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Abstract A comprehensive evaluation system， which focused on optimal selection of raw material forest species for edible fungi， was established by combination of Analytic Hierarchy Process （AHP） and Experts Grading Method （EGM）. The evaluation system had 4 indices of grade I and 12 indices of grade II. Among the 12 indices of grade II， the weighted values of production quality of edible fungi P2 （0.287 4）， usable time P7 （0.187 3）， annual average increment P8 （0.187 3）， edible fungi production suitability P1 （0.095 8） were larger than the values of others. Based on the comprehensive evaluation system， this study analyzed and screened 47 broadleaf species of 40 genera of 25 families. There were 16 broadleaf species having the comprehensive evaluation scores of equal to or greater than 2.400 0， which were available as major tree species for edible fungi development of Guizhou Province， especially species such as Liriodendron chinense， Quercus acutissima， Alnus cremastogyne， Betula luminfera， Elaeocarpus duclouxii， Elaeocarpus sylvestris， Choerospondias axillaris. The 10 broadleaf tree species with comprehensive evaluation score of 2.100 0 ≤ Y < 2.400 0 were recommended as candidates for edible fungi production， while the 21 broadleaf species with the comprehensive evaluation score of less than 2.100 0 were not recommended.
Key words Edible fungi； Raw material forest； Excellent tree species； Tree species selection； Guizhou Province
Sawdust of broad-leaved trees is the major material for the cultivation for edible fungi， an carrying out the selection of excellent raw material forest species for edible fungi is conducive to solving the main contradiction between forest ecological environment protection and economic development in mountainous areas， improving the quality for edible fungi， and promoting industrial development. From 1993 to 2005， Zhejiang Academy of Forestry carried out the projects of Research and Development of Cultivation Techniques of Short-rotation Wood Forest for Mushroom and Research on Development and Utilization of Mushroom Cultivation Substance Resources. The cultivation techniques of short-rotation wood forest for mushroom can effectively solve the problems of cultivation materials for the development of mushroom-based edible mushroom industry. Weng et al.， Zou et al. and Zhu et al.[1-4] conducted researches on the selection of excellent mushroom tree species， the yield of fresh mushrooms of each tree species substrate， and the cultivation technology of short-rotation wood forest for mushrooms[1-4]， and screened 7 fast-growing and high-yielding tree species of Alnus cremastogyne， Elaeocarpus sylvestris， Liquidambar formosana， Liriodendron chinense， Betula luminifera， Castanea henryi and Choerospondias axillaris， which were suitable for the development of mushroom industry in Zhejiang Province[1-4]， found out the usable life of the 7 tree species for short-rotation cultivation[2，4]， established the mode of short-rotation mushroom cultivation. Cultivation Techniques of Short-Rotation Wood Forest for Mushroom has been popularized in the mushroom-producing areas in Zhejiang， Shaanxi， Fujian， Henan and other provinces. According to the statistics and research of Cheng et al.[5]， the annual output of mushrooms in Guizhou Province was 3 000 t in 2001， 4 500 t in 2005 and 4.382 0 × 104 t in 2013， an increase rate of 1 360.07% with the annual growth rate of 25.04%. After 2009， the mushroom industry in Guizhou Province grew exceptionally rapidly. The lack of broadleaf sawdust has become a bottleneck in the development for edible fungi industry in Guizhou Province， and some counties and cities have witnessed the excessive deforestation of broad-leaved trees. Moreover， many farmers and manufacturing enterprises do not pay attention to the choice of sawdust， resulting in low quality mushroom products. At present， Guizhou Province has not yet carried out research and experiments on the selection of raw material tree species with short-rotation for edible fungi in and the cultivation of raw material forest for edible fungi. Nor has it introduced or promoted the Cultivation Techniques of Short-Rotation Wood Forest for Mushroom. Therefore， the raw material tree species for edible fungi in Guizhou Province were studied， aimed at the initial screening of suitable raw material tree species for the development for edible fungi in Guizhou Province to provide reference application for the production sector.
