Resource-use efficiencies of three indigenous tree species planted in resource islands created by shrubs: implications for reforestation of subtropical degraded shrublands
Shrub resource islands are characterized by resources accumulated shrubby areas surrounded by relative barren soils. This research aims to determine resource-use efficiency of native trees species planted on shrub resource islands, and to determine how the planted trees may influence the resource islands in degraded shrublands in South China. Shrub (Rhodomyrtus tomentosa) resource islands were left unplanted or were planted with 0.5- year-old indigenous tree species Schima superba, Castanopsis fissa, and Michelia macclurei. The results indicate that, after 2.5 years, the tree seedlings did not modify the physical traits (light, air temperature, and soil water) but tended to increase soil nutrients (soil organic carbon and soil nitrogen) and soil microbial biomass of the resource islands. Relative to S. superba and M. macclurei, C. fissa had greater effects on soil nutrients and microbial biomass but showed lower plant growth, survival, and resource-use efficiencies (for water, light, energy, and nitrogen). These results rejected our initial assumption that shrub resource islands would effectively promote the growth and resource utility of all the indigenous tree species and shorten the reforestation course in subtropical degraded shrubland. C. fissa performed poorly when growing on shrub resource islands, but its role in soil nutrient accumulation might have long-term impacts on the restoration of degraded shrubland. In contrast, S. superba and M. macclurei could make better use of the shrub resource islands therefore accelerating the construction of native plantations.