Shrub influences on seedling performance when restoring the slow-growing conifer Pilgerodendron uviferum in southern bog forests

Abstract

Forest restoration is most efficient if it can take advantage of facilitative interactions between established vegetation and planted trees. However, positive and negative interactions have been identified in a number of plant communities. After centuries of anthropogenic fires, forest recovery has been extremely slow in southern bog forests previously dominated by the slow-growing and vulnerable conifer Pilgerodendron uviferum on Chiloe Island, Chile. Today, the landscape is dominated by secondary shrublands with scattered patches of Sphagnum moss and limited natural tree regeneration. We hypothesized that the retention of secondary shrubs facilitates the early performance of P. uviferum restoration plantings by providing better microsite conditions. To test this hypothesis, we compared the response of seedlings planted on sites prepared at two levels of intervention: after shrubs had been removed or where shrubs were retained. Shrub retention showed a nurse-plant effect on P. uviferum seedlings 4 years after planting, which resulted in reduced physiological stress (measured as Fv/Fm) for seedlings, as well as reduced browsing. Consequently, the seedlings growing in areas with shrub retention had larger height increment and higher vitality than those in areas where shrubs had been removed. Thus, the more open micro-site conditions created by shrub removal resulted in generally poorer seedling performance, although seedling mortality-which was low overall (approximately 2-4%)-showed no significant difference between the two levels of intervention. These findings have direct implications for the restoration of slow-growing conifers that can tolerate extreme wet conditions in highly degraded forests.

Forest restoration is most efficient if it can take advantage of facilitative interactions between established vegetation and planted trees. However, positive and negative interactions have been identified in a number of plant communities. After centuries of anthropogenic fires, forest recovery has been extremely slow in southern bog forests previously dominated by the slow-growing and vulnerable conifer Pilgerodendron uviferum on Chiloe Island, Chile. Today, the landscape is dominated by secondary shrublands with scattered patches of Sphagnum moss and limited natural tree regeneration. We hypothesized that the retention of secondary shrubs facilitates the early performance of P. uviferum restoration plantings by providing better microsite conditions. To test this hypothesis, we compared the response of seedlings planted on sites prepared at two levels of intervention: after shrubs had been removed or where shrubs were retained. Shrub retention showed a nurse-plant effect on P. uviferum seedlings 4 years after planting, which resulted in reduced physiological stress (measured as Fv/Fm) for seedlings, as well as reduced browsing. Consequently, the seedlings growing in areas with shrub retention had larger height increment and higher vitality than those in areas where shrubs had been removed. Thus, the more open micro-site conditions created by shrub removal resulted in generally poorer seedling performance, although seedling mortality-which was low overall (approximately 2-4%)-showed no significant difference between the two levels of intervention. These findings have direct implications for the restoration of slow-growing conifers that can tolerate extreme wet conditions in highly degraded forests.