Low levels of tree retention do not mitigate the effects of clearcutting on ground vegetation dynamics Samuel Johnson a,⇑ , Joachim Strengbom a , Jari Kouki b a Department of Ecology, Swedish University of Agricultural Sciences, Box 7044, SE-750 07 Uppsala, Sweden b School of Forest Sciences, University of Eastern Finland, PO Box 111, FI-80101 Joensuu, Finland article info Article history: Received 27 March 2014 Received in revised form 24 June 2014 Accepted 26 June 2014 Keywords: Boreal forest Bryophytes Forest fire Lichens Prescribed burning Vascular plants abstract 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 exper- iment in Eastern Finland (FIRE 1 ) with retention levels full (100%), elevated (50 m 3 /ha), low (10 m 3 /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 dif- fered from low- and no retention treatments. When prescribed burning was applied, the functionally impor- tant 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. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Intensified forestry is known to have adverse effects on biodi- versity and ecosystem functions (Butchart et al., 2010; Bengtsson et al., 2000; Puettmann et al., 2009). Consequently, initiatives from the forest industry to also embrace non-economic goals, such as preservation of ecological values, are becoming increasingly com- mon. To be able to reach such goals, several new forestry models and practices have been proposed, including increased use of selec- tive logging, prolonged rotation periods, retention of trees during clear-cutting and the use of prescribed burning (Kohm and Franklin, 1997; Larsson and Danell, 2001). An aspect that have been stressed as important when designing new forestry systems which take biodiversity conservation into account is the role of natural disturbance regimes (Lindenmayer and Franklin, 2002; Bengtsson et al., 2000). Retention forestry (sometimes referred to as ‘‘tree retention’’ or ‘‘variable retention’’), i.e. the practice of retaining trees during clear-cut harvest, is argu- ably the conservation practice within forestry that has grown most rapidly in the last decades (Gustafsson et al., 2012). A key founda- tion of retention forestry is the idea that the retention of structures can mimic the effects of natural disturbances which are rarely as uniform as the effects of clear-cutting (Franklin et al., 1997). Ideally the model of retention is therefore tailored to follow habitat requirements of the local biota and the disturbance to which it is supposed to mimic (Bergeron et al., 2002; Gustafsson et al., 2012). In many regions of the Boreal forest biome, the predominant dis- turbance has been fire (Esseen et al., 1997; Zackrisson, 1977). Now- adays however, effective fire control suppresses fires in managed forests, a phenomenon especially evident in Fennoscandia (Östlund et al., 1997). Before the introduction of intensive forest management, the role of fire in this region was probably comparable to that of other parts of the boreal biome. However, unlike continen- tal regions, i.e. central Canada, the fires were not necessarily stand replacing, but also of lower intensity (Kuuluvainen, 2009). It is thus likely that the importance of fire has varied in both space and time and the most important influence on the landscape was the creation of heterogeneity on multiple scales (Kuuluvainen, 2002). This heterogeneity, caused in part by the variation in fire intensity, was likely of great importance for the vegetational dynamics. Under http://dx.doi.org/10.1016/j.foreco.2014.06.031 0378-1127/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +46 18672718. E-mail address: Samuel.Johnson@slu.se (S. Johnson). 1 http://wanda.uef.fi/jarikouki/project_fire.htm. Forest Ecology and Management 330 (2014) 67–74 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco