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Oak as retention tree in commercial spruce forests

effects on species diversity of saproxylic beetles and wood production

Koch Widerberg, Maria (2013). Oak as retention tree in commercial spruce forests. Diss. (sammanfattning/summary) Alnarp : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2013:66
ISBN 978-91-576-7870-6
eISBN 978-91-576-7871-3
[Doctoral thesis]

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Retaining trees valuable for biodiversity is a common conservation measure. There are
indications that such trees have important benefits for the diversity of many species
groups. However, retaining trees may also have negative effects on timber production.
The aim of this thesis was to study the benefits of retaining oaks (Quercus robur) in
spruce forests (Picea abies) for the diversity of oak associated saproxylic (wood-living)
beetle species and to assess the negative effects on wood production of spruce.

The first three papers, as presented in this thesis, relates to the biodiversity aspect:
the effect of openness on species richness (Paper I); the benefit of retaining oaks in
spruce plantations, in relation to pasture oaks (Paper II); and the short-term effects of
clearing on species richness and composition (Paper III). In Paper IV, the negative
effects of gap formation around oaks on wood production of spruce was assessed.

The results showed a significant decrease in species richness of oak beetles with
decreasing openness. Moreover, spruce trees on the southern side of the oaks appeared
to have a larger impact than trees of than those on the northern side (Paper I).
According to the results in Paper II, low shaded oaks in spruce plantations harbored
slightly more oak associated species than did pasture oaks, and the species composition
differed somewhat, although it seemed to be partially overlapping. The amount of dead
wood in the oak crown appeared to one of the major explanatory factor for differences
in species richness and composition between forest and pasture. Thus, oaks in
plantations can harbor a comparatively high number of species. Regarding the shortterm
effects of clearing (Paper III), there was a significant positive effect on species
richness of saproxylic oak beetles of larger clearings (under and outside the crown)
already the first three years after clearing, compared to non-cleared oaks. Smaller
clearings (solely under the oak crown) did not yield the same increase in species
richness as the larger clearings. However, both small and large clearings differed in
species composition when compared to the non-cleared oaks.

Retaining oaks has a negative effect on the growth of spruce (Paper IV). The basal
area in the area around retained oaks was on average about 83% of the basal area in
satellite plots without retained oaks. Since there was no difference in production level
between large and small gaps, this study indicates that with the thinning treatments
imposed on the studied stands, the reduction in production will be about the same
irrespective of gap size for gaps at least up to about 350 m².

In summary, increased openness has apparent positive effects on species richness of
saproxylic oak beetles and the response to clearing has immediate positive effects on
both species richness and composition of oak associated beetles. Retained oaks in
spruce forests may, if cleared of encroaching spruce trees, harbor a species richness
comparable to, or even higher, than that of pasture oaks. A certain loss in timber
volume from the gaps is expected, however, trees lining the edge of gaps can partly
compensate for the loss with the gap. The increase in timber loss is smaller for smaller
gap sizes, as compared to large. Retaining several oaks in small gaps should thus be
more cost-efficient compared to few oaks in large gaps. However, oaks in large gaps
may attract additional species that favor high levels of insolation. One single large gap
may thus capture more species than several small gaps together, even if the total gap
area is equal. These aspects should be considered when planning for clearing around
retained oaks in a spruce forest or plantation.

Authors/Creators:Koch Widerberg, Maria
Title:Oak as retention tree in commercial spruce forests
Subtitle:effects on species diversity of saproxylic beetles and wood production
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :6 September 2013
Number of Pages:50
I.Maria Koch Widerberg, Thomas Ranius, Igor Drobyshev, Urban Nilsson, and Matts Lindbladh (2012). Increased openness around retained oaks increases species richness of saproxylic beetles. Biodiversity and Conservation 21(12), 3035-3059.
II.Maria Koch Widerberg, Thomas Ranius, Urban Nilsson, and Matts Lindbladh (2013). Oaks retained in commercial spruce forests function as a complementary habitat to oaks in wood pastures for saproxylic beetles. Biological Conservation (under review).
III.Maria Koch Widerberg, Urban Nilsson, and Matts Lindbladh. Short-term effects on beetle diversity of clearing around retained oaks in a spruce plantation. Submitted manuscript.
IV.Maria Koch Widerberg, Urban Nilsson, and Matts Lindbladh. Growth compensation of Norway spruce in gaps around retained oaks. Manuscript.
Place of Publication:Alnarp
Publisher:Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-576-7870-6
ISBN for electronic version:978-91-576-7871-3
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:K Forestry > K10 Forestry production
P Natural resources > P01 Nature conservation and land resources
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Ecology
(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Forest Science
Agrovoc terms:quercus robur, forest trees, deadwood, biodiversity, coleoptera, wood production, picea abies, timber trees, land clearing, biodiversity conservation, costs
Keywords:retention, Quercus robur, saproxylic, coleoptera, clearing, light, product, spruce, economy
Permanent URL:
ID Code:10828
Department:(S) > Southern Swedish Forest Research Centre
External funders:Skogssällskapet
Deposited By: Unnamed user with email maria.koch.widerberg@slu.se
Deposited On:30 Sep 2013 11:56
Metadata Last Modified:14 Dec 2014 19:49

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