DOI: 10.5061/dryad.2547d7wmt
title: Impact of Seriphium plumosum densification on Mesic Highveld Grassland biodiversity in South Africa

description: Mesic Highveld Grassland is important for biodiversity conservation, but
 is threatened by bush densification from Seriphium plumosum. This
 indigenous encroacher spreads rapidly and outcompetes other herbaceous
 species, changing the species composition and structure of grasslands.
 This study looks at three different densities of S. plumosum and how these
 affect grassland biodiversity within Telperion, Mpumalanga, South Africa.
 An intermediate density of S. plumosum resulted in the highest species
 diversity (H = 2,26), a low density was moderately diverse (H = 1,96), and
 a high density was least diverse (H = 1,78). There were differences
 between the three densities in terms of plant species diversity, with the
 intermediate density being significantly more diverse (P &lt; 0.01)
 than both the low and high densities. Findings indicate that there was a
 significant difference between the sites in terms of ecological
 successional status (P &lt; 0,01).  The presence of S.
 plumosum at low densities can be considered an integral part of the
 environment. It is important that in areas where S. plumosum occurs, it
 should be monitored. If this species is not in balance within its
 environment and it starts becoming dense, it will negatively affect the
 biodiversity, species composition and structure of the habitat.
description: 1. Sampling
 design Initial
 vegetation surveys were conducted in all three sites during February 2017
 to calculate the <i>S. plumosum</i> frequency and establish
 the gradient of density between the three study sites. Grass and
 <i>S. plumosum</i> height was measured using a measuring stick
 at one meter intervals along a 100 m line transect, the transect was
 placed diagonally across the study site. At each of the three study sites
 all <i>S. plumosum</i> plants were counted in two 100
 m<sup>2</sup> (10 m x 10 m) sample plots. To determine species
 composition, species richness and species diversity, all plant species
 within twenty 1 m x 1 m quadrants were identified and counted within each
 of the study sites. The biomass of grass vegetation was determined using a
 Disc Pasture Meter (DPM) that was previously calibrated for the reserve (n
 = 100 readings were collected per sample site). Since we were interested
 in the grass component and its grazing value to grassland animal species,
 only open grass areas in the three sample sites were sampled with the DPM.
 The effect of <i>S. plumosum</i> on herbaceous biomass was not
 taken into account when calculating the total biomass for the three study
 sites. All plant species were classified into five successional classes
 (20), i.e. class 1 - pioneer annual; class 2 - pioneer perennial; class 3
 - secondary succession; class 4 - secondary succession with anthropogenic
 disturbance; class 5 – climax.   2. Data
 analysis <b>Density </b>–
 Using densities of <i>S. plumosum </i>plants in each of the
 two sample plots at each study site, means were calculated for each study
 site. Density was reported as the number of plants per hectare.
 <b>Alpha
 diversity</b><i> - </i>The Shannon–Wiener diversity
 index (21) was used to calculate alpha diversity. Index values obtained
 from diversity index calculations were insufficient for further
 statistical analysis and were converted into effective numbers (22). An
 ANOVA was used to determine whether there were significant differences
 between the three sites in terms of effective numbers of species (i.e.
 diversity). A post hoc Tukey test was run to determine where the
 significant difference/s were between the three sites. <b>Species
 evenness</b><i> – </i>The evenness of species was
 calculated using the Pielou’s Evenness Index (24). <b>Beta
 diversity</b><i> – </i>Beta diversity (similarity) for
 the three sites was interrogated using the Extended Sørenson’s similarity
 index (33). The larger the index value, the greater the similarity. To
 understand the similarity between the individual sites, the Sorenson’s
 similarity index was calculated for each pair of sites. <b>Vegetation ecological
 successional classes </b>–<b> </b>A two-way
 classification chi-square test was used to determine if there was a
 significant difference between the 3 sites based on the observed frequency
 distribution of the 5 ecological successional classes. <b>Effect of key ecological
 variables on vegetation diversity</b><i> – </i>A
 constrained correspondence analysis (CCA) ordination of the three sites
 (Grassland, Intermediate and Dense) was undertaken using the R software
 package (25), to determine which variables (effective number, biomass,
 <i>S. plumosum</i> height, grass height and ecological
 successional status/class) had the greatest effect on the vegetation
 diversity of the sites. All statistical analyses were
 done using the IBM SPSS Statistics vs. 25 software package (23). The
 chosen critical significance level <i>α</i> wa s 0.05.   1.            Van Wyk B, Malan S. Field guide to the wild flowers of the Highveld. 2nd editio. Cape Town: Struik Publishers; 1997. 2.            Shannon CE. A Mathematical Theory of Communication. Bell Syst Tech J. 1948;27:379–423. 3.            Jost L. Partitioning diversity into independent alpha and beta components. Ecology [Internet]. 2007 Oct;88(10):2427–39. Available from: http://doi.wiley.com/10.1890/06-1736.1 4.            Pielou EC. The measurement of diversity in different types of biological collections. J Theor Biol [Internet]. 1966 Dec;13:131–44. Available from: http://linkinghub.elsevier.com/retrieve/pii/0022519366900130 5.            R Core Team. R: A language and environment for statistical computing [Internet]. Vienna, Austria: R Foundation for Statistical Computing; 2013. Available from: http://www.r-project.org/ 6.            IBM Corp. IBM SPSS Statistics for Windows. Armonk, New York: IBM Corp.; 2016.
description: Data cleaning SPSS and R software
 package Knowledge of plant ecology, plant succession,
 bush densifiation/encroachment, veld condition and palatability 
 General knowledge of the area