An interregional validation of ECOPHYS, a growth process model of juvenile poplar clones

Field data from poplar plantations in Michigan, Washington, and Wisconsin were used to validate ECOPHYS, a whole-tree growth process model for juvenile poplar. Five clones representing a range of morphological, phenological, and physiological characteristics were planted on the same date at the three sites. Height and diameter measurements were made monthly on 20 trees per clone, and intensive morphological measurements were made every two weeks on two trees per clone. Hourly solar radiation and temperature data were recorded at each site over the growing season. The model was run for each clone x site combination with the weather data and clonal parameters as inputs. A repeated measures ANOVA indicated that there were significant differences in height growth patterns among both clones and sites, as well as significant clone x site interactions. The model generally predicted height growth within a standard deviation of the field plantation means; three of the 15 clone x site simulations were significantly different from the plantation means. The median error between predicted and observed values was 5%. Evaluation of the clonal parameters showed that differences in photosynthetic rates, morphological attributes such as specific leaf area, and timing of budset are primary factors leading to differences in growth.