| Forest health diagnosis and assessment is a rising hotspot in research and development of world forestry since 1990s. On this subject, former researchers have done some research work mainly in the aspects of forest vigor, organization, anti-menace and resilience, ecological service functions and so on, however, few research papers were reported about diagnosing and assessing forest health in virtue of xylophagous insects being bioindicators based on the fact that secondary xylophagous insects prefer attacking sub-healthy and unhealthy trees. In this paper, underlying rules that xylophagous insects are always in accompany with sub-healthy and unhealthy trees were explored and verified in the case of Monochamus alternatus at first. Then, suitable Pinus yunnanensis virgin forests, secondary forests and forest plantations were selected as research plots in core zone and marginal zone of distribution of Pinus yunnanensis in Yunnan. Based on natural qualities of forest ecosystem, tree health status of Pinus yunnanensis was investigated; after that, from point to plane, reverse reasoning were carried: forest health assessment was explored mainly from the aspects of community structures, species diversity, harm conditions of xylophagous insects, soil physical and chemical properties, and climatic status. The research aims were exploring feasibility of forest health assessment in virtue of xylophagous insects, and providing academic and experimental bases for sustainable management of Pinus yunnanensis forest health and future forest protection decision. Main conclusions are as follows:(1)Researches of host selection and information dissemination mechanism of adult Monochamus alternatus to Pinus yunnanensis indicated that, olfaction and vision play important roles in process of host selection of adult Monochamus alternatus. By olfactory judgement to host volatiles and mate-pheromones, visual recognition to host colors, and digestive enzyme activity regulation, Monochamus alternatus could exactly achieve feeding and oviposition selections. Determination of digestive enzyme activities indicated that feeding selection of Monochamus alternatus prefers attacking healthy Yunnan pine(attack order: healthy>unhealthy>sub-healthy); host selection test in the forest and olfaction and vision tests in laboratory all indicated that oviposition selection of Monochamus alternatus prefers attacking sub-healthy and unhealthy Yunnan pines ( oviposited tree ratios of healthy, sub-healthy and unhealthy Yunnan pines were 0.83%, 32.88% and 30.77% respectively). Monochamus alternatus mostly attacks middle and inferior parts of host trunks, this character is closely related to bark physical structures, especially to phellem thickness. Due to its oviposition selection trend, Monochamus alternatus can come under"secondary"xylophagous insect which is sensitive to host physiological status and is always in accompany with sub-healthy and unhealthy trees.(2)Investigations of community structure, health status and species diversity of Pinus yunnanensis forest in different distribution areas of Yunnan indicated that virgin Pinus yunnanensis forest had the most stable and reasonable community structures, populations of the dominant species of tree stratum had the strongest ability in renewing naturally and potential in succession, and also species diversity and habitat diversity were the most abundant, general health status were the best. Features of virgin forests described above were all superior to secondary Pinus yunnanensis forests; and secondary forests preceded forest plantations. General health status of secondary Pinus yunnanensis forests in areas investigated were sub-healthy; and forest plantations were sub-healthy or unhealthy due to simplicity of tree species and community structures, lowest species diversity and habitat diversity, and serious artificial interference. Meanwhile, research discovered that variations of adaptive-growth features induced by differences of geographic distribution and macroclimate status put limited influence on forest health, and forest origin types, artificial interference and woodland microenvironments (microclimate, plant diseases and insect pests, etc.)affected forest health more.(3)Correlations between harm conditions of xylophagous insects and forest health of Pinus yunnanensis forests in different distributions of Yunnan indicated that obvious correlations existed between them, and orders of species richness of xylophagous insects were: virgin forests> secondary forests> forest plantations. Species diversity of xylophagous insects were the most abundant in virgin forests, and also, the better the health status were, the more species and amounts of xylophagous insects were; however, the better the health status were, the less species and amounts of xylophagous insects were while in secondary forests and forest plantations. These phenomena were related to community structures and plant species diversity of different types of forests, and also indicated that virgin forests had the strongest anti-menace and resilience abilities in facing limited insect pests attacking, and were the stable and balanced ecosystems, accorded with the standards of forest health. Comparatively, forest plantations were fragile and sensitive ecosystems, had weak anti-menace and resilience abilities, belonged to unhealthy forest status. Health status, insect pests degree and resilience of secondary forests were in between. By regression analysis, four regression equations were established fitting correlations between forest health indexe(sFHI) of different types of Pinus yunnanensis forest in different regions and harm conditions of xylophagous insects.(4) Correlations between soil properties and forest health of Pinus yunnanensis forests in different distributions of Yunnan indicated that soil physical and chemical properties affected health status of Pinus yunnanensis forests to a considerable degree. Soil physical properties, such as water content, texture and composing and chemical properties, like nutrient content, CEC, pH, organic substance content played dominating roles in forest health. By regression analysis, regression equations were established fitting correlations between forest health indexes(FHI) of different types of Pinus yunnanensis forest in different regions and soil properties.(5)Correlation analyses between forest health of Pinus yunnanensis forests in different distributions and 14 kinds of forest health assessment indexes indicated that forest health was closely related to the indexes as harm conditions of xylophagous insects, stand structure and productivity, soil properties, site environment, and climatic conditions, etc. These indexes should be elected into forest health comprehensive assessment as assessing parameters. Forest health and its dynamics were decided by different environmental factors and their interactions. However, some main assessment indexes(such as stand accumulation amount, annual mean precipitation, oviposition notch amount of longhorns, soil water content, etc.) being elected into quick forest health diagnosis and assessment was good practice also. Pinus yunnanensis stands which had high forest health indexes(FHI) possessed these features: abundant annual mean precipitation(about 1000mm), moderate heat(annual mean temperature 15-19℃), moderate stand ages(above 30a) and crown densities(about 0.7), high stand accumulation amount, few occurance of xylophagous insects such as Monochamus alternatus, etc. |
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