Shifting altitudinal distribution of outbreak zones of winter moth Operophtera brumata in sub-arctic birch forest: a response to recent climate warming?

Abstract

Climatic change is expected to affect the extent and severity of geometrid moth outbreaks, a major disturbance factor in sub-arctic birch forests. Previous studies have reported that the two geometrid species involved, autumnal moth and winter moth, differ in their temperature requirements and, consequently, in their altitudinal and latitudinal distribution patterns. In this study, we document the altitudinal distribution of winter moth outbreaks in a large coastal area in northern Norway. We show that, in the present winter moth outbreak, defoliated birch stands were seen as distinct zones with a rather constant width in the uppermost part of the forest and where the upper limit coincided with the forest line. The outbreak zone closely followed the spatially variable forest line as an undulating belt, although some of the variation in outbreak zone width was also related to variation in topographical variables, such as distance from the coast, forest line altitude, and slope of the terrain. A distinct outbreak zone at the altitudinal forest line is the typical picture that has been depicted in more qualitative historical records on previous outbreaks of autumnal moth rather than winter moth. We suggest that the recent documented climate warming in this region may have induced a shift in distribution of the winter moth both relative to topography and geography. Further investigation is, however, required to substantiate these suspicions.

Opposing plant community responses to warming with and without herbivores

“…Nonetheless, it may have dramatic ecosystem consequences (44). In far northern ecosystems, insect outbreaks can influence growth dynamics of woody plants for several years after the outbreak has passed (45) and are an important component of climate-tree line dynamics (46,47). In addition to the effects of defoliation on aboveground biomass we documented (Fig.…”

“…The second, related concern is how population dynamics in both invertebrate and vertebrate populations will interact with future ecosystem and biome-scale changes associated with warming. Although insect damage and defoliation may become more frequent at northern latitudes with future warming (43,46,47), as evidence from the Paleocene-Eocene Thermal Maximum suggests (48), whether abundance of caribou and muskoxen will increase or decline as a result of climate change is far more difficult to predict (49,50). If the last two remaining large herbivores in this formerly megaherbivore-rich biome (51) were to expand or go extinct, however, it appears likely that plant community composition would undergo rapid and dramatic changes (52).…”

Reversed Impacts by Specialist Parasitoids and Generalist Predators May Explain a Phase Lag in Moth Cycles: A Novel Hypothesis and Preliminary Field Tests

“…Thus, the population dynamics of the two moth species seem to be phase-locked but with a phase lag. Recently, the winter moth outbreak range has expanded from maritime to more continental areas, where previously only outbreaks by the autumnal moth occurred (Hagen et al 2007, Jepsen et al 2008. This overlap in the current distribution has already led to more intense and persistent defoliation of the main host of both species, i.e.…”

Environmental Controls on Needle Gas Exchange and Growth of White Spruce (Picea glauca) on a Riverside Terrace near the Arctic Treeline

“…In some cases, changes in the location, frequency, intensity, and/or duration of infestations have been linked to changes in climate (e.g., Berg et al, 2006;Hagen et al, 2007). The importance of moth herbivory is well known in mountain birch forests near the treeline in northern Scandinavia (Mjaaseth et al, 2005;Hagen et al, 2007), and spruce bark beetle infestation has been documented in white spruce forests near the Arctic treeline in northern Labrador (Payette, 2007), on the FIGURE 6. Midday light-saturated stomatal conductance as a function of parent material depth on 22 July 2007, during a period of warm and dry conditions.…”