Forest restoration for biodiversity conservation: some case studies from Sweden
Because of worldwide forest degradation, eroding biodiversity and ecosystem services, ecological restoration has become a global priority. In many boreal forest areas, intensive management for timber production has caused declines in biodiversity and decrease in habitat quality for a large number of specialized species. As very little undisturbed forest habitats remain in many regions of the world, we have reached a situation where we no longer can rely on passive conservation measures, i.e. setting aside conservation areas under a free development philosophy. Instead, to achieve conservation goals, we need methods for restoration of hitherto managed forest, as well as for active management of forest reserves.
In two separate field experiments we evaluated the effect of three different restorations methods: 1) restoration burning, 2) gap cutting and 3) selective harvest to remove Norway spruce to benefit deciduous trees (originally intended to benefit white-backed woodpeckers) on saproxylic beetles, a group of insects severely threatened by modern forestry. Beetles were collected with 3-5 window traps per stand.
As predicted, saproxylic species known to be ﬁre favoured increased dramatically after burning. The immediate response shows that, initially, ﬁre favoured species are attracted from the surrounding landscape and not produced on site. Gap cutting increased the abundance of cambium consumers but had no signiﬁcant immediate effect on total species richness or assemblage composition of saproxylic beetles. The stronger effect of burning compared to gap cutting on saproxylic assemblages is probably due to the very speciﬁc conditions created by ﬁres that attracts many disturbance-dependent species, but that at the same time disfavour some disturbance-sensitive species.
Selectively harvest to remove Norway spruce benefitted many species and the effects on species associated with sun exposure were particularly important, but many beneficiary species were also linked to dead wood from broadleaved trees. Red-listed saproxylic beetles showed a similar pattern with more species and individuals in restored sites. All three restoration methods clearly benefitted certain groups of saproxylic beetles, but to some degree different species. The implication of this is that several different restoration methods must be used to recreate/mimic natural disturbance regimes and the natural variation in boreal forest and thus benefit saproxylic species disfavoured by current even-aged silviculture.