Functional diversity of high mountain pasture communities: a trait based comparative study
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Objective: Revealing differences in functional structure and diversity of two community types and exploring the effects of plant dominance on the trait variability. Location: Beklemeto region, Central Balkan National Park, 1560-1700m altitude. Method: We established six environmentally similar sampling sites on six hilltops of the mountain ridge. One Nardus stricta-dominated and one Vaccinium spp.-dominated community stand have been sampled at each site. In each stand, we recorded species presence/absence data in 5 x 5cm contiguous micro-quadrats along 52m long transects and used the species frequencies as an estimate for species abundance. We collected information from databases and own measurements about three main plant functional traits - specific leaf area (SLA), seed mass (SM) and plant maximum height (MH) for all the species present in the records. We calculated community-weighted mean trait value (CWM) of every stand to assess shifts in trait means among stands. We calculated Rao’s quadratic diversity index for each trait within each stand to assess functional diversity. Regression analysis was applied to estimate correlation between functional diversity and species diversity on the bases of diversity indices (Rao’s index and Simpson index). We used t-test statistic for comparing functional diversity between two community types. Results: Species diversity was considerably higher within Vaccinium-dominated stands compared to Nardus-dominated ones (Simpson index). There was positive correlation between species diversity and functional diversity considering Rao’s index for seed mass and maximum plant height across all stands. Stronger variability in CWM for specific leaf area was detected among the Nardus-dominated stands compared to the Vaccinium-dominated stands and opposite tendency for seed mass. The t-test showed significant difference in the Rao’s diversity index values between two community types for MH and SM. Conclusions: As there is significant difference in Rao’s index values between community types and functional diversity increase with species diversity we conclude that Vaccinium-dominated community type has higher functional diversity than Nardus-dominated community type. Compositional and abundance variability of the dominant species are of major importance for variability of the trait averages within community types.