Abstracts in English, Afrikaans and Venda / The purpose of this study was to assess the diversity of epiphytic lichens growing on Acacia karroo, A. caffra and Jacaranda mimosifolia trees in Pretoria, and to investigate the influence of air pollution, land use, altitude and climate on lichen diversity. Lichen diversity was first studied at 12 sampling sites under different land use types (high traffic areas, residential areas and industrial areas) and in protected areas (open-air museums and nature reserves). The “European guidelines for monitoring lichen diversity as an indicator of environmental stress” were then tested in 29 sites using the same tree species and under two main land use types (“Industrial areas and busy roads” and “Parks and nature reserves”). Lichen Diversity Values (LDVs) were calculated for 164 trees. Correlations of LDVs and single lichen species with environmental parameters were studied by descriptive statistics, univariate analysis, Principal Component Analysis (PCA) and Generalized Linear Models (GLM). A naturality/alteration interpretative scale based on the percentile deviation of LDVs from natural conditions was developed for the first time in South Africa. Altogether 25 taxa, predominantly foliose and subtropical to tropical species, were recorded and are reported with their ecology and distribution. An identification key was developed for easy identification of species in the field. The highest lichen diversity was found in protected areas. The LDVs of Jacaranda are lower than values for both Acacia species. “Parks and nature reserves” have significantly higher LDVs than “industrial areas and busy roads”, as demonstrated by the PCA. The GLM models were significant for LDV and some lichen species. Sampling sites in industrial areas and the proximity of busy roads are negatively related to LDV and with the frequency of many lichen species. Higher atmospheric concentrations of NOx were negatively related to LDV and to the frequency of the species Candelaria concolor, Lepraria spp. and Pyxine cocoes. Culbersonia nubila and Lepraria spp. were respectively positively and negatively correlated with atmospheric SO2. The intensity of land use appears to have a negative impact on lichen diversity. In conclusion, lichens respond well to human disturbances in Pretoria and can be used as bioindicators of naturality/alteration. The European standardised monitoring method can be applied to estimate the degree of environmental alteration in South Africa, by adopting a stratified random sampling and a more flexible strategy for tree selection. / Die doel van hierdie studie is om die diversiteit van die epifitiese ligene op Acacia Karoo, A. caffra en Jacaranda mimosifolia bome in Pretoria te bepaal, en die uitwerking van lugbesoedeling, grondgebruik, hoogte en klimaat op die ligeendiversiteit te ondersoek. Die ligeendiversiteit is by 12 monsterneemterreine bestudeer. Sommige terreine het op grond met uiteenlopende gebruike (drukverkeergebiede, woongebiede en nywerheidsgebiede) en ander in beskermende gebiede (opelugmuseums en natuurreservate) voorgekom. Die “Europese riglyne vir die monitering van ligeendiversiteit as aanduiding van omgewingstres” is telkens by dieselfde boomspesies op 29 terreine gevolg. Die hoofsoorte grondgebruik van hierdie terreine was “nywerheidsgebiede en besige paaie” en “parke en natuurreservate”. Die ligeendiversiteitswaardes (LDW’s) van 164 bome is bereken. Die korrelasies tussen LDW’s, enkelligeenspesies en omgewingsparameters is aan die hand van beskrywende statistiek, eenveranderlikeontleding, ʼn hoofkomponentanalise (HKA) en veralgemeende lineêre modelle (VLM’s) bestudeer. ʼn Verklarende naturaliteit-/wysigingskaal wat op die persentielafwyking van LDW’s in natuurlike omstandighede berus, is vir die eerste keer in Suid-Afrika ontwikkel. Altesame 25 taksa, oorwegend digblarige en subtropiese tot tropiese boomspesies, tesame met die ekologie en verspreiding van elk, is geboekstaaf. ʼn Kensleutel waarmee spesies maklik in die veld uitgeken kan word, is ontwikkel. Die grootste ligeendiversiteit