Tracking seasonal changes in vegetation phenology with a SunScan canopy analyzer in northwestern England

Abstract

This paper explores the changes in the phenological trends of vegetation through measurement of biophysical properties of leaf area index/plant area index (LAI/PAI) over time in two contrasting vegetation canopies of broadleaf woodland and coniferous forests in the northwest of England for a period of 13 months in the year 2005/06. These biophysical variables were measured at 2 m intervals along 60 m cross-transects at both study sites and a validation site was chosen to test the impact of cloud cover on the measurements. Measurement errors were determined at the three sites and these data were used to ensure the reliability of the biophysical measurements throughout the study period. The results show that the SunScan canopy analyzer actually measures plant area index (PAI) but “effective” leaf area index (LAI) can be estimated for broadleaf canopy by subtracting measurement when there are no leaves from the other measurements when there are leaves. The seasonal variations of biophysical estimates derived can describe the phenological trends of LAI in a broadleaf canopy, but the results of “effective” PAI in both broadleaf and coniferous canopies were subject to larger measurement errors due to the inability of the SunScan canopy analyzer to distinguish between photosynthetic and non-photosynthetic tissues. It is concluded that the SunScan canopy analyzer can estimate “effective” LAI that will be appropriate in providing datasets for environmentally driven processes.