Active, Assisted and Passive: Different Approaches to Ecosystem Restoration

 

Channelling significant funds into ecosystem restoration projects can be difficult – with the private sector hesitant to spend on nature-based projects that don’t deliver the immediate returns on investment that they are used to. However, mounting awareness and pressure to invest in the wellness of our planet is increasing demand for high quality, large-scale and, crucially, cost-effective restoration projects. 

 

A Passive Approach 

To achieve landscape-scale restoration without blowing the budget, we can simply allow nature to take its course. Natural regeneration, aka the process by which trees and shrubs self-seed and spread, has the ability to restore entire ecosystems. Harnessing this process can allow for cost-effective, resilient ecosystem restoration and has, in some instances, proven more successful than active restoration for certain taxa. A major advantage of this passive solution to ecosystem recovery is that it can be applied on a large scale – it is a critical tool for meeting ambitious global restoration targets e.g. the 30×30 initiative. So, why bother with any other approach? 

 

Unfortunately, there are several factors that limit the power of natural regeneration, see table 1. Whilst natural regeneration does tend to be cheaper to deliver, its benefits accrue more slowly; so if a project is relying on carbon credits they might prefer an active component to speed up regeneration and financial returns. Additionally, if ecosystems are severely degraded and isolated, holistic nature recovery may never occur passively. Native Brazilian Atlantic forests may never naturally regenerate as carbon-dense trees with large seeds depend on large seed-dispersing mammal vectors (e.g. tapirs, toucans), however, these mammals have suffered steep population declines and range restrictions – hence certain tree species may never reach and recolonise these areas again. This is a significant shortfall of the passive approach and interventions are necessary to overcome these regeneration barriers.

 

Table 1: Advantages and Disadvantages of Natural Regeneration

Advantages	Disadvantages
Cheaper	Slower
Easier to implement on a large-scale	Uncertainty as to what type, how much and when vegetation will grow
Fewer staff needed e.g. for planting and forest management	Generates fewer jobs for local community members
Very effective where there is intact native habitat nearby that can act as a seed source	Ineffective when adjacent habitats are degraded
Ensures vegetation is local and native	Adjacent habitats acting as seed sources may not represent diverse native ecosystems
Limits soil disturbance and carbon emissions from this disturbance	Difficult to predict project carbon sequestration, reducing the amount of carbon funding available

 

Assisted Natural Regeneration – A Middle Ground

Enter Assisted Natural Regeneration (ANR), a middle ground that combines both active and passive restoration techniques. ANR interventions selected are project dependent; they may include removal of invasive species, elimination of threats to tree growth, supplementary tree planting, area isolation using fencing and species reintroductions. 

 

The level of intervention for ANR projects will often depend on:

• Initial state of the landscape 
• Level of habitat fragmentation
• Desired restoration timelines 
• Project objectives
• Available funding

 

Several rewilding projects within the UK serve as good examples of how biodiverse carbon-rich landscapes can be generated via ANR e.g. by incorporating fencing to retain herbivores, reshaping rivers and reintroducing keystone species such as beavers. ANR projects yield results faster than passive approaches and may better engage communities, fostering stewardship and enhancing local ecological knowledge. 

 

Active Restoration

Finally, we have active ecosystem restoration, this is an important strategy for carbon and/or biodiversity projects. Active projects have higher initial expenses due to the costs associated with active planting, increased number of staff and resources, however, they can deliver incredible targeted outcomes within accelerated timeframes. Degraded environments benefit the most from this approach, as their passive recovery is unlikely within the foreseeable future without active interventions and local species reintroductions.

 

When designing active restoration projects ecological expertise is essential; a mix of native tree species must be selected, trees should be planted at specific distances from each other and forests must be managed after the initial planting stage e.g. by thinning and replanting at suitable intervals. Active projects that receive negative media attention tend to fail or underperform due to lack of scientific knowledge in the design phase and/or the absence of forest maintenance after planting. 

 

Summary

Passive regeneration, ANR and active restoration approaches all possess unique strengths, making them suitable for different contexts and restoration goals. Active restoration is key for restoring degraded land and speeding up carbon sequestration. Whereas, ANR or passive regeneration may be better suited to scenarios where project sites are well connected to intact habitat, where process driven restoration is preferred or where budget and resource are limited. 

rePLANET projects factor natural regeneration into their design. Even our active restoration projects emulate natural recovery processes e.g. by using an accelerator reforestation approach. Applying passive, assisted and active restoration techniques over significant areas of land will be key to restoring the health and resilience of our ecosystems in time to meet our ambitious global restoration targets.