Ecological effects of fire severity and time since fire on the diversity partitioning, composition and niche apportionment models of post-fire understory vegetation in semi-arid oak forests of Western Iran

Monitoring and evaluating changes of the various characteristics of ecosystems after disturbances are essential to protect the services provided by each ecosystem. In the present study, different ecological characteristics including structure, composition and diversity at different post-fire times (one, five and ten years) in low and high fire severities were investigated in semi-arid oak (Quercus brantii L.) forests of western Iran. One hundred twenty-six 1.5 x 1.5 m plots were sampled in 14 patches (12 burned and 2 unburned). Alpha and beta diversity indices as well as species abundance distribution models of ecological niche apportionment were produced. The results showed that the distribution pattern of species, composition and diversity were influenced by the severity and time since fire. Based on Tokeshi's niche apportionment models, the low severity and short post-fire time generated a pattern with higher heterogeneity (MacArthur fraction; MF) than high severity and short post-fire time (dominance decay; DD). In contrast, long-term effects were less pronounced. Non-metric multidimensional scaling (NMDS) showed that there are different patterns of vegetation composition in low and high fire severities. The plant composition of the studied areas at low severity but with a longer time period since fire was more similar to the control area. In contrast, in the high fire severity, unburned and burned plots with different times since fire did not occupy overlapping areas in the ordination space. Severe fires also increased the alpha diversity at all spatial scales whereas the beta diversity only increased at the largest scale. Change of plant diversity pattern with time was more homogenous in low fire severity and more patchy in high fire severity. We concluded that the changes in the structure, composition and diversity of the post-fire vegetation were influenced both by fire severity and time since fire and that restoration actions to promote vegetation recovery should be adapted accordingly.