Life span and biomass allocation of stunted black spruce clones in the subarctic environment

1 Slow growth, maintenance of a high leaf: wood ratio and adoption of ct cl onal growth habit, more than size per sc, may increase the life span in tre es species. The longevity of black spruce (Picea mariana (Mill.) BSP. is in creased from 200 to 300 years, when it grows as a clonal shrub. 2 We measured the surface area and above- and below-ground biomass of 25 po stfire, stunted black spruce clones identified from RAPDs markers. The maxi mum age of each clone was deduced from tree-ring dating or by radiocarbon d ating of charcoal fragments. The oldest clone was > 1800 years of age. The total surface area of the clones increased with age, ranging from 2.8 to 69 1.3 m(2). The ratio of living aerial parts to the total surface area decrea sed from 100% to < 50% with postfire stand age, reflecting fragmentation of clones into many autonomous or potentially autonomous rooted branches (lay ers). The number of layers ina eased with age from 12 layers in a 100-year- old individual to more than 80 in a 1800-year-old clone. 3 Biomass allocation and fragmentation can explain the maintenance of a rel atively stable leaf: wood ratio of approximately 10% through time in stunte d black spruce clones. The fragmentation of lavers is the main mechanism en suring the gnat longevity of prostrate clones in exposed sites. in the abse nce of perturbation, stunted black spruce clones may perpetuate for centuri es or even millennia.