Understanding plant community succession is one of the original pursuits of ecology, forming some of the earliest theoretical frameworks in the field. Much of this was built on the long-term research of William S. Cooper, who established a permanent plot network in Glacier Bay, Alaska, in 1916. This study now represents the longest-running primary succession plot network in the world. Permanent plots are useful for their ability to follow mechanistic change through time without assumptions inherent in space-for-time (chronosequence) designs. This allows not only the generation of data relevant to the local plot environment, but as a check on those assumptions generated by the often more feasible approach of chronosequences. The purpose of this study was to refind the Cooper plots, which had not been visited in approximately 30 years and whose specific location was unknown. Using a combination of historical landscape photographs, original field notes from the 1916 expedition and later revisits, and a variety of orientation techniques the exact original plot locations were rediscovered. Each of the remaining eight plots was resurveyed according to the original methods of Cooper. Community data were analyzed using a multiple diversity metrics and rarefaction analyses; soil samples were analyzed for total carbon and nitrogen content at multiple depths.
Results/Conclusions
After 100-years, these plots show surprising variety in species composition, soil characteristics (carbon, nitrogen, depth), and percent cover, attributable to variation in initial vegetation establishment first noted by Cooper in the 1916-1923 time period, partially driven by dispersal limitations. There has been almost a complete community composition replacement over the century, and a general species richness increase, but the effective number of species has declined significantly due to dominance of Salix species which established 100-years prior (the only remaining species from the original cohort). Where Salix dominates, there is no establishment of “later” successional species like Picea. Plots nearer the entrance to Glacier Bay, and thus closer to potential seed sources after the most recent glaciation, have had consistently higher species richness for 100 years. Location and age of plots are significant predictors of soil N content and C:N ratio, though plots still dominated by Salix had lower overall N; soil accumulation was more associated with dominant species. This highlights the importance of contingency and dispersal in community development. The 100-year record of these plots, including species composition, spatial relationships, cover, and observed interactions between species, provides a powerful view of long-term primary succession.