Epsilon Archive for Student Projects

Abstract

Ett ökat brukande av skog enligt skötselprinciper som leder till skiktade beståndsstrukturer, en blandad trädslagssammansättning och kontinuerligt skogbeklädd mark har potential att öka den biologiska mångfalden och värdet för rekreation (Emborg m.fl. 2000, Berg m.fl. 1995, Mattsson & Li 1994, Holgen m.fl. 2000). I ljuset av detta, tillsammans med svårigheterna som finns att nå goda ekonomiska resultat vid skötsel av ädellövskog (Lindén & Ekö 2002), ses det idag som angeläget att uppmärksamma och studera alternativa skogsskötselmetoder (Cedergren 2008) .

I östra Blekinge har ett antal skogsägare under längre tid praktiserat en metod att sköta naturligt föryngrad ek i blandbestånd som går ut på att, mer eller mindre tidigt, frihugga ekhuvudstammar, och att dana kvalitet genom stamkvistning/beskärning. För att undersöka hur diametertillväxten påverkas av att eken frihuggs, har ett stort antal provträd märkts ut och regelbundet mätts. Den första mätningen gjordes 1951. Diametertillväxtmätningarna och beståndsstrukturerna som utvecklats utgör nu ett värdefullt material över hur eken och de bestånd den ingår i kan utvecklas vid frihuggning.

I arbetet presenteras analyser av diametertillväxten för de frihuggna ekarna, baserat på diameterutvecklingsmätningarna, och resultat från inventeringar av tre särskilt studerade bestånd. Resultaten diskuteras i sin tur i termer av potentialen för kontinuitetsskötsel av ek i denna typ av bestånd, med hänseende bl.a. till möjligheterna för naturlig föryngring och ekonomin. I analysen över ekens diametertillväxt ingår data från närmare 1300 mättillfällen på 157 stycken provträd. 47 kompletterande mätningar utfördes inom ramen för arbetet. Tre bestånd valdes särskilt ut som inventeringsobjekt, ett 87 år och två 106 år gamla. I det förra har upprepade frihuggningar skett sen beståndet var i 30-årsåldern, i de två senare sen 50-årsåldern. Fem provytor, radie 10 m, las ut per bestånd.

Resultaten från analysen av provträdsmätningarna tyder på att diametertillväxten för frihuggna ekar kan överstiga den hos konventionellt skött ek med upp mot 50 % och att växttiden för enskilda ekar troligen kan förkortas med minst 20 år genom tidig och upprepad frihuggning.

Inventeringarna av de särskilt utvalda bestånden visar på förekomst av ett flertal olika trädslag och att diameterspridningen är stor i bestånden. Antalet stammar ökar i de lägre diameterklasserna. I alla bestånd fanns minst nio olika trädslag representerade. Förutom av ek, domineras bestånden av sekundärträdslagen gran och bok. Dock utgör andra trädslag minst 40 % av antalet stammar med dbh < 12 cm, i alla bestånd. Ung ek (4 < och < 20 cm dbh) förekom till ett antal av mellan 38 och 64 stammar/ha. I ett av bestånden uppgick antalet ekplantor till ca 1700 st/ha, i de andra till ca 500 resp. 200 st/ha.

Kontinuitetsskötsel av ekblandbestånd genom frihuggning, ett återkommande uttag av grov ek och rekrytering av huvudstammar genom naturlig föryngring eller plantering av plantgrupper i luckor framstår som ett möjligt, och ekonomiskt fördelaktigt skötselalternativ.
Vid jämförelse av kassaflödet i typbestånden: ek-kontinuietsskötsel, konventionellt skött gran, konventionellt skött ek, och planterat blandbestånd ek-gran, gav kontinitetsskötsel av ek under vissa förutsättningar ett kassaflöde väl i nivå med granalternativet.

Abstract

By managing forest using silvicultural methods that create stands with uneven aged structures, a variety of tree species and a continues tree cover, there is potential to increase the biodiversity and the value for recreation (Emborg m.fl. 2000, Berg m.fl. 1995, Mattsson & Li 1994, Holgen m.fl. 2000). However it is also necessary that the methods will yield a reasonable economic return (Lindén & Ekö 2002). It is therefore of great importance to study alternative silvicultural methods (Cedergren 2008).

