Vegetation and species diversity patterns in conservation areas near big cities are poorly known. These are important recreational areas used also for educational purposes. Therefore, investigations of local diversity patterns are urgently needed. The Baihua Mountain Reserve is close to the city of Beijing and is the northern end of the Taihang mountain range in north China. Sixty-one 10 3 20 m quadrats of plant communities were established along gradients for elevation (750-2043 masl) and disturbance (mainly due to tourism and agriculture). Data on species composition and environmental variables were measured and recorded in each quadrat. Two-way indicator species analysis and canonical correspondence analysis (CCA) were used to analyze the relationships between vegetation and environmental variables, while species diversity indices were used to analyze the pattern of species diversity. Twelve plant communities were found, mostly secondary forests with some plantations. These communities are representative of the vegetation in the mountains west of Beijing. Each community had a different composition, structure, and environment. The variation of plant communities was significantly related to elevation and disturbance and related to litter thickness, slope, and aspect. The cumulative percentage variance of species-environment relationships for the first 4 CCA axes was 89.6%. Elevation and disturbance intensity were revealed as the factors that most influenced community distribution and species diversity. Species richness, heterogeneity, and evenness all showed a ''humped'' pattern along elevational and disturbance gradients-the highest species diversity appeared in the middle elevation and under medium disturbance intensity. Recommendations regarding management measures are made.
The studying of the performance of weeds and weed assemblages associated with different crops through phytosociological researches derives its importance mainly from weeds adverse impact on crop productivity. Hopefully, the current study is bene cial for developing a sustainable long term weed control and soil management strategy. The objective of the present work is to measure three ecological preferences: crop diversi cation, soil type and crop seasonality. A sample area was selected comprising farmland of Nile Delta and its adjoining east and west territories, Egypt. Sixty-four sites in 12 governorates comprising 30 agroecosystems were monitored. 150 species were designated as most in uential weed-species out of 555 species recorded. Ecological preference for species for crop seasonality was evident through the results of Agglomerative hierarchical clustering (AHC). Three weed communities or weed assemblages' groups (WAG) were identi ed. Their diversity evaluated and their linear correlation strength was determined. The delity measurements showed that 60-species have delity to WAG A; 46 to WAG B; 44 to WAG C. Measuring the ecological preference of species for crop diversi cation and soil type indicated that the growth activity of 36-species was more affected by crop diversi cation; 63-species preferential for growth in ne grained soil (FGS) and 87-species in coarse grained soil (CGS). By employing Redundancy analysis (RDA) with variation partitioning (VP), the variability in species frequency in WAG that can be explained by ecological preference of species for the three ecological preferences was determined and variation was partialized out to estimate their partial, linear effect. In fact, weed control is a recalcitrant issue and the current study revealed that a portion of the solution is in a successful crop diversi cation plan. The successful selection for a competitive crop that can be taken seriously as an adequate weed controlling mechanism in a crop rotation technique will cause the strongest population reduction of harmful weeds on infested farmland, especially in relevance for crops grown for organic certi cation. cause the strongest population reduction of harmful weeds on infested farmland, especially in relevance for crops grown for organic certi cation.
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