Soil and Douglas-fir (Pseudotsuga menziesii) foliar nitrogen responses to variable logging-debris retention and competing vegetation control in the Pacific Northwest

Abstract

Experimental treatments of logging-debris retention (0%, 40%, or 80% surface coverage) and competing vegetation control (initial or annual applications) were installed at two sites in the Pacific Northwest following clearcutting Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) stands to assess short term effects on tree N acquisition, soil N supply, and total soil N. Vegetation control treatments began in the first year after harvest, and logging-debris manipulations were installed 2 years after harvest, Annual vegetation control increased foliar N concentration and content in most years at both sites, which was associated with higher available soil N and increased soil water content. Logging-debris retention treatments had no detectable effect on any of the foliar variables or soil available N at either site. There were no treatment effects on total soil N at the site with relatively high soil N, but total soil N increased with logging debris retention when annual vegetation control was applied as the with a low initial soil N pool. Competing vegetation control is an effective means to increase tree N acquisition in the initial years after planting while maintaining soil N pools critical to soil quality. The effect of logging-debris retention on tree N acquisition appears to be limited during early years of stand development, but increased soil N with heavy debris retention at certain sites may be beneficial to tree growth in later years.

Citation

Slesak, Robert A.; Harrington, Timothy B.; Schoenholtz, Stephen H. 2010. Soil and Douglas-fir (Pseudotsuga menziesii) foliar nitrogen responses to variable logging-debris retention and competing vegetation control in the Pacific Northwest. Canadian Journal of Forest Research. 40: 254-264.