Materials and Methods
Test materials
Based on the existing literature， the primary tree species were selected according to the following principles： ① priority was given to broadleaf species as the raw material tree species for edible fungi. ② The selected broad-leaved tree species should be suitable for edible fungi cultivation， and the selected tree species should contain no harmful substances and have heavy odors， such as Melia azedarach， Eucalyptus spp.[6]. ③ Priority was given to the native tree species in Guizhou Province， and exotic tree species could be used appropriately. ④ The selected tree species should have rapid growth and large volume increment， and the 710 year-old trees were the high-quality raw materials for cultivation[3]. ⑤ The selected tree species should have strong ecological adaptability and resistance， and could be used repeatedly. ⑥ The selected broad-leaved tree species should have relatively mature seed collecting， seedling raising techniques and afforestation technology.
Based on the above selection principles， the tested tree species were selected from the major broadleaf species recorded in Afforestation Technology of Major Tree Species in China[7] and Afforestation Technique of Main Broadleaf Species in Guizhou[8]. After primary selection， 47 tree species from 40 genera of 25 families were selected as the alternative species for AHP （Table 1）. Tree species selection method
The indices of the target layer and criterion layer were determined in the combination of AHP[9] and expert scoring based on previous studies， to construct the comprehensive evaluation system of tree species and carry out the selection of tree species. Based on the established evaluation system， the 1-9 scaling method was used to find out the scales for quantitative research， and the weight of each index was directly obtained by using AHP data processing software （yaahp10.5）.
Selection of evaluation index Excellent tree species should have the following characteristics： it should be suitable for the production of edible fungi with high yield， and the produced edible fungi quality should be better than that produced from other broadleaf sawdust or weed tree sawdust （economic suitability）； it should be able to adapt to the complex nature environment in Guizhou， and have wide range of distribution， strong tolerance to infertility， strong resistance to pests and diseases， so as to facilitate the promotion and application in the future（ecological adaptability）； according to the research results of Zhu et al.[3]， the tree species should have easy reproduction， fast growth and early harvest， and can be used repeatedly to reduce operating costs （fast-growing and high-yielding）； taking full advantage of the latest research results of broad-leaved tree cultivation techniques， the tree species should have relatively mature afforestation technology to facilitate afforestation and management， reduce operating costs. The tree species which can meet the development needs of edible fungi industry in Guizhou should be selected from the 4 major indices of economic suitability， ecological adaptability， fast-growing and high-yielding， and technical maturity of afforestation technology.
Establishment of evaluation system The comprehensive evaluation system of excellent tree species was divided into 2 grades. The indices of grade I mainly included economic suitability， ecological adaptability， fast-growing and high-yielding and technical maturity of afforestation technology. Each index of grade I was further divided into several indices of grade II. Economic suitability included 2 grade-II indices of edible fungi production suitability and production quality of edible fungi； ecological adaptability included 4 grade-II indices of distribution range， infertility tolerance， stress resistance， disease and pests resistance； fast-growing and high-yielding included 4 grade-II indices of usable time， annual average tree height increment， annual average woodstorage increment and germination ability； technical maturity of afforestation technology2 grade-II indices of included afforestation technology maturity， silviculture technology maturity. Data statistics and analysis
Determination of index weight In order to reflect the opinions of experts in various fields on the excellent raw material tree species for edible mushroom， the tree species were scored by the experts in edible fungi， forest tree breeding， tree classification， forest cultivation， pest control and edible fungi production. A total of 11 experts in related fields were engaged in the scoring.
Targeting at the target layer of the selection structure model， the data were processed by the analytic hierarchy process software （yaahp10.5） after expert scoring. On the premise of satisfactory consistency of the determined judgment matrix， the importance of indices of each layer were conducted with significance judgment， and then the weights of the target layer， grade-I index layer and grade-II index layer were calculated， thereby determining the weights of the overall ranking levels.
