FEATURE
Key forbs indicate the condition
of mesic grassland
Craig Morris
Current Address: Agricultural Research Council – Animal Production Institute (ARC-API), c/o University
of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa
Email address: [email protected]
A
fter a burn in Spring, mesic grass-
lands are full of wildflowers. Bright
yellow Hypoxis and Gazania flow-
ers stand out vividly among the small
everlastings, carpet beans, and pale
yellow Hibiscus blooms. Fire lilies in
scarlet red or lemon yellow intermingle
with patches of white Gerberas, pink
Asters and the occasional tiny white
wild lettuce flowers. Purples and blues
are harder to find – you have to search
amongst the resprouting ash-black tufts
of luminescent young grass for the few
hidden Ipomoea, Commelina or Ruellia
flowers. Myriad grassland forbs take this
chance to emerge, flourish, flower, and
set seed before the grass canopy closes
in.
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have a consistent, predictable re-
sponse to grazing.
Grazing indicator forbs can speak
for the rest, indexing the state of
overgrazing and predicting total
forb species diversity.
The study to identify grazing indicator
forbs spanned 178 plots in Midlands
Mistbelt Grassland, KwaZulu-Natal
Sandstone Sourveld, and Ngongoni
Veld (with these latter two grouped as
‘Sandstone grassland’) in KwaZulu-Na-
tal, South Africa. Plots were deliberately
placed across a range of grazing inten-
sities from lightly or occasionally grazed
grassland to areas that had been se-
verely overgrazed. Such a grazing gra-
dient allowed the pattern of change in
overall forb species composition to be
described and species with a direction-
al response to grazing to be identified
for each grassland. Examples of some
species that declined markedly with in-
Many of the herbaceous forbs found in
mesic grassland have evolved under-
ground storage units (USOs) from which
they resprout new stems and leaves
each season. However, despite their
protected USOs, forbs are not immune
to disturbance (Chamane et al. 2017)
and many species can be eliminated
from grassland by relentless overgraz-
ing (Scott-Shaw and Morris 2015). De-
pletion of forbs from grasslands can
have important consequences. This is
because a diversity of forb species sta-
bilises grassland and forbs provide hab-
itat and food for many creatures as well
as crucial forage for livestock at certain
times. The essential ecological roles
forbs play in mesic and semi-arid grass-
land (Siebert and Dreber 2019) are not
well understood and we are just begin-
ning to document how disturbances like
grazing, fire, drought, and medicinal
plant collection affect forb populations.
Recently published research has, how-
ever, shed some light on how forbs in
two mesic grasslands respond to graz-
ing (Morris and Scott-Shaw 2019). The
main results of this study, elaborated
further below, are:
•
•
07
Some forbs increase while others
decrease in abundance with in-
creasing grazing intensity.
A small number of indicator forbs
Figure 1: Examples of key grazing indicator forb species with a Decreaser or In-
creaser response along a grazing intensity gradient in Mistbelt grassland (photos by
Rob Scott-Show, unless indicated). GSW = grazing sensitivity weight (0-10).
Grassroots
Vol 19
No 4
November 2019