Non-severe wildfires of Atlantic Canada convert black spruce-Kalmia forests to ericaceous heath dominated byKalmia angustifolia. Post-fire residual organic matter create inhospitable seedbeds, which negatively affect seed regenerating conifers but promote vegetatively regenerating ericaceous shrubs leading to heath formation. Does organic matter (environment filter) selected species traits and fine-scale niche differentiation of ericaceous species confer stability of Kalmia heath? We hypothesised that 1) persistent high cover and stem density of Kalmia is maintained by continuous recruitment of new shoots that replace old shoots and 2) fine-scale niche differentiation through intraspecific trait variation of ericaceous species contributes to niche overlap and confer stable co-existence. To test hypothesis 1, we determined Kalmia cover and mature stems and new shoots annually in ten 60 x 60 cm plots for five years in a Kalmia heath originating from wildfire in Terra Nova National Park, Newfoundland (48° 33′ N, 53° 58.8′W). To test hypothesis 2, we studied four ericaceous species, Kalmia angustifolia,Rhododendron canadense, R. groenlandicum and Vaccinium angustifolium. We sampled 125 plant individuals and measured five functional traits related to nutrient capture and use. We calculated functional hypervolumes of Kalmia when it occurred alone (solo plots) and co-occurred with three other ericads (mixed plots).
Results/Conclusions
We found little year to year difference in Kalmia cover, mature stem and new shoot density. Interspecific trait variation was high for some traits, contributing high niche overlap. Kalmia’s trait hypervolume from mixed plots overlapped less with the other species’ hypervolumes than Kalmia’s hypervolume from solo plots. Other species’ hypervolumes overlapped more with Kalmia’s hypervolume in mixed vs. solo plots. These changes in hypervolume was attributable to organic matter depth. We conclude that Kalmia heath stability is enhanced by i) maintaining high Kalmia cover and stem density through recruitment of new shoots and ii) underutilization of available niche space by ericaceous plants. The dominant species, Kalmia co-occurred despite high niche overlap. This implies that plant communities composed of functionally similar species may remain stable, because co-existence is possible when a significant portion of the species pool is restricted from colonizing a heath.
