Factors controlling the amount and distribution of large woody debris in upper part of Meža

V zgornjem toku reke Meže smo od njenega izvira (1267 m) do sotočja z Bistro (602 m) opravljali sistematične meritve lesenega plavja. V tem delu površina prispevnega območja predstavlja 65,2 km2, medtem ko dolžina struge znaša 11,64 km. Posameznim kosom lesenega plavja, ki so se nahajali v strugi ali v 10 m pasu ob strugi, smo izmerili dolžino in na polovici njihove dolžine premer. V raziskavo so bili vključeni kosi z minimalno dolžino 0,5 m in minimalnim premerom 10 cm. Hkrati smo z GNSS napravo geolocirali koordinate kosov lesenega plavja. Ostale parametre smo ocenili (stopnjo razkroja, položaj v strugi, rabo tal ter ukoreninjenost). Popisali smo 1673 kosov lesenega plavja, ki skupaj predstavljajo 145,15 m3. Povprečna gostota lesenega plavja na 100 m struge je bila ocenjena na 14,4 kosa oz. 1,25 m3. Prevladuje leseno plavje dolžine med 1,5 in 2,5 m, sicer povprečna dolžina znaša 3 m. Povprečni premer je 18 cm ter povprečni volumen 0,09 m3. Rezultati kažejo, da se leseno plavje v strugi in na njenih pobočjih pojavlja v zelo neenakomernih intervalih. Največji vpliv na razporeditev lesenega plavja ima raba tal ob strugi, zlasti prisotnost gozda. Leseno plavje se v zgornjem toku reke Meže najpogosteje vključi zaradi posledic bočne erozije. Prevladujejo kosi lesenega plavja višjih stopenj razkroja.In the upper course of the river Meža, from its spring (1267 m a.s.l.) to the confluence with the Bistra (602 m a.s.l.), we systematically measured large woody debris, LWD. In this section, the surface of the contribution area covers 65,2 km2 and the channel is 11,64 km long. For individual pieces of LWD, located in the channel or in the buffer area of 10 m on each side of the channel, we measured the length and diameter at the midpoint. The minimum length of LWD to be evaluated was 0,5 m and the minimum diameter was 10 cm. We also measured coordinates of large woody debris by using GNSS device. Other parameters were also assessed (decay class, position in the river channel, land use and rootiness). Overall, 1673 pieces of wood were examined and their total volume was 145,15 m3. The average LWD density per 100 m of channel length was estimated at 14,4 pieces, or 1,25 m3 in volume. The average length of LWD was 3 m, while the majority of LWD measured from 1,5 to 2,5 m in length. The average diameter was 18 cm and the average volume was 0.09 m3. The results also show that in the river and on its slopes LWD occurs at highly irregular intervals. Our study also revealed that land use, especially wooden area, has a strong impact on the presence or absence of LWD in the Meža river. The most important factor for the presence of LWD in the upper course of the river Meža is bank erosion. It predominated LWD that was classified into higher stages of decay