Invasive Plant Species Distribution

Diversity 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

View entire presentation