Epsilon Archive for Student Projects

Abstract

This thesis is built on a field study that was carried out in two seed-tree stands near by Götbrunna in Uppland, Sweden. The aim was to examine if scarification carried out in spring time could generate a more dense seedling establishment when using natural generation, than scarification carried out in autumn. It was also investigated whether there were differences in mortality the first season between the two plot-types. Plots were established block-wise with 50 blocks (pairs) on each site. The spring scarification was made with a hoe during 22-23 of April. The shelterwood densities were 120-130 stems ha-1 and the seedfalls were registered by five seed-traps in each stand.

The seedfalls started in April and were completed in early June. The most intensive seedfall occured during the first half of May. There were large differences in registered seedfall amounts between the two stands, which most likely could be explained by differences in tree-crown sizes and influence from wind.

Scarification in autumn clearly affected seed germination and establishment positively, probably due to many factors. The spring plots were not exposed to as many seeds as the autumn plots as a consequence of that the scarification was carried out after the seedfall had started. The autumn plots could during dry periods offer a better water uptake due to a higher degree of compactation. The germination and seedling establishment were significantly improved in exposed mineral soil compared to humus and the amount of exposed mineral soil was 8-10 percentage units higher in the autumn plots than in spring plots. The frequency of plots without seedlings (0-plots) were 38 and 44 %, respectively. There was no significant difference in mortality between the plot-types. In total 6 seedlings died during the first season.

According to this study, scarification in autumn is to be prefered compared to scarification in the following spring. Except from the lower degree of seedling establishment, ground frost and snow can delay scarification in the spring, which leads to that a significant part of the seedfall gets unutilized.

Detta examensarbete utfördes via fältförsök i två bestånd i närheten av Götbrunna i Uppland.
Syftet var att undersöka om markberedning utförd på våren kan generera ett högre
plantuppslag vid naturlig föryngring än markberedning utförd på hösten. Det undersöktes
också om det förelåg skillnader i överlevnad den första säsongen mellan höst- och vårytorna.
Försöksytorna anlades blockvis med 50 block (par) i vardera bestånd. Höstmarkberedningen
utfördes maskinellt under hösten 2002, medan vårmarkberedningen gjordes med hacka under
22-23 april. Skärmställningarna hade stamantal på 120-130 st/ha och tidpunkten för fröfallen
registrerades via fem fröfällor i vardera bestånd.
Fröfallen startade i början av april och avslutades i början av juni. Det mest intensiva fröfallet
inträffade under första halvan av maj. Det var stor skillnad på de registrerade fröfallens totala
mängd mellan de båda bestånden. Detta hade sannolikt att göra med skillnader i kronornas
storlek samt graden av vindpåverkan.
Det var en signifikant högre plantetablering i höstytorna jämfört med vårytorna, detta troligen
beroende av flera orsaker. Vårytorna exponerades inte för lika många frön då
vårmarkberedningen, p g a tjäle i marken, utfördes efter det att fröfallet startat. Höstytorna
kunde under torra perioder erbjuda en bättre vattentillgång till följd av en högre
kompakteringsgrad. Det var en signifikant högre plantetablering i mineraljord jämfört med
humus, och höstytorna blottade 8-10 procentenheter mer mineraljord än vårytorna. Andelen
försökspar som helt saknade plantuppslag (0-plot-par) var 38 och 44 % i de båda
försöksbestånden. Det var ingen signifikant skillnad i antalet avgångna plantor mellan höstoch
vårytorna. Totalt sex plantor avgick under säsongen.
Det går inte, utifrån resultaten i denna undersökning, att ur frögroningssynpunkt
rekommendera markberedning utförd på våren. Vårmarkberedning innebar i denna studie en
mindre gynnsam groningsmiljö. Tjäle och snö riskerar dessutom att senarelägga en
vårmarkberedning vilket kan leda till att man går miste om en betänklig del av fröfallet.