Search

To assess the variations of soil quality among land use types and with altitude in the rocky mountain area of northern Hebei Province is critical for preventing further human-induced degradation of land and vegetation, and for formulating a strategic plan on vegetation restoration after the Beijing Winter Olympics. Taking Betula platyphylla natural forest, Larix gmelinii plantation, natural grassland and abandoned cropland as research objects, 13 soil physicochemical indices ( e.g ., soil bulk density, porosity and soil nutrient content) were measured to compare soil quality among land use types. The results showed that soil quality presented the trend as B. platyphylla natural forest > natural grassland > L. gmelinii plantation > abandoned cropland. B. platyphylla natural forest had the best soil quality due to high total nitrogen (3.24 ±1.42 g·kg -1 ) and phosphorus (0.59±0.10 g·kg -1 ) contents, suggesting that long-term soil nutrient accumulation played an important role in preventing soil degradation. Soil quality in natural grassland was lower than that in B. platyphylla natural forest, due to topographic factors and coarse soil fraction. Soil physical properties in L. gmelinii plantation had been substantially improved after 40 years restoration, as indicated by significant reductions in soil gravel fraction, while soil nutrient contents changed little. The low soil quality in abandoned cropland was attributable to low vegetation coverage and intense human activities in the low-altitude area. Driven by soil total nitrogen, soil quality under the four land use types increased with altitude, and peaked at about 1700 m. We suggested that enclosure and ecological restoration measures should be strengthened in ecologically-fragile, low-altitude areas, taking sustainable development into consideration for high-density stands and promoting plantations to adapt to environmental change.

Forest spatial structure (FSS) directly reflects resource competition and growth space distribution among different trees. The characteristics of FSS play an important role in mastering the growth status of ecological forest, formulating stand structure regulation measures, and improving forest quality and ecological services. In this study, seven plain ecological plantations including Pinus tabuliformis , Fraxinus chinensis , Salix matsudana , Populus tomentosa , Sophora japonica , Robinia pseudoacacia , and Salix babylonica in Tongzhou District, Beijing were selected as the research objects. The spatial structure characteristics of plain ecological plantations were evaluated by aggregation degree, angle index, neighborhood comparison, open degree, canopy index, competition index, edge benefit, and spatial structure comprehensive index. The horizontal distribution pattern of stand was well, with the aggregation degree of 0.32-1.41, the angle index of 0.4, and the neighborhood comparison mainly around 0.5. The vertical distribution pattern of stand was not well and needed to be improved, with the open degree of 0.19-0.52, most canopy indexes of about 0.7. The competition index presented a high competitive status with the all values of >50. Except the comprehensive evaluation index of R. pseudoacacia plantation presented in grade Ⅲ, the other six kinds of plain ecological plantations fell to grade Ⅱ, with low stand openness and low vitality. The comprehensive evaluation indices of FSS followed the order of R. pseudoacacia > S. babylonica > P. tabuliformis > S. matsudana > F. chinensis > S. japonica > P. tomentosa .

The plant species diversity of stands converted from croplands as affected by revegetation approaches and terrains was studied using the transect line plot sampling. The goal of the study was to provide reference for evaluation reforestation effects and forest management in the Loess region of western Shanxi Province. The results showed that revegetation approach had a great influence on plant species diversity in stands. The number of species in the natural restoration forest (NF) was 1.6 times of that of Robinia pseudoacacia plantation (RP), the Shannon index of NF was higher, and the Pielou index of NF was lower. Slope position had significant effect on the species diversity, and the three species diversity indices were all in order of bottom of loess gully > middle slope of loess gully > slope of loess hill > top of loess hill. The species diversity indices on the shady slope were higher than those on the sunny slope, while the difference was not significant. Integrated effects of terrain and revegetation approach had significant influences on species diversity. The species diversity was highest at the bottom of shady slope of NF, and the species evenness was highest at the bottom of shady slope of RP. For improving the species diversity, the afforestation design in the Loess area must consider terrain position and the natural forest recovery process following the principle of 'selecting suitable tree species for the right site'.

