Ecological effects of Festuca costata on the Drakensberg grasslands.
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Date
2018
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Abstract
Fire and herbivory are important in determining the vegetation structure in savannas and
grasslands. In addition, anthropogenic activities have significantly contributed to alterations in
the relative abundance and distribution of plant species in many grasslands through increased
nitrogen deposition and elevated concentration of carbon dioxide in the atmosphere. Using a
field experiment, the study explored the effect of neighbouring plants, defoliation, and fire on
the ecological performance of a major C3 grass, Festuca costata, whose range is expanding in
Afro-temperate grasslands of the Drakensberg Mountains in South Africa.
The experiment had three factors: fire at two levels (burned, unburned), defoliation by clipping
50mm above-ground surface, at four levels (no defoliation, defoliation of focal plant,
defoliation of neighbouring plant within a 300 mm radius, and defoliation of both the focal and
the nearest neighbouring grass within a 300 mm radius from the focal plant). The third factor
was plant neighbourhood types at three levels (the focal plant growing alone, focal plant
growing with other F. costata plants, focal plant growing with any other grass species) for a
total of 24 treatment combinations with five replicates. Using a pot experiment under garden
conditions, the study evaluated the influence of soil nutrient amendment with 140 KgHaˉ¹
limestone ammonium nitrate in the performance of F. costata. The variables of interest in both
experiments were; above-ground biomass production, tuft circumference, number of tillers and
specific leaf area of the focal plant. Generalised Linear Models in SPSS were used to analyse
the data from both experiments.
The results showed that burning had a significant negative effect on above-ground biomass
production, number of tillers and tuft circumference of the focal plant (P < 0.001), with the
unburned grassland showing greater mean values for all parameters than the burned grassland.
Defoliation had significant negative effects on above-ground biomass production, number of
tillers, tuft circumference while it showed strong positive influence on specific leaf area of the
focal plant. Neighbourhood types were significantly negative for above-ground biomass
production, number of tillers and tuft size of the focal plants (P< 0.001 in all cases).
Nutrient addition reduced the number of tillers of F. costata and tuft size and showed no
significant effects on above-ground biomass production and specific leaf area. Defoliation
significantly increased SLA, above-ground biomass production, number of tillers and tuft circumference were not affected.. Plant neighbourhood types showed significant negative
influences on tuft circumference. Defoliation accounted for the most variations in reduced tuft
size, above-ground biomass and number of tillers, however, it resulted in increased specific leaf
area.
These results suggest that defoliation by herbivores and use of fire may be complementary tools
for managing high altitude grasslands under climate change. The findings of both the field and
pot experiment suggest that F. costata may not be tolerant to selective herbivory. In addition,
the study shows that the increase in nitrogen availability due to anthropogenic activity may
have a negative influence on the performance of F. costata.
Description
Masters Degree, University of KwaZulu-Natal, Pietermaritzburg.