PS 66-92
Regeneration of the endangered limber pine is uncoupled from seed availability at the northern limits of its range
When biotic interactions such as disease alter both the seed production capacity of stands, and seedling survivorship, the relative importance of seed availability versus substrate specificity may alter future regeneration opportunities for plant populations. We investigated the importance of seed vs. substrate limitation to regeneration dynamics of 17 populations of the endangered limber pine, Pinus flexilis, in low versus high white pine blister rust (WPBR; Cronartium ribicola) infested landscapes (1% and 38% live tree infection, respectively) in the northern portion of the species range (Alberta, Canada).
Results/Conclusions
Surprisingly, the landscape with high rates of WPBR infection produced 69.8% more cones per tree, and coupled with greater seed tree density, appear to have more seed available for avian dispersers. Despite higher seed production, recent seedling regeneration was significantly lower in the high WPBR landscape than in the low WPBR landscape (83 vs. 251 seedlings /ha, respectively). The greater availability of preferred substrates such as mineral soil and scree in low vs. high WPBR landscapes (> 60 % ground cover vs. 20 %, respectively) may explain the higher levels of seedling regeneration, and may suggest that substrate availability overrides seed availability. Additionally, seedling age structures suggest that WPBR may influence regeneration patterns; landscapes with severe WPBR infestations had proportionately fewer small seedlings available to recruit into larger size classes than landscapes with low WPBR infestations (40 vs. 72.8 %, respectively, of seedlings < 25 cm tall). Our study suggests that at the northern limits of limber pine’s range, substrate availability and seedling mortality caused by WPBR are more important than seed availability to successful limber pine regeneration.