Norway spruce production and static stability in IUFRO thinning experiments in the Czech Republic

Despite recent issues, Norway spruce remains the most important commercial tree species which might be demanded henceforth for its broadly utilizable wood. Even before foresters faced both the bark beetle outbreaks and spruce decline, spruce monospecific stands were known to be prone also to other damage due to snow and wind. On this basis, measures that help prevent such failures were looked for, which resulted in the establishment of international IUFRO experimental series focused on impacts of different thinning regimes on stability and production of spruce stands. The thinning treatments differed in numbers of trees removed and retained on the site when dominant height of crop trees was reached or allowable cut in non-crop trees was accumulated. Also effects of different width of skid trails were tested. The study summarizes the results from the two IUFRO experiments in the Czech Republic. Effects of thinning regimes on spruce were found positive though thinning reduced the total volume production of wood while improving crop-tree stability which enhanced production safety. Different widths of skid trails had no effect on wood increment. Early thinning of spruce can be used to prevent their damage. No such measure, however, can alleviate the spruce decline.

Spruce Decline andDiaporthe: Incidence, Taxonomy, Virulence, and Tree Susceptibility in Michigan

In the early 2000s, spruce trees in Michigan began displaying basal needle drop and branch death that slowly progressed upward, symptoms of what we call spruce decline. A survey in 2013 revealed that spruce decline was common throughout Michigan’s Lower Peninsula, and Diaporthe was the most likely pathogen causing the cankers associated with these symptoms. Greenhouse inoculation studies completed Koch’s postulates, confirming that Diaporthe could cause cankers that cause needle loss and branch death. The five different Diaporthe haplotypes isolated from symptomatic branches during the survey differed in virulence. Haplotypes 2, 4, and 5 were more virulent, and differed from each other by only one or two base pairs using the internal transcribed spacer (ITS) region and did not differ using the β-tubulin (TUB) gene. These haplotypes were unresolved phylogenetically. Haplotypes 1 and 3 were weakly virulent to avirulent on multiple spruce taxa, and fell into a resolved Diaporthe eres clade. Spruce taxa varied in susceptibility, with Colorado blue spruce (Picea pungens) the most susceptible, followed by Norway (P. abies), then white spruce (P. glauca). Spruce taxa that were much less susceptible were Black Hills (P. glauca var. densata), Serbian (P. omorika), and Meyer spruce (P. meyeri). We demonstrate that one or more Diaporthe species is causing cankers on declining spruce in Michigan, and these cankers elicit symptoms similar to the branch death expressed by declining spruce in the landscape. Future work will focus on further characterizing Diaporthe to species, and determining biotic and abiotic stressors that may predispose spruce trees to express decline symptoms.

The correlation between the changes in climate, the intensity of spruce decline and the abundance of of spruce bark beetles in 'Golija' Nature Park

The paper presents the results of the research on the correlation between changes in microclimate, the intensity of spruce decline and active abundance of its two economically most significant harmful insects-eight-toothed (Ips typographus) and six-toothed (Pityogenes chalcographus) spruce bark beetles (Coleoptera: Curculionidae) in Golija Nature Park whose pure and mixed conifer stands are dominated by spruce. The route method and ocular inspection were applied to study the presence and determine the intensity of spruce decline-both of individual trees and groups of trees in the management units of Dajićke planine, Kolješnica, Golija and Brusničke šume. Population dynamics of the two species of bark beetles and their active abundance were monitored by the method of trapping with barrier traps and the use of combined pheromone dispensers-PCIT Ecolure. Although the decline of individual conifer trees, primarily of spruce, had already been present in certain areas of these management units for several decades, it reached epidemic proportions due to extreme adverse climatic conditions in the period between 2011 and 2012 and culminated in 2015. A large number of physiologically weakened trees raised the population levels of secondary harmful insects and the number or the active abundance of the two investigated species of insects reached a peak in 2016. The inability to take appropriate and timely remedial measures in the areas under stricter protection regimes greatly contributed to this situation.

To the trends in the forest forming process in northeastern Moscow region

Case studies of 75 permanent sample plots examine the directions of species composition change in different tree formations in case of normal evolution of biocoenoses and mass spruce decline. In case of natural development of forest biocoenoses, only on 5 plots of total 75 species composition of new tree generations is similar to that of the upper tree layer. On other 5 plots, the restoration of conditionally indigenous mixed spruce and lime forests proceeds. In all other cases, the forests develop towards the formation of broad-leaved communities with the predomination of lime. The expansion of maple in the undergrowth layer is observed on some plots. The change from spruce to lime forests is the most pronounced in the stands where the decline of spruce element occurred after bark beetle invasion.

Black spruce decline triggered by spruce budworm at the southern limit of lichen woodland in eastern Canada

Black spruce (Picea mariana (Mill.) BSP) is the dominant tree species of the southernmost (48°N) lichen woodlands in eastern Canada. Most spruce trees in mature lichen woodlands appear to be declining, as shown by the massive invasion of the epiphytic lichen Bryoria on dead branches of dying trees. A dendroecological study was undertaken to identify the main causal factors of the decline. A decline index based on the abundance of Bryoria on spruce trees was used to distinguish healthy from damaged lichen–spruce woodlands and to select sampling sites for tree-ring measurements. Three conifer species (black spruce, balsam fir (Abies balsamea (L.) Mill.), and jack pine (Pinus banksiana Lamb.)) were sampled to compare their growth patterns in time and space. In the late 1970s and mid-1980s, black spruce and balsam fir experienced sharp and synchronous radial-growth reductions, a high frequency of incomplete and missing rings, and mass mortality likely caused by spruce budworm (Choristoneura fumiferana (Clem.)) defoliation. Jack pine, a non-host species, showed no such trend. Because black spruce layers were spared, lichen woodlands will eventually regenerate unless fire occurs in the following years. Black spruce decline can thus be considered as a normal stage in the natural dynamics of the southern lichen woodlands.

Decline and physiological response to foliar-deposited salt in Norway spruce genotypes: a comparative analysis

Severe spruce decline in Denmark at the end of the 1980s led to investigations of the physiology and genetics of the decline and the importance of sea salt deposition. Narrow-sense heritability of health in a progeny trial with 8-year-old Norway spruce families (Picea abies (L.) Karst.) was 0.58. Broad-sense heritability in a seed orchard with clones from ortets of southeastern European origin was 0.53. The health of the ortets correlated with family and clone health. Health of families and clones were not correlated. The health of three spruce provenances in the progeny trial varied from 6.3 to 7.7 on a 0-9 scale. Salt stress responses of 12 two-year-old open-ollinated families from the above clones were investigated after dipping branches into different salt solutions. Photosynthesis and transpiration decreased with increasing salt deposition, respiration increased, and water use efficiency increased initially and decreased later. Correlations between field health and physiological salt responses suggested that airborne salt predisposes to spruce decline rather than triggers it. Health of Norway spruce is unlikely to be improved by salt-resistance selection in the laboratory but may be improved by low transpiration and high water use efficiency selection. Visible injuries were primarily determined by the amount of salt taken up.