#1Article diversity MDPI Composition, Distribution, and Factors Affecting Invasive Plants in Grasslands of Guizhou Province of Southwest China Qin Yang 1, Baocheng Jin 10, Xuechun Zhao 1, Chao Chen 1, Hua Cheng 2, Huanhuan Wang 1, Dengming He 1, Yaoyao Zhang1, Jing Peng ³, Zhongcai Li 3 and Min Han ³,* 3 check for updates Citation: Yang, Q.; Jin, B.; Zhao, X.; Chen, C.; Cheng, H.; Wang, H.; He, D.; Zhang, Y.; Peng, J.; Li, Z.; et al. Composition, Distribution, and Factors Affecting Invasive Plants in Grasslands of Guizhou Province of Southwest China. Diversity 2022, 14, 167. https://doi.org/10.3390/ d14030167 Academic Editors: Michael Wink and Anatoliy A. Khapugin 1 2 3 * College of Animal Science, Guizhou University, Guiyang 550025, China; [email protected] (Q.Y.); [email protected] (B.J.); [email protected] (X.Z.); [email protected] (C.C.); [email protected] (H.W.); [email protected] (D.H.); [email protected] (Y.Z.) School of Tourism, Henan Normal University, Xinxiang 453000, China; [email protected] Guizhou Institute of Natural Resources Survey and Planning, Guiyang 550001, China; [email protected] (J.P.); [email protected] (Z.L.) Correspondence: [email protected]; Tel.: +86-139-8502-5461 Abstract: Southwest China is an important route for invasive species. In this study, 49 invasive plants of 15 families and 41 genera were found within 373 grassland sampling sites of Guizhou Province, a typical karst mountainous region with a high invasion risk located in Southwest China. Invasive plants could be found within over 90% of the grassland sampling sites, and malignant invasive species were found in 60% of the sites. In about 30% of the sampling sites, more than one malignant species coexisted. The malignant invasive species were mainly distributed in the southwestern part of Guizhou Province. Their distribution patterns were affected by environmental and traffic factors; they preferred areas with low elevation, high temperature, high rainfall, high soil nutrient content, and traffic accessibility and could adversely affect plant cover and biomass. Conversely, seriously invasive species and other low-level invasive species had a positive or neutral effect on grassland communities. Therefore, the focus of invasive plant control measures should be on malignant invasive species. Specific control policies and practices, especially in areas with resource-rich environments and well-developed traffic networks, should be carried out to facilitate grassland ecosystem sustainability and to prevent the spread of invasive species to inland China. Keywords: Ageratina adenophora; biodiversity; invasion risk; karst; soil nutrient content; traffic accessibility Received: 3 February 2022 Accepted: 24 February 2022 Published: 26 February 2022 Publisher's Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. CC BY Copyright: 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1. Introduction Alien invasive species, introduced outside of their natural range either intentionally or unintentionally by human activities [1], can significantly impact ecosystem functions [2–4] and biodiversity [5-8]. In particular, this can lead to a reduction in spontaneous species useful to humans (e.g., crop wild relatives) [9] and can cause economic damage to the in- vaded habitats [10,11]. This means effective and specific management measures are needed to facilitate the sustainability of ecosystems [12-14], which must include the involvement of plant systematics and an improvement of the floristic knowledge on invasive plant species [15]. Grasslands cover more than 13% of the global land surface [16-18] and are susceptible to alien invasive species. Resource and traffic accessibility are two key factors affecting biological invasion [19-21], and resource-rich habitats often experience more invasion than resource-poor ones [19,22]. For example, Phragmites australis (Cav.) Trin. ex Steud. benefits more from nitrogen addition than its native competitor Spartina pectinata Bosc ex Link [23]. Previous research conducted in the Czech Republic also found that alpine- subalpine grasslands at high elevations are more resistant to alien plant invasions than other grassland types [24]. Traffic networks could promote the spread of invasive plants Diversity 2022, 14, 167. https://doi.org/10.3390/d14030167 https://www.mdpi.com/journal/diversity#2Diversity 2022, 14, 167 2 of 16 and increase invasibility, depending on traffic volume, road density, road and other features of transportation corridors [20,21,25]. age, road type, China is one of the countries most vulnerable to invasive species (e.g., Eichhornia crassipes (Mart.) Solms, Ageratina adenophora (Spreng.) R.King & H.Rob., and Solenopsis invicta Bu- ren, 1972) [21,26-29]. Currently, it contains more than 500 invasive plant species (e.g., Solidago Canadensis L., Bidens pilosa L., and Spartina alterniflora Loisel.), including more than 30 malignant invasive