Effects of grazing and forestation on functional diversity indices: A case study of Cheshmeh Dalav, Northern Khorasan

Biodiversity includes not only the species number and their abundance but also the differences in the functions of any species, which is measured by the functional diversity indices. On the other hand, land-use change and grazing are two important factors affecting biodiversity and ecosystem services. This study was carried out to investigate the effects of grazing and forestation on functional diversity indices at Cheshmeh Delav in the western part of Northern Khorasan Province, Iran.

To measure the functional diversity, the single-trait indices (community-weighted mean; CWM) and also the multiple-trait indices (functional richness, functional evenness, functional divergence, functional dispersion, Rao quadratic diversity) were used and measured by the "FD" statistical package in "R.3.3.1" software. The one-way analysis of variance (ANOVA) followed by Duncan’s test was used to compare the mean diversity.

The results showed that grazing and forestation have different effects on functional diversity indices. Based on the results, functional richness, Rao index, CWM of height and therophyte had a significant difference in the studied areas. The highest values of functional richness, Rao and CWM of the height index were related to grazing areas. Therefore, the low levels of disturbance factors such as grazing are necessary to reduce competition between plants and an increase in ecosystem function. As CWM of height was the highest at grazing sites, there was a positive relationship between functional richness and CWM. On the other hand, the maximum value of the CWM of therophyte life form was observed in the ungrazing – forestation site due to environmental adverse conditions such as high competition (due to lack of grazing) and disturbance (forestation).

Using functional diversity indices as an index of biodiversity that considers not only species abundance, but also functional traits was an effective mean in the study of the effects of different factors on biodiversity and the function of different ecosystems.