In the eastern part of the county of Blekinge in Sweden, some forest owners have for a long time practiced a way of managing naturally regenerated oak in mixed stands by early freeing future main stems of competition and promoting good timber quality by manual pruning. To examine how the diameter growth on these oaks has been affected by this early release, a big number of sample trees have been marked and repeatedly measured up to present. The first tree was measured in 1951. The diameter growth measurements, and the present composition of the stands, now form a valuable material describing how selected oaks and the stand develop. This makes it possible to make comparisons with conventional even aged oak forestry.

In the study, analyses of the diameter growth of released oaks in the study stands was made. The results are discussed in relation to a system for a continuous cover forestry (CCF). In the analyses data from about 1300 measurements on 157 sampel trees were included. 47 additional measurements were made as a part of this study. Three stands were chosen as reference stands, where extensive measurements were made-, one of the stands was 87 and the two others were 106 years old. In the younger stand cuttings have repeatedly been made since the stand was in its thirties, in the other two since their fifties. Five sample plots in each stand with the radius of 10 metres were used for assessments.

The results indicate that the diameter growth of released oaks can exceed the growth of conventionally managed oaks by up to 50 % and that the cutting age for the single oak can be reduced by at least 20 years. The inventories showed that the stands contain most of the Swedish tree species and that there are trees in a wide range of diameter classes. The number of stems increases in the lower diameter classes. At least nine different tree species were represented in each stand. Beside oak, the stands are dominated by Norway spruce (Picea abies) and beech (Fagus sylvatica).The number of stems of young oaks-, between 4 and 20 cm, were between 38 and 64 per ha. In one of the stands the number of oak seedlings (<4cm) were about 1700 per ha, in the others 500 and 200 per ha respectively.

CCF in mixed stands with oak, with repeated harvest of good quality mature oaks and recruitment of new future stems -using natural regeneration or planting of groups of seedlings seem to be a possible and economically feasible management method. A comparison was made between cash-flow in CCF, simulated with starting point from the study stands, and conventionally managed spruce. The analyses showed that CCF -under certain circumstances gave as high cash-flow as the spruce monoculture alternative.

By managing forest using silvicultural methods that create stands with uneven aged
structures, a variety of tree species and a continues tree cover, there is potential to increase the
biodiversity and the value for recreation (Emborg m.fl. 2000, Berg m.fl. 1995, Mattsson & Li
1994, Holgen m.fl. 2000). However it is also necessary that the methods will yield a
reasonable economic return (Lindén & Ekö 2002). It is therefore of great importance to study
alternative silvicultural methods (Cedergren 2008).
In the eastern part of the county of Blekinge in Sweden, some forest owners have for a long
time practiced a way of managing naturally regenerated oak in mixed stands by early freeing
future main stems of competition and promoting good timber quality by manual pruning. To
examine how the diameter growth on these oaks has been affected by this early release, a big
number of sample trees have been marked and repeatedly measured up to present. The first
tree was measured in 1951. The diameter growth measurements, and the present composition
of the stands, now form a valuable material describing how selected oaks and the stand
develop. This makes it possible to make comparisons with conventional even aged oak
forestry.
In the study, analyses of the diameter growth of released oaks in the study stands was made.
The results are discussed in relation to a system for a continuous cover forestry (CCF). In the
analyses data from about 1300 measurements on 157 sampel trees were included. 47
additional measurements were made as a part of this study. Three stands were chosen as
reference stands, where extensive measurements were made-, one of the stands was 87 and
the two others were 106 years old. In the younger stand cuttings have repeatedly been made
since the stand was in its thirties, in the other two since their fifties. Five sample plots in each
stand with the radius of 10 metres were used for assessments.
The results indicate that the diameter growth of released oaks can exceed the growth of
conventionally managed oaks by up to 50 % and that the cutting age for the single oak can be
reduced by at least 20 years. The inventories showed that the stands contain most of the
Swedish tree species and that there are trees in a wide range of diameter classes. The number
of stems increases in the lower diameter classes. At least nine different tree species were
represented in each stand. Beside oak, the stands are dominated by Norway spruce (Picea
abies) and beech (Fagus sylvatica).The number of stems of young oaks-, between 4 and 20
cm, were between 38 and 64 per ha. In one of the stands the number of oak seedlings (<4cm)
were about 1700 per ha, in the others 500 and 200 per ha respectively.
CCF in mixed stands with oak, with repeated harvest of good quality mature oaks and
recruitment of new future stems -using natural regeneration or planting of groups of seedlings
seem to be a possible and economically feasible management method. A comparison was
made between cash-flow in CCF, simulated with starting point from the study stands, and
conventionally managed spruce. The analyses showed that CCF -under certain circumstances
gave as high cash-flow as the spruce monoculture alternative.