Biodiversity assessments using remote sensing and integrative modelling for improved conservation management

Thesis (PhDConsEcol)--Stellenbosch University, 2022.ENGLISH ABSTRACT: Insect diversity is declining globally, threatening ecosystem collapse and human well-being. Accurate information on biodiversity dynamics is needed to guide landscape management. This is important within actively managed production landscapes (especially forestry and agriculture), where land use change and habitat degradation impacts biodiversity, which in turn influences ecological resilience. Satellite remote sensing allows for collection of data over time, which enables a greater understanding of species distributions and drivers of change. Combining satellite-derived variables with advanced integrative modelling approaches, such as time series analysis, habitat suitability modelling, functional connectivity analysis and deep learning image fusion, allows for better understanding of biodiversity dynamics to guide landscape management. In this dissertation, I focus on grasshoppers, indicators of high-quality grasslands, and study their diversity within grassland corridors between plantation forests, to gain a greater understanding of how plantation landscapes can be managed (e.g. prescribed burning, invasive plant management, tree harvesting) to ensure ecological resilience. Satellite time series showed that changes in grassland structure can have a lasting positive impact on grasshoppers for up to three years. Prescribed burning, measured using historic Normalised Burn Ratio index, helps maintain high-quality grasshopper habitat, while also influencing functional connectivity of grassland corridors. Normalised Difference Vegetation Index (NDVI) was a useful tool to monitor grassland corridor condition and to assist with planning of prescribed burning. Large corridors with an elevation gradient support diverse assemblages and should be prioritised for conservation. Deep learning image fusion classified American bramble (Rubus cuneifolius), an aggressive invasive species in South African grasslands, with high accuracy compared to conventional satellite imagery. Bramble had negative impact on plant species richness, larger-sized grasshopper species, as well as species of conservation concern. Bramble invaded riparian areas more frequently, threatening Ensifera grasshopper species habitat. Harvesting timber compartments and prescribed burning increased bramble cover within the landscape. Active management of plantation tree saplings after harvesting can lead to enhanced functional landscape connectivity and reduced bramble cover. Grassland corridors have high vegetation heterogeneity caused by prescribed burning, which contribute to high species turnover. Corridors should be burned every 2-3 years. Using NDVI will help foresters to identify where and when to burn corridors, thereby maintaining high-quality grasshopper habitat and functional connectivity. Rotational harvesting of timber compartments is recommended, as logging only some compartments will have positive impact on functional connectivity as well as helping prevent bramble invasion through the landscape. I recommend combining prescribed burning with grazing by domestic cattle to control bramble invasion. Special attention is needed to control bramble two years after harvesting, as this is when bramble cover is highest. This dissertation demonstrated that grassland corridors maintain biodiversity within actively managed production landscapes when management incorporates biodiversity response to disturbance. This motivates for the maintenance and protection of grassland corridors in other parts of the world to conserve biodiversity and help address insect decline. Lastly, the techniques used here provide valuable insights into biodiversity response to actively manage landscapes, and can therefore be applied to other vegetation types for protecting biodiversity.AFRIKAANSE OPSOMMING: Insekdiversiteit verminder wêreldwyd wat ekosisteem ineenstorting en menslike welstand bedreig. Ons benodig akkurate inligting op biodiversiteitsdinamika om landskapbestuur te lei. Dit is belangrik in produksielandskappe wat aktief bestuur word (veral bosbou en landbou), omdat verandering in grondgebruik en habitatdegradasie biodiversiteit impak, wat dan ekologiese veerkragtigheid beïnvloed. Satelliet-afstandwaarneming versamel data oor tyd, wat vir ons ‘n beter begrip van spesieverspreidings en hul drywers verskaf. Die gebruik van satelliet-afgeleide veranderlikes en geïntegreerde modelleringsbenaderings, soos tydreeksanalise, habitatgeskiktheids-modellering, funksionele konnektiwiteitsanalise en diep-leer beeldsamesmelting, laat toe vir beter begrip van biodiversiteitsdinamika om landskapbestuur te lei. In hierdie tesis, fokus ek op sprinkaane, aanwysers van hoë kwaliteit grasvelde, en bestudeer hul diversiteit binne grasveldgange tussen plantasiewoude, om ‘n beter begrip te kry van hoe plantasielandskappe bestuur kan word (bv. Voorgeskrewe veldbrande, indringerplantbestuur, boomoes) om ekologiese veerkragtigheid te verseker. Satelliettydreekse wys dat veranderinge in grasveldstruktuur ‘n blywende positiewe impak op sprinkane het tot en met drie jaar. Voorgeskrewe veldbrande, gemeet deur die historiese “Normalised Burn Ratio” indeks, help om hoë-gehalte sprinkaanhabitat te handhaaf, terwyl dit ook funksionele konnektiwiteit van grasveldgange beïnvloed. “Normalised Difference Vegetation Index” (NDVI) is 'n nuttige hulpmiddel om grasveldgang toestand te monitor en om te help met beplanning van voorgeskrewe brande. Groot grasveldgange met ‘n hoogtegradiënt ondersteun diverse springkaan gemeenskappe en moet geprioritiseer word vir bewaring. Diep-leer beeldsamesmelting het Amerikaanse braambos (Rubus cuneifolius), 'n aggressiewe indringerspesie in Suid-Afrikaanse grasvelde, met hoë akkuraatheid geklassifiseer in vergelyking met konvensionele satellietbeelde. Braambos het 'n negatiewe impak gehad op plantegroei, groter sprinkaanspesies sowel as sprinkane van belange vir bewaring. Braambos het oewergebiede gereeld binnegeval, wat Ensifera sprinkaanspesies se habitat bedreig. Die oes van houtkompartemente en voorgeskrewe brande het braambedekking in die landskap verhoog. Aktiewe bestuur van plantasie boomsaailinge na die oes van bome kan 'n positiewe impak hê op funksionele landskapkonnektiwiteit sowel as om braambedekking te velaag. Grasveldgange het hoë plantegroei-heterogeniteit wat veroorsaak is deur voorgeskrewe brande, wat bydra tot hoë spesie-omset. Grasvelde moet elke 2-3 jaar gebrand word. Die gebruik van NDVI sal bosbouers help met tydsberekening en bepaling van brande in grasveldgange, wat dan help om hoë kwaliteit sprinkaanhabitat en funksionele konnektiwiteit te handhaaf. Rotasie-oes van houtkompartemente word aanbeveel, aangesien die afkap van sommige houtkompartemente 'n positiewe impak op funksionele landskapkonnektiwiteit sal hê, as ook om braambos verspreading deur die landskap te voorkom. Ek beveel aan dat voorgeskrewe brande en beweiding deur mak beeste gebruik word om braambos te beheer. Spesiale aandag is nodig om braambos te beheer twee jaar na die oes van houtkompartemente, omdat braambos bedekking dan hoog is. Hierdie tesis demonstreer dat grasveldgange biodiversiteit binne produksielandskappe bewaar wanneer bestuur biodiversiteitreaksie op versteuring inkorporeer. Dit motiveer die instandhouding en beskerming van grasveldgange in ander dele van die wêreld om biodiversiteit te bewaar, wat help om insekafname te voorkom. Hierdie tegnieke bied waardevolle insigte op biodiversiteitsreaksie binne produksielandskappe, en kan dus toegepas word op ander plantegroei tipes vir die beskerming van biodiversiteit.Doctora