ABSTRACT To improve the micro climate for Norway spruce (Picea abies (L.) Karst.) regeneration and achieve higher growth, a system of birch shelterwoods with naturally regenerated birch (Betula spp.) creating an overstory sheltering planted spruce is implemented in southern Sweden. Even though the primary objective is to establish a new spruce stand, the economic viability depends on efficient birch overstory harvest with little damage to spruce regeneration. This study aimed to analyze time consumption and net revenues for harvester and forwarder work when removing the birch overstory, and to describe the frequency of logging damage in the residual spruce stand. Time consumption data was collected through time studies of harvesting and forwarding of 10 study plots. Sample plots were inventoried after harvesting and forwarding operations to identify damage on the residual spruce. Average harvester productivity was 2.8 oven dry ton per efficient work hour. The variation in time consumption was up to 94%, explained by a positive correlation with the number of trees harvested per hectare and a negative relationship with removed volume per hectare. Forwarder loading time correlated with forwarded volume along the strip road and the number of birch trees per ha prior to logging. Approximately 7–17% of the residual trees were damaged, and the harvester caused 83% of the damage. Due to high harvesting costs and low revenues, only plots with large removals provided positive net revenues. Birch shelterwoods can therefore not be expected to increase net revenues but are best seen as a regeneration method for addressing stand re-establishment challenges.

中文翻译：

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桦树庇护木移除 - 收割机和货运代理的时间消耗、林下云杉的损坏和净收入

摘要 为了改善挪威云杉 (Picea abies (L.) Karst.) 再生的微气候并实现更高的生长，在瑞典南部实施了一种带有自然再生桦树 (Betula spp.) 的桦树防护林系统，用于创建上层防护种植云杉. 尽管主要目标是建立一个新的云杉林分，但经济可行性取决于有效的桦树上层采伐，对云杉再生的损害很小。本研究旨在分析移除桦树覆盖层时采伐机和货运代理工作的时间消耗和净收入，并描述残留云杉林分中伐木损坏的频率。时间消耗数据是通过对 10 个研究地块的收获和转发的时间研究来收集的。在采伐和运输操作后对样地进行盘点，以确定残留云杉的损坏情况。收割机的平均生产率为每有效工作小时 2.8 烘箱干吨。时间消耗的变化高达 94%，解释为与每公顷采伐的树木数量呈正相关，而与每公顷移除量呈负相关。货运商装载时间与沿条状公路的货运量和伐木前每公顷的桦树数量相关。大约 7-17% 的剩余树木受损，而收割机造成了 83% 的损坏。由于高收割成本和低收入，只有采伐量大的地块才能提供正的净收入。