INVERTEBRATES
3.2 MATERIALS AND METHODS
5) To test these recommendations for use in monitoring using burned and unburned Afrotemperate forest patches.
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Figure 3.1. Location of Injisuthi and Royal Natal National Park (RNNP) in the Maloti- Drakensberg Bioregion (indicated by the MDTP Planning domain) in KwaZulu-Natal, South Africa (top), with an enlargement of Injisuthi (bottom left) showing the three forest sites and an enlargement of Royal Natal National Park (bottom right) showing the eight forest sites used to test the performance of the "best practice" approaches to monitoring. Afrotemperate forest is shown in black. Site data are presented in Appendix 3a.
3.2.2 Sampling methods
Five sampling methods were used in each forest to collect flightless invertebrates. These sampling methods included soil samples, pitfall traps, leaf litter samples, active search quadrats and tree beats. Refer to Appendix 3b for tree species sampled in tree beats. Five
invertebrate target taxa were sampled: molluscs, earthworms, centipedes, millipedes and ants. Sampling methods are described in Chapter 2.2.2.
Sampling saturation
Sampling intensity was low because of time and cost constraints. Sampling was nevertheless close to saturation since field sample-based species-accumulation curves all approached an asymptote (Appendix 3c). Refer to Chapter 2.2.2 for a discussion of sampling saturation.
3.2.3 Analyses
Evaluation and comparison of the effect of season on flightless invertebrate species richness and community structure
The results from all sampling methods were combined to calculate the number of species collected from each site in each month (species richness). The total species richness of all target taxa combined and the mean species richness (n
=
3 sites at Injisuthi) in each of the four sampling months were calculated. The number of unique species was also calculated for each sampling month. Here, unique species are those collected in one month only,regardless of which site(s) the species was found in. Rarefraction and Hill's diversity number were not used because only one site per forest was sampled. Since the number of replicates in each season was low and the same sites were sampled each month, non-parametric analyses were used. A triangular matrix of Bray-Curtis dissimilarity in the species composition between every pair of sites in every season was used to map the site inter- relationships in an ordination by non-metric multidimensional scaling (NMDS) using PRIMER (Clarke and Gorley, 2001). NMDS is often the method of choice for graphical representation of community relationships because of the flexibility and generality of its dependence only on a biologically meaningful view of the data, and its distance-preserving properties (Clarke, 1993). In an NMDS plot, the direction of maximal variation lies along the x-axis. The stress value is a reliability measure - the greater the stress, the greater the risk of drawing false inferences from an ordination. The same triangular matrix of Bray-Curtis dissimilarity
between seasons was used for pairwise one-way analysis of similarity (ANOSIM) to test the null hypothesis of no difference between seasons.
Determination of suitable flightless invertebrate taxa for use in biodiversity assessment and monitoring
Data from the three Injisuthi sites were combined to calculate species richness for molluscs, centipedes, millipedes and ants in each sampling month. Earthworms and onychophorans were not analysed individually because they were not collected in all months and differences in species richness and abundance among sites and months were too low to test statistically.
NMDS ordination was performed to summarize differences in species composition of the three Injisuthi sites sampled in four different seasons for molluscs, centipedes, millipedes and ants. The same triangular matrices of Bray-Curtis dissimilarity between sites were used for pairwise one-way ANOSIM to test the null hypothesis of no difference between seasons for each of the four target taxa.
Determination of suitable sampling methods for use in biodiversity assessment and monitoring
To compare the contribution of different sampling methods to species richness counts in different seasons, the number of species collected at Injisuthi using each sampling method was calculated. Species richness from each sampling method in each month was plotted for all taxa combined and each target taxon. The number of species collected by only one sampling method in each month for all flightless invertebrate taxa combined was also plotted.
This analysis was used to determine which sampling method(s) were most suitable for targeting rare species and species with short adult life cycles or short periods of surface activity. The efficiency of each sampling method (i.e. sampling effort) was calculated as the total number of species recorded in three forests combined, divided by the number of person hours required for sampling and processing. Efficiency (species per person hour) was
calculated for each sampling method in each month. Mean efficiency for each sampling method was calculated as the mean of four months.
Determination of the "best practice" approaches for season, taxa and sampling methods for use in biodiversity assessment and monitoring
Data on flightless invertebrate taxa collected during seasonal sampling in Afrotemperate forest at Injisuthi were used to construct a summary table of the "best practice" approaches to (a) biodiversity assessment and (b) monitoring for the impact of management actions. This summary was based on criteria for recommended season, taxa and sampling methods.
Test of proposed "best practice" approaches using burned and unburned Afrotemperate forest sites
To test the "best practice" approaches to monitoring, total mollusc species richness and mean species richness were compared between unburned and burned valleys at Royal Natal National Park using analysis of variance (ANOVA). According to Ezemvelo KZN Wildlife fire records, Devil's Hoek valley was last burned in 2003, while Thukela Gorge forests have not been burned during the same time period. Mollusc species richness measured by quadrat, litter sample and tree beat sampling was compared to determine methods required to sample mollusc species richness for monitoring purposes. The species richness of live molluscs was
compared to the species richness of mollusc shells to determine whether shells alone could be used for monitoring. To determine whether mollusc species richness reflected the influence of fire on the species richness of other flightless invertebrates, total and mean species richness were calculated for the unburned and burned valleys. Mollusc data were also compared with centipede, millipede and ant data.