1. Succession of saproxylic beetles associated with decomposition of white spruce logs in the boreal forest Seung-Il Lee¹, John R. Spence¹, and David W. Langor² ¹Department of Renewable Resources, University of Alberta; ²Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre
What are Saproxylic Beetles?
Results
Saproxylic beetles are the beetles that depend on dying or deadwood during some part of their life cycle. They play important roles in nutrient cycling and food web dynamics, but they are also highly sensitive to environmental changes.
Importance of Deadwood
Deadwood is a key functional ecosystem attribute and a vital component for conservation of many deadwood dependent species. Deadwood provides a range of structural characteristics uniquely associated with specific habitats used by species ranging from microorganisms to vertebrates. Thus, deadwood management is increasingly included as a central aspect of forest ecosystem management.
Figure 1 Species richness of adult saproxylic beetles among decay classes (DC). Black bars represent mean species richness per replicate. Green bars represent total species richness for all replicates combined. Error bars represent +1 SE for nine substrates in each DC.
Figure 2 Abundance of adult saproxylic beetles among decay classes (DC). Black bars represent mean abundance per replicate. Error bars represent +1 SE for nine substrates in each DC. Different small letters indicate significant post hoc results
Objectives
The overall goals of the study were to: 1) compare saproxylic beetle assemblages in white spruce downed CWD across a decomposition gradient ranging from freshly dead to well-decayed; and 2) understand how species assemblages and functional guilds change along this decomposition trajectory.
Early DC
Intermediate DC
Advanced DC
(12%)
(24%)
Materials & Methods
The study was conducted in a 10 ha uncut stand of white spruce (Picea glauca (Moench) Voss) during the summer of 2009 and 2010 at the Ecosystem Management Emulating Natural Disturbance (EMEND) research site in NW Alberta.
Bolts c. 60 cm in length were cut and moved to rearing drums near the research camp. We reared saproxylic beetles and regularly sampled from 54 white spruce logs; these logs represented six decay classes (DC) ranging from freshly dead to well decayed.
Downed Deadwood Classification
Figure 3 Non-metric multidimensional (NMS) scaling ordination of adult saproxylic beetles grouped by decay class (DC). Singletons were excluded, and the data were transformed to log (x + 1) prior to analysis (stress = 16.2 %)
Figure 4 Changes in percentage of feeding guilds on abundance of adult saproxylic beetles among different decay classes (DC).
DC1
DC2
DC3
DC4
DC5
DC6
Diameter (cm)
21.4 ± 4.9
22.3 ± 3.6
20.8 ± 2.8
20.5 ± 3.3
22.4 ± 2.6 -
Bark (%)
100
0 - 70
(mostly < 30)
0 - 20
(mostly < 10)
Bark Tight
tight
tight to loose
loose
no bark or loose
no bark
Wood Texture
hard
relatively soft, variable
mostly soft
soft
Shape
round
round to oval
oval
Branches (%)
> 80
< 50
mostly 0
Needles
present
absent
Ground Contact
cm off
0-120 cm off
slightly off
or sunken
10-50 % sunken
> 50 %
sunken
Plant (%)
5-30
10-60
Moss (%)
0-5
0-70
mostly > 70
mostly 100
Results & Conclusions
Implications for Conservation
Species richness did not change among decay classes (Fig. 1).
The abundance was highest in the earliest decay class, then decreased rapidly (Fig. 2).
NMS reflects that the beetle assemblages change continuously as decay classes increase along the axis 3, and the assemblages in early, intermediate, and advanced decay stages were clearly separated each other, suggesting that each decay stage harbours distinct group of beetles (Fig. 3).
Feeding guild structure changed profoundly as wood decayed. Phloeophagous and predaceous beetles dominated early and advanced decay class, respectively (Fig. 4).
Maintaining a full range of continuously recruiting decay classes is critical to conservation of various species of saproxylic beetles that use white spruce downed deadwood.
Careful logging to retain a considerable fraction of advanced decay stage may have highly important conservation value, because it is likely to require a long time to reconstitute it naturally.
Acknowledgements: Field assistants (Jeremy Katulka, Bill Sperling), Discussion (Charlene Wood), Camp management (Jason Edwards & Charlene Hahn), Identification (Stéphane Bourassa, James Hammond, Jan Klimaszewski, Greg Pohl), Data analysis (Jaime Pinzon), EMEND partnership (CANFOR & DMI), ACA Grants in Biodiversity Feb Designed by Seung-Il Lee