Soil-Site Influences on Northern White-Cedar (Thuja occidentalis, L.) Stem Quality and Growth

Northern white-cedar (NWC, Thuja occidentalis L.) has been present in mixed species forests since the mid-Holocene -7500 ypb (Yu 1997). The modern-day primary range of NWC extends from southern Canada east to Maine. Many aspects of the third most abundant conifer in Maine are unknown in comparison to its common associates spruce (Picea rubens Sarg.) and fir (Abies Balsamea (L.) Mill), despite the high value of NWC as both raw material for industry and as wildlife habitat. As part of an ongoing program in NWC research, this study sampled 10 mixed species stands from Hofmeyer (2008) for a description and analysis of NWC soil-sites on a gradient of drainage based on the Briggs (1994) soil drainage guide (BSC, Briggs\u27 Site Class), modified for the inclusion of Histosols. BSCs used here ranged from moderately well-drained (BSC2) to very poorly drained (BSC5), and organic soils (i.e., Histosols, represented here as BSC6 or ORG). Two sites were selected to represent each of the 5 BSCs by sampling 13 pedons and live foliage from three NWC trees per site. Sampling based on the BSC system captured a gradient in soil morphology from Spodosols to Histosols. A tendency for greater variability in the data from individual horizons from BSC2 to BSC5 resulted in less vertical stratification of the chemical properties. The ORG site class was the extreme, showing essentially no depth trend in chemical properties. Significant between-site differences in foliar and soil chemistry were present with the most outstanding differences occurring in the ORG site class, which had consistently higher soil pHca, Ca, CECe and BSe, and lower exchangeable acidity. Trees on the ORG sites had higher foliar Al, Ca, and Fe. NWC adapts to a diversity of site conditions; surface horizons ranged in pHca from 2.99 to 6.36, and the dominant exchangeable cation Ca ranged from 2.71 to 90.62 cmolc kg-1, while exchangeable Al concentrations ranged from 0.02 to 18.46 cmolc kg-1. NWC basal area growth and growth efficiency were positively correlated with soil pHca, Ca, Mg, CECe, BSe, and negatively correlated with soil exchangeable acidity. This could be related to Al stress in mineral soils. Stem soundness (measured as the % BA decayed of individual sample trees) decreased in median value and range from BSC2 to ORG, and showed the highest negative correlation with foliar Fe. The BSC system utilized in this research could be simplified for application to NWC by creating two groups: mineral (BSC 2-5, with or without a histic epipedon), and Histosols (BSC ORG). As a hydrophyte, NWC has adaptations facilitating development on hydric sites, and this research has shown strong positive correlations with BSe, especially %Ca