Where have all the tree diameters grown? Patterns in Fagus sylvatica L. diameter growth on their run to the upper canopy

Abstract

The diameter growth of a tree reflects the success of that tree in competition. We investigated patterns of Fagus sylvatica diameter growth in the Žofín Forest Dynamics Plot, which is part of Smithsonian's Forest Global Earth Observatory as a research plot representing European natural mixed temperate forests. We focused primarily on the spatial patterns of beech diameter growth from the viewpoint of the most successful individuals in different ontogenetic stages. We analyzed the reaction of trees along a gradient of disturbance intensity as well as the effects of neighborhood competition. We used stem maps of trees with a diameter at breast height (dbh) ≥ 10 cm carried out in 1997 and 2012. Various types of the pair correlation function were applied to the data to describe the tree density variability. Tree spatial pattern analyses were performed on six 1.5‐ha square plots. Our results show an increasing trend of general increment growth in the interval between dbh 10 cm and dbh 40 cm. Average increment first peaked between dbh 40–42 cm with values higher than 5 mm/year, after which the absolute average increment slightly decreased and stagnated; dbh increment again increased only after dbh 79 cm, but with a much wider range of confidence intervals. An analysis of the variability in diameter growth at intermediate spatial scales showed that disturbance events influence diameter growth differently in connection with dbh. Diameter growth in thinner trees was strongly positively correlated with disturbance intensity, while disturbance had no effect on the variability in diameter growth in larger trees. The spatial pattern of elite‐growth recruits differed from the generally clustered pattern of recruits, with mutual negative interactions up to 2 m. Elite‐growth small‐sized trees (dbh 10–19 cm) showed a positive association with dead individuals in the same size category. In contrast, elite‐growth medium‐sized trees (dbh 20–39 cm) had no positive associations at all. At the same time, negative correlations with canopy beeches were observed across all categories. In conclusion, current tree spatial patterns of trees and their diameter growth are the results of multiple interactions accumulated over the long term with high inertia.

Distribution of biomass dynamics in relation to tree size in forests across the world

“…Climate variation and periodic disturbances, such as El Niño events, can alter size‐structured mortality and productivity patterns (Meakem et al ., 2018). For example, the low mortality of small stems observed in Zofin can be largely attributed to the recovery from two winter windstorms in 2007 and 2008 that created large gaps in the canopy and, thus, increased productivity and decreased mortality of small stems (Janík et al ., 2018). Analyses such as ours that rely on a single 5–10 yr time period may not adequately represent long‐term averages, nor the shorter term responses to weather events such as wind storms or droughts.…”