• Rehabilitation aims to revive important ecological services, or to restore a natural dynamic to ecological communities.

• Rehabilitation is used to regain some but not all of the original biodiversity of an area (WRI, 2003).

• It might mean to regain agricultural value or to vegetate with species merely to have a natural system in place, (not necessarily an indigenous system).

Defining restoration

DEFINING RESTORATION

• Reclamation suggests bringing something back to its original condition. It includes any process promoting soil conservation and productive use of derelict land (Peterson and Etter, 1970). The best methods use vegetation cover that is self-renewing, attractive and long-term.

• Restoration aims at facilitating natural processes in disturbed areas that will eventually lead to self-sustaining ecosystems similar to what was present before disturbance.

• Most complete restoration is rarely realistic because determining the pre-disturbance state of most ecosystems is difficult, and because ecosystems continually change (WRI, 2003).

• Goal: return a habitat to a more desirable condition involving a particular species composition, community structure, and/or set of ecosystem functions.

• Revegetation means to establish a plant cover of any type (Mentis and Ellery, 1994).

Defining restoration cont.

DEFINING RESTORATION

Relationship: ecosystem function and structure

• Restoration ecology aims to re-establish or rehabilitate damaged or lost plant or animal populations or species assemblages indigenous to the area of interest (Jordan et al, 1987).

Relies on fundamental knowledge of the target species, but it also provides opportunities for

testing basic ecological theories.

Benefits include:

• Maintenance of diversity of plants and animals• Improving wildlife habitats• Creating more aesthetically pleasing surroundings• Restoring natural communities• Protecting locally rare species

RESTORATION ECOLOGY

Restoration ecology

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• Setting realistic objectives is most NB step (Pastorok et al, 1997).

• In a mountain catchment, the most NB function may be to supply clean water. Alien trees must be removed and indigenous cover must be there to prevent erosion (Holmes and Richardson, 1999).

• Less transformed sites - reintroducing missing plant species

THE PLANNING PROCESS

The planning process

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• More transformed sites - reintroduce soil biota before some species can establish (Holmes and Richardson, 1999).

• Realistic objectives consider extent of damage (caused by IAS and the control or clearing of them), ecological potential, land-use goals and socio-economic constraints (available funds, time and trained staff).

• Landscape interactions must be considered.

The planning process

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• There is an important relationship between scale of disturbance and species abundance, distribution and persistence (Pavlovic, 1994)

• Restoration of disturbance processes must include those to which the indigenous plants are adapted (e.g. natural flooding, herbivory, trampling).

• Restoration may require reintroduction or management of the natural disturbance regime, elimination of a damaging anthropogenic disturbance regime, or introduction of a new disturbance regime (Pavlovic, 1994)

More to consider

MORE TO CONSIDER

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• Planned disturbances are often accompanied by revegetation plans.

• Topsoil is frequently collected and stored, to be replaced at the surface during revegetation. This practice is important for restoring the indigenous seed bank and soil microbial community.

• The longer the time that topsoil is stockpiled, the more likely it is that viable seeds of indigenous species will decline. Many harmful alien species have persistent seed banks.

Revegetation

REVEGETATION

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Ecosystem condition

Aim Example Actions Evaluation

Most pristine Maintain or enhance local biodiversity

Locally extirpated species

Sow seed of desired species, or transplant seedlings, after disturbance

Monitor establishment & survival of introduced species

Vulnerable species As above As above

Non-local indigenous species

Remove planted indigenous species & their hybrids

Monitor sites for non-local species & their hybrids

Invasive alien species Remove alien species Monitor sites for alien species

Re-establish ecosystem diversity, structure and function

Young, dense stands of alien species

Remove alien plants & burn Monitor species recruitment i.t.o diversity, guild structure & canopy cover

Aims of restoration

Old, dense stands of alien species

Remove alien plants & burn; sow locally collected indigenous species

Monitor species recruitment i.t.o diversity, guild structure & canopy cover

Ecosystem condition

Aim Example Actions Evaluation

Old, dense alien stands with evidence of soil damage

Remove alien plants & burn; stabilize slopes against further soil erosion; sow locally collected indigenous species

