A comprehensive observing system was established at the Da Xing'anling (Hinggan) Mountains Station (Gen'he) of China Forest Ecological Research Network (CFERN) in Northeast China in 2009 and gradually improved since in order to evaluate the influences of boreal forest vegetation with complex structures and various components on the thermal regimes of active layer and shallow permafrost soils. At three selected typical forest sites with similar micro-reliefs, soils, and drainage conditions, the soil temperatures on the ground surface and at various depths ranging from 0.05 to 5.0 m were measured with thermistor cables permanently installed in boreholes. The temperature data were compared and contrasted for various vegetative features. In a control experiment, trees and shrubs were removed to better understand the hydrothermal effects of vegetation removal. Results show that: (1) The vegetative layer provides an evident effect of thermal insulation on the ground. The ground temperature at the same depth was lower at a stand with denser vegetation when other conditions are held the same. (2) The ground warms up when the vegetation degrades, and the ground temperature rises from the vegetation degradation could reach much deeper in winter than in summer. (3) In cases of extensive vegetation degradation, the resultant ground warming persists for a long time, resulting in a deepening active layer.