Abstract: Stony desert shrub forests with similar habitat factors and vegetation development were investigated using twelve 200 m² (20 m×10 m) plots, including ninety-six 25 m² (5 m×5 m) subplots in central Guizhou karst desertification area. We assessed the impacts of plot size on plant diversity using the improved nest method, to provide a scientific framework for determining the minimum sampling plot size. Our results showed that an increase in the ordered sampling area in stony desert shrub forest caused the increase of the values of Patrick index, Gleason index and Margalef index, while caused the values of Shannon index, Pielou index and Alatalo index to increase first and then decrease. There was a significant difference in the values of six plant diversity indices among the different plot sizes. Simpson index and McIntosh index increased first and then decreased, but there was no significant difference between the two indices for the plot sizes. We classified the eight diversity indices into two groups according to the information retention rate ≥80%: for the 100 m² plot size, the Patrick index that reflects the number of species was selected, and for the 25 m² plot size, the Gleason index, Margalef index, Simpson index, Shannon index, Pielou index, Alatalo index and McIntosh index that reflect plant diversity and evenness were selected. The Connor & McCoy model, with eight plant diversity index values, had a better fitting effect, the de Caprariis model and MichaelsMenton model had a worse fitting effect, and the Arrhenius model and Logistic model with Patrick index and Margalef index had a better fitting effect. There was a significant correlation between the eight plant diversity indices and the average height of shrubs and the average coverage of herbs, but no significant correlation between these indices and the average height of herbs across the 96 subplots. Results of principal component analysis showed that the contribution rates of site elements, stand density and stand spatial properties to the shrub diversity were 4.3%-11.7%, 35.4%-67.9%and 20.4%-60.2%, respectively. The shrub diversity was mainly affected by forest structure and development level.

Key words: biochar, soil water infiltration, cumulative infiltration, permeability, stable infiltration rate.