species [30-32] (http://www.iplant.cn/ias/, accessed on 1 January 2022). Chinese grasslands contain more than 200 invasive plant species (e.g., Alternanthera philoxeroides (Mart.) Griseb., Chromolaena odorata (L.) R.King & H.Rob., and Erigeron sumatrensis Retz.) [32]. Southwest China is an important route for invasive species from Southeast Asia to inland China [30,33,34]. For example, Ageratina adenophora, native to Central Amer- ica, has been spreading into Southern China since the 1940s through Burma and Viet- nam [21]. The species is dispersing northwards and eastwards at an average speed of 20 km year¹ from the Yunnan-Guizhou Plateau to inland China [35]. Chromolaena odorata, also native to Central America, has spread to Southern China since the 1930s through Thailand [21]. Guizhou Province, located in Southwest China and a typical karst moun- tainous region, has one of the highest invasion risks in the country [36]. According to a previous study, the province hosts 30 invasive plant species [37], and subsequent studies mainly explored invasive plants in different regions of Guizhou Province and in some nature reserves (including Hongfeng Lake, Dashahe Nature Reserve, and Zhaozishan Nature Reserve, among others). For example, one study found 67 invasive plant species in Tongren City in the northeast [38], whereas other authors found 52 invasive plant species in Hongfeng Lake, Baihua Lake, and the Aha reservoir of Guiyang City in Central Guizhou [39]. Guo et al. determined 46 invasive plant species using 380 plots in the four nature reserves Chishui Alsophila, Xishui, Fanjingshan, and Mayanghe [40]. Other authors found 29, 16, 19, and 112 invasive plant species in Dashahe Nature Reserve [41], Zhaozishan Nature Reserve [42], Bijiang National Wetland Park [43], and Leigong Moun- tain National Nature Reserve [44]. Other studies focused on the histories, physiologi- cal and ecological characteristics, and potential distributions of specific invasive plants, including Ageratina adenophora [35,45-47], Chromolaena odorata [48,49], Soliva anthemifolia R.Br. [50], Xanthium mongolicum Kitag. [50,51], Alternanthera philoxeroides [52,53], Eichhornia crassipes [47], Solanum aculeatissimum Jacq. [47], Ambrosia trifida L. [54], Ageratum conyzoides L. [55], Cyclospermum leptophyllum (Pers.) Sprague ex Britton & P.Wilson [56], and Mikania micrantha Kunth [49,57]. Despite these efforts, there is no complete list, and the distribution patterns of invasive plant species in the grasslands of Guizhou Province, Southwest China, as well as the factors affecting their growth, are largely unclear. In this context, the objectives of this paper were to (1) provide a catalogue of invasive plants in the grasslands of Guizhou Province, (2) quantify the spatial distribution patterns of these plants, (3) quantify the factors affecting the distribution patterns, and (4) explore ap- propriate invasive plant management strategies in the grasslands of the Guizhou Province of China. 2. Materials and Methods This study was conducted in Guizhou Province, Southwest China (24°37'-29°13' N, 103°36'-109°35' E; 150-2900 m elevation; Figure 1). The climate is a humid subtropical monsoon climate, with a mean (1981-2010) annual temperature of 14.2 °C and a mean annual precipitation of 1069.9 mm. The mean daily temperatures of the coldest (January) and warmest (July) months are 4.4 and 22.2 °C, respectively (data from the China Meteo- rological Data Center; https://data.cma.cn/, accessed on 11 July 2021). Although forest is the main vegetation type, there are about 200,000 hectares of grassland including nat- ural grasslands, artificial grasslands, and abandoned fields in Guizhou Province (data from the third national land survey of China). According to the FAO 90 taxonomy [58], the main soils are Haplic Alisols, Haplic Luvisols, and Dystric Regosols. The terrain is a#3Diversity 2022, 14, 167 25° N 27° N 29° N 3 of 16 hilly mountainous karst area, and the grassland plant community is mainly composed of Arthraxon hispidus (Thunb.) Makino, Artemisia argyi H.Lév. & Vaniot, Imperata cylindrica (L.) P.Beauv., Eragrostis pilosa (L.) P.Beauv., Miscanthus floridulus (Labill.) Warb., Ficus tikoua Bureau, Erigeron annuus (L.) Desf, Erigeron acris L., and Agrimonia pilosa Ledeb. 