Vegetation composition of crane-disturbed vs. intact patches
We found that biopedturbation by
foraging cranes created habitat patches with different vegetation
structure and species composition compared to undisturbed stands of dry
alkaline grasslands. The disturbed
patches were characterised by sparse vegetation with small cover of
vascular plants and cryptogams. The cover of perennial graminoids
decreased, while that of perennial forbs and short-lived graminoids and
forbs increased as a result of crane ploughing. The availability of open
microsites and the low cover of competitor perennial graminoid species
probably supported the germination of several plant species which
resulted in larger plant diversity in disturbed areas compared to intact
grassland (Deák et al. 2011). Similar patterns were found in Peruvian
deserts where avian biopedturbations by burrow-nesting birds created
more favourable areas for seedling establishment compared to undisturbed
patches (Rengifo-Faiffer & Arana 2019).
In their meta-analysis Romero et al. (2014) showed that the overall
effect of ecosystem engineers on diversity is positive and corresponds
to a 25% increase in species richness, indicating that ecosystem
engineering is a facilitative process globally. We detected a
significant, approximately two-fold increase in plant diversity in the
crane-disturbed plots compared to intact grasslands. This is
particularly interesting, as such strong effect of engineer species has
not been found for foraging bird species before and engineer effect was
reported to be weaker at latitudes higher than 23º (Romero et al. 2014).
The species composition of disturbed and intact areas was clearly
separated as shown by the multivariate analysis which implies that
cranes create distinct habitat patches within the grasslands. Disturbed
patches were characterised by early successional short-lived graminoids
and forbs that are natural elements of the open, trampled and grazed
patches of alkaline grasslands (Deák et al. 2015). Invasive or strong
competitor weed species were absent on the disturbed plots, which might
be due to the high salt content of the soil (see also Valkó et al.
2017). The disturbed plots were characterised by high inter-annual
vegetation fluctuation, while this seasonality was less apparent in the
intact grasslands.