Instrument for Measuring Temperature, Photosynthetically Active Radiation and Daylength, and its Use in the Measurement of Daylength and Temperature in Coppice

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Abstract
1. An electronic instrument is described which integrates temperature and photosynthetically active radiation (PAR) to provide measurements of 24-h, day and night temperatures, PAR and daylength, averaged for the period between readings. The day/night threshold was set at 0.cntdot.1-1.cntdot.0 .mu.mol m-2 s-1 PAR. 2. Measurements were made in chestnut (Castanea sativa Mill.) coppice in Sussex on five sites covering the first to tenth seasons of regrowth. Coppices are important sites for nature conservation and microclimatic measurements will aid experimental work on the ground flora. 3. Under a complete leaf canopy in summer, daylength was up to 1.cntdot.5 h shorter than in the open and about 0.cntdot.2 h shorter in winter. The night length for photoperiodism and the length of the respiring period are therefore extended for woodland plants in summer. 4. The sites with incomplete canopies were warmer (by 2-3.degree.C, May-July) and had greater day-night temperature amplitudes than the sites with closed canopies.