Water use characteristics of the artificial forests black locust (Robinia pseudoacacia) and Chinese pine (Pinus tabulaeformis) on the Loess Plateau of China

The broad leaf, deciduous black locust (Robinia pseudoacacia) and needle leaf, evergreen Chinese pine (Pinus tabulaeformis) are the major afforestation species on the Loess Plateau of China, accounting for 29.5% and 15.9% of the afforestation area, respectively. The decay of black locust and drying of the forest land soil in this region have caused serious concerns among scientific community and local management authorities. Understanding the hydrological characteristics of the afforestation plantation may provide clues for choosing proper species. However, previous studies demonstrated diverse or even contradictory understandings due to incomplete observations of the water balance. We used a model to reconstruct the water balance based on 5 years (2015-2019) of incomplete soil water and transpiration observations at the field for these two species. The R-squares of linear regression analysis of simulated and observed soil water in black locust and Chinese pine plantations were 0.69 and 0.90, respectively; and transpiration was 0.62 and 0.69, respectively. Based on the reconstructed water balance components, we found that (1) black locust and Chinese pine had similar annual evapotranspiration in quantity. However, the Chinese pine transpired less and evaporated more water from the canopy than the black locust, with their ratios to the annual precipitation 50.7% and 69.7%, 26.3% and 17.2%, respectively; (2) the Chinese pine has higher evapotranspiration than the black locust in the non-growing season, accounting for 19.5% and 9.2% of the annual evapotranspiration, respectively; and (3) the Chinese pine is more tolerable to soil water drought than black locust. The findings may suggest that the Chinese pine is a more favourable species for afforestation than the black locust from the point view of drought resistance in this region.

Automated summary

The broad leaf, deciduous black locust and needle leaf, evergreen Chinese pine are the major afforestation species on the Loess Plateau of China. However, concerns have been raised about the decay of black locust and drying of the forest land soil in this region. A study using a model and incomplete observations found that Chinese pine is more tolerant to soil water drought than black locust.