Fire and substrate interact to control the northern range limit of black spruce ( Picea mariana) in Alaska

• Published in: Canadian Journal of Forest Research
• Main Authors: Lloyd, Andrea H., Fastie, Christopher L., Eisen, Hilary
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2007
• Subjects: Canada; Brooks Range; Alaska
• Online Access: http://dx.doi.org/10.1139/x07-092; http://www.nrcresearchpress.com/doi/full-xml/10.1139/X07-092; http://www.nrcresearchpress.com/doi/pdf/10.1139/X07-092

Black spruce ( Picea mariana (Mill.) BSP) is a common treeline species in eastern Canada but rare at treeline in Alaska. We investigated fire and substrate effects on black spruce populations at six sites along a 74 km transect in the Brooks Range, Alaska. Our southern sites, on a surface deglaciated >50 000 years ago, had significantly more acidic soils, more black spruce, and higher seed viability than our northern sites, which were deglaciated approximately 13 000 years ago. Despite similar fire history at five of our six sites, postfire recruitment dynamics varied with surface age. Sexual reproduction was vigorous in both postfire and nonfire years in populations on the older surface. On the younger surface, vigorous sexual reproduction was restricted to postfire decades and clonal reproduction by branch layering predominated in nonfire years. At the northernmost site, which was unburned, black spruce reproduced almost exclusively by layering. The species’ northern range limit thus reflects an interaction between fire and substrate: on recently deglaciated surfaces, sexual reproduction is restricted to postfire years. This substrate-induced dependence on fire may restrict the range of black spruce to sites that burn sufficiently often to allow occasional sexual reproduction.