Determination of evaluation index assignment According to the weight of each index of evaluation system， most scores of the tree species were determined according to literatures based on the requirements of the evaluation index and the characteristics of each tree species， and some tree species which lacked relative data were scored using expert scoring method. Finally， all data were processed with unified standardized processing. The indices of grade II were to evaluate using 3-point system， and the weight standard of each index was shown in Table 2.
Calculation of comprehensive evaluation indices of the primarily selected tree species The comprehensive index of each tree species was calculated using Y = ΣWiYi， where， Wi is the weight of the ith index， and Yi is the score of the ith index. Excel was used to calculate the comprehensive score of each tree species， which was the comprehensive evaluation index of the tree species. Considering the effects of each factor on the yield and quality of edible fungi， the comprehensive indices of primarily selected tree species were divided into 3 grades by referring to the research of Huang et al.[10] and Zhou[11] based on the distribution， intuitive experiment and expert opinion of the comprehensive evaluation indices， and a total of 47 tree species were involved in the comprehensive evaluation. The tree species with the comprehensive evaluation score of Y≥2.400 0 were used as the major raw material forest species for edible fungi， evaluation score of 2.100 0 ≤ Y <2.400 0 as candidate species， and the evaluation score of Y <2.100 0 species not recommended for edible fungus production. Results and Analysis
Index weight analysis using AHP
After calculation and evaluation， the consistency ratio and index weight of the indices in each layer were shown in Table 3.
As shown in Table 3， first， the consistency ratio （CR） of the evaluation system was 0.021 4， which was smaller than 0.1， and the CR of each index of grade 1 was smaller than 0.1. Thus， the evaluation system could be used for the selection of excellent raw material forest species for edible fungi. The weight value of fast-growing and high-yielding C3 was the largest of 0.0443 2， followed by that of economic suitability C1 （0.383 2）， both of which were important indices for the selection of excellent raw material forest species for edible fungi. Second， among the 12 indices of grade II， the weighted value of production quality of edible fungi P2 （0.287 4） was the largest， which was determined by the particularity of the production of high quality edible fungi， and the weighted values of usable time P7 （0.187 3）， annual average increment P8 （0.187 3）， edible fungi production suitability P1 （0.095 8） were also large， which was determined by the economical efficiency of the raw material forest for edible fungi. These 4 factors were important factors to be considered in the screening of raw material forest species for edible fungi.
Primary selection of excellent raw material forest species for edible fungi
The comprehensive evaluation scores of 47 tree species were calculated by using the evaluation system. the one with the highest score was Quercus acutissima of 2.961 9， and the one with the lowest score was Schima superba of 1.198 6. The average score was 2.105 5 （Table 4）. According to the scores of the comprehensive evaluation indices， the primary-selected tree species were divided into 3 grades.
There were 16 tree species with comprehensive evaluation score ≥2.400 0， namely Liriodendron chinense， Magnolia officinalis， Manglietia conifera， Broussonetia papyrifera， Quercus aliena， Alnus cremastogyne， Betula luminifera， Elaeocapus duclouxii， Elaeocapus duclouxii， Choerospondias axillaris， Jujube， Toona sinensis， Paulownia fortunei， Catalpafargesii f. duclouxii， Catalpa bungei， Catalpa ovata， which could be used as the main tree species of the raw materially for edible fungi.
There were 10 species with comprehensive evaluation scores of 2.100 0 ≤Y < 2.400 0， namely Michelia chapensis， Parakmeria lotungensis， Idesia polycarpa， Alniphyllum fortunei， Zenia insignis， Robinia pseuduacacia， Camptotheca acuminata， Cornus wilsoniana， Tapiscia sinensis， Toona ciliata， which could be used as alternative tree species. There were 21 species with comprehensive evaluation scores <2.100 0， namely Manglietia insignis， Michelia martinii， Michelia maudiae， Sassafras tzumu， Semiliquidambar cathayensis， Pteroceltis tatarinowii， Cyclocarya paliurus， Pterocaryas tenoptera， Schima superba， Pterostyrax psilophyllus， Styrax suberifolia， Photinia davidsoniae， Gleditsia sinensis， Ormosia hosiei， Davidia involucrata， Cornus japonica-var. Chinensis， Eurycorymbus cavaleriei， Bretschneidera sinensis， Koelreuteria paniculata， Pistacia chinensis and Castanea henryi， which were not recommended for the application of edible fungi production.
