© iForest -Biogeosciences and Forestry IntroductionNorway spruce is the second most abundant tree species in Latvian forests, occupying 0.52 million hectares, and nearly 0.14 million are second age class (21-40 years old) forest stands (Latvian State Forest Service 2011). Therefore, it is critical to assess the management risks in growing stand volume now, because it is these stands that will comprise the majority of the cutting volume in 40-60 years. Spruce is a species quite vulnerable to biotic and abiotic factors; therefore its cultivation is increasingly associated with high-risk levels. One of the most widespread causes of Norway spruce stand damage is development of large spruce bud scale colonies.The first cases of Norway spruce damage were observed in 2009 in middle-aged stands on drained soils. In August of 2010, monitoring by Riga Forests revealed 24% of the stands were damaged, and 10% of Picea abies stands were reported dead. Management made the decision to avoid further spruce bud scale propagation by felling 300 ha of Norway spruce forests in sanitary clear-cuts . Physokermes piceae Schrnk. belongs to the Coccidae family, order Hemiptera, and are characterized by sexual dimorphisms, with a high ability to adapt to a parasitic lifestyle on host plants (Rasina & Rupais 1994). Adult females are globular with a pronounced curvature, shiny, and brown to reddishbrown in color. Female length averages 3.5 mm, width 3.0 mm, and height 3.5-4.0 mm.Males are winged, average 1 mm long, and rarely encountered (Ozols 1985). Males have a discernable head, chest and abdomen, three pairs of legs, and one pair of wings (Graora et al. 2012). The species develops one generation per year. Immature stages winter at the base of terminal buds, less often on needles. In May, the instar larvae move to the base of new buds by old bud fissures. By the end of May or beginning of June, the females have already developed. Settling on the trunk and twigs, individuals suck sap through the bark vascular tissue. At the end of June or beginning of July, the insects lay eggs beneath themselves, and soon die (Ozols 1985). Several studies report one female lays 800-3 000 reddish eggs (Novak 1974, Turguter & Ülgenturk 2006, State Forest Service 2010. Pink first instars, called "crawlers" hatch in July, and attach themselves to new buds or the underside of needles. In October, crawlers molt into the second instar, and change color from pink to brown. The second instar larvae continue to suck sap, and subsequently overwinter on the branching parts or the lower side of the spruce needles. In spring, a small portion of the overwintering population travels to the needles, where in May the individuals pass through prepupal and pupal stages, developing into winged males (State Forest Service 2011, Lazdins et al. 2011. After wintering, most second instars attach themselves among the budding forked branch apices, where molting occurs, and round yellowish females emerge that gradually darken, and are easily noticeable (State Forest Service 2010.Sp...

To identify general patterns in the effect of climate-driven changes in the outbreak frequency of forest defoliating species, we examined 60 years of records (1950–2010) of outbreaks of five defoliating species. Data on Lymantria dispar, Lymantria monacha, Bupalus piniarius, Panolis flammea, and Operophtera brumata from five Central European countries (Slovakia, Czech Republic, Austria, Hungary, and Germany), where the current climate is comparable with the projections of climate for the Eastern Baltic region by the end of the 21st century, were analyzed. Time series approach was applied to estimate the linkage between outbreaks and climate warming. Mean annual, summer, and winter deviations for the period of 1850 to 1900 were assessed as proxies of warming. To estimate the legacy effect, warming proxies were lagged by one year. Among those tested, warming proxies showed a linkage with outbreaks. Three significant outbreaks occurred in the analyzed period (at the beginning and end of the period). During the middle part of the analyzed period, the frequency and magnitude of outbreaks were low, implicating a higher insect outbreak risk with warming in Central Europe. In the latter part of the analyzed period, more frequent yet smaller outbreaks occurred, which supports the outbreak linkage with one-year lag, summer, and annual temperatures.

ABSTRACT:In management of young forest stands, it is often the case in forestry that several risk factors, biotic, abiotic and anthropogenic ones, have to be dealt with. An anthropogenic factor is of great importance in management of forests, because humans, using ecosystems for their needs, still have to maintain the spatial structure of the forest and prevent the worsening of the health state. Covering all territory of Latvia, empirical material was gathered in 25 pure stands. To find out how neighbouring stands impact the young forest stands of spruce, the location in forest array was detected. In identifying the risk factors, attention should be paid to the shape of compartment and its location in forest array. A correlation between the occurrence and intensity of damage caused by cloven-hoofed game is relevant r fact = 0.988 > r crit = 0.088 with 95% probability. Also the occurrence and intensity of Lophophacidium hyperboreum Lagerb., and damage by Heterobasidion spp. are relevant r fact = 0.991 > r crit = 0.062 and r fact = 0.981 > r crit = 0.088 with of 95% probability.

Dead wood is a significant component in forested ecosystems. In Fennoscandia and Baltic countries, set-aside forest areas, also called woodland key habitats (WKHs), have been created for nature conservation purposes in the production forest landscape. We performed a comparative study on dead wood substrate availability in different WKH types in Latvia. We measured standing trunks and downed logs to estimate biological quantities and qualities for coarse woody debris substrate. In this study, we found out that dead wood availability ranges, on average, from 38.2 to 149.5 m 3 ha-1. This study showed that moderate quantity and quality of dead wood has been found in different types, but the fine quality coarse woody debris was scarcely presented. In general, WKHs provide moderate and high level of qualities and quantities of structural features in the production forest landscape.

Climate change manifests itself as a change in the probability of extreme weather events, and it is projected that windstorms will become more frequent and intense in Northern Europe. Additionally, the frequency and length of warm periods with wet, unfrozen soil in winter will rise in this region. These factors will lead to an increased risk of storm damages in forests. Factors affecting trees’ resistance to wind uprooting have been well quantified for some species but not for a common and economically important tree, the silver birch (Betula pendula Roth.). Therefore, this study aimed to assess the root-soil plate characteristics of silver birch on wet and dry mineral soils in hemiboreal forests. The root-soil plate and aboveground parameters were measured for 56 canopy trees uprooted in destructive, static-pulling experiments. The shape of the root-soil plate corresponds to the elliptic paraboloid. A decreasing yet slightly different trend was observed in root depth distribution with increasing distance from the stem in both soils. The main factors determining root-soil plate volume were width, which was notably larger on wet mineral soils, and tree diameter at breast height. Consequently, the root-soil plate volume was significantly larger for trees growing on wet mineral soils than for trees growing on dry soils, indicating a wind adaptation.