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

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.

Large old trees increase growth under shifting climatic constraints: Aligning tree longevity and individual growth dynamics in primary mountain spruce forests

“…By shifting resources from growth towards production of secondary metabolites, “slow‐growers” gain selective advantage over “fast‐growers” by improving their defenses against environmental stressors and increasing wood resistance, but at the cost of reduced growth (Wiley & Helliker, 2012). On the other hand, “fast‐growers” get larger sooner, but rarely reach the same age as “slow‐growers,” as the initial advantage of dominant canopy position (i.e., increased light availability) and fast growth are offset by generally declining growth rates, decreased resilience to pests and pathogens, and reduced investments in defenses and biomechanical stability (Vašíčková et al, 2021). However, trees with more than half of a lifetime with suppressed growth seldom reach an age above 300 years (Figure 4), as continuous growth suppression and limited resources increase mortality risks (Munné‐Bosch, 2018).…”

The fate of remnant trees after wind disturbances in boreal and temperate forests

“…Moreover, pest infestation and wildfire do not necessarily occur after wind disturbance, even if weather conditions favor such events (Szwagrzyk et al, 2017). Soil conditions (e.g., periodically waterlogged or hydromorphic soils) also add to the variation in mortality (Mitchell, 1995;Vašíčková et al, 2021).…”

“…At the same time, for trees with broken stems the mortality probability increased to 0.84 and uprooted trees had only marginal chances (mortality probability 0.98) to survive throughout the study period. Interestingly, Vašíčková et al (2021) noticed that storm Herwart (2017) selectively impacted the conifer population in the Czech Republic. They found that trees that germinated under the canopy and experienced several periods of suppression and release were more likely to survive the storm.…”