Understanding how plant communities recover following disturbance has important implications for improving our understanding of basic successional dynamics. In many systems, fire is a major disturbance that both structures vegetation communities and influences nitrogen availability. Although plant performance following disturbance is hypothesized to be driven by the supply of limiting resources, the extent to which fire history or resource availability drives plant recovery is not clear. In this study, we asked (1) How do burn history and nitrogen availability affect short-term resprouting rates? (2) Over the full growing season, how do burn history and nitrogen availability affect regrowth and net productivity? To answer these questions, we amended frequently burned and infrequently burned longleaf pine communities with a pulse of nitrogen, continuous nitrogen, or water-only control. We clipped aboveground biomass to simulate biomass loss from fire. We used allometric equations to estimate cumulative biomass production of five species (Arundinaria tecta, Clethra alnifolia, Ilex glabra, Gaylussacia frondosa, Pteridium aquilinum) each week over the growing season. We compared short-term (one month) resprouting rates, seasonal regrowth rates, and seasonal net productivity across fire and nitrogen treatments.
Results/Conclusions
Previous disturbance history, but not nitrogen availability, strongly influenced plant disturbance response. In the short term, C. alnifolia (p=0.038), G. frondosa (p=0.022), and I. glabra (p<0.001) all resprouted faster when conditioned to frequent versus infrequent burns. In contrast, over the full growing season plants had higher growth rates when conditioned to infrequent burns (A. tecta p=0.013; G. frondosa p=0.009; P. aquilinum p=0.005). Individuals of these species also showed higher productivity when conditioned to infrequent burns, but fire frequency did not influence plot-level productivity because other species had higher productivity when exposed to frequent burns. Since temperate forests are thought to be nitrogen limited, fires release a nitrogen pulse, and species differ in their ability to assimilate a nitrogen pulse, we expected N availability to have a strong impact on recovery following disturbance. Surprisingly, however, N supply had little to no impact on resprouting. Instead, fire history affected demographic processes by altering resprouting trajectories. Differences in biomass accumulation were observed within species only, and not at the plot level. This indicates that the effects of fire history on vegetation occurred not through a filtering of the community, but through physiological plasticity at the species level.