-les, ki se tvori v mladostnem obdobju, odvisno od vrste, 5-30 let.

-les, ki se tvori v mladostnem obdobju, odvisno od vrste, 5-30 let.

-krajša vlakna z velikim mikrofibrilarnim kotom, ki povzroča zelo veliko osno (vzdolžno) nabrekanje in krčenje.

Nima kasnega lesa. Zato se branike neizrazite, gostota lesa pa večinoma nižja od zrelega (adultnega) lesa. Je produkt mladega kambija in dobre oskrbljenosti z rastnim hormonom. Juvenilnemu lesu v debelni sredici je analogen krošnjev les.

•Zaradi tehnološko manjvrednega juvenilnega lesa, mnogokrat visoke koncentracije reakcijskega tkiva in razkroja, je srčevina oz. debelna sredica tehnološko manj vredna in jo pred nadaljnjo predelavo lesa v vrednejše izdelke praviloma odstranimo.)

- problematičen pri vrstah, ki v mladosti hitro rastejo (topol, breza), medtem ko je pri počasi rastočih»sencovzdržnih« (jelka) njegov vpliv zanemarljiv.

juvenilni/mladostni les srčevina

JUVENILNI LES

Juvenile wood has a tendency for development

JUVENILNI, ZRELI, STAROSTNI LES

Since juvenile wood tends to form only for a certain period of time, and not thereafter, this kind of wood occupies the center portion of every tree. Moreover, the proportion of the tree stem that is composed of juvenile wood increases with height, so that at the very top of the tree, the stem cross section is virtually 100% juvenile wood

the height growth of a tree is traceable to production of new cells at the tip of the main stem and branches, and that diameter growth results from cell division in a 1-cell-wide layer of cells that sheath the main stem, branches, and roots. Because of this, the distance of any one growth increment from the center of the tree varies by height along the stem. For instance, a new growth ring found near the ground level or butt of a very large tree might represent the 100th year of growth at that height above ground, but only the third growth ring near the top of the main stem. Thus, much of the wood comprising the ring will be “normal, mature” wood, while the portion of the ring (that closest to the top of the tree) will be juvenile wood. This is true regardless of tree age. As long

as a tree continues to grow in height, it continues to produce juvenile wood

it shrinks and swells along the grain as moisture content changes, and

strength is lower, and in some cases much lower, than mature wood of the

same tree.

juvenilni/mladostni les srčevina

POŠKODBE

RAZPOKE

-notranje razpoke

Notranje napetosti v deblu.

-mraznePogostejše pri

listavcih z izrazitimi trakovi.

-sušilneZaradi krčenja

lesa med sušenjem –

napetosti v lesu!

-krožnePo letnici –

spodnji del debla; jelka, hrast,

kostanj, jesen, bukev,…

radialne natezne napetosti•šibko mesto v živem drevesu

KOLESIVOST -KROŽNE RAZPOKE

BARVNE SPREMEMBELESA

Parenhimske pegebreza, jelša, topol

Dvojna beljavaRedko!

Diskoloriran les/mokrina

modrivost

Obarvana jedrovina pri macesnu (a) in hrastu (b) ter neobarvana jedrovina pri jelki (c) in smreki (d).

Normalen, neobarvan les bukovine (a, b) in diskoloriran les (c, d).

MOKRO SRCEokuženo z bakterijami,visoka vlažnost,Spremenjenapermeabilnost,po sušenju lesa izgine.K. Čufar

UČNO GRADIVO

• http://www.cpi.si/files/cpi/userfiles/Lesarstvo_tapetnistvo/5-NAPAKE_LESU.pdf