Aspects of the ecology of grass seedlings used for revegetation of degraded land.
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Date
2010
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Abstract
As restoration ecology has matured as a science there has been increased
interest in the relationship between species diversity and landscape health.
Degraded landscapes tend to be resource poor, which limits species diversity as
only species which are capable of growing and reproducing in these resource
limiting environments can inhabit the area. Additionally, the established species
are strong competitors for resources and will exclude, by way of inter-specific
competition, weaker competitor species attempting to invade the degraded area.
Several studies have demonstrated that with increased species diversity the
overall productivity and functionality of the grassland increases.
Seedling development and competitive interactions between grass seedlings
has a significant impact on the final community structure and species diversity. It is
for this reason that aspects of the ecology of grass seedlings were investigated.
The growth and competitiveness of Chloris gayana, Cynodon dactylon,
Digitaria eriantha, Eragrostis curvula and E. tef seedlings were determined under
three environmental stimuli, namely nitrogen availability, light availability and
exposure to plant-derived smoke (in the form of smoke-infused water).
The primary conclusion from the competition experiments was that the species
can be split into superior and inferior competitors at the seedling stage. Chloris
gayana, E. curvula and E. tef were the most competitive seedlings as they had the
largest negative effect on the growth of other species (high nitrogen Relative
Interactive Index (RII) = -0.449, -0.203 and -0.379 respectively) and they were
least affected by competition (high nitrogen RII = -0.251, -0.168 and -0.248
respectively). The calculated RII indicates the strength of the competitive
interactions, the more negative the RII the stronger the competitive interaction.
Nutrient availability had limited effect on the competitive hierarchy of the tested
species. Chloris gayana seedlings, however, increased in competitiveness with an
increase in available nutrients. In other words, there was a decreased negative
response to competition in a high nutrient environment (high nitrogen RII -0.251,
no nitrogen RII -0.605). When D. eriantha was grown under varying shade, nutrient
and competition levels it was evident that the primary stress factor was light
deficiency (p<0.001), and nutrient availability had no affect on seedling growth
(p=0.069). Smoke-infused water had no consistent affect on the germination
success or the seedling’s root and shoot vigour for the five grasses.
These results indicate that the introduction of a “2-phase” or “multi-phase”
restoration plan may be beneficial for the development of species diverse
rehabilitated grasslands. Manipulating the time and space that the different
species are planted, or the distribution of nutrient concentration over the area, may
increase the survivorship of all the species that are introduced to a restoration site.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
Keywords
Grasses--Seedlings--Ecophysiology--South Africa., Competition (Biology)--South Africa., Smoke--Physiological effect--South Africa., Grassland restoration--South Africa., Germination--South Africa., Grasses--Seedlings--Growth., Theses--Grassland science.