het in beskermde gebiede voorgekom. Die LDW’s van Jacaranda was laer as dié van die twee Acacia-spesies. Volgens die HKA het “parke en natuurreservate” beduidend hoër LDW’s as “nywerheidsgebiede en besige paaie” gehad. Die VLM’s vir LDW en sommige ligeenspesies was veelseggend. In nywerheidsgebiede en naby besige paaie was die LDW en die voorkoms van verskeie ligeenspesies laag. ʼn Hoë konsentrasie van NOx het ʼn negatiewe verband getoon met die LDW en die voorkoms van die spesies Candelaria concolor, Lepraria spp. en Pyxine cocoes. Daarteenoor het Culbersonia nubila en Lepraria spp. onderskeidelik positief en negatief met atmosferiese SO2 gekorreleer. Die intensiteit van grondgebruik benadeel blykbaar ligeendiversiteit. Ten slotte reageer ligene goed op menslike versteurings in Pretoria. Hulle kan as bioaanwysers van naturaliteit/wysiging gebruik word. Die gestandaardiseerde Europese moniteringsmetode kan toegepas word om die mate van omgewingswysiging in Suid-Afrika te skat deur gestratifiseerde, ewekansige steekproewe te neem en ʼn buigsame strategie in boomkeuring te volg. / Ndivho ya ngudo idzi ho vha u ela ha phambano ya nzulatshinya dza epiphytic lichens dzi aluwaho kha Muunga wa Sogani, Caffra na Muṱonḓowa wa Piṱori, u sedzulusa ṱhuṱhuwedzo ya tshikafhadzo, u shumiswa ha mavu, vhunṱha na kilima kha u fhambana ha nzulatshinya. Phambano ya nzulatshinya yo thoma u gudiwa kha saithi dza 12 dza sambula nga fhasi ha tshaka dzo fhambanaho dza tshumiso ya mavu (vhupo ha vhuendi, vhupo ha vhudzulo na vhupo ha dzifeme) na kha vhupo ho tsireledzwaho (miziamu yo vuleaho na kha tsireledzo ya mupo). Nyendedzi dza Yuropa dza u lavhelesa phambano ya nzulatshinya sa tsumbo ya “mutsiko kha mupo” dzo lingiwa kha saithi dza 29 hu tshi khou shumiswa miri ya tshaka dzi fanaho nga fhasi ha tshaka mbili dza ndeme dza tshumiso ya mavu (“vhupo ha dzifemeni na bada dzi re na vhuendi ho tsitsikanaho” na “phakha na fhethu ha tsireledzo ya mupo”). Ndeme dza Phambano ya Nzulatshinya (LDV) dzo rekanywa u itela miri ya 164. U elana ha LDV na tshaka dza nzulatshinya na phimo dza mupo zwo gudiwa nga mbalombalo dza ṱhalutshedzo, musaukanyo nga phambano nga nthihi, Musaukanyo wa Zwipiḓa zwa Ndeme (PCA) na Tshiedziswa Tswititi tsho Angaredzwaho (GLM). Tshikalo tsha ṱhalutshedzo ya tshanduko ya mupo zwo ḓisendeka nga u fhambana ha phesenthe ya LDV u ya kha nyimele ya mupo tsho bveledzwa lwa u thoma kha ḽa Afrika Tshipembe. Zwo ṱangana zwoṱhe, tshaka dza 25, dzine nnzhi dza vha nzulatshinya dza tshaka dza fhasi ha ṱiropika na kha ṱiropika dzo rekhodiwa na u vhigiwa na saintsi ya mupo yadzo ya phaḓaladzo. U topola ha ndeme ho bveledzwa u itela u kona u ḓivha dzitshaka nnḓa. Phambano khulwane ya nzulatshinya yo wanala kha vhupo ho tsireledzeaho. LDV dza muṱonḓowa dzi fhasi kha ndeme u fhira u itela tshaka dza Muunga. “Phakha na fhethu ha tsireledzo ya mupo” hu na LDV dza nṱha u fhira “vhupo ha dzifemeni na bada dzi re na vhuendi vhunzhi”, sa zwe zwa sumbedziswa nga kha PCA. Zwiedziswa zwa GLM zwo vha zwi zwa ndeme u itela LDV na tshaka dza nzulatshinya. Saithi dza tsumbonanguludzwa kha vhupo ha dzifemeni na u vha tsini ha bada dzi re na vhuendi ho tsitsikanaho dzi elana lu sa takadzi na LDV na tshivhalo tsha tshaka nnzhi dza nzulatshinya. Pfutelelo ya nṱha ya dzingamufhe ya NOx yo vha i sa elani zwavhuḓi na LDV na tshivhalo tsha dzitshaka dza Candelaria concolor, Lepraria spp. na Pyxine cocoes. Culbersonia nubila na Lepraria spp. dzo vha dzi tshi livhanywa zwavhuḓi na lu si lwavhuḓi na SO2 ya dzingamufhe. Kushumiselwe kwa mavu ku nga ku na masiandaitwa a si avhuḓi kha mutevhe wa nzulatshinya. Ndi tshi fhedzisa, nzulatshinya dzi fhindula zwavhuḓi u thithiswa nga vhathu Piṱori nahone dzi nga zwisumbedza vhutshilo ha tshanduko/mupo. Ngona ya tshilinganyo ya vhulavhelesi ya Yuropa i nga shumisa u anganyela tshikalo tsha tshanduko dza vhupo kha ḽa Afrika Tshipembe. Nga u dzhia tsumbonanguludzwa dzo dzudzanywaho nga zwigwada zwa tshayandivhiswa na tshiṱirathedzhi tshi shandukiseaho tsha munanguludzo wa miri. / Environmental Sciences / D. Phil. (Environmental Science)