased and CI explained the variation best. Almost all spruces close to strip-roads had lower growth than was expected from their CI relationships; for pine, 13 of 23 trees had higher growth than expected. For the years after thinning, diameter was mostly at least as good as the other variables for predicting BA growth. It was concluded that a competition index is potentially useful for scaling, and that strip-roads affected both sapflow and growth of nearby trees. This should be considered in sampling design as well as in scaling up to stand level.

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