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Abstract:
1. Fire is a key determinant of woody vegetation structure in savanna ecosystems, acting both
independently and synergistically through interactions with herbivores. Fire influences biodiversity
and ecological functioning, but quantifying its effects on woody structure is challenging
at both species and community scales.
2. Deeper insight into fire effects, and fire–herbivore interactions, can be gained through the
examination of species-specific demographic and dynamic changes occurring across areas with
different fire regimes in the presence of large herbivores. We used the Carnegie Airborne
Observatory (an integrated LiDAR and imaging spectroscopy system) to map woody tree
structure, species and dynamics over a four-year interval across two adjacent savanna landscapes
with contrasting fire histories in Kruger National Park, South Africa.
3. A history of higher fire frequency was associated with reduced woody canopy cover (17%
vs. 23%) and an increased overall rate of treefall (27% vs. 18%). The landscape with a history
of higher fire frequency displayed a shift in woody canopy height distribution from a unimodal
curve to a bimodal pattern at the community scale, with large reductions in height classes
<7 m.
4. Differences in tree height distributions and treefall rates across sites were underpinned by
species-specific responses to fire frequency. Acacia nigrescens displayed the highest rates of
treefall, most likely related to elephant activity, with losses exceeding 40% in the 6- to 9-m
height classes.
5. Synthesis. Our findings indicate that fire history imparts demographic legacies not only on
vegetation structure, but also on current vegetation dynamics. Current treefall rates of certain
tree species are exacerbated by a history of higher fire frequency. Species-specific and contextconscious
investigations are critical for elucidating the driving mechanisms underlying broader
community patterns.