105° E 108° E 105° E Bijie Guiyang Zunyi Tongren Qiandongnan Liupanshui Anshun Qiannan Qaxinan 0 50 100 Km Sampling Sites 108° E 25° N 27° N Figure 1. Distribution of the sampling sites in Guizhou Province, Southwest China. The geographic coordinate system of the map is the China Geodetic Coordinate System 2000. Overall, 373 sampling sites, covering nearly all counties of Guizhou Province, were established from July to October in 2021. Within each sampling site, 20 sampling plots (1 × 1 m in size and well separated from each other) were surveyed to determine the plant community composition. At the same time, within each site, three sampling plots (1 × 1 m in size and well separated from each other) were established, and their numbers of species, average plant height, plant cover, and plant biomass for both invasive and non- invasive species were determined. The aboveground vegetation in each plot was collected by species. Plant samples were dried for 90 h at a temperature of 60 °C and weighed to determine aboveground plant biomass. The publications "Alien invasive plants in Chinese grassland" [32], "Invasive alien species of China" (website: http://www.iplant.cn/ias/, accessed on 1 January 2022), and "The checklist of the Chinese invasive plants" [30,31] were used to determine whether a plant was an invasive plant. The invasion levels of each plant species were classified according to previous publications [30,31], using the following five levels: 1, malignant invasive species, that cause malignant economic and ecological damage at a national scale and affect more than one geographical region; 2, seriously invasive species, that cause serious economic and ecological damage at a national scale and affect more than one geographical region; 3, local invasive species, that cause local economic and ecological damage within one or more geographical regions but not nationwide; 4, general invasive species, that will not cause serious or obvious economic and ecological damage based on their biological and ecological characteristics and will most likely not cause new invasions; 5, species requiring further observation; these are newly found, newly reported, or poorly understood species whose invasion trends require further observation. N 29° N#4Diversity 2022, 14, 167 4 of 16 We collected the corresponding environmental factors of each site, including mean (1970-2000) annual temperature, mean (1970-2000) annual precipitation, elevation, and SOC (Table 1) [58,59]. We also collected traffic network data (including railways, express- ways, national roads, and country roads) from the GIM-Cloud (geographical information monitoring cloud platform, http://www.dsac.cn/, accessed on 1 January 2022), and the dis- tance from each sampling site to the closest road was calculated using ArcMap (version 10.8, ESRI, Redlands, CA, USA). Their Pearson correlations with plant invasion intensity (namely the number and biomass of invasive species) were calculated using IBM SPSS Statistics (version 19, IBM). Table 1. Possible environmental and traffic network factors affecting invasive plant distribution. Item Mean annual temperature Mean annual precipitation Elevation SOC Traffic Network Source WorldClim Data version 2.1 (https://www.worldclim.org/, accessed on 1 January 2022) ASTER GDEM (https://www.gscloud.cn/, accessed on 1 January 2022) Harmonized World Soil Database version 1.21 (http://webarchive.iiasa.ac.at/Research/LUC/External-World- soil-database/, accessed on 1 January 2022) Geographical Information Monitoring Cloud Platform (http://www.dsac.cn/, accessed on 1 January 2022) 3. Results 3.1. Catalogue of Invasive Plants Overall, 49 invasive plant species, belonging to 15 families and 41 genera, were found within the 373 grassland sampling sites (Table 2). Asteraceae (19 species), Poaceae (6 species), Amaranthaceae (5 species), and Fabaceae (4 species) were the main families, with Ipomoea L. (3 species), Trifolium Tourn. ex L. (2 species), Sonchus L. (2 species), Ambrosia L. (2 species), Crassocephalum Moench (2 species), Solanum L. (2 species), and Veronica L. (2 species) being the main genera (Table 2). Trifolium repens L., Bidens Pilosa, and Ageratina adenophora appeared in more than 20% (41.29, 39.14, and 23.06%) of the sampling sites. Cyperus rotundus L. and Praxelis clematidea (Griseb.) R.King & H.Rob. ap- peared in 10-20% (15.01 and 14.75%) of the sampling sites, whereas Erigeron sumatrensis, Sonchus wightianus DC., Crassocephalum crepidioides (Benth.) S.Moore, Solanum quitoense Lam., Chromolaena odorata, and Avena fatua L. were present in 5-10% of the sampling sites. Trifolium pretense L., Alternanthera philoxeroides, and Ageratum conyzoides, along with 10 other species, were found in 1-5% of the sampling sites. As relatively rare species, Euphorbia dentate Michx., Dysphania ambrosioides (L.) Mosyakin & Clemants, Solanum aculeatissimum, Ambrosia trifida, Ambrosia artemisiifolia L., and Solidago Canadensis, along with other species, appeared in less than 1% of the sampling sites. There was no significant difference in the average frequencies among the five invasive levels. Invasive plants were found in over 90% (90.35%) of the grassland sampling sites, whereas malignant invasive plants were detected in about 60% (59.79%) of all sites. Fur- thermore, in about 30% (29.23%) of the sampling sites, more than one malignant invasive species coexisted. There may be two (57 sites, 15.28%), three (39 sites, 10.46%), four (12 sites, 3.22%), or five (1 site, 0.27%) malignant invasive plant species within one site. Overall, 