CR 12:65-75 (1999)  -  doi:10.3354/cr012065

ABSTRACT: This study investigates the occurrence of low summer night temperatures in relation to plant mortality in a confined clear-felled area. The work was carried out in highly complex and elevated mountainous terrain in central Sweden. Indices for air and soil frost were developed to identify the relationship between low temperatures and plant mortality during the peak of the growing season. The indices are based on air temperature measurements at 29 stations and soil temperature measurements for 2 depths at 4 stations. The terrain was classified according to its curvature at each sampling site. Four main terrain types and 2 subtypes were identified, which allowed for an analysis that links the air frost index to a specific terrain feature. An inventory of plant mortality was carried out in circular areas of 500 m² which were centred around the sampling sites. It was found that terrain curvature and aspect in relation to solar azimuth angle around sunrise and sunset have a significant impact on the frequency of low night temperatures in summer. This was also reflected by the distribution differences of surviving plants between various terrain types. The air frost index was highly correlated to the mortality (r = 0.91, N = 29). However, an analysis of the residual in the regression indicates that other factors are also important. The soil frost index helps explain the relatively high mortality in convex terrain. Also, the influence of temperature-induced frost hardening on the mortality during the vegetative period is discussed.

KEY WORDS: High elevation · Complex terrain · Vegetative period · Plant mortality · Temperature indices · Air frost · Soil frost