Osmo Heikkala

Effects of green tree retention and prescribed burning on the crown damage caused by the pine shoot beetles (Tomicus spp.) in pine-dominated timber harvest areas

Abstract:  We explored how two recently introduced methods to promote biodiversity during the timber harvest in boreal forests – green tree retention and use of fire – may affect damages caused by pine shoot beetles (Tomicus piniperda and Tomicus minor; Col., Scolytinae) in the surrounding pine forests. The experimental design included 24 separate study sites, 3–5 ha each, which were assigned to different treatments according to factorial design. Retention levels included 0, 10, 50 m3/ha and uncut controls. Twelve of the sites were burned and thus there were three replicates of each treatment combination. Old and new fallen pine shoots were counted from transects in adjacent pine‐dominated forests 2 and 3 years after the treatments. Populations of Tomicus spp. in the sites were monitored using window traps before and after the treatments, and by examining felled sample trees. Numbers of fallen shoots returned to background levels around unburned and burned clearcuts with no retention trees in 3 years after the treatments, but remained still at increased level in burned harvested sites with 10 and 50 m3 of retained trees per hectare. Numbers of fallen shoots in burned uncut forests increased in one site only, where the fire was intense enough to kill large pine trees, but the damage did not extend outside the burned area. Shoot numbers remained at such low levels (<18 000 shoots/ha) in all treatment combinations that growth losses were not likely. Numbers of egg galleries of Tomicus spp. in trees killed by fire were low, indicating that burnings that take place after the swarming of Tomicus beetles create dead wood that is not optimal for the breeding of these pests. We conclude that green tree retention and prescribed use of fire do not automatically affect populations of Tomicus spp. more than traditional forestry operations (thinnings and clearcuttings) do.

Prescribed burning is an effective and quick method to conserve rare pyrophilous forest‐dwelling flat bugs

Fire suppression and reduced volumes of dead wood have led to a major decline in pyrophilous and saproxylic insects in Fennoscandian boreal forests. As a consequence, several species are currently seriously threatened. Flat bugs (Heteroptera, Aradidae) is an important invertebrate group that includes several pyrophilous species, including many threatened ones. We explored whether specific conservation measures – prescribed burning and retention forestry – can facilitate the survival of flat bugs in managed forests. The large‐scale field experiment consisted of a burning treatment (yes/no) and four levels of logging intensity (clear‐cut, retention levels of 10 and 50 m3 ha−1, and unharvested controls). The data included 1224 individuals of 12 species, sampled over a 4‐year period. Burning increased the species richness and abundance of the pyrophilous species. Two Red‐Listed and very rare pyrophilous species, Aradus angularis J. Sahlberg (Vulnerable) and A. laeviusculus Reuter (Near Threatened), were abundant after burning. The number of non‐pyrophilous flat bugs collapsed after burning but they re‐colonised the stands quickly, becoming as abundant as at the unburned stands. Logging increased the abundance of flat bugs only when retention forestry was applied. This study shows that pyrophilous flat bugs are quickly able to locate recently burned forests and that these forests are important for their survival. The effect of fire is, however, transient at the stand level and pyrophilous species disappear almost completely quickly after fire. To maintain these species, recently burned forests with a sufficient volume of retention trees should be available continuously at the landscape level.

Trade‐offs in berry production and biodiversity under prescribed burning and retention regimes in boreal forests

Green tree retention and prescribed burning are the practices used to mitigate negative effects of boreal forestry. Beside their effects on biodiversity, these practices should also promote non-tim ...