Low levels of tree retention do not mitigate the effects of clearcutting on ground vegetation dynamics

Several new forestry practices directed at mitigating the influence of clear-cutting on biodiversity and other ecosystem properties have been launched recently. Retention forestry is the most widespread of these practices, but so far most studies have evaluated effects of retention levels that are higher than commonly applied by forestry in many parts of the world. Furthermore possible interaction effects between retaining forest structures and other common forestry practices, such as prescribed burning are still largely unexplored. Here we present results from a ten year stand-level factorial forestry experiment in Eastern Finland (FIRE1) with retention levels full (100%), elevated (50 m3/ha), low (10 m3/ha) and no retention (0%) combined with or without prescribed burning. We show that neither low, nor elevated retention is sufficient to influence the vegetation composition, or dynamic relative to no retention in unburned sites at stand level. However, retention in combination with prescribed burning influenced post-harvest community composition, so that species composition of the elevated retention treatment differed from low- and no retention treatments. When prescribed burning was applied, the functionally important species Vaccinium vitis-idaea had two times higher cover in stands with elevated retention compared to stands with low or no retention. We conclude that at the stand level, low retention levels do not mitigate clear-cut induced disturbance and retention can neither preserve the pre-harvest vegetation nor change the post-harvest vegetational dynamic.