Based on the Forest Ecosystem Services Assessment Standards (LY/T 1721－2008) issued by the State Forestry Administration, this paper evaluated four key functions of forest ecosystems, i.e., water conservation, soil conservation, carbon fixation and oxygen release, and nutrient accumulation. Focusing on the project area of Majiang County in Guizhou Province, this study provided some quantitative evidence that the implementation of the small hydropower substituting fuel project had positive effects on the values and material quantities of ecosystem service functions. The results showed that the small hydropower substituting fuel project had a significant effect on the increase of forest ecosystem services. Water conservation quantity of Pinus massoniana and Cupressus funebris plantations inside project area was 20662.04 m 3 ·hm -2 ·a -1 , 20.5% higher than outside project area, with soil conservation quantity of 119.1 t·hm -2 ·a -1 , 29.7% higher than outside project area, carbon fixation and oxygen release of 220.49 t·hm -2 ·a -1 , 40.2% higher than outside project area, and forest tree nutrition accumulation of 3.49 t·hm -2 ·a -1 , 48.5% higher than outside project area. Small hydropower substituting fuel project for increasing the quota of forest ecosystem service function value was in the order of carbon fixation and oxygen release function (71400 yuan·hm -2 ·a -1 ) > water conservation function (60100 yuan·hm -2 ·a -1 ) > tree nutrition accumulation function (13800 yuan·hm -2 ·a -1 ) > soil conservation function (8100 yuan·hm -2 ·a -1 ). Small hydropower substituting fuel project played an important role for improving the forest ecological service function value and realizing the sustainable development of forest.

Water use strategy in growing seasons plays a great role in the management of riparian poplar plantations in northern China. The research was conducted on a poplar (Populus × euramericana cv. '74/76') plantation located near the floodplain of Chaobai River in the northeastern su-burb of Beijing. The influencing factors of poplar sap flow (SF) were presented based on the measurements on the stem SF with thermal dissipation sap flow probe (TDP), soil volumetric water content (VWC) with time-domain-reflectometer (TDR) and environmental factors with eddy cova-riance system from June to July, 2014, to explore the impact of shallow ground water on SF. The results showed that the diurnal variation of SF presented single or double peaks depending on the varia-tion of solar radiation (R). The SF density decreased in soil water relative deficient period (RDP), and the peak time advanced to 12:30 from 14:00, while the time lag between the SF density and R showed no obvious change. The solar radiation and air vapor pressure deficit were the predominant factors of SF during soil water relative sufficient period (RSP), while soil water became the limiting factor in RDP. During the RDP, the daily water consumption of individual poplar tree was significantly negatively correlated with soil VWC at the depth of 100 cm, and significantly positively correlated with soil VWC of the other depths. The shallow ground water (at the depth of ≥150 cm where the soil water content showed little change) might move to the upper soil layer controlled by the capillary force and supply for poplar growth during the soil water-relatively deficient period.

Based on the field survey and laboratory analysis, this paper studied the soil aggregate stability and soil organic carbon characteristics in Quercus variabilis and Pinus tabulaeformis plantations in Beijing area. In the two plantations, the contents of soil macro-aggregates decreased with soil depth. In P. tabulaeformis plantation, soil macro-aggregates (>0.25 mm) occupied the majority, accounting for 71% -77% of the total; whereas in Q. variabilis plantation, no significant difference was observed in the contents of soil macro-aggregates and micro-aggregates (< or =0.25 mm), which accounted for 51% -58% and 42% -49%, respectively. Both the mean mass diameter and the geometrical mean mass diameter of the soil aggregates in P. tabulaeformis plantation were significantly higher than those in Q. variabilis plantation, and the fractal dimension (D) of the soil water-stable aggregates in P. tabulaeformis plantation was lower than that in Q. variabilis plantation, suggesting that P. tabulaeformis plantation was more favorable for the soil aggregate stability than Q. variabilis plantation. Also in the two plantations, the organic carbon content in soil water-stable aggregates decreased with soil depth. The organic carbon content in soil macro-aggregates was significantly higher in P. tabulaeformis plantation (58% -83%) than in Q. variabilis plantation (49% -66% ). It was suggested that in Beijing area, P. tabulaeformis plantation was more beneficial to the soil organic carbon protection, as compared with Q. variabilis plantation.