Gradacije smrekovog prelca (Lymantria monacha) i područja njegove učestale pojave u Češkoj

The paper, based on a literature review, presents an overview of the nun moth outbreaks in Czech forests from 1784 to 2010. A database of outbreaks was created and presently contains 2,557 records. The oldest written record dates from 1784. The greatest calamity of nun moth outbreaks occurred during the years 1917–1927. The last nun moth outbreaks appeared in the years 1993–1996. A map of high-risk areas in the Czech Republic was created based on this historical data.Smrekov prelac (Lymantria monacha) izraziti je polifag, čije se gusjenice hrane iglicama četinjača i lišćem mnogih listača. Smreka (Piceasp.), ariš (Larixsp.) i bor (Pinussp.) najčešće su napadnuti ovim štetnikom, ali jake defolijacije mogu se pojaviti i na drugim vrstama tijekom njegovih gradacija. U Hrvatskoj je rijedak i javlja se tek sporadično, podjednako u različitim šumskim sastojinama. Unatoč velikom broju dokumentiranih gradacija u Europi, mali je broj radova u kojima se analizira prostorno gledište njegove pojave. Prvi masovni napad smrekovog prelca zabilježen je u Središnjoj Europi 1449. godine. Do kraja 19. stoljeća zabilježeno je barem 26 značajnijih razdoblja njegovih gradacija. U Češkoj je evidentirano više od 100 pojava defolijacije smrekovog prelca tijekom 20. stoljeća. Izrazite i prostorno značajne gradacije bilježene su uglavnom nakon 1900. godine i takva je situacija potrajala do 1940. godine. Najveće kalamitete smrekov prelac uzrokovao je u Češkoj u dvadesetim godinama 20. stoljeća. Od 1996. do danas nisu zabilježene izrazitije gradacije. Različita učestalost pojave, kao i jačina defolijacije u pojedinim dijelovima teritorija, autorima rada bili su poticaj za pokušaj izrade prostorne analize i izrade karte povišenog rizika ovog defolijatora na području Češke. Koristeći metodu običnog kriginga, analizirali su i geostatistički obradili više od 2 500 izvornih povijesnih podataka defolijacija i gradacija smrekovog prelca na području Češke od 1784. do 2010. godine. Glavna razdoblja i područja masovne pojave i najžešćih gradacija prikazana su u Tabli ci 1. Intenzitet defolijacije preuzet iz brojnih literaturnih i ostalih izvora klasiran je u 4 kategorije (vidi sliku 1). Rezultat ovako klasiranih izvornih podataka prikazan je na dvije karte (slika 1 i slika 2). Na slici 1 prikazana je distribucija pojave i žestine defolijacije smrekovog prelca, svedeno prostorno na gospodarske jedinice. Na slici je vidljiva neujednačena distribucija registriranih defolijacija, kao i činjenica da u dijelu teritorija nikada nije zabilježena šteta od ovog defolijatora. Ovo se objašnjava izrazito nepovoljnim klimatskim uvjetima (visoka planinska područja) ili izostankom biljke domaćina (u nižim područjima). Jasno se uočavaju područja jakih gradacija (crvene točke). Na drugoj slici jasnije se razaznaje koja su područja napadnuta jače i češće (crve na boja). Također, autori dolaze do zaključka da je u promatranom razdoblju došlo do prostornog pomaka optimalnog područja pridolaska i gradacija smrekovog prelca. Taj se pomak dogodio u smislu povećanja nadmorske visine na kojima su se javljale gradacije. Na početku istraživanog razdoblja najžešće gradacije bilježene su na srednjoj nadmorskoj visini od 457 m n.m. Intenzitet i učestalost gradacija kasnije se javlja na srednjoj nadmorskoj visini od 640 m n.m. Autori zaključuju kako je očigledno kako se izvorišta gradacija “sele” na veće nadmorske visine. Također, analizom podataka utvrđeno je kako je glavna vrsta na “udaru” ovog defolijatora početkom 20. stoljeća bio bor, dok se u desetljećima koja su sljedila najveće štete bilježe na običnoj smreci. Dijelom se kao razlog tomu navode obimna pošumljavanja ovom, nekad popularnom šumskom vrstom drveća. Bez obzira na nedostatke kojih su autori svjesni u korištenju metode kriginga, zaključuju kako se ovim putem, zahvaljujući velikom broju podataka, može pokazati prostorna dinamika pojave smrekovog prelca na teritoriju Češke, uočiti “izvorišna područja” odakle započinju gradacije, kao i trend prostornog pomaka kojega povezuju s promijenjenim stanišnim uvjetima. Kao jedan od mogućih scenarija utemeljenih na recentnim klimatskim promjenama (povišenje temperature) navode pomicanje gradacijskih žarišta ovog važnog defolijatora Središnje Europe na veće nadmorske visine, odnosno više geografske širine. Prevedeno na naše geografsko područje, ovo bi značilo da bi smrekov prelac mogao postati još rjeđi u područjima gdje je i do sada bio prisutan u niskoj gustoći populacije

What Happens to Wood after a Tree Is Attacked by a Bark Beetle?

