The Effects of Biochar Application and Soil Transfer on Survival and Growth of Tree Seedlings in Restoration

Abstract

Harsh conditions hinder the growth and survival of woody plants in restoration of forests and degraded landscapes. Transplanted tree seedlings often desiccate within the first few weeks. Management options to increase survival such as watering or shading may be costly or infeasible. However, low-cost techniques may improve seedling survival by increasing water availability to plants or ameliorating soil conditions. One such restoration technique gaining attention in recent decades is the amendment of soil with biochar. Biochar may increase the moisture retention of the soil, mitigate the effects of soil contaminants, alter soil physicochemical properties, and may even enhance mycorrhizal fungi colonization of the roots. However, negative effects of biochar have been reported in some agronomic settings. Thus, research is needed before its use in forest restoration can be recommended. Another low cost technique that improves transplant success is soil transfer, intended to inoculate transplanted seedlings with beneficial microbiota and accelerate the establishment mycorrhizal relationships. To test the potential effects of biochar and forest soil inoculation on tree seedling establishment in a restoration setting, we conducted a systematic review and meta-analysis of the literature in the topic and carried out a field experiment. Results from the meta-analysis of the use of biochar on woody plants in various restoration contexts suggest positive effects of biochar on woody plant growth and survival, with an effect size (ES±SD) of 0.95±0.05 overall, 1.02±0.01 on biomass, and 1.04±0.01 on survival. However, the heterogeneity of biochar production and application—and of restoration context and focal species—prevents broad generalization and indicates the need for additional field studies assessing the effects of biochar on woody plants. For our field experiments, we transplanted seedlings of northern red oak (Quercus rubra) into three disturbed forest areas: a pine plantation ten years post-thinning, a post-plantation recent clear-cut, and an urban forest preserve with an understory cleared of invasive species. Seedlings were planted under four treatments: soil inoculation and biochar (SB), only biochar (BC), only soil inoculation (SI), and control (C). We then monitored seedlings growth and survival. Mortality was high in all treatments and across sites. Our findings suggest that treatments of biochar and soil transfer had no significant influence on Q. rubra growth and survival in the first year. In both years, however, the highest positive impact on survival resulted from the SI (- 2.09±0.31) and BC (-2.28±0.29) treatments, with the most negative in C (-3.13±0.43). The effect of treatment on average biomass was highest in C (0.43±0.25) and SI± and lowest in BC (- 0.10±0.20). Overall, this work contributes to the body of knowledge on the use of biochar and soil transfer in restoration experiments. Use of either or both soil amendment techniques may not be necessary in all systems and should be tailored to the suit the focal species and ecosystem.