Conclusion and Discussion
Selection of excellent raw material forest species for edible fungi
Based on the comprehensive evaluation system， the primary-selected tree species were divided into 3 grades. There were 16 broadleaf species having the comprehensive evaluation scores of ≥2.400 0， which were available as major tree species for edible fungi development in Guizhou； there were 10 broadleaf tree species with comprehensive evaluation scores of 2.100 0 ≤ Y < 2.400 0，which could be used as candidates for edible fungi production， while the 21 broadleaf species with the comprehensive evaluation scores of less than 2.100 0 were not recommended. Among the 16 tree species with the comprehensive evaluation scores of ≥2.400 0， the performances of 7 were verified by Weng et al.[2]， Zou et al.[4]， namely Liriodendron chinense， Quercus acutissima， Alnus cremastogyne， Betula luminfera， Elaeocarpus duclouxii， Elaeocarpus sylvestris， Choerospondias axillaris， and they could be vigorously developed； further production tests were needed for 9 species， such as Toona sinensis， Catalpa fargesii， Catalpa bungei， which needed further analysis and selection by measuring the production yield， amino acid content as well as the shape and quality determination of edible fungi. Castanea henryi， which was popularized vigorously in Zhejiang， only got the score of 1.939 0， which was mainly due to the lack of systematic research on all aspects of Castanea henryi in Guizhou Province.
Selection of excellent raw material forest species of selenium-enriched mushroom
The use of biological transformation method to produce natural selenium-enriched mushrooms has become a research hotspot at home and abroad[12]. It is of unique advantages for Guizhou to make full use of the rich selenium resources to develop green selenium-enriched mushroom industry， create the geographical brand of "selenium-enriched mushrooms" and build brand of selenium-enriched mushrooms. At present， there is no research and report on the selenium-enriched ability of tree species. Therefore， it is necessary to study the selenium enrichment ability of 16 species like Liriodendron chinense， Quercus acutissima and Alnus cremastogyne， so as to provide the basis for the development of natural selenium-enriched mushroom industry in Guizhou Province. References
[1] WENG YF， WANG RD， DU GJ， et al. Study on the selection and plantation technique of superior short-rotation wood forest for mushroom[C]. China Science and Technology Association. Harmonious development of energy conservation and environmental protection—Annual Meeting of China Association for Science and Technology in 2007 （III）. Beijing： Sound and Video Center， China Association for Science and Technology， 2007： 829-837.
[2] WENG YF， DU GJ， WANG RD， et al. Study and promotion of the cultivation techniques for short-rotation wood forest for mushroom[C]. Zhejiang Science and Technology Association. The Third Zhejiang Midwest Science and Technology Forum Proceedings （Volume III： forestry）. Hangzhou： Zhejiang Science and Technology Association， 2006.
[3] ZHU GQ， WU XQ， WANG KH， et al. Effects of tree ages on the output and content of the nutritive components of Lentinus edodes[J]. Chinese edible fungus， 2005， 24 （5）： 23-27.
[4] ZOU DM， ZHU GQ， WU SY， et al. Preliminary report on species selection of good mushroom wood[J]. Journal of Zhejiang Forestry Science and Technology， 1997， 17 （1）： 18-23.
[5] CHENG LL， ZHANG JB. Spatial and temporal evolution of main edible fungi species in China-based on Shiitake mushroom and Oyster mushroom[J]. Journal of Huazhong Agricultural University （Social Science Edition）， 2015 （5）： 48-58.
[6] ZHANG JX， JIA SM， ZUO XM， et al. NY 5099-2002， requirements for the technology of non-pollution food edible mushroom cultivation substrate safety[S]. Beijing： China Standard Press.
