FEATURE
On the other extreme , the exclusion of fires entirely in an agro-ecosystem can have opposing effects . Without the influence of fire , certain plant species may dominate , altering plant diversity and palatability , changing grazing habits and overall utilization of the grassland habitat by livestock . The accumulation of dead plant material over time can also pose a greater risk of increased burn intensity and burn temperatures when fire is eventually reintroduced , accidentally in the event of a lightning strike or intentionally through management interventions .
Grazing and fire at Wakefield ’ s research farm
Figure 2 . Grazing exclosures were built and placed on transects that were burnt annually and those excluded from burning . The aim was to establish the effect of grazing on the two burn scenarios . ( Photo : Nicolay and Tedder )
Figure 3 . The portable Licor 6400 meter with soil respiration chamber attachment was used to measure soil respiration on grazed sites burnt annually and those sites excluded from burns entirely on Wakefield farm . ( Photo : Nicolay and Tedder )
ics and functioning . Fires applied too frequently may lead to adverse effects : burning annually may deplete vegetative biomass and hinder its ability to recover adequately between fire events . This may lead to changes in plant diversity , loss of habitat for certain species , and potential shifts in vegetative structure . Additionally , nutrient cycling processes may be disrupted , and the burnings may interfere with the selective grazing habits and preferences of ungulates through changes in vegetative composition and palatability .
Ongoing research at Wakefield Farm ( 29 ° 29 ’ 54 ’’ S , 29 ° 54 ’ 01 ’’ E ), Fort Nottingham , KwaZulu-Natal , is a prime example of existing extremes of fire and grazing management in a mesic grassland agroecosystem . Wakefield Farm currently employs a no-burn approach and relies on grazing cattle as the primary source of defoliation . This extreme of complete pyric exclusion is compared to the opposite extreme of burning grasslands annually on the farm as mandatory fire breaks along the border of the property . We looked at the changes in mesic grasslands between these two pyric-herbivory management extremes to better understand synergistic effects between fire and grazing ; where they work together and influence the vegetation structure , how they contribute to soil organic carbon stocks and soil respiration , as well as their influence on livestock grazing habits and potential in terms of biomass availability and palatability .
Firebreaks along the farm ’ s boundaries are burnt annually in June with the remaining veld left unburnt . The property comprises of grazed grassland over a varied topography , adjacent to the Umgeni River and managed under short periods of intensive grazing followed by prolonged post-grazing recovery . Sites on the farm comprised two parallel transects , one burnt annually and one left unburnt for over ten years . Paired soil samples to depths to 15 cm ( horizons 0-5 cm , 5-10 cm , 10-15 cm ) were collected along these transects and analysed for Soil Organic Carbon ( SOC ) and Nitrogen ( N ). Soil respiration was quantified using a LICOR 6400 portable flux system during the peak growing season in March . Biomass samples were collected along the same transects to determine Aboveground Annual Net Primary Production ( ANPP ), Acid Detergent Lignin ( ADL %), Acid Detergent Fibre ( ADF %), and Biomass moisture %. Grazing exclosures ( 1 m x 1 m basal area , 70 cm height ) were built and erected to account for grazing effects reducing standing biomass on both the annually burnt and burn exclusion sites ( Figure 2 ).
13 Grassroots Vol 23 No 2 July 2023