Ecosystem Guidelines for Environmental Assessment

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MAINLAND THICKET INCORPORATING THICKET, VALLEY THICKET & ARID THICKET MAINLAND THICKET ECOSYSTEMS MAINLAND THICKET Doug Euston-Brown What are the key ecological “drivers” in terms of maintaining ecosystem function, pattern or structure Herbivory is an integral part of thicket evolution and therefore function, pattern and structure. Thicket represents the backbone resource for browsing animals in Southern Africa: it is drought tolerant, reliable and enduring. Being further from the savannas and associated animals, thicket in the Western Cape may have been less influenced by herbivory than in the Eastern Cape. However, many animals such as kudu continue to make seasonal east-west migrations to escape winter droughts in the Eastern Cape and summer droughts in the Western Cape. Seed dispersal by animals (especially birds) results in the development of bush clumps around solitary perch sites such as pioneer trees and termite mounds. Bush clumps enlarge and, depending on local site conditions, eventually coalesce into dense thickets. Fires are important in maintaining thicket boundaries when they occur in the adjacent grassland and fynbos biomes. Thicket mosaics tend to develop in these boundary areas. Solid or uniform thicket tends to be associated with topographically-determined fire refugia - such as deep kloofs, cliffs and scree - or climatically-determined fire refugia, i.e. areas too arid to support flammable vegetation. Heavy grazing can reduce fuel loads, which can retard the spread of fire and allow the establishment and spread of thicket clumps. Climate variability - droughts, floods and heat waves - has little impact on thicket vegetation. Relative to the other biomes in the Western Cape, thicket is probably the most resilient to climate change. Thicket is therefore critically important for the health and persistence of broader ecosystems. Arid Thicket is probably the most resilient to climate change, but is most vulnerable to disturbance resulting from heavy browsing or grazing. Winter versus summer rainfall ratios (≥ 20% annual rain in winter, April-August) strongly influence the distribution of thicket. The western limit of Mainland Thicket correlates closely with the transition to a higher proportion of winter rainfall, and dominance by the Fynbos or Succulent Karoo biomes. Coastal Thicket only penetrates inland in the Western Cape where the maritime influence on the climate ameliorates summer drought. Topography, geology and soil type also drive the distribution of thicket vegetation. Mainland Thicket in the Western Cape is usually associated with the base of, or valleys within, the Cape Fold Mountains. This correlates with a transition to a more arid climate and a change from sandstone to non-sandstone soils. Thus, thicket acts as a buffer or barrier between the Fynbos Biome on the mountains and the Succulent Karoo Biome on the drier hills and flats. What are the key issues, vulnerabilities and threats Overgrazing, especially by goats, in combination with drought has led to the demise of spekboom Portulacaria afra. Spekboom is an essential component of thicket, especially in the Western Cape, where it is often the dominant species at the base of north-facing sandstone slopes. It appears to be a pioneer species that may facilitate the establishment of other thicket species. Once spekboom is lost, many other thicket species also die, and the slope becomes barren and prone to erosion. Such areas do not JAN VLOK 62 : MAINLAND THICKET ECOSYSTEMS
Spekboom Portulacaria afra (foreground) is an essential component of Mainland Thicket. MAINLAND THICKET
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ECOSYSTEM GUIDELINES FOR ENVIRONMEN
Page 4 and 5:
CHARL DE VILLIERS (EDITOR) Conserva
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CONTENTS 7 : 8 : 10 : 14 : 22 : 24
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“Environmental Assessment provide
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PREFACE Charl de Villiers These gui
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INTRODUCTION Susie Brownlie Purpose
Page 14 and 15: The drafting process, which was co-
Page 16 and 17: INCLUDING BIODIVERSITY CONSIDERATIO
Page 18 and 19: UNEP's voluntary guidelines on biod
Page 20 and 21: Breede River valley: CAPE and SKEP
Page 22 and 23: STEP 4: WHEN SIGNIFICANT IMPACTS AR
Page 24 and 25: A NOTE ON FIRE All fynbos types req
Page 26 and 27: COASTAL ESTUARIES COASTAL ECOSYSTEM
Page 28 and 29: COASTAL non-linear manner over wide
Page 30 and 31: COASTAL SANDY BEACHES & DUNE SYSTEM
Page 32 and 33: COASTAL What are the “bottom line
Page 34 and 35: COASTAL INCORPORATING WEST AND SOUT
Page 36 and 37: COASTAL Strandveld is also increasi
Page 38 and 39: What are the critical things to mai
Page 40 and 41: LOWLAND FYNBOS INCORPORATING SAND F
Page 42 and 43: LOWLAND FYNBOS Veld clearance for r
Page 44 and 45: NICK HELME LOWLAND FYNBOS Leipoldtv
Page 46 and 47: MIDLAND & MOUNTAIN INCORPORATING AL
Page 48 and 49: MIDLAND & MOUNTAIN Altered fire reg
Page 50 and 51: MIDLAND & MOUNTAIN What are the cri
Page 52 and 53: MIDLAND & MOUNTAIN will move in fro
Page 54 and 55: RENOSTERVELD INCORPORATING COAST &
Page 56 and 57: RENOSTERVELD Urban expansion is a p
Page 58 and 59: RENOSTERVELD What, if any, reliable
Page 60 and 61: SUCCULENT KAROO INCORPORATING VYGIE
Page 62 and 63: SUCCULENT KAROO Quarrying for grani
Page 66 and 67: MAINLAND THICKET appear to recover
Page 68 and 69: MAINLAND THICKET What are the criti
Page 70 and 71: FRESHWATER FRESHWATER ECOSYSTEMS: W
Page 72 and 73: FRESHWATER What are the key issues,
Page 74 and 75: FRESHWATER exotic garden escapees i
Page 76 and 77: FRESHWATER INCORPORATING MINOR DRAI
Page 78 and 79: FRESHWATER Introduction to the syst
Page 80 and 81: SCEPS SPATIAL COMPONENTS OF ECOLOGI
Page 82 and 83: JAN VLOK SCEPS Quartz patches can s
Page 84 and 85: SCEPS those characterised by mosaic
Page 86 and 87: TABLE 4: EXAMPLES OF SPATIAL COMPON
Page 88 and 89: SCEPS ecosystems (e.g. Granite Fynb
Page 90 and 91: REFERENCES & RESOURCES There is a w
Page 92 and 93: APPENDIX 1 SOUTH AFRICAN VEGETATION
Page 94 and 95: APPENDIX 2 RECOMMENDED TERMS OF REF
Page 96: SALDANHA CAPE TOWN VANRHYNSDORP CER
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Ecosystem Guidelines for Environmental Assessment

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