[7] Chinese Silva Editorial Board. Afforestation technology of major tree species in China[M]. Beijing： China Forestry Publishing House， 1993.
[8] LUO Y. Afforestation technique of main broadleaf timber species in Guizhou[M]. Guiyang： Guizhou Science and Technology Press， 2011.
[9] HUANG SX， LU MM， CHEN J， et al. The application of analytic hierarchy process on choice of greening tree species along expressway in north of Guangdong Province[J]. Subtropical Plant Science， 2016， （45） 2： 177-182.
[10] HUANG YQ， XU XY， CHEN W， et al. The comprehensive evaluation of introduction of color-leaf species in Dalian City based on AHP[J]. Northern Horticulture， 2012 （6）： 79-82.
[11] ZHOU MH. Comprehensive evaluation， selection and graduation of the trees for urban landscaping in Lanzhou[D]. Lanzhou： Gansu Agricultural University， 2004.
[12] QIAO YM， CHEN WQ， XU H. Status and application prospect of selenium-enriched Lentinula edodes[J]. Journal of Shaanxi University of Technology （Natural Science Edition）， 2012，31 （6）： 46-50， 56.
Key words Edible fungi； Raw material forest； Excellent tree species； Tree species selection； Guizhou Province
Sawdust of broad-leaved trees is the major material for the cultivation for edible fungi， an carrying out the selection of excellent raw material forest species for edible fungi is conducive to solving the main contradiction between forest ecological environment protection and economic development in mountainous areas， improving the quality for edible fungi， and promoting industrial development. From 1993 to 2005， Zhejiang Academy of Forestry carried out the projects of Research and Development of Cultivation Techniques of Short-rotation Wood Forest for Mushroom and Research on Development and Utilization of Mushroom Cultivation Substance Resources. The cultivation techniques of short-rotation wood forest for mushroom can effectively solve the problems of cultivation materials for the development of mushroom-based edible mushroom industry. Weng et al.， Zou et al. and Zhu et al.[1-4] conducted researches on the selection of excellent mushroom tree species， the yield of fresh mushrooms of each tree species substrate， and the cultivation technology of short-rotation wood forest for mushrooms[1-4]， and screened 7 fast-growing and high-yielding tree species of Alnus cremastogyne， Elaeocarpus sylvestris， Liquidambar formosana， Liriodendron chinense， Betula luminifera， Castanea henryi and Choerospondias axillaris， which were suitable for the development of mushroom industry in Zhejiang Province[1-4]， found out the usable life of the 7 tree species for short-rotation cultivation[2，4]， established the mode of short-rotation mushroom cultivation. Cultivation Techniques of Short-Rotation Wood Forest for Mushroom has been popularized in the mushroom-producing areas in Zhejiang， Shaanxi， Fujian， Henan and other provinces. According to the statistics and research of Cheng et al.[5]， the annual output of mushrooms in Guizhou Province was 3 000 t in 2001， 4 500 t in 2005 and 4.382 0 × 104 t in 2013， an increase rate of 1 360.07% with the annual growth rate of 25.04%. After 2009， the mushroom industry in Guizhou Province grew exceptionally rapidly. The lack of broadleaf sawdust has become a bottleneck in the development for edible fungi industry in Guizhou Province， and some counties and cities have witnessed the excessive deforestation of broad-leaved trees. Moreover， many farmers and manufacturing enterprises do not pay attention to the choice of sawdust， resulting in low quality mushroom products. At present， Guizhou Province has not yet carried out research and experiments on the selection of raw material tree species with short-rotation for edible fungi in and the cultivation of raw material forest for edible fungi. Nor has it introduced or promoted the Cultivation Techniques of Short-Rotation Wood Forest for Mushroom. Therefore， the raw material tree species for edible fungi in Guizhou Province were studied， aimed at the initial screening of suitable raw material tree species for the development for edible fungi in Guizhou Province to provide reference application for the production sector.
