Developmental plasticity allows Betula nana to dominate tundra subjected to an altered environment

We investigated how three co-dominant arctic shrubs (Betula nana, Salix pul chra, and Ledum palustre ssp. decumbens) responded to long-term treatment w ith N+P fertilizers and greenhouses in a factorial field experiment at Tool ik Lake, Alaska. Our goal was to understand the relationship between growth of individuals and species abundance in the community, and the mechanism b y which one species achieves dominance under changed environmental conditio ns. We compared aboveground growth and allocation patterns in individual ra mets 15 yr of age with community abundance measured by quadrat harvests. Ra mets of all three species substantially increased their stem biomass with f ertilization, but the increase was much larger for Betula than for the othe r two species. In quadrat sampling, only Betula appreciably increased its b iomass per unit area with fertilization or greenhouse treatment. For Salix in all treatments, and Ledum in the two fertilizer treatments, ramet densit y per unit area decreased more than growth of surviving 15-yr-old ramets wa s promoted, so community biomass of these species declined. In contrast, Be tula increased its ramet density in all treatments by producing new shoots from stems older than 15 yr, even though stem mortality was also increased in the two fertilizer treatments. Betula increased its growth in part by a major change in allocation, from p roducing mostly short shoots to producing many more long shoots. As a resul t, the number of branches and the rate of production of new meristems great ly increased. This developmental plasticity allowed extensive growth that l ed to development of a dense canopy and imposed light limitation on the oth er species. The flexible growth strategy of Betula points to the importance of meristem availability and developmental constraints in determining plan t response to environmental change. Developmental controls over meristem av ailability are not usually considered in ecological paradigms for allocatio n, but they may be useful for predicting plant response to changes in nutri ent availability in other ecosystems.