| Forestry in China is implementing its developing strategy which focuses on ecological construction in an all-around way, accelerating the transform from the traditional forestry to a modern one. It is experiencing an important period when efforts are concentrated on the construction of forestry ecology and industrial system for a rapid and steady progress. Various monitoring projects belonging to the forestry monitoring system have come into being and developed under certain social economic and demanding conditions, having their own characteristics. Every monitoring project has its own clear aim, content, method and period. According to the demand of social situation for the monitoring work, at different scale (e.g. the scale of an area or a province and its management unit), sampling design is crucial for the unification of the present monitoring projects, the construction of a universal and comprehensive monitoring indicators of forest resources and the creation of the ground plot scheme appropriate to the monitoring objects. At the same time, matching different indicators with their corresponding sampling methods has important research value and practical significance as well. This paper is aimed at:(1) From the core concept, the inventory and monitoring methods were introduced, and characteristics of national forest inventory at home and abroad was compared. At the same time, the current condition of forest resources monitoring in mainly developed forestry countries was analyzed. Based on the current condition and existing problem in China, according to the actual condition in forest resources monitoring and the monitoring need from the social practice, the development trend and construction goal of forest resources comprehensive monitoring in China was pointed out, that is, the diversification of monitoring content, annually monitoring period, the standardization of monitoring technology, the integration of monitoring measures and the sharing of monitoring information.(2) Sampling survey technique is key to forest resources comprehensive monitoring. The historical of sampling survey was briefly introduced. Classification and comparison of sampling theory were carried out in detail. Based on the analysis of forest resources comprehensive monitoring at home and abroad, according to the sampling classification of Michael Kohl, et al., the application condition of different sampling method on forest resources comprehensive monitoring was reviewed. In order to meet the new need of the current monitoring, improving the sampling survey system in China was discussed.(3) The indicators system framework of comprehensive monitoring was put forward. The classification method(k-NN, k-Nearest Neighbor and ik-NN, improved k-Nearest Neighbor) of remote sensing was summarized. At the same time, three-stage sampling for stratification was put forward, it would provide the theoretical basis for comprehensive forest resources monitoring.(4) Based on the some concepts, such as limiting distance, basal area factor, plot radius factor, estimation of population total, basal area, population size, mean, variances and product of point sampling was systematically built. At the same time, the method of double point sampling was systematically deduced, it would provide the sampling guidance for setting up the forest resources monitoring at the management sacle.(5) To meet the new need at present, the conditional estimation and unconditional estimation of population total, density and mean, at the same time, variance, estimation interval and precision of various kinds of line intersect sampling(including straight-line, Ell-shaped transects and Y-shaped transects) was systematically deduced so that it can provide the scientific proof for forest resources comprehensive monitoring.(6) The formula of calculation of total volume, density, mean and total number of log, estimation precision, variance and estimation interval was systematically deduced. Based on the method control, according to the need of the forest ecological system at present, the straight-line intersect sampling was applied in the inventory of log in the fourth small section of I section. The results show that the lengthen of transect is a main factor impacting the precision, A inventory could't be carried out by one transect with the length equivalent to the total length of all transects, because the probility of selecting sample will be affected too much, and it was not good for statistical estimation.(7) Relationship between the inventory factors of logs and the length of transect was analysed. The analysis shows that:the precision of the total volume of logs increased with the increase length of transect; Both the total number of logs and the density of volume firstly increased and then decreased with the increase length of transect. When the interval of the length of transect arrived at [50,100] m, they relatively stable. In the end, the best transect length was determined 50 meter, then the total volume of logs in the research area was 536.85 m3, the density of volume was 27.53 m3·hm-2, the total number of logs was 5887 and the sampling precision gained 90.05%(reliability was 95%), it can provide the scientific and practical proof of ground plot design for forest resources comprehensive monitoring.(8) Ground Plot Design techniques for National Forest Inventory of major countries in the world are reviewed. They cover sample unit, plot configuration, plot size, selection of trees in sample unit, and investigation variables and interval. Clustered circular plots are commonly adapted. Forest health, biomass, biodiversity and soil carbon are also included in the investigation variables besides normal ones. Based on the plots of national forest inventory, Small plots including rectangle, circle, line, and so on should be configurated to get more information.(9) On the hypotheses of no edge effect of plots, estimation following fixed area plot sampling was carried out. Singular and small plots(10 m x 10 m) were systematically nested in the plots of the method control, and regeneration survey was carried out. According to the builded model, the number of seedings and small trees was estimated. The unbiased estimation of the number per hectare of spruce, fir, other tree species and total seedlings was 420,2252,4501,7178 respectively.At the same time, on the basis of all the fixed plots, the general expression of increment, variance and its estimation were built, as well as the increment of different domains. It has provided theoretical evidences for the comprehensive monitoring of forest resource.In summary, three-stage sampling for stratification, point sampling, line intersect sampling and dynamical estimation of resources based on fixed and nested plot was buildt, they will benefit to improve the forest resources monitoring system.
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