Materials and Methods
Test materials
Based on the existing literature， the primary tree species were selected according to the following principles： ① priority was given to broadleaf species as the raw material tree species for edible fungi. ② The selected broad-leaved tree species should be suitable for edible fungi cultivation， and the selected tree species should contain no harmful substances and have heavy odors， such as Melia azedarach， Eucalyptus spp.[6]. ③ Priority was given to the native tree species in Guizhou Province， and exotic tree species could be used appropriately. ④ The selected tree species should have rapid growth and large volume increment， and the 710 year-old trees were the high-quality raw materials for cultivation[3]. ⑤ The selected tree species should have strong ecological adaptability and resistance， and could be used repeatedly. ⑥ The selected broad-leaved tree species should have relatively mature seed collecting， seedling raising techniques and afforestation technology.
Based on the above selection principles， the tested tree species were selected from the major broadleaf species recorded in Afforestation Technology of Major Tree Species in China[7] and Afforestation Technique of Main Broadleaf Species in Guizhou[8]. After primary selection， 47 tree species from 40 genera of 25 families were selected as the alternative species for AHP （Table 1）. Tree species selection method
The indices of the target layer and criterion layer were determined in the combination of AHP[9] and expert scoring based on previous studies， to construct the comprehensive evaluation system of tree species and carry out the selection of tree species. Based on the established evaluation system， the 1-9 scaling method was used to find out the scales for quantitative research， and the weight of each index was directly obtained by using AHP data processing software （yaahp10.5）.
Selection of evaluation index Excellent tree species should have the following characteristics： it should be suitable for the production of edible fungi with high yield， and the produced edible fungi quality should be better than that produced from other broadleaf sawdust or weed tree sawdust （economic suitability）； it should be able to adapt to the complex nature environment in Guizhou， and have wide range of distribution， strong tolerance to infertility， strong resistance to pests and diseases， so as to facilitate the promotion and application in the future（ecological adaptability）； according to the research results of Zhu et al.[3]， the tree species should have easy reproduction， fast growth and early harvest， and can be used repeatedly to reduce operating costs （fast-growing and high-yielding）； taking full advantage of the latest research results of broad-leaved tree cultivation techniques， the tree species should have relatively mature afforestation technology to facilitate afforestation and management， reduce operating costs. The tree species which can meet the development needs of edible fungi industry in Guizhou should be selected from the 4 major indices of economic suitability， ecological adaptability， fast-growing and high-yielding， and technical maturity of afforestation technology.
Establishment of evaluation system The comprehensive evaluation system of excellent tree species was divided into 2 grades. The indices of grade I mainly included economic suitability， ecological adaptability， fast-growing and high-yielding and technical maturity of afforestation technology. Each index of grade I was further divided into several indices of grade II. Economic suitability included 2 grade-II indices of edible fungi production suitability and production quality of edible fungi； ecological adaptability included 4 grade-II indices of distribution range， infertility tolerance， stress resistance， disease and pests resistance； fast-growing and high-yielding included 4 grade-II indices of usable time， annual average tree height increment， annual average woodstorage increment and germination ability； technical maturity of afforestation technology2 grade-II indices of included afforestation technology maturity， silviculture technology maturity. Data statistics and analysis
Determination of index weight In order to reflect the opinions of experts in various fields on the excellent raw material tree species for edible mushroom， the tree species were scored by the experts in edible fungi， forest tree breeding， tree classification， forest cultivation， pest control and edible fungi production. A total of 11 experts in related fields were engaged in the scoring.
Targeting at the target layer of the selection structure model， the data were processed by the analytic hierarchy process software （yaahp10.5） after expert scoring. On the premise of satisfactory consistency of the determined judgment matrix， the importance of indices of each layer were conducted with significance judgment， and then the weights of the target layer， grade-I index layer and grade-II index layer were calculated， thereby determining the weights of the overall ranking levels.
