The microclimate of a 65 m tall, old-growth coniferous forest

This study presents over a year of direct observations of microclimatic data in and above an old-growth Douglas-fir/Western hemlock stand, at an AmeriFlux site in the southern Washington Cascades. The measurement site, the Wind River Canopy Crane Research Facility, is one of the last remnants of virgin old-growth forest in a highly managed matrix of second growth forest. Microclimatic data are discussed, in terms of both temporal (inter-seasonal) and spatial (vertical) variation. The extreme height of this forest seems related to some of the unusual vertical profiles in microclimatic data. An 83 m high tower-crane facilitates the collection of micrometeorological data along a vertical profile, with air temperature, relative humidity, wind speed and direction, and downwelling photosynthetically active radiation observed at heights of 2, 10, 20, 40, 60, and 70 m. Carbon dioxide concentrations were measured at these same heights and in addition at 30 m, and at several horizontal locations. Precipitation was measured over and under the canopy. Incoming and outgoing short-wave radiation and thermal infrared long-wave radiation were monitored above the canopy. The albedo was somewhat lower than for other forests, probably related to the tall, dense vegetation of this old-growth forest. Albedo values showed the typical diurnal variation observed in other forests, with values maximum at high solar zenith angles, and also showed some seasonal changes.