Microclimate and Plant Growth at Isachsen and Mould Bay

Résumé

In discussing the botany of the northwestern Queen Elizabeth Islands I noted that the available climatic data did not suggest a significant difference between the summer climate of Isachsen and of Mould Bay; yet Mould Bay harbours plant species that are absent from Isachsen, and specimens from there are less depauperate than those from Isachsen. It seemed probable that Mould Bay, which is better protected from winds off the Arctic Ocean, might have less of the very low stratus that often covers Isachsen and which must pass less sunlight than do sheets of high stratus and altostratus. The available data on cloud cover, which do not include cloud height and which are inevitably somewhat subjective, indicated no marked difference between the stations, and sunshine records were lacking for both. With three years' bright sunshine data now available for Isachsen and Mould Bay, I have extracted the summer figures from the Monthly Record of Meteorological Observations in Canada. The growth period at Isachsen extends from mid June to early August, and July is clearly the critical month. The Isachsen total for August 1969 is missing, but for the other 8 months Isachsen exceeded Mould Bay only once. The Mould Bay excess for July was 25 per cent or more in each year. Although soil surface and screen temperatures differ little at Isachsen on heavily overcast days, thermograph records kept by D. St-Onge showed: that on predominantly sunny days the soil surface maxima exceeded the screen maxima by 20-30°F (11-17°C). Thus modest differences in total bright sunshine can be very important to plant growth in this region where almost all activity is confined to the lowest 10 cm of air and much of it to the lowest 3 cm. A longer record is needed before we can fully accept a higher July sunshine figure for Mould Bay; but if the three years of record are nearly representative they must go far in explaining the better growth at this station. However, there is a distinct possibility that diffuse sunlight through thin cloud, not registered by the Campbell-Stokes recorder, adds to Mould Bay's advantage.