Impact of leaf removal on initial survival and growth of container-grown and bare-root seedlings of Hinoki cypress (Chamaecyparis obtusa)

Abstract

As a part of improving forest management practices, we tested the idea that partial defoliation of container-grown and bare-root Hinoki cypress (Chamaecyparis obtusa) seedlings prior to outplanting can reduce transplant shock and enhance seedling survival during their first growing season after transplanting. For container-grown seedlings, the remaining leaves of defoliated seedlings showed photosynthetic capacity (Amax) about 1.5 times higher than the non-defoliated control in the first 3weeks. For defoliated bare-root seedlings, Amax ranged 3.3–4.8 times higher than non-defoliated control in the first 4weeks after transplanting. Thereafter, Amax of defoliated seedlings of both types began to decrease slowly. Amax of newly emerged leaves after transplanting was significantly higher than that of existing leaves for container-grown seedlings but not bare-root seedlings. For container-grown seedlings, both defoliated and non-defoliated plants showed high survival rate (>90%) and there were no significant differences among levels of defoliation. For bare-root seedlings, non-defoliated control showed highest mortality (30%) by the end of the growing season but seedlings that were 25%, 50%, 75% defoliated all suffered little mortality. In terms of initial growth, there was no significant difference between defoliated and non-defoliated control in container seedlings suggesting that defoliation treatment had no effect on reducing their growth. In comparison, bare-root seedlings showed marginally but significantly greater height growth in defoliated plants, suggesting that non-defoliated seedlings suffered greater transplant shock and reducing the amount of leaves may contribute to minimize water stress and mortality. Therefore, we found that for bare-root seedlings, partial defoliation can effectively reduce transplant shock resulting in high survivorship and growth performance; the lack of defoliation response in container-grown seedlings would suggest that defoliation is unnecessary for improving their transplant success.