Eight-year survival and growth of Sakhalin fir (Abies sachalinensis) seedlings with one weeding operation: Impact of mechanical site preparation, vegetation release, summer planting, stock type, and forwarder trail

Abstract

Abstract In Hokkaido, northern Japan, bareroot Sakhalin fir seedlings are conventionally planted in short periods during spring and fall following strip site preparation that alternates managed and unmanaged strips to reduce labor requirements. Postplanting, seven years of weeding are imperative owing to the relentless encroachment of evergreen dwarf bamboo from unmanaged strips. Given diminishing forest labor availability, this protocol poses increasing challenges. We hypothesized that comprehensive mechanical site preparation (MSP) to eradicate dwarf bamboo across the entire site could reduce weeding frequency by delaying the regeneration of competing vegetation. Furthermore, using container seedlings could extend the planting season to summer. Over an eight-year period, we examined the survival and growth of summer-planted bareroot and container seedlings in a fully MSP-treated site, with a single weeding operation conducted in the fifth year. Whole-site MSP induced a shift from dwarf bamboo to deciduous woody and herbaceous species, fostering consistently high Sakhalin fir seedling survival and growth rates despite the lone weeding operation. Container seedlings exhibited superior establishment after summer planting and maintained higher survival rates over eight years relative to bareroot seedlings. Planting in the forwarder trail detrimentally impacted overall seedling growth and survival. These findings advocate for container seedling summer planting alongside comprehensive MSP as an effective Sakhalin fir reforestation technique, mitigating weeding frequency and broadening the planting timeframe.