| This study examined germination and survival of the 1999 to 2004 cohorts of artificially sown jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) BSP), white spruce (Picea glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.) in five aspen (Populus tremuloides Michx.) - conifer mixedwood stands following the 1999 Black River Fire in southeastern Manitoba, Canada. A total of 84 seeding plots were established on three different post-fire seedbeds within days after the end of the fire in May 1999. Seedbed fire severity classes were severely burned (complete consumption of litter and duff exposing mineral soil), lightly burned (surface litter consumed with little or no duff consumption), and scorched (surface litter only partially consumed). Severely burned seedbeds had poor germination, while scorched seedbeds had the highest germination in 1999. The reverse was true in 2001. After the first growing season, continued survival of seedlings was greater on severely burned seedbeds for all cohorts. However, better survival on severely burned seedbeds was not sufficient to overcome poor germination in 1999 and 2000. Two year survival (% of viable seeds sown) was greatest for the 2001 cohort of all species. The expected steep decline in recruitment with time-since-fire was not found on severely burned plots. When assessed on a per-plot basis there was no significant difference in survival between the 2001 and 2004 cohorts. The severity classes were most similar in 1999 and most dissimilar in 2001 in air, surface and soil temperature with severely burned plots being higher. Significant differences in the plant communities among the fire severity classes continued to be found seven years post-fire, but are diminishing with time. Coverage of mosses were significantly higher, while coverage of shrubs and trees were significantly lower, on severely burned plots. The possible effect of forest floor ash on seed germination and viability was also studied in the laboratory. Ash from the forest floor was not found to be toxic or to delay conifer germination except for balsam fir. Balsam fir had significantly less germination on ash derived from forest floors sampled under the highest aspen composition. |
