Temperatures at the margins of a young spruce stand in relation to aboveground height

Air temperature was monitored at a summit of the Jizerské hory Mountains (Czech Republic) in the vicinity of the northern and southern margins of a young Norway spruce stand (tree height ca 4.5 m) at 30, 60, 90 and 140 cm aboveground. Height intervals of temperature sensors were selected to represent terminal shoot heights in the planting stock of different tree-height categories (seedlings, semi-saplings and saplings). Another monitored reference point was 30 cm aboveground in an adjacent treeless gap between stands. The evaluation utilized measurements taken in two periods, from April to October 2010 and 2011. Differences were evaluated in mean temperature characteristics and minimum temperatures for the ground air layer in the stand gap and in the individual locations at the stand margins. Differences in values representing temperature extremes (minimum, maximum, amplitudes) showed a more conspicuous fluctuation than did mean values. The difference in the course of daily temperature characteristics in the ground layer of air (at 30 cm aboveground) between the stand gap and the southern margin of the spruce stand was small. The ground layer of air at the northern margin was markedly colder and showed a more stable course of temperatures. Decreasing temperature fluctuation was observed also with increasing height aboveground, and the frequency and intensity of ground frosts also was decreasing. At 140 cm aboveground (i.e. at approximately one-third of the spruce stand’s height), the differences between daily temperature characteristics at the southern and northern stand margins were small during the growing period, and there was comparable frequency as to the occurrence of late or early frosts. In conclusion, higher risk of damage to small-sized planting stock due to temperature stress was confirmed for higher mountain elevations. For sapling plantings during reconstruction of young coniferous stands, the selection of a suitable planting location within a small clear-cut area does not have such importance in terms of temperatures near the terminal shoot as it has for planting stock of smaller dimensions