Advancing climate change is affecting the health and vitality of forests in many parts of the world. Europe is currently facing spruce bark beetle outbreaks, which are most often caused by wind disturbances, hot summers, or lack of rainfall and are having a massive economic impact on the forestry sector. The aim of this research article was to summarize current scientific knowledge about the structure and physical and mechanical properties of wood from bark beetle-attacked trees. Spruce stands are attacked by a number of beetles, of which Ips typographus is the most common and widespread in Central Europe. When attacking a tree, bark beetles introduce ophiostomatoid fungi into the tree, which then have a greater effect on the properties of the wood than the beetles themselves. Fungal hyphae grow through the lumina of wood cells and spread between individual cells through pits. Both white rot and brown rot fungi are associated with enzymatic degradation of lignin or holocellulose, which is subsequently reflected in the change of the physical and mechanical properties of wood. Wood-decay fungi that colonize wood after infestation of a tree with bark beetles can cause significant changes in the structure and properties of the wood, and these changes are predominantly negative, in the form of reducing modulus of rupture, modulus of elasticity, discolouration, or, over time, weight loss. In certain specific examples, a reduction in energy consumption for the production of wood particles from beetle-attacked trees, or an increase in surface free energy due to wood infestation by staining fungi in order to achieve better adhesion of paints or glues, can be evaluated positively

How Bark Beetle Attack Changes the Tensile and Compressive Strength of Spruce Wood (Picea abies (L.) H. Karst.)

Since 2014, forestry in the Czech Republic has been significantly affected by a bark beetle outbreak. The volume of infested trees has exceeded processing capacity and dead standing spruce (Picea abies) remain in the forest stands, even for several years. What should be done with this bark beetle wood? Is it necessary to harvest it in order to preserve the basic mechanical and physical properties? Is it possible to store it under standard conditions, or what happens to it when it is “stored” upright in the forest? These are issues that interested forest owners when wood prices were falling to a minimum (i.e., in 2018–2019) but also today, when the prices of quality wood in Central European conditions are rising sharply. To answer these questions, we found out how some of the mechanical properties of wood change in dead, bark beetle-infested trees. Five groups of spruce wood were harvested. Each of these groups was left upright in the forest for a specified period of time after bark beetle infestation, and one group was classified as a reference group (uninfested trees). Subsequently, we discovered what changes occurred in tensile and compressive strength depending on the time left in the stand and the distance from the center of the trunk. When selecting samples, we eliminated differences between individual trees using a CT scanning technique, which allowed us to separate samples, especially with different widths of annual rings and other variations that were not caused by bark beetle. The results showed the effect of log age and radial position in the trunk on tensile and compressive strength. The values for tensile strength in 3-year infested trees decreased compared to uninfested trees by 14% (from 93.815 MPa to 80.709 MPa); the values for compressive strength then decreased between the same samples by up to 25.6% (from 46.144 MPa to 34.318 MPa). A significant decrease in values for compressive strength was observed in the edges of the trunks, with 44.332 MPa measured in uninfested trees and only 29.750 MPa in 3-year infested trees (a decrease of 32.9%). The results suggest that the use of central timber from bark beetle-infested trees without the presence of moulds and fungi should not be problematic for construction purposes

How Bark Beetle Attack Changes the Tensile and Compressive Strength of Spruce Wood (<i>Picea abies</i> (L.) H. Karst.)

Since 2014, forestry in the Czech Republic has been significantly affected by a bark beetle outbreak. The volume of infested trees has exceeded processing capacity and dead standing spruce (Picea abies) remain in the forest stands, even for several years. What should be done with this bark beetle wood? Is it necessary to harvest it in order to preserve the basic mechanical and physical properties? Is it possible to store it under standard conditions, or what happens to it when it is “stored” upright in the forest? These are issues that interested forest owners when wood prices were falling to a minimum (i.e., in 2018–2019) but also today, when the prices of quality wood in Central European conditions are rising sharply. To answer these questions, we found out how some of the mechanical properties of wood change in dead, bark beetle-infested trees. Five groups of spruce wood were harvested. Each of these groups was left upright in the forest for a specified period of time after bark beetle infestation, and one group was classified as a reference group (uninfested trees). Subsequently, we discovered what changes occurred in tensile and compressive strength depending on the time left in the stand and the distance from the center of the trunk. When selecting samples, we eliminated differences between individual trees using a CT scanning technique, which allowed us to separate samples, especially with different widths of annual rings and other variations that were not caused by bark beetle. The results showed the effect of log age and radial position in the trunk on tensile and compressive strength. The values for tensile strength in 3-year infested trees decreased compared to uninfested trees by 14% (from 93.815 MPa to 80.709 MPa); the values for compressive strength then decreased between the same samples by up to 25.6% (from 46.144 MPa to 34.318 MPa). A significant decrease in values for compressive strength was observed in the edges of the trunks, with 44.332 MPa measured in uninfested trees and only 29.750 MPa in 3-year infested trees (a decrease of 32.9%). The results suggest that the use of central timber from bark beetle-infested trees without the presence of moulds and fungi should not be problematic for construction purposes