COS 139-2 - Restoration treatments enhance conifer seedling and sapling growth on seismic lines in boreal fens

Background/Question/Methods

Seismic lines in the western boreal region of Canada create long-lasting narrow linear disturbances in peatlands that affect carbon dynamics and the habitat of threatened woodland caribou (Rangifer tarandus caribou). The effectiveness of active restoration treatments on seismic lines in these ecosystems, like mounding and planting, have not yet been systematically assessed. We sampled conifer seedlings growing on 37 decommissioned seismic-line sites in treed fens within three restoration blocks. The sites included both lines with active restoration treatments and lines that had been left to naturally regenerate. Seedling-level factors, such as increment growth, understory competition, microsite position, and the presence of woody material, were measured using non-destructive sampling. We used generalized linear mixed models (GLMMs) to assess the effects of treatments and seedling-level factors on survival and growth of planted and naturally occurring black spruce (Picea mariana) and tamarack (Larix lariciana).

Results/Conclusions

We found no significant difference between seedling and sapling survival rates on treated and untreated seismic lines. However, seedlings and saplings on treated lines had significantly higher annual growth rates. On average, planted black spruce had 67% higher growth (2.2 ± 0.7 cm), and planted tamarack had 72% higher growth (4.1 ± 1.4 cm) relative to natural seedlings on untreated lines. Competition from understory vegetation decreased growth rates, while the presence of woody material had a positive effect. Favourable microsites (nearby coarse woody material and understory vegetation that does not overtop the seedling) promoted seedling growth and were influential in the successful establishment of planted seedlings. This study shows that silvicultural practices can effectively promote initial tree establishment in disturbed fens. In addition to mounding and planting, land managers should also consider the application of coarse woody material so that seedlings can be planted nearby to enhance the effects of other silviculture treatments.