Influence of different forest protection strategies on spruce tree mortality during a bark beetle outbreak
Under an outbreak scenario in a buffer zone of a protected area, bark beetle-caused tree mortality was modulated by earlier natural disturbances (wind and bark beetles), sanitary management and seasonal temperature. In buffer zones, the effects of sanitary management on tree mortality remained limited due to the migration of bark beetles from unmanaged areas.
The European spruce bark beetle (Ips typographus L.) is regarded as an economically significant pest of Norway spruce (Picea abies [L.] Karst). However, in protected areas, it is regarded as a keystone species for biodiversity. This results in two contrasting management strategies that meet in buffer zones of protected areas.
To assess which environmental and management variables are most important for tree mortality in an ongoing bark beetle outbreak and to gain a better understanding of the challenges and recommendations for buffer zone management under the influence of nearby unmanaged stands in a protected area.
Norway spruce tree mortality was assessed in 419 forest stands in the High Tatra Mountains. To account for spatial and temporal autocorrelations, generalized additive mixed models (GAMM) were used, and an information-theory (I-T) approach was adopted for model selection to test the influence of environmental variables, natural disturbances and the previous year’s sanitary cutting on bark beetle-caused tree mortality.
In buffer zones, P. abies tree mortality caused by I. typographus was positively correlated to natural disturbances and sanitary cutting in the previous year.
The previous year’s sanitary cutting, maximum temperature sums, wind disturbance and trees left in no-intervention stands contributed to tree mortality in buffer zones. In these zones, the decrease of tree mortality in response to sanitary management remained limited due to the migration of bark beetles from unmanaged areas. However, sanitary management in buffer zones remains necessary for the isolation of bark beetle outbreaks in unmanaged areas.
KeywordsPicea abies Ips typographus Disturbance Temperature Wind Protected area
The authors wish to thank the staff of the state forests of Tatranský Národný Park (TANAP) in Slovakia and the staff of Tatrzański Park Narodowy (TPN) in Poland for their cooperation in data collection.
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