Changing Soil Characteristics during Succession in the Alaskan Boreal Forest

Core Ideas Repeated sampling compared to a chronosequence can display changes due to climate change. Carbon quantities increased across the floodplain chronosequence, upland sites displayed no change. Nitrogen displayed a chronosequence increase in both concentration and quantity on the floodplain sites. Repeated sampling and chronosequence approaches can be used to develop an understanding of successional dynamics in forest ecosystems. The chronosequence approach enables a relatively rapid and consistent assessment of key variables, but relies on an assumption that spatial variability is a good substitute for temporal dynamics. Repeated sampling gives a more direct measure of temporal dynamics, but by definition requires much more time and is vulnerable to changes in investigators and methodologies. In this study, we compared these techniques in two well‐studied Alaska boreal forest landscape positions—upland (UP) and floodplain (FP)–and found a number of contrasting trends. In UP stands, soil C concentration increased with stand age across the chronosequence, but declined in individual stands over time. Conversely, soil P concentration declined across the UP chronosequence, but increased in individual stands. Both approaches yielded consistent trends for several variables, including N, pH, CEC (UP and FP), and K (UP). No changes were observed for 5 factors (upland C quantity, floodplain C concentration and quantity, and total P and Ca quantity on the floodplain) between sampling years that displayed either a positive or negative chronosequence trend. Changes in the one meter depth profile chemistry between sample time periods were investigated and showed the same differences that were found for the total profile average values of the soil property. Differences observed between these two values were tied to the depth structure of the observed soil characteristic.