Drought effects on carbon allocation to resin defences and on resin dynamics in old-grown Scots pine

Droughts and other rapid changes in abiotic environmental conditions can predispose trees to damage by pest insects and pathogens. For survival of coniferous trees, functional resin-based defences are essential, and it is important to know how they react to changes in environmental conditions at various time scales. We studied the effects of differing water availabilities on resin-based defences in mature Scots pine (Pinus sylvestris) trees in a naturally drought-prone forest within a long-term irrigation experiment. Our objectives were to understand the effects of long-term drought on carbon allocation to resin production and to analyse its influence on resin flow and pressure in comparison to the shorter-term effects of seasonal drought. We tracked carbon allocation to resin after C-13-pulse labelling experiment in late summer 2017 and compared the observed resin dynamics between drought-exposed control trees and irrigated trees from June to August during the dry hot summer of 2018. Dry control trees showed higher allocation of labelled carbon to resin than irrigated trees. Resin pressure was higher in dry control than in irrigated trees with similar water potentials, and resin flow in June was higher in dry control than in irrigated trees with similar crown transparency. Yet, resin pressures of dry control trees in particular decreased with decreasing water availability from June to August. Resin flow was little affected by short-term changes in water availability and mostly associated with crown transparency. We suggest that because of differing timescales of direct drought effects and changes in allocation patterns, dry conditions may support resin-based defences in the long term, but a drought period decreases resin pressure in the short term.Peer reviewe

Population trends of Rosalia alpina (L.) in Switzerland: a lasting turnaround?

Many species that depend on old trees and dead wood are suffering from habitat losses and intensive forest management. For the conspicuous cerambycid beetle Rosalia alpina, a relative sampling analysis combined with a distribution model showed a population decrease in Switzerland between 1900 and World War II. This negative trend can be ascribed to the abandonment of traditional management such as wooded pasture and to the expansion of high forest promoted by modern forestry. Since that period, the population of R. alpina, has been increasing and each single relict population of this species was maintained. These positive population trend can be explained by less intensive forest management and a shift from fuel-wood production to timber wood. Today, many more old beech trees and much more dead wood remain in Swiss forests than 50years ago. Consequently, the habitat conditions necessary for the development of the Rosalia longicorn have improved, especially on steep terrain in colline and submontane regions. However, it is still uncertain whether current population sizes can guarantee the survival of this species in the long term, especially as fuel-wood production is expected to become more intensive in Switzerland in future decades. The conservation of this species requires, therefore, the establishment of natural forest reserves and dead wood islands or the restoration of wooded pastures with scattered habitat trees. The Rosalia longicorn could then act as an umbrella species for other species that depend on old trees and dead woo

Fire and windthrow in forests: Winners and losers in Neuropterida and Mecoptera

The mid-term impact of forest fires and windthrows on species compositions in the insect orders Neuroptera, Raphidioptera and Mecoptera was assessed in Swiss forests using standardized flight interception traps. For 50 species the abundances in intact control plots were compared to those in moderately or strongly disturbed forest stands. The catches were combined over four forest disturbance projects ranging from windthrows in alpine spruce forests and lowland deciduous forests to winter forest fires in Southern Switzerland and a large summer fire in southwestern Switzerland. As a result 82% of the 50 species benefited from the disturbance and became more abundant in the years after the fire or windthrow. More species (19) had their maximum abundance in intermediately disturbed plots than in heavily disturbed forests (17). Only 11 species mainly Hemerobiidae and Coniopterygidae peaked in the undisturbed forest stands. The species are listed per impact and ranked as winners (more than 66% specimens per treatment collected in disturbed forest plots) losers (more than 66% specimens per treatment in undisturbed forest plots) and indifferent species. An additional 29 species that were too scarce for an assessment are listed in Appendix 1. We conclude that for Neuropterida and Mecoptera catastrophic incidences are natural ecological events which create new habitats and by this foster their occurrence and abundance

Return of the moth: rethinking the effect of climate on insect outbreaks

Abstract: The sudden interruption of recurring larch budmoth (LBM; Zeiraphera diniana or griseana Gn.) outbreaks across the European Alps after 1982 was surprising, because populations had regularly oscillated every 8–9 years for the past 1200 years or more. Although ecophysiological evidence was limited and underlying processes remained uncertain, climate change has been indicated as a possible driver of this disruption. An unexpected, recent return of LBM population peaks in 2017 and 2018 provides insight into this insect’s climate sensitivity. Here, we combine meteorological and dendrochronological data to explore the influence of temperature variation and atmospheric circulation on cyclic LBM outbreaks since the early 1950s. Anomalous cold European winters, associated with a persistent negative phase of the North Atlantic Oscillation, coincide with four consecutive epidemics between 1953 and 1982, and any of three warming-induced mechanisms could explain the system’s failure thereafter: (1) high egg mortality, (2) asynchrony between egg hatch and foliage growth, and (3) upward shifts of outbreak epicentres. In demonstrating that LBM populations continued to oscillate every 8–9 years at sub-outbreak levels, this study emphasizes the relevance of winter temperatures on trophic interactions between insects and their host trees, as well as the importance of separating natural from anthropogenic climate forcing on population behaviour

Cerambicidi invasivi provenienti dall\u2019Asia: Ecologia e gestione \u2013 Sherwood 203 \u2013 Giugno 2014: 6-9.

Cerambicidi invasivi provenienti dall\u2019Asia: Ecologia e gestion