15 invasive plants, including Chromolaena odorata, Erigeron sumatrensis, Bidens pilosa, and others, were classified as malignant invasive plants (Level 1), whereas 12 species, including Trifolium pratense L., Avena fatua, and others, were classified as seriously invasive plants (Level 2). Five species, namely Pennisetum purpureum Schumach., Paspalum dilatatum Poir., Oenothera rosea Aiton, Veronica persica Poir., and Euphorbia dentate, were local invasive plants (Level 3). Ten species, including Medicago sativa L., Sida acuta Burm. fil., and others, were classified as general invasive species (Level 4), and seven species, including#5Diversity 2022, 14, 167 5 of 16 Amorpha fruticose L., Axonopus compressus (Sw.) P.Beauv., and others, were species requiring further investigations (Level 5). Table 2. Catalogue of invasive plants in grasslands of Guizhou Province, Southwest China. The five invasion levels are as follows: malignant invasion (Level 1), serious invasion (Level 2), local invasion (Level 3), general invasion (Level 4), and plants requiring further observation (Level 5) [30,31]. Name Frequency (%) Rank Family Invasive Level 1 Asteraceae Bidens pilosa L. 1 2 Asteraceae Ageratina adenophora (Spreng.) R.King & H.Rob 1 Source Area America Mexico 39.14 23.06 Praxelis clematidea (Griseb.) 3 Asteraceae 1 South America 14.75 R.King & H.Rob 4 Asteraceae Erigeron sumatrensis Retz. 1 South America 9.65 5 Asteraceae Chromolaena odorata (L.) R.King & H.Rob 1 Mexico 6.97 9 Amaranthaceae Alternanthera philoxeroides (Mart.) Griseb 1 Brazil 4.02 7 Asteraceae Ageratum conyzoides L. 1 Tropical America 3.75 8 Convolvulaceae Ipomoea purpurea (L.) Roth 1 America 2.95 6 Dysphania ambrosioides (L.) Amaranthaceae 1 Mosyakin & Clemants Tropical America 0.8 10 Convolvulaceae Ipomoea cairica (L.) Sweet 1 America 0.27 Central America, 11 Asteraceae Ambrosia artemisiifolia L. 1 0.27 North America 12 Asteraceae Ambrosia trifida L. 1 North America 0.27 13 Asteraceae Parthenium hysterophorus L. 1 Tropical America 0.27 14 Asteraceae Solidago canadensis L. 1 North America 0.27 15 Amaranthaceae Amaranthus spinosus L. 1 Tropical America 0.27 North Africa, 16 Fabaceae Trifolium repens L. 2 Central Asia, 41.29 West Asia, Europe 17 Crassocephalum crepidioides (Benth.) 17 Asteraceae 2 Africa 7.51 S.Moore South Europe, 18 Poaceae Avena fatua L. 2 6.17 Mediterranean North Africa, 2222 19 Fabaceae 20 Apiaceae 21 Trifolium pratense L. 2 4.83 Central Asia, Europe Daucus carota L. Solanaceae Amaranthaceae Solanum aculeatissimum Jacq. 22 Europe 2.68 Brazil 0.8 Celosia argentea L. 2 India 0.8 23 Nyctaginaceae Mirabilis jalapa L. 2 Tropical America 0.54 24 Amaranthaceae Gomphrena celosioides L. 2 Tropical America 0.54 25 Convolvulaceae Ipomoea triloba L. 2 India 0.27 26 Cactaceae Opuntia dillenii (Ker Gawl.) Haw. 2 Caribbean 0.27 27 Asteraceae Tridax procumbens L. 2 Tropical America 0.27 28 Poaceae Paspalum dilatatum Poir. 3 South America 3.22 29 Poaceae Pennisetum purpureum Schumach. 3 Africa 2.68#6Diversity 2022, 14, 167 6 of 16 Table 2. Cont. Rank Family Name Invasive Level Source Area Frequency (%) 30 Euphorbiaceae Euphorbia dentata Michx. 3 North America 0.8 31 Scrophulariaceae Veronica persica Poir. 3 West Asia 0.54 32 Onagraceae Oenothera rosea Aiton 3 Tropical America 0.54 33 Cyperaceae Cyperus rotundus L. 4 India 15.01 Europe, 34 Asteraceae Sonchus oleraceus L. 4 7.77 Mediterranean 55 35 Poaceae Setaria palmifolia (J. Koenig) Stapf 4 Africa 3.22 36 Asteraceae Sonchus asper (L.) Hill Europe, 4 1.34 Mediterranean 37 Fabaceae Medicago sativa L. 4 West Asia 1.07 38 Malvaceae Sida acuta Burm. fil. 4 Tropical America 0.54 39 Scrophulariaceae South Europe, Veronica arvensis L. 4 0.27 West Asia Europe, Central Asia, 40 Asteraceae Cichorium intybus L. 4 West Asia, 0.27 North Africa 41 Asteraceae Helianthus tuberosus L. 4 North America 0.27 42 Asteraceae Senecio vulgaris L. 4 Europe 0.27 43 Solanaceae Solanum quitoense Lam. 5 Asia 7.51 44 Poaceae Axonopus compressus (Sw.) P.Beauv. 5 Tropical America 3.49 45 Asteraceae Crepis tectorum L. 5 Europe 1.34 46 Iridaceae Sisyrinchium rosulatum E.P.Bicknell 5 North America 0.54 Crassocephalum rubens 47 Asteraceae 5 (Juss. ex Jacq.) S.Moore Tropical Africa 0.54 48 49 49 Poaceae Fabaceae Chrysopogon zizanioides (L.) Roberty 5 Amorpha fruticosa L. 5 India America 0.27 0.27 All malignant invasive plant species originated from America (including Brazil, Mex- ico, South America, Tropical America, Central America, and North America). Five of the seriously invasive plants originated from America and seven from Africa, Europe, and Asia. Three of the local invasive plants originated from America and two from Africa and Asia. Two of the generally invasive plants originated from America and eight from Africa, Europe, and Asia. Three species requiring further investigations originated from America and four from Africa, Europe, and Asia (Table 2). 