Tree retention practices in boreal forests: what kind of future landscapes are we creating?

Tree retention practices promoting biodiversity may reshape future boreal forest production landscapes. Using the Heureka system, scenarios of 0%, 5%, and 20% retained patches at the stand level were projected over 200 years in a 533 ha boreal landscape. Visualizations of future forest states at a landscape scale and a more detailed scale were made based on the projections. The no retention results in no forest >120 years old, and no large trees (diameter at breast height >40 cm for conifers and >35 cm for broadleaved trees) 100 years from now. With retention levels of 5% and 20%, the area of old forest will comprise 7% and 19% of the total area, respectively. The average number of large trees per ha will be 4 and 13, respectively. Deadwood volumes will be 2.5 times higher at 5% retention and 4 times higher at 20% retention compared to no retention. Landscape visualizations indicate that retention patches covering 5% will marginally modify the visual impression, compared to clear-cuts, while 20% cover will create a much more varied landscape. We conclude that the retention approach is essential for restoring natural conditions. Landscape transformation will be slow and depend on starting conditions and retention levels.

林木保留措施可促进生物多样性，或重塑未来寒温带森林（boreal forest）的生产景观格局。本研究采用Heureka系统（Heureka system），在533公顷的寒温带森林景观中，针对林分尺度（stand level）下0%、5%、20%保留斑块的情景开展了200年的模拟预测。基于上述预测结果，分别生成了景观尺度与更精细尺度下的未来森林状态可视化成果。无保留情景下，100年后将不存在林龄超过120年的森林，也无胸径（diameter at breast height）大于40厘米的针叶树与大于35厘米的阔叶树等大径级立木（large trees）。当保留比例为5%与20%时，老龄林（old forest）面积占比将分别达到总景观面积的7%与19%，每公顷大径级立木的平均数量则分别为4株与13株。枯倒木蓄积量（deadwood volumes）方面，5%保留比例情景下较无保留情景提升2.5倍，20%保留比例情景下则提升4倍。景观可视化结果显示，相较于皆伐（clear-cuts）场景，覆盖5%的保留斑块仅会对视觉观感产生小幅影响，而20%覆盖比例的保留斑块则可显著提升景观异质性。本研究表明，林木保留措施对于恢复自然生态条件至关重要。景观格局的改造进程将相对缓慢，且取决于初始状态与林木保留比例。