En jämförande studie av några maskinella och motormanuella röjningsmetoder utmed järnväg : uppföljning av skottutveckling efter röjning samt utvärdering av selektiv röjning
Lundh, JanErik; Huisman, Mark
A comparative study of shoot development in deciduous trees after cleaning of railway verges was carried out during the period 1999-2001. The trials were located in Långsele (Västernorrland County), Garsås (Dalarna County), Herrljunga (Västra Götaland County) and Tockarp (Skåne County). The methods of cleaning compared in the study were: motor-manual cleaning with normal stump height; motor-manual cleaning with low stump height; mechanical cleaning with a chain cutter once; mechanical cleaning with chain cutter annual three times (1999, 2000, 2001) and mechanical cleaning with a blade cutter. Cleaning operations were carried out April-June, 1999-2001. Tree species included in the study were pubescent birch (Betula pubescens Ehrh), pendula birch (Betula pendula Roth), aspen (Populus tremula L.), goat willow (Salix caprea L.) and common alder (Alnus glutinosa (L.) Gaertn.). Shoot density, shoot height and shoot diameter were estimated before cleaning. The effects of cleaning were evaluated by calculating annually for three years: the number of living stumps per m2, the number of shoots per stump and the height of the shoots. The study had two objectives, namely to evaluate the biological effects of various vegetation cleaning methods and to act as a demonstration project for the Swedish Rail Authority and the Swedish Roads Authority, who commissioned the work. There were differences in stump height after cleaning using the different methods. In the four trials, stump height was 2-25 cm after mechanical cleaning with a chain cutter. After repeated mechanical cleaning of pubescent birch on peat soil (Herrljunga) with a chain cutter to leave 2 cm high stumps, there was a greater reduction in the number of shoots and a smaller number of living stumps compared with the other cleaning methods. The reason for this was that greater numbers of the stumps were totally destroyed or that higher placed sprouts were cut away. After repeated cleaning of clumps with several generations of stumps, there was also a tendency for the number of main stumps with sprouts to be reduced. After a single cleaning of birch, the choice of cleaning method had no effect on sprout development. The number and length of aspen suckers decreased after repeated mechanical cleaning in Långsele and a similar trend was observed in Tockarp. Grasses and herbaceous vegetation grew quickly and inhibited sucker development, particularly in Långsele. Aspen is very susceptible to fungal attack after repeated grazing and cleaning, which may explain this result. Goat willow was included in the study and was favoured in areas which had drainage water in the ditch below the railway embankment. Access on sloping embankments was often poor, which resulted in the stump height after mechanical cleaning being two to three times higher than on flat ground. In the Herrljunga trial, willow had many high placed spruts on the stump. Repeated cleaning or grazing gave rise to a bushy thicket. It could be seen in a number of sites that willow was particularly attractive to wild animals. Motor-manual cleaning with low stump height (average 8-18 cm) left a smaller number of uncleaned fast-growing sprouts remaining on the stump than mechanical cleaning with normal stump height (average 15-20 cm). It is easier to cut the main stump under a wide clump with a mechanical chain cutter than with a brush saw. The view from the track is affected by the density of the thicket (stems) and its maximum height. After three years growth in Garsås, the average height of the highest shoots per birch stump was 112 cm and the sprout (stem) density was 18.2 sprouts per m2. After seven years, the corresponding sprout height and density were 441 cm and 2.9 sprouts per m2. There were differences in height between treatments. Differences in shoot height were a result of the tree species, the site and the position in the country. Mechanical cleaning with a cutter chain thrashes the thicket apart completely. However, when the thicket is cut with a mechanical circular saw or by motor-manual cleaning, the cut brushwood can be collected. In Garsås, the production of birch biomass in track areas which were not cleared for seven years was 22 tonnes d.w. (dry weight) per ha along a kilometre of track with a 5 metre strip on each side. On the Herrljunga trial on peat soil, the total biomass production on a similar area with less dense thicket was 5.6 tonnes d.w. per ha from six-year old sprouts of pubescent birch. The corresponding production from six-year aspen suckers was 6.2 tonnes d.w. per ha in Långsele and 9.7 tonnes d.w. per ha in Tockarp. The removal of the biomass probably prevented embankments being set on fire and reduced the green manure effect. There is also the advantage that the woody biomass removed can be utilised as a mulch or as a biofuel. Selective motor-manual cleaning of previously identified tree specimens was also included in the study. Two variants of selective motor-manual cleaning were tested, either sparing selected specimens or cleaning half the normal treatment area. Specimens that were spared were located at appropriate safety distances from the tracks and often had characteristic growth patterns and attractive flowering. Selective cleaning was carried out at all four sites, but was more successful in open landscape (Tockarp, Långsele) where the light allowed in helped to stimulate the undergrowth, which competed with suckers and stump sprouts from cleared trees. The effects of shoot formation and growth after different forms of repeated cleaning should be investigated further under more controlled conditions. The practicality and cost of selective mechanical cleaning should also be investigated.
maskinella röjningsmetoder; motormanuella röjningsmetoder; skottskjutning; stubbskott; röjningsförsök
Rapport - Sveriges lantbruksuniversitet, Institutionen för lantbruksteknik
Publisher: Institutionen för lantbruksteknik, Sveriges lantbruksuniversitet
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