3.2. Distribution of Invasive Plants Regarding the malignant invasive species, Bidens pilosa covered most regions of Guizhou Province (Figure 2a), whereas Ageratina adenophora was mainly found in the south- western part (Figure 2b). Praxelis clematidea was mainly reported from the southern part (Figure 2c) and Erigeron sumatrensis from the eastern part (Figure 2d). Chromolaena odorata had its main distribution range in the southeastern part (Figure 2e). Alternanthera philoxeroides was mainly found in the central and eastern parts (Figure 2f), whereas Ageratum conyzoides was mostly located in the central and southern parts (Figure 2g) and Ipomoea purpurea (L.) Roth in the southwest part (Figure 2h). Occasional species, such as Dysphania ambrosioides, Ambrosia artemisiifolia, Solidago canadensis, Parthenium hysterophorus L., Amaranthus spinosus L., and Ipomoea cairica (L.) Sweet were found in different regions (Figure 2i).#7Diversity 2022, 14, 167 27° N 29° N 25° N 27° N 29° N 25° N 25° N 105° E 1 (a) Bidens pilosa Guiyang 108° E Tongren Qiandongnan pans Ans Qiannan 105° E 105° E Ominan ⚫ Detected 0 25 50 Km (c) Praxelis clematidea 108° E 108° E Undetected unyi Tongien Guiyang Qiandongnan Lpansin Anshun Qiannan 105° E 105° E Oinan ⚫ Detected 0 25 50 Km (e) Chromolaena odorata 105° E 105° E Qianxinan (g) Ageratum conyzoides Guiyang Guiyang Qiannan 108° E 108° E ⚫ Undetected Tongren Qiandongnan ⚫ Detected 0 25 50 Km Undetected 108° E 108° E anyi Tongren Qiandongnan Lipansk Anshun Qiannan 105° E Qaxinan • Detected 0 25 50 Km ⚫ Undetected Figure 2. Cont. 108° E N 25° N N Z 25° N 25° N 27° N N 25° N 25° N 25° N 105° E 1 (b) Ageratina adenophora 105° E 105° E Guiyang 108° E Zanyi Tongren Qiandongnan Ansh Qiannan N z inan 0 25 50 Km ⚫ Detected Undetected 25 (d) Erigeron sumatrensis Zanyi 108° E 108° E © Tongtern Guiyang Qiandongnan Lipansk Anshun Qiannan 105° E 105° E Qianxinan 0 25 50 Km (f) Alternanthera philoxeroides Guiyang 108° E 108° E ⚫ Detected ⚫Undetected unyi Tongren Qiandongnan s Anshum Qiannan 105° E 105° E N N Z Manxinan ⚫ Detected 0 25 50 Km 2 ⚫ Undetected (h) Ipomoea purpurea Guiyan 108° E 108° E anyi Tongren Qiandongnan Lipansk Anshun Qiannan 105° E Qinan ⚫ Detected 0 25 50 Km 108° E ⚫ Undetected N Z Z 7 of 16#8Diversity 2022, 14, 167 25° N 27° N 29° N 25° N 27° N 29° N T z (i) Others 105° E Guiyang Zunyi 108° E Tongrens Qiandongnan Lipansm Anshun Qiannan 105° E 105° E (a) Trifolium repens Qrankinan ⚫ Detected 0 25 50 Km • Undetected 108° E 8 of 16 Figure 2. Distribution of malignant invasive species (Level 1). Red and grey dots indicate detected and undetected invasive species, respectively. Regarding the seriously invasive species, Trifolium repens, Crassocephalum crepidioides, Avena fatua, and Trifolium pretense covered most regions of Guizhou Province (Figure 3a-d), whereas Daucus carota L. was concentrated in the central part of Guizhou Province (Figure 3e). Occasional species, such as Solanum aculeatissimum, Celosia argentea L., Gomphrena celosioides L., Mirabilis jalapa L., Tridax procumbens L., and Opuntia dilleniid (Ker Gawl.) Haw., were found in various different regions (Figure 3f). Guiyang 108° E Zunyi Tongren Qiandongnan Liansu Ans Qiannan 105° E 105° E (c) Avena fatua Qianxinan Detected 0 25 50 Km Undetected Bijie Guiyang nyi 108° E 108° E ⚫Tongren Qiandongnan Bansk Anshum Qiannan 105° E Qianxinan Detected 0 25 50 Km Figure 3. Cont. 108° E Undetected 25° N 27 N 105° E N Z (b) Crassocephalum crepidioides No6 25 25° N 25° N 25° N 27° N Guiyang 108° E Zenyi ongren Qiandongnan ansu Ansam Qiannan 105° E 105° E Qraxinan 0 25 50 Km (d) Trifolium pratense Guiyang 108° E 108° E Detected ⚫Undetected Lunyi Tongren Qiandongnan Limpansuk Anshum Ofannan 105° E Qianxinan ⚫ Detected 0 25 50 Km 108° E ⚫ Undetected N N 25° N 27° N#9Diversity 2022, 14, 167 Z 25 27° N 29° N 25° N 27° N 105° E (e) Daucus carota Biji Guiyang 108° E Zunyi Tongren Qiandongnan Lipansu Anshum Qiannan • 105° E 105° E kinan 0 25 50 Km Detected • Undetected 108° E 25° N (f) Others 105° E 108° E Tongten Qiandongnan Lipans Anshun Qannan 105° E Qrankinan 0 25 50 Km ⚫ Detected Undetected 108 E A Z 9 of 16 Figure 3. Distribution of seriously invasive plants (Level 2). Red and grey dots indicate detected and undetected invasive species, respectively. Regarding locally invasive plants, Paspalum dilatatum was mainly found in the cen- tral part of Guizhou Province (Figure 4a) and Pennisetum purpureum in the central part (Figure 4b). Occasional species, such as Euphorbia dentata Michx., Oenothera rosea, and Veronica persica, were located in different regions (Figure 4c). 