Determination of evaluation index assignment According to the weight of each index of evaluation system， most scores of the tree species were determined according to literatures based on the requirements of the evaluation index and the characteristics of each tree species， and some tree species which lacked relative data were scored using expert scoring method. Finally， all data were processed with unified standardized processing. The indices of grade II were to evaluate using 3-point system， and the weight standard of each index was shown in Table 2.
Calculation of comprehensive evaluation indices of the primarily selected tree species The comprehensive index of each tree species was calculated using Y = ΣWiYi， where， Wi is the weight of the ith index， and Yi is the score of the ith index. Excel was used to calculate the comprehensive score of each tree species， which was the comprehensive evaluation index of the tree species. Considering the effects of each factor on the yield and quality of edible fungi， the comprehensive indices of primarily selected tree species were divided into 3 grades by referring to the research of Huang et al.[10] and Zhou[11] based on the distribution， intuitive experiment and expert opinion of the comprehensive evaluation indices， and a total of 47 tree species were involved in the comprehensive evaluation. The tree species with the comprehensive evaluation score of Y≥2.400 0 were used as the major raw material forest species for edible fungi， evaluation score of 2.100 0 ≤ Y <2.400 0 as candidate species， and the evaluation score of Y <2.100 0 species not recommended for edible fungus production. Results and Analysis
Index weight analysis using AHP
After calculation and evaluation， the consistency ratio and index weight of the indices in each layer were shown in Table 3.
As shown in Table 3， first， the consistency ratio （CR） of the evaluation system was 0.021 4， which was smaller than 0.1， and the CR of each index of grade 1 was smaller than 0.1. Thus， the evaluation system could be used for the selection of excellent raw material forest species for edible fungi. The weight value of fast-growing and high-yielding C3 was the largest of 0.0443 2， followed by that of economic suitability C1 （0.383 2）， both of which were important indices for the selection of excellent raw material forest species for edible fungi. Second， among the 12 indices of grade II， the weighted value of production quality of edible fungi P2 （0.287 4） was the largest， which was determined by the particularity of the production of high quality edible fungi， and the weighted values of usable time P7 （0.187 3）， annual average increment P8 （0.187 3）， edible fungi production suitability P1 （0.095 8） were also large， which was determined by the economical efficiency of the raw material forest for edible fungi. These 4 factors were important factors to be considered in the screening of raw material forest species for edible fungi.
Primary selection of excellent raw material forest species for edible fungi
The comprehensive evaluation scores of 47 tree species were calculated by using the evaluation system. the one with the highest score was Quercus acutissima of 2.961 9， and the one with the lowest score was Schima superba of 1.198 6. The average score was 2.105 5 （Table 4）. According to the scores of the comprehensive evaluation indices， the primary-selected tree species were divided into 3 grades.
There were 16 tree species with comprehensive evaluation score ≥2.400 0， namely Liriodendron chinense， Magnolia officinalis， Manglietia conifera， Broussonetia papyrifera， Quercus aliena， Alnus cremastogyne， Betula luminifera， Elaeocapus duclouxii， Elaeocapus duclouxii， Choerospondias axillaris， Jujube， Toona sinensis， Paulownia fortunei， Catalpafargesii f. duclouxii， Catalpa bungei， Catalpa ovata， which could be used as the main tree species of the raw materially for edible fungi.
There were 10 species with comprehensive evaluation scores of 2.100 0 ≤Y < 2.400 0， namely Michelia chapensis， Parakmeria lotungensis， Idesia polycarpa， Alniphyllum fortunei， Zenia insignis， Robinia pseuduacacia， Camptotheca acuminata， Cornus wilsoniana， Tapiscia sinensis， Toona ciliata， which could be used as alternative tree species. There were 21 species with comprehensive evaluation scores <2.100 0， namely Manglietia insignis， Michelia martinii， Michelia maudiae， Sassafras tzumu， Semiliquidambar cathayensis， Pteroceltis tatarinowii， Cyclocarya paliurus， Pterocaryas tenoptera， Schima superba， Pterostyrax psilophyllus， Styrax suberifolia， Photinia davidsoniae， Gleditsia sinensis， Ormosia hosiei， Davidia involucrata， Cornus japonica-var. Chinensis， Eurycorymbus cavaleriei， Bretschneidera sinensis， Koelreuteria paniculata， Pistacia chinensis and Castanea henryi， which were not recommended for the application of edible fungi production.
