Standing timber volume and mean periodic volume increment (of Norway spruce - Picea abies - age 40-100 yr) were determined over a period of 10 yr (1974-84) in a 3000 ha forest area in Austria. The results of a Two-Phase Linear Regression Sampling (TPLRS) method (using 112 circular photo plots in the first phase, and 55 dependent field plots in the second phase, each covering 0.05 ha) were compared with those of a Simple Random Sample (SRS) of only field plots (112). The crown cover percentages

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... er plot were taken as independent variables in the TPLRS. They were stereoscopically determined on 1:10 000 scale black and white infrared aerial photographs of 1974 and 1984. Results from TPLRS were comparable to those from SRS and did not require re-enumeration of the field plots in 1984. (Abstract retrieved from CAB Abstracts by CABI's permission)