Influence of slope on root system anchorage of Pinus yunnanensis

In southwestern China, Yunnan pines (Pinus yunnanensis) have been extensively cultivated on barren hills for reforestation and ecological engineering. The objective of this work is to study the influences of slope gradient on anchorage of root systems of P. yunnanensis. Pulling experiments were carried out at low (5–6°), moderate (25–26°) and high gradient (42–43°) by using selected 15-year-old P. yunnanensis. The results showed that the anchorage resistances induced by the slope gradient were significantly (P < 0.01) different from each other and followed in the order of high slope > moderate slope > low slope. Anchorage strength of upslope-grown roots increased with size and length of first-order lateral roots as well as the number of second-order lateral roots. Contributions of upslope-grown roots for preventing plants from overturning varied considerably between those from different slopes. The contribution of roots growing on upslope side on high slope to the anchorage of root system reached 50%, whereas those on moderate and low slopes were about 44% and 37%, respectively. It was concluded that the anchorage resistance was closely related to slope gradient and root distribution, while upslope-grown roots were positively related to anchorage resistance.