The pattern of the vegetated landscape in Beijing was analyzed using fractals and the GIS software ARC/INFO. Patch complexity was examined for a range of defined vegetation types. Significant positive linear correlations were found between fractal dimensions calculated using two different methods, and between each of the two fractal dimensions and average patch size. Fractal dimensions for the types within a type in the higher level are more similar than those not within a type in the higher level. Two domains of scale were identified: those larger and smaller than about 2.7km2. Patches in the large domain are more complex than those in the smaller domain. The main reason for which is that large patches are often inlaid with smaller ones while this phenomenon rarely occurs among smaller patches.

Trend surface analysis is a method commonly used in community and population ecology: in this paper it was introduced as a tool to reveal pattern at the landscape level. A reasonable and reliable approach was presented to the application of this technique which enables the exploration of the role of the spatial distribution of landscape elements in landscape ecological research. Uniform grid point sampling was a key element in the described approach. It was well suited to complex secondary forest regions composed of confusing mosaics of land cover, and an example of its application in the Guandishan forested landscape was presented. The results of this application showed that, at the spatial scale of the study area (30～50km), horizontal geographical position as a determinant of the spatial pattern of landscape elements does not impact significantly on the spatial pattern of complex secondary forest mosaics. In contrast, aspect, slope and altitude were found to be the dominant features controlling landscape pattern in study area. Further, the orientation and the intensity of the controlling effects of aspect and slope in the landscape distribution pattern are differed markedly at different ranges of altitude. These differences are analyzed and discussed. Some basic rules of spatial distribution of landscape elements are proposed. It was anticipated that these rules will be of benefit to further study aimed at the enhancement of sustainable management of forests and landscape planning in the region.

Using the buried-bag method we measured nitrification and net N mineralization rates for soils (0～10cm) under a variety of forest types in Xishuangbanna, Southwest China in July of 1998. The forest types studied were: tropical seasonal rainforest, Melettia leptobotrya secondary forest, forest gap, and slash-and-burn agricultural land. Net N mineralization rates were 6.55 mg N·kg-1· 30d-1 in seasonal rainforest and 6.37 mg N·kg-1·30d-1 in secondary forest. Nitrification rates were 16.28 mg N·kg-1·30d-1 in seasonal rainforest, 16. 38 mg N·kg-1·30d-1 in secondary forest. Nitrification and net N mineralization rates were –2.78 mg N·kg-1·30d-1 and –7.85 mgN·kg-1·30d-1 in forest gap , –3.69mgN·kg-1·30d-1and –10.69mgN·kg-1·30d-1 in agricultural land, respectively. Ammonification rates were negative in all the studied sites, with the result that net N mineralization rates were lower than nitrification rates.

Experiments were conducted on the grassland watershed at the Heshan Hill Region Experimental Station. Rainfall and runoff records were kept for four years, while evapotranspiration in the grassland watershed was studied in just one year, 1994. These studies indicate: 1) average annual precipitation was 1761mm,and there is significant seasonal variation. Dry season rain accounted for 12 % of the annual precipitation, while wet season rain made up 88 %. Moderate and light rain events were the most frequent though most precipitation was derived from by heavy rain and downpours. 62 % of rain fell in events sufficient to cause surface runoff. 2) The annual runoff and surface runoff coefficient were respectively 50% and 17%. Variation in surface runoff was closely related to variation in precipitation, though less with variation in rainfall intensity. 3) The water balance for 1994 included rainfall input of 1842mm and the output via runoff and evapotranspiration were 970mm and 852mm respectively. Annual moisture variation for the entire system was just 19.7mm, but monthly variation was significant, ranging from-68mm to 104mm. This adjusted water distribution over a single year ,and between years so that the water balance of the grassland was in a form of dynamic balance. 4) Unbalanced seasonal distribution of both water availability and heat, large rainfall events causing surface runoff and the large proportion of surface runoff are three important factors restricting vegetation improvement. Managing change in the way the system losses and reserves its water is a key element in the restoration mechanisms of damaged ecosystem.

