Dead or Alive: Drivers of Wind Mortality Initiate Multiple Disturbance Regime in a Temperate Primeval Mountain Forest

Ivana Vašíčková,Jakub Kašpar,Pavel Šamonil,Dušan Adam,Tomáš Chuman,Andrea Román-Sánchez

doi:10.3390/f12111599

Abstract

The driving forces of tree mortality following wind disturbances of mountain mixed European temperate forests belongs among issues not comprehensively resolved. Hence, we aimed to elucidate the key factors of tree resistance to historical severe disturbance events in the Boubínský Primeval Forest, one of the oldest forest reserves in the Czech Republic. By using spatially explicit tree census, dendrochronological and soil data, we study spatial and temporal patterns of past disturbances and mathematically compared selected characteristics of neighboring trees that were killed by a severe storm in 2017 and those that remained undisturbed. The tendency of trees toward falling was primarily driven edaphically, limiting severe events non-randomly to previously disturbed sites occupied by hydromorphic soils and promoting the existence of two spatially-separated disturbance regimes. While disturbed trees usually recruited in gaps and experienced only one severe release event, surviving trees characteristically regenerated under the canopy and were repeatedly released. Despite the fact that disturbed trees tended to reach both lower ages and dimensions than survivors, they experienced significantly higher growth rates. Our study indicates that slow growth with several suppression periods emerged as the most effective tree strategy for withstanding severe windstorms, dying of senescence in overaged life stage. Despite the selective impact of the Herwart storm on conifer population, we did not find any difference in species sensitivity for most characteristics studied. We conclude that the presence of such ancient, high-density wood trees contributes significantly to the resistance of an entire stand to severe storms.

Highlights

Natural disturbances are widely acknowledged to be a primary force in the dynamics of diverse primeval forest ecosystems, shaping the forest structure and composition and maintaining species and soil diversity [1,2,3,4,5,6]
Trees killed by the Herwart storm occupied significantly wetter sites compared to survivor trees (p < 0.001), with the mean degree of soil hydromorphism being 3.78 for the positions of disturbed trees and 2.74 for survivors
The distribution of tree populations along a gradient of soil moisture [40] resulted in a selective impact of the Herwart storm on conifers, primarily on Norway spruce

Summary

Introduction

Natural disturbances are widely acknowledged to be a primary force in the dynamics of diverse primeval forest ecosystems, shaping the forest structure and composition and maintaining species and soil diversity [1,2,3,4,5,6]. Though fine-scale processes have been abundantly studied in Central European forests, the long-term dynamics of mountain sites following high-severity disturbances needs further investigation, in respect to tree-species coexistence, spatial patterns, tree-soil interactions and factors controlling mortality. It is widely acknowledged that larger and older trees are more predisposed to disturbance (e.g., [21,22,23]) Another element predicting the stand resistance to wind mortality is species composition [24,25], primarily through differences in shape of root system of various tree species [26], as well as their level of shade tolerance [27]. Pavlin et al [32]

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