1 (a) Paspalum dilatatum 108° E Zenyi Tongfen 105° E Z Z 29 (b) Pennisetum purpureum 108° E Zenyi ° Tongten Guiyang Guiyang Qiandongnan Qiandongnan Lipansu Anshum Qiannan Lipans Anshun Qiannan (c) Others 105 E 105° E Onxinan 0 25 50 Km • Detected Undetected Guiyang nyi 108°E 108° E Tongrens Qiandongnan Lisansl Anshum Qiannan 105° E Qrxinan ⚫ Detected 0 25 50 Km Undetected 108° E 105° E Ormxinan 0 25 50 Km Detected Undetected 108°E N Figure 4. Distribution of locally invasive plants (Level 3). Red and grey dots indicate detected and undetected invasive species, respectively. Regarding general invasive plants, Cyperus rotundus and Sonchus oleraceus L. were present in most regions of Guizhou Province (Figure 5a,b), whereas Setaria palmifolia (J. Koenig) Stapf was mainly found in the southern part (Figure 5c). Occasional species, in-#10Diversity 2022, 14, 167 27° N 29° N 25° N 27° N 29° N 105° E (a) Cyperus rotundus 10 of 16 cluding Sonchus asper (L.) Hill, Medicago sativa, Sida acuta, Cichorium intybus L., Senecio vulgaris L., Helianthus tuberosus L., and Veronica arvensis L., were located in different regions (Figure 5d). Guiyang 108° E nyi Tongren Qiandongnan Bansk Anshum Onnan 105° E 105° E Orixinan (c) Setaria palmifolia 0 25 50 Km nyi 108° E 108° E Detected • Undetected • Tongren N 25° N 29 N Z Z 29 25° N 105° E (b) Sonchus oleraceus (d) Others Guiyang 108° E Zunyi Tongrens Qiandongnan pans Anshum Qiannan 105° E 105° E Orankinan 0 25 50 Km • Detected Undetected 25 108° E 108° E Bijie Guiyang Zunyi Tongren Guiyang Qiandongnan Qiandongnan Lipansu Anshun Qiannan Lipansu Anshum Qiannan 105° E Orankinan Detected 0 25 50 Km Undetected 108 E 105 E Qraakinan 0 25 50 Km • Detected Undetected 108 E N Z Figure 5. Distribution of generally invasive plants (Level 4). Red and grey dots indicate detected and undetected invasive species, respectively. Regarding the invasive plants requiring further investigations, Solanum quitoense and Axonopus compressus were mainly found in the southwestern part of Guizhou Province (Figure 6a,b) and Crepis tectorum L. in the western part (Figure 6c). Occasional species, including Crassocephalum rubens (Juss. ex Jacq.) S.Moore, Sisyrinchium rosulatum E.P.Bicknell, Amorpha fruticose, and Chrysopogon zizanioides (L.) Roberty were located in various different regions (Figure 6d). 3.3. Factors Affecting the Distribution of Invasive Plants At the sampling plot scale, we found 0.43 ± 0.49 (mean ± std) invasive species within each 1 × 1 m sampling plot, including 0.17 ± 0.36 malignant invasive species, 0.19 ± 0.34 seriously invasive species, 0.01 ± 0.08 locally invasive species, 0.05 ± 0.14 gen- erally invasive species, and 0.01 ± 0.06 species requiring further observation. The total biomass of all invasive species within each sampling plot was 11.08 ± 25.35 g, among which malignant invasive species, seriously invasive species, locally invasive species, generally invasive species, and species requiring further observation accounted for 3.28 ± 11.54 g, 4.71 ± 16.98 g, 0.40 ± 5.16 g, 2.64 ± 14.86 g, and 0.05 ± 0.43 g, respectively. For the malignant invasive species, there was a significant negative correlation be- tween plant invasion intensity (namely the number and biomass of invasive species) and elevation, and a positive correlation for precipitation, temperature, SOC, and distance to roads (Table 3). For the seriously invasive species, there was a significant positive correlation between plant invasion intensity and elevation and a negative correlation for precipitation, temperature, and SOC (Table 3). The correlations with distance to roads were#11Diversity 2022, 14, 167 27° N 29° N 25° N 27° N 105° E (a) Solanum quitoense 11 of 16 inconsistent for different types of roads (Table 3). The invasion intensity-environmental factors correlation was weak for locally invasive plants, generally invasive plants, and invasive plants requiring further investigations (Table 3). Guiyang 108° E Zunyi Tongren Qiandongnan ansl Anshum Qiannan Orakinan ⚫ Detected 0 25 50 Km L • Undetected 105° E 108° E 105° E (c) Crepis tectorum Guiyang, 108° E Zenyi Tongfen Qiandongnan Pansu Anshun Qiannan 105° E Qaxinan Detected 0 25 50 Km • Undetected 108°E 25° N 25° N 29° N 25° N 105° E (b) Axonopus compressus Guiyang 108° E nyi •Tongren Qiandongnan pansan Anshum Qiannan (d) Others 105° E 105° E 105° E Qraxinan 0 25 50 Km 108°E 108° E • Detected Undetected Zenyi Tongren Guiyang Anshum Qiannan 0 Qiandongnan Qnxinan ⚫ Detected 0 25 50 Km • Undetected 108 E N Z 29 Figure 6. Distribution of invasive plants requiring further investigations (Level 5). Red and indicate detected and undetected invasive species, respectively. grey dots Table 3. Pearson's correction coefficients between plant invasion intensity and environmental factors. * indicates significant correlation at the level of 0.05. Invasive Level Elevation Precipitation Temperature SOC Distance to Railways Distance to Expressways Distance to National Roads Distance to Country Roads 1 -0.24* 0.30 * 0.39* 0.18* 0.14* 0.03 0.18* 0.01 Number of 2 0.38 * -0.33* -0.44* -0.11 * -0.06 0.16* 0.01 -0.16* Invasive 3 0.11* -0.02 -0.08 0.00 0.00 -0.01 0.21 * -0.08 Species 4 -0.01 0.02 0.02 0.00 -0.10 -0.07 -0.04 0.03 5 0.05 0.04 -0.01 -0.06 0.01 -0.08 -0.01 0.04 1 -0.15* 0.22* 