10.5061/DRYAD.83BK3J9NN
Johansson, Maria Ulrika
0000-0001-8032-6075
Stockholm University
Swedish University of Agricultural Sciences
Granström, Anders
Swedish University of Agricultural Sciences
Data from: Fire and grazing controlling a tropical tree line: Effects of
long‐term grazing exclusion in Bale Mountains, Ethiopia
Dryad
dataset
2020
Sida*
(SWE-2004-276)
Sida
(SWE-2004-276)
2020-05-16T00:00:00Z
2020-05-16T00:00:00Z
en
https://doi.org/10.1111/jvs.12905
57019 bytes
3
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Aims: Tropical tree lines are often associated with abrupt shifts in
vegetation, soils and disturbance regimes, but the underlying mechanisms
are poorly understood. We analysed the role of grazing, fuels and fire in
maintaining a sharp tree line with flammable heathland above non-flammable
forest. Location: Bale Mountains, Ethiopia. Methods: Grazing exclosures,
repeated vegetation sampling, soil analyses and burning and sowing
experiments along an altitudinal gradient with Hagenia abyssinica forest,
Erica trimera forest and Erica heathland; all heavily grazed, the latter
burnt on short rotation. Results: Contrary to expectation, livestock
exclusion did not increase forest fuel flammability, but instead resulted
in a dense carpet of non-flammable herbs. In the heathland, livestock
exclusion led to somewhat faster post-fire fuel recovery, but no major
vegetation change. Seeding of tree species resulted in some seedling
establishment, but notably Hagenia grew poorly in the heathland, even when
protected from livestock. A bioassay, as well as observations of outpost
trees on atypical soil above the treeline, suggest that this poor growth
is caused by the acidic soils, rather than harsh climate. Despite frequent
fires, heathland soils had lower pH and higher organic matter content than
forest soils. Below the tree line, tree seedling establishment was
successful only in forest gaps, and if livestock was excluded. In both
forest and heathland rapid vegetative regeneration in the ground flora
after disturbance restricted major species shifts. Conclusions: These
results suggest that the contrasting fire potential between heathland and
forest, and thus the sharp tree line would be maintained, or possibly even
accentuated, in the absence of livestock grazing, and that Hagenia
colonisation upwards into the heathland is restricted not only by fire and
grazing, but also the acidic soils, a legacy of centuries of Erica
dominance.
Collected by ourselves in the field 2005-2011,processed in Excel and Minitab