Prioritizing the retention of border zones in production forests: The projected benefits for Swedish broadleaf habitats

Swedish forestry is characterized by relatively intensive silvicultural practices primarily focused on the rotational even-aged management of Norway spruce and Scots pine. The diversification of these management practices, via the increased use of mixed forests and broadleaves, is a recommended means of promoting biodiversity conservation and reducing climate change-related risks. One complementary and underexplored pathway to diversifying production forest landscapes is to increase the ecological quality of retention patches at final felling. Recent studies indicate that border zones towards water, arable land and other land uses have a higher share of broadleaves and, together with other functions, should be prioritized for retention. This study investigates the benefits of prioritizing the retention of these ecological transition zones at final felling in a typical southern Swedish region, focusing on the amount of broadleaves retained. With input from a key regional actor in nature conservation (the County Administrative Board), two different retention scenarios were simulated: Retention patches representative of average stand conditions (AveCOND) and border zones (BORDER). The forest data, sourced from remote sensing, indicated that border zones towards open land and water had a higher volume share of broadleaves than the average found on productive forestland (> 1 m3/ha/year) in the study region. Simulating the development of the landscape over a 100-year period and prioritizing the retention of border zones increased the share of broadleaves over time. Since only a limited share of the total forest area is subject to retention, 8% in our study, the advantage of BORDER over AveCOND is not dramatic; BORDER yields 50 m3 broadleaves per ha compared to 47 m3 for AveCOND after 50 years and 47 compared to 43 after 100 years. In the study, retention patches and border zones were left with no management. Active management to promote broadleaf trees using targeted thinning regimes could add to the ecosystem's provision of border zones relative to no management. The economic outcome suggests that allocating retention to border zones could be advantageous compared with allocation to the harvesting site. However, this result hinges very much on what, in reality, is attained in the BORDER case. Another aspect refers to the unevenly distributed border zones among forest properties. Thus, retaining all border zones would require some landscape approach. We discuss various barriers and opportunities to implementing this retention strategy, for which our findings suggest multiple conservation benefits exist.