Effects of Fire Regime on the Serotiny Level of Jack Pine

Abstract

1 Serotiny, the capacity to retain seed in the plant canopy, has evolved in many species under the selective pressure of fires. The effect of disturbance type (lethal or nonlethal fire), time-since-fire and different fire regimes on the serotiny of jack pine (Pinus banksiana), was evaluated in populations from two adjacent landscapes in the southern part of the Canadian boreal forest. The island landscape (Lake Duparquet) has a complex fire regime of small fires of variable intensity, whereas the adjacent mainland has a fire regime characterized by large intense fires. 2 Twenty-four jack pine populations (11 island and 13 mainland) on xeric sites were sampled for the degree of serotiny of trees. Fire history and age structure were reconstructed for each population using the fire scar method. For each tree, recruitment was categorized as after a lethal fire, after a nonlethal fire or in the absence of fire. 3 Likelihood chi-square tests were used to investigate the variation in serotiny at individual, population and landscape levels. 4 At the individual level, the results support our prediction that the occurrence of lethal fires favours trees with high serotiny while low serotiny trees are favoured by other types of disturbances. 5 At the population level, the frequency of low serotiny trees increases with time since stand initiation, as a result of higher establishment opportunities after disturbances other than lethal fires. The proportion of low serotiny trees also increases with the occurrence of nonlethal fires. 6 Significant differences were found between the two landscapes. On the mainland, serotinous trees were more abundant, whereas on the islands where nonlethal fires were recorded, low serotiny trees were more frequent. These results support the hypothesis that fire imposes differential selective pressures on serotiny in jack pine.