Early field performance of three planted inland northwest conifer species: Effects of root growth potential, morphology, and environmental conditions

Abstract

A common concern to planting for reforestation is seedling failure that is directly measurable by seedling early field performance of growth and survival. Root growth potential (RGP) is a commonly used metric of seedling quality and has been considered indicative of seedling field performance. The effect of RGP is thought to be dependent on planting site and underlining environmental conditions. Moisture stress often is considered the primary cause of seedling failure in addition to other environmental factors such as soil physicochemical properties in regions such as the Inland Northwest of the United States that is prone to growing season drought. In addition, it is interesting to test whether seedling early field performance is related to their morphological attributes and whether the morphological attributes are related to RGP. A comprehensive evaluation on early field performance of three planted conifer species of interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco), grand fir (Abies grandis (Douglas ex D. Don) Lindl.), and western larch (Larix occidentalis Nutt.) was conducted in this study. It was found that RGP did not show clear correlation with early field performance across species. RGP also was not significantly correlated with seedling morphological measures such as below- and above-ground biomass and root-to-shoot ratio (R:S, by mass). Early field performance of growth and survival varied greatly across individuals of seedlings. The most influential predictors of early seedling growth and survival were their initial size (indicative of energy reserve) and soil temperature that likely interacted with soil moisture. Our findings suggest that seed stock selection for reforestation probably should favor species and genotypes with greatest heat tolerance that may be better adapted to future conditions in the region.