Rep 11 - RESULTS FROM ORDINATION 4.1 Correspondence Analysis (CA)

CHAPTER 4: RESULTS FROM ORDINATION 4.1 Correspondence Analysis (CA)

I--.- Rep 11

Winter High SR

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Figure 4.12: Cumulative fit along axis 1 for Canonical Correspondence Analysis appliedtofull data set with plot ID variables and rainfall variables used as covariables. Species 74 (bare ground) and species 9, Ehrharta calycina were removed from species matrix. The first 3 species are 73 = Zygophyllum morgsana (0.18), 61=Melothria sp (0.13),65=Ruschia caroli (0.13).

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Time (Years)

Figure 4. Ba: Change in cover abundance in the spring grazing treatments of species with high cumulative fit for the Canonical Correspondence Analysis appliedtothe full data set without sp.74 and 9 using 'Plot ID' variables and rainfall variables as covariables. Relative abundance of species 61, Melothria sp, for treatments I (spring low SR), 2 (spring medium SR) and 3 (spring high SR) from year 1 to 9. 11= Treatment I, rep 1; 12= Treatment 1, rep 2 etc.

Ruschia caroli

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Figure 4.13b: Change in cover abundance in the spring grazing treatments of species with high cumulative fit for the Canonical Correspondence Analysis applied to the full data set witbout sp.74 and 9 using 'Plot ID' variables and rainfall variables as covariables. Relative abundance of species 65, Ruschia carolifor treatments 1 (spring low SR), 2 (spring medium SR) and 3 (spring high SR) from year I to 9. 11=Treatment 1, rep 1; 12=Treatment 1, rep 2 etc.

Zygophyllum morgsana

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Figure 4.13c: Change in cover abundance in the spring grazing treatments of species with high cumulative fit for the Canonical Correspondence Analysis applied to the full data set without sp.74 and 9 using 'Plot ID' variables and rainfall variables as covariables. Relative abundance of species 73, Zygophyllum morgsana. for treatments 1 (spring low SR), 2 (spring medium SR) and 3 (spring high SR) from year 1 to 9. 11 =Treatment 1, rep 1; 12=Treatment 1, rep 2 etc.

4.2.5 Euclidean distance

Euclidean distance values were obtained for treatment sample years relative to year 1 from the full data set, the relative abundance data set and the relative abundance data set from which Ehrharta calycinahad been removed. The significance of change in species composition over time is illustrated by the euclidean distance value of a sample, relative to that sample in year 1, rising above the upper confidence limit (VCL, see Chapter 3: Methodology).

The euclidean distance graphs for the absolute abundance data set (Figure 4.14.1) show samples changing dramatically from year to year in what appears to be a response to fluctuating rainfall (particularly PS rainfall - Figure 4.15.1). The significance of these fluctuations can be attributed to changes in cover of species such asEhrharta calycina and 'bare ground' both of which were shown by the ordination analyses as responding significantly to rainfall. This assumption is further supported by comparison of the euclidean distance graphs with rainfall data (Figure 4.15). The peaks associated with the euclidean distances for the absolute abundance data set) correspond to years of high PS rainfall during years 3 and 6 (Figure 4.15.1). From a significance perspective, it is during years of high rainfall that euclidean distances are highest above the VeL line emphasizing the overriding effect of rainfall on cover caused by fluctuations inEhrharta calycina in particular. While this is the case, it is also apparent that very few treatment samples return to a species composition similar to that characterising the treatment in year 1. One would expect this to be the case if peaks and troughs in the euclidean distance graph were simply a consequence of eruptions and die offs of species responding to years of high and low rainfall. This suggests that perhaps an underlying directional trend, caused by the treatment variables, may be adding to the euclidean distance values experienced by samples relative to year 1. This deduction is confinned by the results of the euclidean distance analysis applied to data sets from which species responding to rainfall have been removed.

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Time (Years)

1-+-11 12 21 ~22 -.-31 _ 3 2 -+-UCl

Figure 4.14.1 a: Euclidean distance of treatment samples relative to year 1 for absolute abundance species matrix. 11= Treatment 1, rep 1; 12= Treatment 1,rep2 etc. DCL= DpPer Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample 1.

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Figure 4.l4.lb: Euclidean distance of treatment samples relative to year 1 for absolute abundance species matrix. 41 = Treatment 4, rep I; 42 = Treatment 4, rep 2 etc. UCL = Upper Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample1.

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Figure 4.14.1c: Euclidean distance of treatment samples relative to year 1 for absolute abun~c~

species matrix. 71 == Treatment 7. rep 1; 72 == Treatment 7. rep 2 etc. UCL= Upper Confidence LImIt (p<O.05) which represents the level above which samples differ significantly from sample 1.

