Capacity-development workshop for Central, Eastern and Southern Africa on the restoration of forests and other ecosystems to support the achievement of the AichiBiodiversity Targets, 2-6 October 2017, Durban, South Africa Rehabilitating the biodiversity and productivity of moist forests and deciduous woodlands through active resource use Coert J. Geldenhuys Forest and Wood Science, Stellenbosch University, Stellenbosch Plant and Soil Sciences, University of Pretoria, Pretoria cgelden@mweb.co.za
What would be your thoughts about these situations? Every time I ask myself: Is this OK or bad? If it is BAD, how bad? Why? How does this relate to natural processes? Timber harvesting Bark harvesting Charcoal production Can it be restored? Is human resource use always bad? Or is conservation always good? What criteria do we use for objective assessment? Slash & burn Fire Plant invasions I suggest that we have many wrong perceptions: Consider that: What looks good may be ecologically bad; Road construction Powerlines Mining Residences Or, what looks bad may be ecologically very good!
What are the causes of forest/woodland degradation? • Uncontrolled resource use beyond recovery potential of targeted species? – Timber products - large-dimensions – Non-timber forest products – poles, fuel wood (charcoal & firewood), wood carving, etc – Non-wood forest products – bark for fiber and/or traditional medicine • Changed fire regimes in fire-prone systems? – Exclusion of fire – Cooler fires • Alien plant invasions? – Light-demanding versus shade-tolerant species • Forest/woodland cleared for alternative uses? – Crop cultivation - Food, bio-energy products, timber plantations, etc – Development of settlements, urban development, infrastructure, mining, etc
Why do we want to restore the specific landscape, ecosystem, species? • Major global concerns underlying need for cost-effective approaches to rehabilitate natural forests/woodlands – Degraded and cleared through • slash-and-burn traditional agriculture • charcoal production • uncontrolled timber-harvesting practices with no silvicultural management • clearing for commercial agriculture, plantation forestry, infrastructure development and mining – Alien plant invasions threaten biodiversity & ecological processes of natural vegetation systems, including natural forests – Climate change, Green-house gas emissions, etc
Why do we want to restore the specific landscape, ecosystem, species? • Restore essential ecological processes – Basis for maintaining optimum biological diversity – Adaptations to imposed stresses, disturbances, etc • Restore their biological diversity per se – Many floral and faunal components depend on forest ecosystem – Cannot be done without considering ecological processes at different levels • Restore productive capacity – for diverse resource use options of diverse resource users for diverse forest products • Restore their environmental services – nutrient cycling, carbon sequestration, soil and water conservation, etc • Combination of ALL = Basic good forest management
When is a forest in degradation or in recovery?
FORESTS have INTEGRAL NATURAL DISTURBANCE & RECOVERY PROCESSES on the outside on the inside Lightning without fire Lightning with fire Windfall gaps
Disturbances a natural part of all vegetation formations • Biological components (species) of all forest/woodland types - represent adaptations to different disturbance regimes - form part of different (recovery) stages of vegetation - they show different • Growth/Life forms: trees, shrubs, herbs, etc. • Bark types; Fruit & seed types • Relative tolerances of forest/woodland species to • Shade (pioneer vs early regrowth vs mature forest) • Browsers (fire, fauna, people)
A disturbance is ….. • A discrete event (fire, browsing, tree fall,..) changing - species & structure - physiological processes resources: ± light, o C, nutrients - • Called a - Non-event – frequency/impact too minor to cause response - Incorporated – within adaptation & tolerance limits of entity; necessary to maintain entity in current state - Disaster – changes entity into new state; increases fitness - Entity level: individual, population, community or landscape • Human activities need to simulate natural disturbances to which the forest/woodland system & its components are adapted • Keep human resource use disturbances to level of Non-event & Incorporated disturbance at level of population & community • Focus rehabilitation at level of disaster to population, community, ...
Disturbances a natural part of all vegetation formations • Total biodiversity of a particular vegetation system - Depends on maintenance of different natural disturbance-recovery processes in that vegetation - If we totally protect a system, we loose important biodiversity components of the system • Action of disaster to one level may benefit - Another level • Eg breakdown of community structure (disaster) may benefit population of pioneer/early regrowth species (eg Prunus ) - Another component at same level • Eg lack of regeneration of pioneer species (disaster) may benefit regeneration of more shade-tolerant species • Greater disaster of disturbance at one level - Longer period of recovery of that component/level towards original condition of forest/woodland prior to disturbance event
Diversity in adaptations to disturbance • Each forest has species adapted to different disturbance factors at different regimes, mainly - Shade tolerance in closed evergreen forests - Fire tolerance in deciduous woodlands - Other secondary factors = primary factors in some species • Each species functions best under optimum conditions related to primary factor of adaptation, in terms of - Regeneration, establishment & productive growth - = Main ecological criteria for sustainable functioning! • Species dominance changes from early regrowth stands towards mature forest - In which stage do our target species show optimum development & growth? - What would be the best approach to rehabilitate specific species/systems
A disturbance … • may vary in its effect or impact, depending on - its regime (intensity, frequency or area of impact) - component species of system & their adaptations • regime x habitat/site = landscape patterns = Vegetation types & Biodiversity patterns • forest-woodland-shrubland-grassland in same area
Forest/woodland formations in Africa And how do they determine the composition & dynamics of the different systems, resource use practices, rehabilitation actions?
Everything we do causes changes – even doing nothing! • Forest/Woodlands not museum pieces – DYNAMIC SYSTEMS!! • How should we deal with Disturbance-Recovery processes in the forest/woodland environment? • Is it the inability of the vegetation to respond? • OR is it our poor understanding [despite good intentions] of natural forest & woodland dynamics? • What multiple-use management systems will maintain natural diversity when we use forest products & services? • Can we rehabilitate natural complexities (species x age) in degraded forests/woodlands?
Detailed forest location pattern with fire pathways: Storms River Solid = fire burn, thickness = severity Broken = fire jump, up to 4 km 1 2 Storms River bridge
FOREST LOCATION PATTERN & PROCESS: Plantations planted in fire pathway Forest location pattern determined by fires driven by prevailing winds (Bergwinds) in dry season: …. & regularly destroyed! Forests persist in ‘ fire-shadow ’ areas in landscape In South Africa, natural forests occur in areas with rainfall >725 mm/a in summer rainfall & >500 mm/a in winter/all year rainfall 7% of RSA has rainfall >800 mm/a; Forests cover only 0.1% Similar patterns can be seen in other parts of Africa Rehabilitating natural forest in the fire pathway will be fatal
Woody plants establish in landscape with disturbance (fire) exclusion • Fast-growing pioneer trees – often invasive alien species (eg Wattle) • Buffer/nurse more variable & extreme conditions of regularly disturbed grassland, shrubland & agricultural fields • Facilitate establishment of shade-tolerant forest species • Typical forest succession process AND we can manage the process, or benefit from it, at low cost! Stage 1: Stage 2: Stage 3: Stage 4: Dense pioneer stand Growing up & Further development/ Pioneer stand totally self-thinning thinning removed No understorey Sparse understorey Young regrowth forest Mixed regrowth forest Alien clearing action Rehabilitation action Invader plant, or Invader plant or planted Forest trees and other Planted tree for woodlot tree removed species establishing timber, fruit, etc. for use or other purpose naturally or interplanted (thinning) (potentially traditionally used species)
Our CONCEPT: Recovery of natural forest species follows a natural succession process towards diverse systems Keurboom (Virgilia divaricata) after fire Same happens with plantation stands on forest margin! Pines Eucalypts Acacias AND with INVADER PLANT stands!!
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