Jostein Gohli
Research Scientist
Abstract
In 2024, spruce bark beetle (Ips typographus) catches decreased in all counties except Telemark, Sør-Trøndelag, and Nordland. The highest catches this year were observed in Telemark and Buskerud. In Telemark, the catches are the highest recorded since the major spruce bark beetle outbreak that started in the mid-1970s. In Buskerud, while catches have declined compared to last year, they remain historically high. In Oppland, the catches have decreased markedly from the record-breaking year of 2023 but remain at moderately high levels. Across Southern Norway, this year’s catches are slightly above the 46-year average. The relatively high catches in Buskerud and Oppland are likely a delayed response to the storm damage in November 2021, as municipalities heavily affected by the storm report especially high catches. Additionally, field reports in 2024 indicate attacks on standing trees in areas with much windfall after the 2021 storm. Many of these damage reports likely pertain to trees attacked by beetles in 2023 or earlier but that are only now showing visible symptoms. The 2024 bark beetle season was characterized by extremely dry and warm weather in May, followed by a very wet summer with normal to slightly below-average temperatures. The warm May weather coincides with the beetles' primary flight period, favoring beetle dispersal and egg-laying. Additionally, the dry conditions in May may have stressed spruce trees, reducing their resistance to beetle attacks. The wet weather later in the summer likely benefited the trees while being sub-optimal for the beetles. Overall, the weather conditions during the 2024 season were probably relatively favorable for the beetles. A temperature-based development model estimate that, by September 17, the spruce bark beetle could have completed two generations near the Oslofjord, along the southern coastline, and in low-lying inland valleys. However, these model results do not necessarily mean that the beetles completed two generations in 2024 but indicate that conditions were warm enough to make it possible.
Abstract
Increasing levels of global environmental change may have negative impacts on fertility and embryo viability in animals that could explain a recently reported increase in hatching failure in bird eggs across the globe. Here we test this relationship again by analyzing a dataset containing almost twice as many species and covering a longer time period than earlier works (n = 431 species during the period 1906–2022). We also tested for effects of Red List status and global population size. We found that hatching failure rates in a combined group of bird species currently classified as threatened (IUCN Red List categories Critically Endangered, Endangered and Vulnerable) or Near Threatened, peaked in the late 1970s to early 1980s and thereafter declined. A similar trend also existed in species with relatively small global populations. In contrast, no temporal trends were found in species in the Least Concern category, or in species with large global populations. Moreover, hatching failure rates declined significantly with increasing global population sizes. The temporal peak of hatching failure rates in threatened and Near Threatened species corresponds with the peak in environmental levels of the insecticide DDT. While this could suggest that environmental pollution caused the temporal trends in hatching failure rates, effects of inbreeding in small and threatened populations sampled more frequently during this period could not be excluded. Although we found no evidence suggesting that the rates of hatching failure in bird eggs are increasing, the current study supports previous works showing that species of high conservation concern appear to be more susceptible to factors leading to reproductive failure than other species.
Abstract
1. Climate change is already reducing carbon sequestration in Central European forests dramatically through extensive droughts and bark beetle outbreaks. Further warming may threaten the enormous carbon reservoirs in the boreal forests in northern Europe unless disturbance risks can be reduced by adaptive forest management. The European spruce bark beetle (Ips typographus) is a major natural disturbance agent in spruce-dominated forests and can overwhelm the defences of healthy trees through pheromone-coordinated mass-attacks. 2. We used an extensive dataset of bark beetle trap counts to quantify how climatic and management-related factors influence bark beetle population sizes in boreal forests. Trap data were collected during a period without outbreaks and can thus identify mechanisms that drive populations towards outbreak thresholds. 3. The most significant predictors of bark beetle population size were the volume of mature spruce, the extent of newly exposed clearcut edges, temperature and soil moisture. For clearcut edge, temperature and soil moisture, a 3-year time lag produced the best model fit. We demonstrate how a model incorporating the most significant predictors, with a time lag, can be a useful management tool by allowing spatial prediction of future beetle population sizes. 4. Synthesis and Applications: Some of the population drivers identified here, i,e., spruce volume and clearcut edges, can be targeted by adaptive management measures to reduce the risk of future bark beetle outbreaks. Implementing such measures may help preserve future carbon sequestration of European boreal forests.