Multi‐decade tree mortality in temperate old‐growth forests of Europe and North America: Non‐equilibrial dynamics and species‐individualistic response to disturbance

Abstract

Aim Old‐growth, mesic temperate forests are often assumed to be structured by gap‐phase processes, resulting in quasi‐equilibrial long‐term dynamics. This assumption influences management focused on simulation of natural disturbance dynamics and is embedded in most models of forest successional dynamics. We use multi‐decade monitoring of permanent plots in old‐growth forests to assess demographic assumptions directly with respect to tree mortality rates. Location Sixteen sites in mesic, temperate old‐growth forests in eastern North America and Europe with multi‐decade monitoring. Time period Variable across sites, spanning c. 20–78 years from 1936 to 2014. Major taxa studied Tree species of late‐successional, cool‐temperate forests of Europe and eastern North America. Methods We calculated and compared the annualized mortality rates (m), with confidence intervals, by species, size class and measurement interval, for tree species of sufficient abundance. Results Retrospective analysis shows dynamic and diverse demographic properties across populations and sites. Stand‐scale mortality rates of 0.7–2.5%/year average higher than previous estimates for old‐growth temperate forests. Variations among species, over time and among size classes, suggest that gap‐phase models are inadequate to explain stand dynamics, implying instead that rare disturbance events of moderate severity have long‐lasting effects in old‐growth forests and that indirect anthropogenic influences affect old‐growth, unlogged forests. Main conclusions Multi‐decade baseline data, essential for understanding community assembly and long‐term dynamics in these “slow systems,” are rare and poorly integrated. Our analysis demonstrates the value of the few long‐term, “legacy” data sets. Results suggest that differences in life history interact with complex disturbance histories, resulting in non‐equilibrial dynamics in old‐growth temperate tree communities, and that changes in disturbance patterns through anthropogenic climate change might, therefore, be an important driver of ecosystem change.

Intermediate disturbances are a key driver of long‐term tree demography across old‐growth temperate forests

“…Given the scarcity of old-growth and direct long-term monitoring of tree populations from permanent plot data in the temperate region of Europe, there are few studies that allow direct comparison with our results. Consistent with our findings, a recent assessment of multi-decade mortality rates in mesic, temperate old-growth forests in eastern North America and Europe found that mortality rates were variable over time, with long-term averages higher than previous published estimates (i.e., generally c. 1%/year), results which were partly attributed to the occurrence of rare disturbance events (Woods et al, 2021). In a long-term study of mortality rates from permanent plots in mixed forests across Switzerland, Etzold et al…”

“…We build on the study of Woods et al (2021) using a network of small old-growth remnants located across temperate mountain forests of Slovenia, where long-term observations of tree populations have been carried out in permanent plots since the 1980s. We quantify multi-decade rates and drivers of tree demography, using data on mode of mortality and disturbance observations to disentangle background and disturbance related mortality.…”

“…approach asWoods et al (2021), we use these CIs around m and r to indicate ecologically meaningful differences in rates across time at a given site, such as between adjacent intervals that capturem = 1 − Ns T ∕N 0 1∕T r = 1 − Ns T ∕N T 1∕TTA B L E 2 Plot and census characteristics within each old-growth forest site…”

Toward a High Spatial Resolution Aerial Monitoring Network for Nature Conservation—How Can Remote Sensing Help Protect Natural Areas?

“…The development of an automated learning algorithm is underway. The size of canopy gaps is important factor and indicator in forest ecosystems [72]. Propagation vectors of invasive plant species are also traceable in the sample areas using aerial remote sensing [11].…”

“…However, for the top of the trees or canopy structure, the flight altitude can cause considerable perspective distortions. Due to the strong perspective distortion of the The size of canopy gaps is an important factor and indicator in forest ecosystems [72]. Propagation vectors of invasive plant species are also traceable in the sample areas using aerial remote sensing [11].…”