Conclusion and Discussion
Selection of excellent raw material forest species for edible fungi
Based on the comprehensive evaluation system， the primary-selected tree species were divided into 3 grades. There were 16 broadleaf species having the comprehensive evaluation scores of ≥2.400 0， which were available as major tree species for edible fungi development in Guizhou； there were 10 broadleaf tree species with comprehensive evaluation scores of 2.100 0 ≤ Y < 2.400 0，which could be used as candidates for edible fungi production， while the 21 broadleaf species with the comprehensive evaluation scores of less than 2.100 0 were not recommended. Among the 16 tree species with the comprehensive evaluation scores of ≥2.400 0， the performances of 7 were verified by Weng et al.[2]， Zou et al.[4]， namely Liriodendron chinense， Quercus acutissima， Alnus cremastogyne， Betula luminfera， Elaeocarpus duclouxii， Elaeocarpus sylvestris， Choerospondias axillaris， and they could be vigorously developed； further production tests were needed for 9 species， such as Toona sinensis， Catalpa fargesii， Catalpa bungei， which needed further analysis and selection by measuring the production yield， amino acid content as well as the shape and quality determination of edible fungi. Castanea henryi， which was popularized vigorously in Zhejiang， only got the score of 1.939 0， which was mainly due to the lack of systematic research on all aspects of Castanea henryi in Guizhou Province.
Selection of excellent raw material forest species of selenium-enriched mushroom
The use of biological transformation method to produce natural selenium-enriched mushrooms has become a research hotspot at home and abroad[12]. It is of unique advantages for Guizhou to make full use of the rich selenium resources to develop green selenium-enriched mushroom industry， create the geographical brand of "selenium-enriched mushrooms" and build brand of selenium-enriched mushrooms. At present， there is no research and report on the selenium-enriched ability of tree species. Therefore， it is necessary to study the selenium enrichment ability of 16 species like Liriodendron chinense， Quercus acutissima and Alnus cremastogyne， so as to provide the basis for the development of natural selenium-enriched mushroom industry in Guizhou Province. References
[1] WENG YF， WANG RD， DU GJ， et al. Study on the selection and plantation technique of superior short-rotation wood forest for mushroom[C]. China Science and Technology Association. Harmonious development of energy conservation and environmental protection—Annual Meeting of China Association for Science and Technology in 2007 （III）. Beijing： Sound and Video Center， China Association for Science and Technology， 2007： 829-837.
[2] WENG YF， DU GJ， WANG RD， et al. Study and promotion of the cultivation techniques for short-rotation wood forest for mushroom[C]. Zhejiang Science and Technology Association. The Third Zhejiang Midwest Science and Technology Forum Proceedings （Volume III： forestry）. Hangzhou： Zhejiang Science and Technology Association， 2006.
[3] ZHU GQ， WU XQ， WANG KH， et al. Effects of tree ages on the output and content of the nutritive components of Lentinus edodes[J]. Chinese edible fungus， 2005， 24 （5）： 23-27.
[4] ZOU DM， ZHU GQ， WU SY， et al. Preliminary report on species selection of good mushroom wood[J]. Journal of Zhejiang Forestry Science and Technology， 1997， 17 （1）： 18-23.
[5] CHENG LL， ZHANG JB. Spatial and temporal evolution of main edible fungi species in China-based on Shiitake mushroom and Oyster mushroom[J]. Journal of Huazhong Agricultural University （Social Science Edition）， 2015 （5）： 48-58.
[6] ZHANG JX， JIA SM， ZUO XM， et al. NY 5099-2002， requirements for the technology of non-pollution food edible mushroom cultivation substrate safety[S]. Beijing： China Standard Press.
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