Population dynamics in changing environments: the case of an eruptive forest pest species

Abstract

In recent decades we have seen rapid and co-occurring changes in landscape structure, species distributions and even climate as consequences of human activity. Such changes affect the dynamics of the interaction between major forest pest species, such as bark beetles (Coleoptera: Curculionidae, Scolytinae), and their host trees. Normally breeding mostly in broken or severely stressed spruce; at high population densities some bark beetle species can colonise and kill healthy trees on scales ranging from single trees in a stand to multi-annual landscape-wide outbreaks. In Eurasia, the largest outbreaks are caused by the spruce bark beetle, Ips typographus (Linnaeus), which is common and shares a wide distribution with its main host, Norway spruce (Picea abies Karst.). A large literature is now available, from which this review aims to synthesize research relevant for the population dynamics of I. typographus and co-occurring species under changing conditions. We find that spruce bark beetle population dynamics tend to be metastable, but that mixed-species and age-heterogeneous forests with good site-matching tend to be less susceptible to large-scale outbreaks. While large accumulations of logs should be removed and/or debarked before the next swarming period, intensive removal of all coarse dead wood may be counterproductive, as it reduces the diversity of predators that in some areas may play a role in keeping I. typographus populations below the outbreak threshold, and sanitary logging frequently causes edge effects and root damage, reducing the resistance of remaining trees. It is very hard to predict the outcome of interspecific interactions due to invading beetle species or I. typographus establishing outside its current range, as they can be of varying sign and strength and may fluctuate depending on environmental factors and population phase. Most research indicates that beetle outbreaks will increase in frequency and magnitude as temperature, wind speed and precipitation variability increases, and that mitigating forestry practices should be adopted as soon as possible considering the time lags involved.

Spruce Beetle Biology, Ecology and Management in the Rocky Mountains: An Addendum to Spruce Beetle in the Rockies

“…Weather-related mechanisms for example, directly affect spruce beetle population dynamics through the influence of temperature on cold tolerance (winter survival) and life history strategies that lead to the synchrony of population emergence [9,38,91], or indirectly by predisposing host trees to attack [92]. Forest heterogeneity influences the development of spruce beetle outbreaks by limiting population spread to susceptible stands [8,93]. The synchronous occurrence of outbreaks at multiple spatial and temporal scales evident in spruce beetle outbreak histories from the central Rocky Mountains alludes to the influences of both weather and forest conditions [7,15,16,19].…”

Effect of different tree mortality patterns on stand development in the forest model SIBYLA

“…This is, however, not a realistic assumption because various transitions between random and patchy tree mortality patterns are typical of bark beetle population dynamics. Typically, small populations generate a scattered pattern because the beetles search for suitable hosts, while beetles in large populations tend to infest the trees in a closer vicinity (Kausrud et al 2011;Hlásny & Turčáni 2013). Large populations might tend to collapse after a several-year period of the outbreak culmination because of the effect of diverse density dependent regulation mechanisms (Raffa et al 2008).…”

Is it possible and necessary to control European spruce bark beetle Ips typographus (L.) outbreak in the Białowieża Forest?

“…Concerns on the excessive hampering of the saproxylobiont populations are in this context unreasonable as the trees will be left in forest after they have been debarked. Though, it is necessary to maintain certain balance between the needs of active protection and the demand of leaving deadwood or fragments of deadwood in forests (Kausrud et al 2012).…”