Grassroots Grassroots - Vol 19 No 4 | Page 8

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. • 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