BOT 251 ST 1

• Succulent Karoo Biome


  Location: West Coast from escarpment westwards, 0 to > 1 500 m a.s.l., extends eastwards into the interior of the Eastern Cape, 4th largest biome similar in size to fynbos biome
• Climate: Rainfall


  Arid, generally 100 – 200 mm p.a., largely winter, frontal rainfall, widespread, gentle showers, some areas more bimodal or year round (eastern areas), hailstorms and thunderstorms rare, fairly predictable, more predictable than in Nama Karoo and Desert, no prolonged droughts, fog important along coast

  
• Climate: Temperature

  Warm and temperate, strong maritime (oceanic) influence along coast, absolute max. 44°C, Berg winds from interior - hot and very dry winds, frost inland at higher altitudes but rare
• Growth forms


  • Shrubs and dwarf shrubs
  • Succulents (Aizoaceae, Crassulaceae, Euphorbiaceae)
  • Geophytes (Iridaceae, Hyacinthaceae)
  • Asteraceae (many annuals)
• Aizoaceae


  Also known as Mesembryanthemaceae, includes vygies, mesembs, stone plants, midday flowers, ice plants

  
• Crassulaceae


  • e.g. Crassula columnaris, CAM photosynthesis
• Euphorbiaceae


  • e.g. Euphorbia mauritanica, also includes trees, shrubs and forbs
• Geophytes


  • 18% of flora, Iridaceae e.g. Romulea spp., Hyacinthaceae e.g. Lachenalia spp.

  
• Asteraceae


  • Many annuals, 390 species, contribute to flower display

  
• Succulent Karoo bioregions


  • Richtersveld
  • Namaqualand Hardeveld
  • Namaqualand Sandveld
  • Knersvlakte
  • Trans-escarpment Succulent Karoo (including Hantam Bokkeveld)
  • Rainshadow Valley Karoo (Tanqua Karoo, Little Karoo & Worcester-Robertson Karoo)
• Richtersveld


  • Mountainous area, winter rainfall, arid
• Namaqualand Hardeveld


  • Hilly, escarpment region, rugged, 30 to 1 700 m altitude, granite & shallow soils, massive flower displays
• Namaqualand Sandveld


  • Namaqualand coast, sandy plain, aeolian origin (windblown)
• Knersvlakte


  • Below the escarpment, flat to gently undulating, quartz fields
• Trans-escarpment Succulent Karoo


  • High altitude plateau, loamy soils, includes the Hantam-Bokkeveld "bulb capital of the world"
• Rainshadow Valley Karoo


  • Higher rainfall than rest of Succulent Karoo, rainfall gradient from west to east, winter to autumn & early summer, Roggeveld Escarpment very rugged, Tanqua Karoo extremely arid, Little Karoo between Swartberg & Langeberg Mountains

  
• Geology

  • Complex & diverse, sedimentary rocks, intrusive igneous rocks, granite domes (Namaqualand)
• Diversity and Endemism


  • Exceptionally diverse, global hotspot of biodiversity, 1 of 2 arid hotspots, 6 356 plant species, 38% of species endemic, 17% of species on Red Data list, 1 002 plant genera (80 endemic), dwarf leaf-succulents important (1 700 species, 16% of the world's succulents)

  
• Centres of endemism


  • Gariep Centre
  • Knersvlakte Centre
  • Little Karoo Centre
  • Worcester-Robertson Karoo Centre
  • Hantam-Roggeveld Centre
• Greater Cape Floristic Region

  • Winter-rainfall biomes (Succulent Karoo, Fynbos) floristically distinct from other South African (and African!) biomes, many shared genera, exceptionally high (80%+) endemism, constitute a greater whole
• Reasons for high diversity levels: relatively predictable rainfall, potential for rapid diversification, limited climatic change, diverse geology & soils, plant-pollinator interactions

  
• Spring flower display


  • Goegap Nature Reserve, tourist attraction
• How to manage for flowering display: occasional ploughing of fields favours showy annuals associated with disturbance, but annuals only comprise 8% of biome's flora, higher diversity of species in less disturbed areas, perennial species also contribute to flower display
• Threats


  • Overgrazing
  • Mining (open cast diamond, heavy metal mining, restoration difficult)
  • Alien invasive plant species
  • Plant collectors (ornamentals, medicinal plants)
  • Climate change
• Status


  5.8% formally protected, c. 5% transformed, c. 90% livestock farming (good management essential), SKEP international conservation effort (Succulent Karoo Ecosystem Programme)
• Distinguishing arid biomes


  • Desert: Short, hot growing season, lowest and least predictable rainfall, high relative diversity
  • Nama Karoo: Short, warm growing season, unpredictable summer rainfall, low relative diversity
  • Succulent Karoo: Short, cool growing season, predictable (winter/bimodal) rainfall, very high diversity and endemism
  • Fynbos: Long, cool growing season, higher (predictable, winter) rainfall, very high diversity and endemism

  
• Invasive species


  Alien (i.e. exotic, non-indigenous) species that produce reproductive offspring at considerable distances from parent plants
• Invasion process


  1. Transport from native range

  2. Introduction and colonization

  3. Establishment and reproduction

  4. Spread

  
• Biological invasions framework


  • Transport
  • Introduction / colonization
  • Establishment
  • Spread
• Eight advanced concepts


  • Transport - dispersal pathways
  • Introduction / colonization - propagule pressure
  • Establishment - residence time
  • Spread - lag time, disturbances, empty niches, biotic resistance, enemy release

  
• Dispersal pathways


  How species are introduced to an area and how they spread within that area

  
• Introduction pathways


  • Accidental
  • Intentional
• Accidental introductions


  • Species adapted for dispersal, produce many small seeds, occur over wide area and/or with crops and humans, no human-assistance after introduction, often very few seeds transported, may have low genetic variation
• Intentional introductions


  • Species considered useful by humans, agricultural or ornamental species, can be poor dispersers, transported to suitable area, sometimes many seeds giving high genetic variation, planting trials and cultivation, environment modified to enhance survival
• Accidental introductions to Marion Island


  • Poa annua
  • Cerastium fontanum
  • Sagina procumbens
• Introductions to the Karoo


  • Intentional: Prosopis sp., Atriplex sp., Bromus sp., Opuntia sp., Schinus molle
  • Accidental: Salsola kali, Argemone ochroleuca
• Propagule pressure


  Total number of seeds (or other propagules) introduced, number of introductions x number of individuals per introduction, greater propagule pressure increases establishment probability
• Propagule pressure can be quantified, predicted and managed
• Most seeds dispersed short distances

  Propagule pressure generally highest adjacent to established populations
• Residence time


  Time since (first) introduction, species with longer residence time will have wider distribution and worse invasion status