By Unna Chokkalingam, Wil de Jong and Cesar Sabogal of CIFOR
There are two aspects to secondary forest (SF) formation: first, a disturbance of the original forest and, second, a secondary forest re-growth. Key criteria used for defining SF in Latin America and Asia are contrasted in the table below, and are to be explored for the African context.
Nature of the |
Latin America |
Asia |
Africa |
influence |
Human Original forest fully destroyed - Farming, grazing |
Human Original forest significantly disturbed Single or cumulative Farming, grazing, logging, fire, rehabilitation, others |
? ? ? Similar to Asia? |
re-growth |
Natural Totally regrown Trees/forest stage |
Largely natural Major difference in structure and /or composition Trees/forest stage |
? ? ? |
Human vs natural disturbance
Only human disturbances were considered in both the previous workshops because the behaviour of human beings can be influenced and changed but natural processes cannot be changed.
Degree of canopy disturbance and secondary forest
All forests are disturbed to an extent and all disturbed forests are not secondary forests. The degree of canopy disturbance matters. The disturbance should be significant enough to set off successional processes, and should not be just small gap disturbances that could be caused by activities such as selective logging or limited NTFP extraction. In Latin America, total clearing was a criterion, followed by land conversion and abandonment or fallowing. In Asia, the definition was expanded to include heavily logged-over forests and a significant level of disturbance was considered sufficient instead of total clearing. The difference arises because, in Latin America, wood exploitation in the past has been highly selective leaving behind a largely intact residual forest. In Southeast Asia, logging has involved more intense exploitation and greater disturbance and change.
The significant disturbance effect could be the result of a single event or cumulative series of events - this was specified in the Asian definition.
Nature of activities
In Latin America, focus was on swidden agricultural and ranching systems, where secondary forests grow when land is left fallow or after pastoral land is abandoned. The human activities considered as a source of disturbance giving rise to SF were expanded in Asia to include all the sources of significant disturbance and/or re-growth in the region such as logging (wood extraction), swidden agriculture, fire, degraded land rehabilitation, and abandonment of alternative land use systems.
Perceptions varied in different regions given the varying nature of dominant disturbance. An attempt was made to be more comprehensive in Asia with potential to extend to other places, yet having a clear threshold or definition.
Artificial vs natural regeneration
In Latin America, only natural re-growth was included as a secondary forest. However, in Asia there were mixed indigenous agroforest and natural vegetation systems. Planting to catalyse natural vegetation and abandoned plantations taken over by secondary vegetation was also quite common. Thus a boundary was drawn to address the gradient between natural and artificial systems by allowing some planting but requiring that most of the regeneration be natural.
Secondary forest vs secondary vegetation
SF could be positioned in the middle area between the dotted lines (see figure below). There should be trees and there should be a forest as different from shrubland, grassland and other secondary vegetation to the left of the dotted line. Trees have been variably defined as woody vegetation > 5 m or > 3 m tall. Definitions of forests also vary. FAO uses > 10 percent canopy cover to describe a forest.
And related to the criteria of significant disturbance outlined above, the SF should be significantly different from the primary forest (PF) to the right of the dotted line (see figure below), and there should have been a major change in structure and composition as a result of human influence. So selective logging that removes a few trees or other use that does not cause major change does not qualify.
The figure also illustrates successional processes from grasslands and non-forest vegetation into secondary forest and into primary forest over a long period. Over a long time, similar structures and functions can develop though not exactly like the original forest.
Figure 2.1: Illustration of a successional process related to the formation of secondary forests
Extending the criteria to look at secondary forests in Africa
Using the criteria developed for Asia, the country papers suggest that most of the forests in Anglophone Africa are secondary, being natural re-growth following heavy human influence. This raises the following questions: If most of the forests in the region are secondary, then is it useful to talk about secondary forests at all? Is the distinction between secondary forest and primary forest more obvious and useful in moist areas?
But it is unclear whether the criteria and definition have been strictly followed in country assessments. The vegetation appears to be mainly woodlands and savannas in semi-arid to sub-humid Africa. It is also unclear as to whether they have been historically subject to heavy human and natural influences and/or have always been secondary in nature. Likewise, it is uncertain if pressure towards this resource has increased in recent times with increasing populations and economic changes?
Whatever the situation, a secondary forest focus is still potentially useful for the following reasons:
For understanding and influencing the processes (and actors) of forest interference and re-growth in the long term.
For managing a landscape as a shifting mosaic of seral stages that contribute to an overall cover of forest and other land uses at the larger scale.
For sustainable management of dynamic regrowing forests in terms of sustainable production cycles or sustained flow of goods and services that could change as the forest develops, rather than sustaining a particular forest structure or composition.
A secondary forest typology could be based on successional stages, vegetation types, ownership patterns, land use/nature of influence, or other criteria. All of them have their value. In Asia, a secondary forest typology was developed based on land use origin and/or nature of human influence. These categories depend on the type of land-use system in place. After a fire, the growing forest is referred to as a post-fire secondary forest; after timber extraction, it is post-extraction secondary forest.
A secondary forest typology based on land use origin was useful for the following reasons.
Secondary forest (SF) types - Asia versus Africa
Secondary forest types |
Asia |
Africa |
Post-extraction SF Swidden fallow SF SF gardens Post-abandonment SF Post-fire SF Rehabilitated SF |
Very common Common In moist areas Limited Unknown extent Limited |
Very common Common? ? Limited to poor soils Common, in semi-arid to sub-humid areas Limited to reserves |
Are the land use activities and actors leading to different types of SF development distinct?
Would this typology be more useful for wet than for dry African forest conditions?
Is a seral stage or vegetation-based typology more useful for technical management?
Is a combination or hierarchy of typologies required for:
