How should fast-growing broadleaf trees, such as planted birch, be regenerated and managed in future production forests? This was discussed by researchers, forest owners, and forestry sector officials during the final excursion for Phase I of Trees For Me, at Asa Experimental Forest.
The first five-year period of Trees For Me was concluded in beautiful Småland autumn weather for around a hundred committed participants, serving as a springboard for the continued research and activities of the coming five years.
“We wouldn’t have planted as much birch as we have without the research efforts of Trees For Me,” summarized Gisela Björse, director of silviculture at Sveaskog, one of the centre’s around 50 partner organisations.
Challenges and solutions
A major challenge for the successful establishment of fast-growing broadleaf trees, such as planted silver birch, is browsing, particularly during early and late summer. To improve the chances of successful establishment, effective protection methods are needed that are practical in the daily forestry operations and do not require costly fencing.
“The issue of browsing must be resolved in the forest if we are to succeed in achieving greater diversification in forestry,” emphasized Urban Nilsson, director of Trees For Me and professor of silviculture at SLU, during the field trip.
Andis Zvirgzdins, researcher at Skogforsk, presented results showing that planted silver birch tolerates low to moderate browsing, particularly on more productive sites.
"The birch’s lateral shoots develop and replace the browsed leading shoots, which may be one reason why browsing does not affect the trees as much as expected," said Andis Zvirgzdins.
Mixed forest with mixed results
During the field trip, results from trials involving mixed stands of spruce and birch in southern and central Sweden were also presented. The trials test mixtures arranged by individual stems as well as group mixtures.
“Group-based mixtures may be easier to manage, but single-tree mixtures might offer other benefits, such as increased variation and the ability to control the tree species composition over time”, said Nils Fahlvik, researcher at Skogforsk.
In another trial, a stem-wise mixture of Scots pine, Norway spruce, birch, and larch, among others, is being tested. This mixture poses a major challenge for future management, as the trees have very different growth rhythms.
Birch seedlings for the future
Research also highlights the importance of matching the right seedling to the right site. Trials within Trees For Me indicate significant differences in both growth and survival of birch seedlings between site-prepared and non-site-prepared areas, favoring site preparation. The size and characteristics of the seedlings also play a role in their vitality and resilience.
“Current systems for seedling production are adapted for spruce and pine, not birch,” noted Gudmund Vollbrecht, coordinator of Trees For Me and associate professor of forest management.
Developing more cost-effective seedling production, producing vital seedlings that are easier to handle, and identifying suitable planting sites for birch seedlings will therefore be key issues for research, nurseries, and the forestry sector moving forward.
“When the next phase of Trees For Me concludes in 2031, the goal is for Sweden to produce and plant 40 million birch seedlings annually. It takes time to introduce a new tree species like improved birch, but we are well on our way,” Urban Nilsson emphasized.