Monitor species recruitment & soil erosion

Re-establish indigenous plant cover

Denuded & eroding footpaths

Reconstruct footpath & stabilize surrounding slopes; plant denuded areas with local seedling material in winter; sow with locally collected species after disturbance

As above

Revegetation following mining or other short-term construction operations

Replace topsoil; sow with suitable seed mix

Monitor indigenous plant cover & alien species

Improve remnant connectivity

Grassy road verges with potential to become indigenous vegetation corridors

Remove non-indigenous cover (herbicide as last resort); sow or plant with suitable indigenous species

As above

Creation of indigenous vegetation corridors in agricultural land

As above As above

Highly degraded

Establish plant cover

Stabilise slopes after road construction

If little topsoil is available, add mulch & sow with fast-growing non-invasive alien annuals; oversow with indigenous seed

Monitor plant cover & alien species

Aims of restoration

• IAS may be part of the reason or need for restoration

• IAS may be the first to re-colonize after disturbances associated with vegetation removal (unplanned or “natural” disturbance)

• IAS may be the first to colonize after a planned disturbance, even if they were not present in the pre-disturbance community, and may interfere with restoration efforts

• IAS may leave behind a legacy after removal that makes long-term restoration difficult (e.g. seed bank, chemical or physical alteration of the habitat)

• Alien spp. may be used in restoration to restore particular functions if indigenous spp. aren’t suitable or available

ROLE OF IAS IN RESTORATION (D’Antonio and Meyerson, 2002)

The role of IAS

• Myrica faya has colonized young volcanic soils in Hawaii, where fixes nitrogen at a rate four times as high as all other sources of fixation combined. When it is killed, it leaves a legacy of high soil nitrogen. Introduced grasses appear to benefit from this die-off, complicating restoration efforts (Adler et al, 1998).

• Invasive alien species often have very large persistent seed banks. They often maintain a much larger seed bank in their new habitat. Species with buried seed banks or extensive and persistent rhizomatous networks require repeated follow-up treatments (D’Antonio and Meyerson, 2002).

Long-term effects of IAS

LONG-TERM EFFECTS OF IAS

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• In South African riverbanks, erosion has been accelerated by many introduced species (Acacia and Pinus spp.).

• Restoration of sites degraded by alien species and soil erosion pose a particular challenge.

• The topography may no longer resemble the pre-invasion conditions, and removal of the aliens may cause further erosion.

• Highly degraded sites may no longer be able to support the desired species assemblages. Under these conditions it may be necessary to stabilise the soil using synthetic or biodegradable materials or establish indigenous vegetation before alien removal (D’Antonio and Meyerson, 2002).

Long-term effects of IAS cont.

LONG-TERM EFFECTS OF IAS cont.

• In some degraded sites it may be necessary to introduce an alien species to assist with the restoration process.

• Where soil erosion or the potential for it is severe, many practitioners use fast-growing but sterile alien grasses to quickly establish cover. These grasses do not seed and presumably give way to indigenous species (D’Antonio and Meyerson, 2002).

• Introduced species used in restoration must be monitored over time, and only used if no other options.

• Introduced species do sometimes have a role to play in restoring functional aspects of ecosystems, but this must be related to the overall goal of restoration and the context within which restoration is carried out (Hobbs and Mooney, 1993).

The role of IAS in restoration

THE ROLE OF IAS IN RESTORATION

Links to other chapters

Chapter 1 Definitions

Chapter 2 History, globalisation and GMOs

Chapter 3 The human dimension

Chapter 4 Pathways of introduction

Chapter 6 The ecology of biological invasions

Chapter 5 Characteristics of invasive alien species

Chapter 7 Impacts of invasive alien species

Chapter 8 Invasive species management

Chapter 10 Ecological restoration

Chapter 9 Predicting invasive spp. occurrence and spread

Chapter 11 International perspectiveNext

Chapter 12 South African perspective

I hope that you found chapter 10 fun to do and that you will enjoy the next chapter in this course.