0.26* 0.14* 0.09 0.00 0.08 0.06 Biomass of 2 0.23 * -0.23* -0.25* -0.07 0.04 0.05 -0.04 -0.11* Invasive 3 0.03 -0.03 -0.02 -0.03 -0.04 0.03 0.10 Species 4 0.00 0.01 0.00 0.09 -0.09 -0.08 -0.08 5 0.04 0.07 0.02 -0.05 -0.02 -0.07 0.02 -0.03 0.03 -0.06 Regarding the malignant invasive species, there were significant negative correlations between invasion intensity and plant cover and biomass, but these correlations were not significant for number of species and plant height (Table 4). There also was a significant positive correlation between the invasion intensity of seriously invasive species and number of species, and a negative correlation for plant height, but these correlations were not significant for plant cover and biomass (Table 4). There was a trend toward negative#12Diversity 2022, 14, 167 12 of 16 correlations between the invasion intensity of local invasive species and plant height, a positive correlation between the invasion intensity of general invasive species and plant cover, and a negative correlation between the invasion intensity of species requiring further observation and plant cover and biomass (Table 4). Table 4. Pearson's correlation coefficients between invasion intensity and plant community character- istics. * indicates significant correlation at the level of 0.05. Number of Invasive Species Biomass of Invasive Species Invasion Level Number of Species Height Plant Cover Biomass 1234512345 -0.09 0.08 -0.13* -0.15* 0.33 * -0.46 * 0.09 -0.05 0.06 -0.10* -0.02 -0.07 -0.01 -0.07 0.07 -0.04 -0.01 -0.06 -0.14* -0.11* -0.07 0.05 -0.13* -0.10 0.10* -0.32 * 0.08 -0.05 -0.01 -0.06 -0.01 -0.02 -0.06 -0.06 0.13* 0.07 0.00 -0.08 -0.12* -0.10 4. Discussion 4.1. Grasslands in Guizhou Province Are Severely Invaded by Non-Native Species Southwest China is an important route for invasive species [30,33,34]. Guizhou Province, located in Southwest China, is an important part of the invasion route and has one of the highest invasion risks [36]. Although previous studies have found that the number of alien invasive plant species in Guizhou Province is lower than that in the southwestern neighboring provinces of Yunnan and Guangxi, the number is close to that of other inland neighboring provinces such as Hunan and Chongqing and exceeds that of inland provinces such as Gansu and Shanxi [30]. This paper provides a catalogue of invasive plants in the grasslands of Guizhou Province of China and quantifies their spatial distribution patterns. Invasive plants (15 families, 41 genera, 49 species) in the grasslands of Guizhou Province accounted for about 30% of the grassland plants in China (41 families, 123 genera, 183 species) [32] and were more numerous than those within the grasslands of three northeastern provinces in China (12 families, 35 genera, 38 species) [60]. However, their number was much lower than that of the invasive plants found within the Serengeti- Mara ecosystem in East Africa (245 species) [61], the Chilean Mediterranean grasslands (66 species) [62], and the Leigong Mountain National Nature Reserve (38 families, 88 genera, 112 species) [44] and close to that of Hongfeng Lake, Baihua Lake, and the Aha Reservoir of Guiyang City in central Guizhou (52 invasive plants from 20 families) [39]. However, it was greater than that of the invasive plants found in other nature reserves of Guizhou Province [40-43]. Fifteen invasive plant species, namely Chromolaena odorata, Erigeron sumatrensis, Bidens pilosa, Ageratum conyzoides, Praxelis clematidea, Ambrosia trifida, Ambrosia artemisiifolia, Solidago canadensis, Parthenium hysterophorus, Ageratina adenophora, Dysphania ambrosioides, Alternanthera philoxeroides, Amaranthus spinosus, Ipomoea cairica, and Ipomoea purpurea, were classified as malignant invasive plants. They all originate from America (including Brazil, Mexico, South America, Tropical America, Central America, and North America), which is in agreement with previous studies reporting that Southern and Northern America were the first and second source areas, respectively, for invasive plant species in China [30]. Species originating from America account for more than 50% of the grassland invasive plants [32], suggesting that species from America should be the focus of invasive plant management policies and practices in the future in Guizhou Province.#13Diversity 2022, 14, 167 13 of 16 The malignant invasive species could adversely affect plant cover and biomass. This is consistent with previous research showing a negative correlation between grassland cover and the intensity of invasion [63]. The ecological processes leading to these correlations warrant future research. Invasive plant species were present in more than 90% of the grassland sampling sites, and malignant invasive species were found in about 60% of these sites. In about 30% of the sampling sites, more than one malignant species coexisted. There were 0.43 (or 11.08 g in weight) invasive species, including 0.17 (or 3.28 g in weight) malignant invasive species within each 1 × 1 m sampling plot; these percentages indicate over 20,000 and 6000 tons of invasive species and malignant invasive species in Guizhou Province, respectively, given that the total grassland area is about 200,000 hectares (data from the Third National Land Survey of China). Therefore, this paper addressed the severe plant invasion problem of the grassland of the Guizhou Province. 