A foundation of ecology rediscovered: 100 years of succession on the William S. Cooper plots in Glacier Bay, Alaska

Abstract

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. After 100-yr, 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 general species richness increase, but the effective number of species has declined significantly due to dominance of Salix species which established 100-yr 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 yr. Age of plots is the best predictor 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-yr record of these plots, including species composition, spatial relationships, cover, and observed interactions between species provides a powerful view of long-term primary succession.

100 yr of primary succession highlights stochasticity and competition driving community establishment and stability

“…For woody species and erect herbaceous plants, individuals were tracked through time; mosses and mat-forming species (e.g., Dryas) were mapped by area covered rather than tracked by individual, and cover was converted to individual count estimates via published methods (Buma et al 2017). For woody species and erect herbaceous plants, individuals were tracked through time; mosses and mat-forming species (e.g., Dryas) were mapped by area covered rather than tracked by individual, and cover was converted to individual count estimates via published methods (Buma et al 2017).…”

“…To test the idea that early nutrient limitation determined current trajectories, we compared carbon (C) and nitrogen (N) percentages from Buma et al (2017) to historical measures of Dryas coverage at the quadrat scale: the maximum number of Dryas individuals observed in a single year and average number of Dryas observed over all observations. We then also compared current Alnus percent coverage at the plot scale to N percentage to explore if current species composition is a better predictor of nitrogen.…”

“…2; Appendix S3: Fig. Three quadrats (Q1, Q7, and Q8) are Alnus dominated, one is Picea dominated (Q2, growing slightly off plot but extending completely over), and four are Salix dominated (Q3, Q4, Q5, and Q6 [Q6 has a high overstory component of Alnus; Buma et al 2017]). Three quadrats (Q1, Q7, and Q8) are Alnus dominated, one is Picea dominated (Q2, growing slightly off plot but extending completely over), and four are Salix dominated (Q3, Q4, Q5, and Q6 [Q6 has a high overstory component of Alnus; Buma et al 2017]).…”

“…We were specifically curious whether or not Cooper's original 1-m 2 quadrats, which were large enough for early successional communities (Buma et al 2017), were representative of the broader community surrounding the quadrats 100 yr later. We additionally used this network to test the utility of historic plant community sampling methodologies over the many stages of plant community development.…”

Scale sensitivity of the relationship between alpha and gamma diversity along an alpine elevation gradient in central Nepal

“…space-for-time substitution that uses space as a proxy for time (Pickett 1989;Johnson & Miyanishi 2008), and temporally replicated vegetation surveys (Cooper 1923 and subsequent expeditions;Peet & Christensen 1980;Buma et al 2017). Based on numerous underlying assumptions, space-for time substitution has been applied in ecological modelling to infer past or future trajectories of ecological systems from contemporary spatial patterns.…”