Temporal shifts in the importance of environmental factors and management interventions among species in the early stages of forest restoration

Abstract

Both abiotic conditions and management influence the success of forest restoration. Despite growing interest and practical effort in restoring degraded forest landscapes, understanding of how disparate factors, such as terrain, soil conditions, climate and silvicultural treatments, directly or collectively control species performance and shape community recovery remains limited. In this study, we assessed how topography and management intervention affect seedling survival and growth in the early stages of restoration. To do so, we established seven experimental plots, each measuring 20 m × 20 m (400 m²) subdivided into 48 subplots, in coarse, anthropogenic grassland on a mid-elevation mountain slope in Hong Kong, and planted a total of 3975 native tree seedlings belonging to 12 tree species within them. To characterise topography, we modelled the elevation, slope, convexity and aspect of each subplot. Two types of tree guard (enclosed blue plastic sleeve and open yellow mesh), two types of fertiliser (organic and inorganic) and cardboard weeding mats were used to assess the impact of management interventions on the establishment of the seedlings. Survivorship, height and basal diameter were measured at 1, 2 and 4 years after planting. We used generalised linear models to examine the effect of these factors and their interactions on seedling survival, and we applied linear models and hierarchical partitioning to explore their relative importance in determining the relative growth rate (RGR) of each species. The most parsimonious models were selected using the Akaike Information Criterion. Survivorship was 98.1%, 95.2% and 86.4% across all plots in the first, second and fourth year, respectively. On average, topographic and management variables explained 1.48–3.34% of total variation in RGR, respectively, for all species. The models revealed that type of tree guard, aspect and elevation were the most important factors explaining RGR and survival. Results of hierarchical partitioning by species and growth period showed that the key determinants of performance vary by species and shift over the course of early seedling establishment, emphasising the importance of both spatial and temporal scales in the restoration of degraded tropical forests. Our findings support the use of enclosed tree guards and fertiliser to improve survivorship and growth across a range of broadleaved Asiatic species. All potential limiting factors pertaining to both site factors and management, as well as their interactions, should be considered in restoration planning to maximise restoration success.

Keywords

Tree planting / Relative growth rate / Survivorship / Native species / South China

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