The effects of seabuckthorn (Hippophae rhamnoides L. ), a nitrogen-fixing plant, on growth and biomass production in poplar plantations in subhumid-arid area of China were examined. In a 3 years project seabuckthorn was introduced into poplar stands of three different varieties (Populus cv. "Xiaohei", P. cv. "Zhaolin06" and P. euramericane cv. "N3016") in two different mixing designs (individual- or strip-mixing patterns). The positive effect of seabuckthorn on tree growth was found in all poplar plantations, irrespective of poplar variety or mixing pattern. The increases in diameter at breast height and mean height ranged from 6% to 38% and from 8% to 23%, respectively. In the individual-mixing pattern, the above-ground biomass of poplar trees was larger in mixed stands than in pure stands, but the reverse occurred in the strip-mixing patterns due to the lesser stock number per hectare. The aboveground net primary productivity was significantly larger (27 % to 113 % ) in mixed stands than in pure stands, regardless of poplar variety of mixing pattern. The increases was due largely to the contribution of the mixed seabuckthorn plants, accounting for 20% to 41 % of the total above-ground net productivity. Herbs comprised a negligible proportion of the total net productivity of stands in all three mixing patterns.

Using specially designed chambers and an infrared gas analyzer, we examined the photosynthetic responses of six woody species to elevated CO2, from 325 μmol·mol-1 to 650 μmol·mol-1. Six temperate forest woody species under natural growth conditions in the Quercus liaotungensis forest in Beijing Mountainous Areas were tested: Quercus liaotungensis koidz. , Fraxinus mandshurica Rupr. , Tilia mongolica Maxim. , Acer mono Maxim. , Abelia biflora Turcz. and Corylus mandshurica . The results showed that the six species displayed variable degrees of enhancement in net photosynthetic rates to elevated CO2, from 37% (Abelia biflora Turcz. ) to 93% (Quercus liaotungensis koidz. ), with an average value of 75%. Shrub species were less affected than tree species. Remarkable enhancement in net photosynthetic rates with elevated CO2 were found during the diurnal courses in both summer and autumn.

Dynamics of plant biodiversity and structure were studied at three different stages of Mongolian Oak-Korean pine forest regeneration. Forest regeneration was good in the early period with Korean pine and broad-leaved tree species having similar numbers of individuals regenerating. Later, the number of abundance of Korean pine regeneration comes to exceed that of other tree species. With the development of forest, firstly Mongolian Oak and other shade-intolerant tree species initially dominate stands, these are replaced by Korean pine and broad-leaved tree species in a mixed stand, while Korean pine dominates older stands. The modeled dynamics of shrubs and herbs were more complex. Analysis of stem diameter distributions showed that there were more large trees of broad-leaved tree species and fewer small trees of conifer species at early stage, but these conditions are reversed at a later stage. Diameter distributions of the different forest stages were fitted with theoretical models. The results showed that Weibull distribution had the best fit in these Mongolian Oak-Korean pine forest.

Catalase and NR activity and soluble sugar content was analyzed in leaves of tobacco plants grown for 10 days in a nutrient solution containing heavy metal pollutants (Cd2+, Pb2+ and Cd2+ + Pb2+). Cadmium and lead induced changes in the ultra-structure of tobacco leaf cells, particularly in the structure of the chloroplast, mitochondrion and nucleus, were observed using electron microscopy. This showed that: 1) The activity of catalase was heavily inhibited by Cd, and first stimulated then inhibited with increasing concentrations of Pb; 2) The activity of NR was first stimulated and then inhibited with increasing concentration of Cd, but was inhibited by lead, with a small resistant peak at 1000mg·L-1; 3) Soluble sugar content was reduced by Cd, Ph and Cd + Pb; 4) Cadmium destroyed the cell membrane system. It is suggested that this may result from cadmium combining with, and denaturing, proteins. This would lead to change in structure and loss of function in the membrane and to disorder in the protoplasm; 5) Massive lead deposits were observed in the outer cell membrane, and lead deposits were found in the cytoplasm and chloroplast. The cell membrane was found to be a major barrier to lead migrating into the protoplasm. Lead also had a strong effect on the ultra-structure of chloroplasts, mitochondria and nuclei.

We investigated changing patterns of plant community composition together with population dynamics under grazing pressure in a strict, long-term grazing test. This was achieved with a TWINSPAN (Two-way Indicator Species Analysis) analysis of quadrat data. The main results are that: 1) community composition diverged under varying grazing pressure to form distinct different groups in test fields, while the application of replicate grazing intensity treatments resulted in composition covergence. 2) With increasing grazing pressure perennial species decreased and annual herbs increased in communites.