The plant diversity of agro-landscapes in typical maize planting areas in the Northeast Plain, China-A case study of Changtu County

Non-cropped habitats in agricultural landscapes constitute an important landscape for biodiversity preservation. Such habitats in agro-ecosystems can support both food production and biodiversity. In order to explore the relationship between plant species diversity and heterogeneity of agricultural landscape, and furthermore, to probe the suitable proportion of non-cropped habitats in agricultural landscape, we investigated plant diversity in Changtu County in the Northeast Plain, China. A total of 20 sampling plots (1 km×1 km) were selected for area proportions 0-50% of non-cropped habitats, and were divided into five groups according to area proportion of non-cropped habitats, which were 0-10%, 10%-20%, 20%-30%, 30%-40% and 40%-50%. The plant species in non-cropped habitats were investigated using the Braun-Blanquet method. The surveyed non-cropped habitats included woodland, grassland, ditch, orchard and field road. The heterogeneity indexes of agricultural landscape with different proportions of non-cropper habitats were calculated. The results showed that plant species diversity and evenness of agricultural landscapes gradually increased initially and later decreased with increasing area proportion of non-cropped habitats. Peak plant species diversity and evenness were in landscapes with 20%-30% area of non-cropped habitats. Meanwhile, plant species richness gradually increased initially and decreased later when area proportion of non-cropped habitats was 0-40%. However, peak plant species richness was in agricultural landscape with 40%-50% area of non-cropped habitats. The Shannon diversity index, Shannon evenness index of agricultural landscape increased with increasing of area proportion of non-cropped habitats, while landscape contagion metrics showed contrary tendency, indicating that lower area proportion of non-cropped habitats induced higher landscape dominance. The plant species with highest important values in different non-cropped habitats was Gramineae plants, but the species were different. The order of dominant degree of dominant species was orchard, ditch, grassland, field road and woodland. Species diversity and evenness in orchard, grassland and ditch were significantly higher than those in woodland and field road. Species richness (from high to low) was grassland, woodland, ditch, orchard and field road. There were obvious variation in plant community diversity among orchards, grasslands and ditches. The correlation between landscape heterogeneity and species diversity decreased from grassland to orchard, ditch, field road and to woodland. Thus the optimum area proportion of non-cropped habitats was 20%-30% within agricultural landscapes in typical maize planting areas in the Northeast Plains, China. Woodland and ditch had a positive effect on species diversity and on maintenance and conservation of hygrophytes. Different non-cropped habitats disturbances resulted in different correlation coefficients between landscape heterogeneity and plant species diversity. Thus future research should concentrate on comprehensive analysis of various factors such as area proportion of non-cropped habitats and habitat disturbances that influenced biodiversity, ecosystem services and agricultural production.