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Figure 4.14.1d: Euclidean distance of treatment samples relative to year I for absolute abundance species matrix. 101 == Treatment 10. rep 1; 102 == Treatment 10. rep 2 etc. VCL == Upper Confidence Limit (p<0.05) which represents the level above which samples differ significantly from sample 1.

To remove the fluctuation inthe euclidean distance measures caused by rainfall, the 'bare ground' variable was removed from the species matrix which was then relativised, creating a relative abundance matrix which provided the subject of the Euclidean distance analyses presented as Figure 4.14.2. The relative abundance species matrix (Figure 4.14.2) confirms the results of the relative abundance ordination analyses with the euclidean distances of samples increasing over time

relative to year 1. This occurs at a decreasing rate until a levelling off occurs, following which sporadic fluctuations are evident. A number of the samples change directionally to the extent that they can be considered significantly different post treatment application to what they were prior to the grazing trial. While a directional change is characteristic of all samples, not all change to an extent considered significant (i.e. above theDeL). This may be a consequence of the conversion of the data set from absolute abundance to relative abundance, a procedure which removed much of the variation from the ordination analyses. Even so, the distinct change in species composition over time, the directional nature of this change and the manner in which change levels off over time all suggest a response by the veld to the treatment variables.

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Figure 4.14.2a: Euclidean distance of treatment samples relative to year 1 for relative abundance species matrix. 11 =Treatment 1, rep 1; 12=Treatment 1,rep2 etc. UCL= Upper Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample 1.

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Figure 4. 14.2b: Euclidean distance of treatment samples relative to year 1 for relative abundance species matrix. 41 = Treatment 4, rep 1; 42= Treatment 4, rep 2 etc. UCL= Upper Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample 1.

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Figure 4.14.2c: Euclidean distance of treatment samples relative to year 1 for relative abundance species matrix. 71= Treatment 7, rep 1; 72= Treatment 7, rep 2 etc. UCL= Upper Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample1.

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The same trend exposed by the relative abundance euclidean distance tests is evident in the relative abundance matrix from which Ehrharta calycina has been removed (Figure 4.14.3). The removal of 'bare ground' and Ehrharta calycina serves to remove the two main variables fluctuating in response to rainfall. Most of the variation remaining in the data set is, as a result, a consequence of the various grazing treatments and any directional changes in euclidean distance can be attributed to the impact of grazing on the veld resource. As with the euclidean distance graphs for the relative abundance matrix, the changes in species composition in the shrub/herb complex appearto be directional innature approaching the VeL and levelling off as the trial progresses. These characteristics suggest a relation between the various grazing treatments and the veld's dynamics.

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Figure 4. 14.3a: Euclidean distance of treatment samples relative to year I for relative abundance species matrix withEhrharta calycinaremoved. 11 = Treatment 1, rep 1; 12= Treatment 1, rep 2 etc.

UCL = Upper Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample 1.

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Figure 4.14.3b: Euclidean distance of treatment samples relative to year I for relative abundance species matrix withEhrharta calycinaremoved. 41 = Treatment 4, rep 1; 42= Treatment 4, rep 2 etc.

UCL = Upper Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample 1.

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1 2 3 ⁴ 5 6 7 8 9

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Figure 4.14.3c: Euclidean distance of treatment samples relative to year 1 for relative abundance species matrix withEhrharta calycinaremoved. 71 = Treatment 1, rep 1; 72= Treatment 7, rep 2 etc.

UCL = Upper Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample I.

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1 2 3 4 5 6 7 8 9

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Figure 4. 14.3d: Euclidean distance of treatment samples relative ^to year 1 for relative abundance species matrix withEhrharta calycmaremoved. 101= Treatment 10, rep 1; 102:;; Treatment 10, rep 2 etc. UCL "" Upper Confidence Limit (p<O.05) which represents the level above which samples differ significantly from sample I.

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Figure 4.15.1: Previous Season rainfall (mm). Previous Season rainfall refers to rainfall which fell during the season prior to the season inwhich sampling took place. I.e. rainfall during autumn for samples taken during winter.

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Time (Years) 2 3

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Figure 4.15.2: Year prior rainfall (mm). Includes rainfall from the three seasons priortothe season of sampling as well as the season in which sampling took place.

Dalam dokumen An assessment of the effect of season of grazing, stocking rate and rainfall on the dynamics of an arid rangeland on the west coast of South Africa. (Halaman 89-101)

Rep 11

CHAPTER 4: RESULTS FROM ORDINATION 4.1 Correspondence Analysis (CA)

I--.- Rep 11

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