In areas affected by bark beetle infestations, it is crucial to preserve the hydrological functions of forests
Forest ecosystems in Central Europe have been experiencing significant changes in recent decades, with one of the most noticeable impacts being the widespread decline of spruce monocultures due to infestations by bark insects, particularly the spruce bark beetle.
These bark beetle outbreaks often exceed historical precedents in both scale and speed. The consequences include not only the loss of timber resources but also the disruption of biogeochemical cycles, with the hydrological cycle being especially affected.
Photo: Disaster area where a stream flows, and soil may be washed away during heavy rains. Author: Jan Řezáč
Modern approaches to restoring damaged forests should be based not only on forest engineering knowledge but also on the integration of insights from hydrology, soil science, and plant ecophysiology. Scientists at the Opočno Research Station, VÚLHM, v. v. i., are addressing this important issue. One of their recent contributions is a practical methodology titled “Hospodářské postupy pro zachování hydrických funkcí lesů v oblastech postižených kůrovcovou kalamitou” (Silvicultural procedures for maintaining forest hydrological functions in bark beetle-impacted areas). This methodology was developed with the support of a grant from the Ministry of Agriculture as part of the project NAZV QK22010189, which focuses on “The impact of deforestation on the water regime of small river basins” (Vliv odlesnění na vodní režim malých povodí).
The methodology outlines effective management practices to address the challenges posed by bark beetle infestations, aiming to maintain and restore hydric functions even when forest stands are damaged or destroyed. The hydric functions of a forest can be categorised into three primary roles: Retention Function (The forest’s ability to retain water within the watershed and slow down runoff); Accumulation Function (The capability to hold water in both the soil profile and biomass); Qualitative Function (The function of purifying water and preventing erosion). The bark beetle crisis and the resulting remedial logging impact all these components.
Photo: A stream winds through a large, deforested area, and young trees show signs of damage from wildlife. Author: Jan Řezáč
This methodology represents a shift from traditional cultivation practices to adaptive strategies that prioritise hydrological safety. When establishing forests, it emphasises the hydrological benefits and potential risks associated with using specific native tree species for combined (two-phase) restoration of areas affected by disasters, particularly focusing on the selection of preparatory tree species.
Measures across the entire spectrum of forest management are recommended for their positive impacts on the forest’s ability to retain water, reduce the risk of erosion, and maintain water quality. The scientists also outlined principles for cultivating more diverse tree species and their effects on the forest’s hydrological regime.
The methodology addresses current changes in forest ecosystems, which are caused by the decline of spruce monocultures due to bark beetle infestations and global climate change. The goal is to provide forestry practitioners with clear knowledge and tools to maintain and accelerate the restoration of the forest’s hydrological functions.
Ing. David Dušek, Ph.D. states: “The analysis of hydrological, soil, and ecophysiological data indicates that restoring areas affected by disasters cannot rely on the standardised procedures of the past. Instead, it must incorporate knowledge about the specific requirements and functions of individual tree species. There is a clear need to shift away from cultivating even-aged monocultures towards stands that are both species-diverse and spatially varied. Preliminary tree species, such as birch, aspen, and rowan, play a crucial role in modern management by quickly stabilising the microclimate, enhancing water infiltration, and preparing the soil for the target tree species.”
Photo: In waterlogged soils, the edges of stands affected by the disaster are significantly unstable, making the remaining trees easily uprooted. Author: Jan Řezáč
The methodology emphasises that the water dynamics in the forest are influenced not only by the species composition and structure of the stand but also by the management of dead wood and logging residues. Retaining biomass on-site effectively prevents unproductive evaporation and erosion. Consequently, within the context of logging procedures, which are often unplanned and highly variable due to the nature of disaster logging, the methodology recommends leaving a portion of both thick and thin growth to sustain the forest’s hydrological functions.
Specifically, it is suggested to leave 30–50% of logging residues in the area. While this may represent a loss of potential profit from selling energy chips, it should be viewed as an investment in soil preservation. Removing these residues could lead to soil degradation, erosion, and compaction, and the cost of remedial action would likely far exceed the short-term gains from harvesting biomass.
“The proposed procedures, ranging from two-phase restoration to targeted educational interventions, represent a way to creating forests that will not only produce timber but also retain water in the basin, mitigate flood waves, and withstand future climate extremes,” concludes Ing. Ondřej Špulák, Ph.D.
The methodology „Hospodářské postupy pro zachování hydrických funkcí lesů v oblastech postižených kůrovcovou kalamitou“ (Silvicultural procedures for maintaining forest hydrological functions in bark beetle-impacted areas) can be downloaded here.
Authors: Ing. David Dušek, Ph.D., Ing. Ondřej Špulák, Ph.D., VÚLHM, v. v. i., research station (VS) Opočno, e-mails: dusek@vulhmop.cz; spulak@vulhmop.cz
Prepared according to the original by Ing. Jan Řezáč, VÚLHM, v. v. i., rezac@vulhm.cz