4.2. Distribution Pattern, Affecting Factors, and Management Implications The malignant invasive species were mainly distributed in the southwestern part of Guizhou Province. This is consistent with the spreading trend for these newly introduced malignant invasion plants from southwest to inland China [35,36,45,46,64]. These malig- nant invasive species prefer areas with low elevation, high temperature, high rainfall, high soil nutrient contents, and traffic accessibility, which is consistent with their biological characteristics [64-66] and the results of previous studies [19-21,67,68]. This is also con- sistent with previous studies conducted in the Czech Republic, where alpine-subalpine grasslands were more resistant to alien plant invasions [24]. Although these malignant invasive species do not affect the number of species and plant height, they could adversely affect plant cover and biomass, suggesting that they have negative impacts on the local grassland ecosystem. The seriously invasive species tended to be distributed in areas with high elevation, low temperature, low rainfall, and low soil nutrient content. Most likely, this is due to the fact that these plants are mainly forage plants, such as Trifolium repens, Avena fatua, Trifolium pretense, and Daucus carota [69], and have been intentionally introduced to these areas to improve grassland [70,71]. Therefore, the seriously invasive species could enrich plant biodiversity without reducing the height, cover, and biomass of local grassland ecosystems, suggesting that they have positive impacts. Regarding other low-level invasive species (including local invasive plants, general invasive plants, and invasive plants requiring further investigation), their plant invasion intensity was lower than that of malignant and seriously invasive species. Although there was a trend toward negative correlations between the invasion intensity of local invasion species and plant height, and a positive correlation between the invasion intensity of generally invasive species and plant cover, this was inconsistent for the number and biomass of invasive species. The invasion intensity of species requiring further observation, however, surprisingly showed obvious negative effects on the plant cover and biomass of grassland. Considering the intensity and invasion levels [30,31], and their correlations with plant community characteristics, we suggest that these low-level invasive species had an effect close to neutral on grassland ecosystems, but further research is needed. At the same time, the interactions and correlations among environmental factors (such as between temperature and elevation) deserve further studies. In summary, the focus of invasive plant control measures should be on malignant invasive species, which could adversely affect plant cover and biomass. In particular, the five malignant invasive species (Bidens pilosa, Ageratina adenophora, Praxelis clematidea, Erigeron sumatrensis, and Chromolaena odorata) that appeared in over 5% of the sampling sites require further attention. Seriously invasive species and other low-level invasive species were positive or neutral to grassland ecosystems. Given the wide distribution of invasive plants in this area, specific control policies and practices, especially in areas with resource-rich environments and a well-developed traffic network, should be carried out to#14Diversity 2022, 14, 167 14 of 16 facilitate grassland ecosystem sustainability and to prevent the spread of invasive species to inland China. Author Contributions: Conceptualization, Q.Y., M.H., B.J. and X.Z.; methodology, Q.Y., B.J., X.Z., H.C., H.W., D.H., C.C. and Y.Z.; software, Q.Y., M.H., J.P. and Z.L.; validation, Q.Y., B.J., X.Z. and J.P.; investigation, Q.Y., B.J., X.Z., H.C., H.W., D.H., Y.Z., J.P., Z.L., C.C. and M.H.; writing-original draft preparation, Q.Y., M.H., B.J., X.Z. and H.C. All authors have read and agreed to the published version of the manuscript. Funding: This work was supported by grants from the National Natural Science Foundation of China (31700390) and Guizhou University (2016-75), Qian Ke He Zhicheng ([2020]1Y076 and [2021]YIBAN503) from the Science and Technology Department of Guizhou Province, and the Guizhou provincial grassland resource survey project from the Guizhou Department of Natural Resources. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. 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