Objective  Coniferous forests (CF) and broadleaved forests (BF) constitute the bulk forests in the northern hemisphere at high latitudes. This paper aims to precisely identify their differences in stand characteristics, distribution and carbon sink functions, favoring forest-type-oriented precise management and diversity conservation.

  Method  In this research, we surveyed 1 275 sample plots (CF, 698; BF, 577) in the Greater and Lesser Khingan Mountains of Northeast (NE) China. We recorded the plant families, genus, species, plant size, density, and geographical location (latitude, longitude, elevation) and calculated the relative abundance of dominant species, aboveground carbon stock, and carbon stability. Comparisons with historical data and neighbor Russia were also performed.

  Result  (1) The plant resources of coniferous forests were 79 families, 228 genera, and 479 species; the broadleaved forest had 81 families, 255 genera, and 546 species. The key species of CF and BF varied significantly with the most remarkable differences in the tree layer. CF had more Larix gmelinii, Pinus koraiensis, and Pinus sylvestris var. mongolica, while BF had more Betula platyphylla, Populus davidiana, and Quercus mongolica. Shrub layers were dominated by Vaccinium vitis-idaea and Spiraea salicifolia in CF, which were 1.6−2.3 times higher than BF; CF had a higher proportion of Carex spp. in herbs. As a whole, > 90% of the indicators of trees differed significantly between the two forests, while 65% of shrubs and only 35% of herbs had significant differences. (2) The CF trees were taller and thicker, i.e., 1.5 m taller and 2.4 cm thicker DBH than the BF, but the density of the CF was 15% lower than the BF. The shrub layer did not differ significantly, and the herb layer showed that the CF plants were shorter in height but densely distributed. (3) CF had 25.54% and 43.24% higher carbon stock density and recalcitrant stability than BFs, respectively, but environment stability was 8% lower (P < 0.05) than BF. On average, the national forest inventory-based method underestimated the biomass carbon density by 35% compared with our detailed survey data. (4) Historical data comparison showed that tree height declined nearly half, tree density increased by 700−1 000 tree/ha, forest plant resources declined evidently in the past 50-years; total forest layer depth declined at a rate over 10 cm/year, cautioning the losses of forest ecological services. (5) Compared with neighbor Russia data, our forests had fewer evergreen pine, spruce, and abies, but a higher percentage of larch and birch, and carbon storage density of both CF and BF were at the lowest regime of the Russian forests.

  Conclusion  Based on over a thousand sample plots and reference data, this paper gives detailed statistics of forest resources in NE China, with special emphasizing coniferous and broadleaved forest types and comparing historical data. Our finding provides an essential data update for forest management in NE China, highlighting the importance of in-depth studies on the significance and risk control of long-term plant species alternations. In the future forest conservation process, precise management based on forest-type differences should be advocated. Much longer strict conservation policy is needed for the co-enhancement of different ecological functions of forests to fulfill the carbon neutrality strategy of China.