Lodgepole pine site index in relation to synoptic measures of climate, soil moisture and soil nutrients

Lodgepole pine site index was examined in relation to synoptic measures of topography, soil moisture, and soil nutrients in Alberta. Data came from 214 lodgepole pine-dominated stands sampled as a part of the provincial permanent sample plot program. Spatial location (elevation, latitude, and longitude) and natural subregions (NSRs) were topographic variables that might be considered as synoptic measures of climate. Soil moisture regimes (SMRs) were used as synoptic measures of soil moisture supply. Soil nutrient regimes (SNRs) were used as synoptic measures of soil nutrient supply. Simple measures of geographic location (elevation, latitude, longitude) carried the most predictive power, explaining between 33% and 37% of the variation. Site index decreased with elevation, increased with latitude, and had a quadratic relationship with longitude. The Lower Foothills NSR had higher site index (16.1 m) than the Upper Foothills (14.0 m), Montane (11.8 m) and Subalpine (10.3 m) NSRs. Soil moisture regime variables were not significant. Soil nutrient regime variables were also not important, although one was significant in conjunction with elevation, latitude, and longitude (41% explained variation). Standard errors of estimate ranged between 2.64 and 2.94 m for the various synoptic models. Interaction terms between synoptic variables were examined but were found to be non-significant.