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  • Cut less, leave longer: decades of data show we are over-exploiting tropical rainforests

Cut less, leave longer: decades of data show we are over-exploiting tropical rainforests


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We are logging more than can be sustained by tropical forests. Plinio Sist, Fourni par l'auteur
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Tropical rainforests currently cover 1070 million hectares of the world’s surface. More than 90% of them are located in three regions: Central Africa, in the Congo Basin; South America, mostly in the Amazon; and in Southeast Asia, in Indonesia, Malaysia and Papua New Guinea.

It is estimated that 400 million hectares of these forests are currently given over to timber production. But our research over many decades shows the rules that govern timber harvesting in tropical forest – currently based on logging intensity and cutting cycle – do not allow for the long-term recovery of the timber volume being harvested from these ecosystems.

These observations question the very foundations of the so-called “sustainable management” of these forests, and indicates that we will see further degradation of the planet’s last timber-producing tropical rainforests. It is therefore urgent that we seek out new sources of timber. Natural forests alone will not be able to meet current and future demand.

The principles of tropical silviculture – the management of forests to meet the needs of diverse groups and industries – must also be completely revised.

No time to recover

Timber harvesting in tropical forests concerns only a very small number of trees of commercial interest: one to three trees per hectare in Africa, five to seven in the Amazon, and eight in Southeast Asia. Just a few species, including ipe, cumaru, okoumé and sapelli are exploited worldwide.

Among these, only the largest trees of more more than 50 to 80 cm in diameter are felled and harvested. The forest is then left to rest, generally for 25 to 35 years, depending on a specific country’s legislation. These rest periods, known as “rotations”, should theoretically allow the forest to recover the stock of harvested timber.

But our data shows that, in reality, these resting periods are vastly underestimated.

Since the early 1980s, CIRAD and its partners have set up experimental plots to monitor tropical forest dynamics in order to assess the effects of selective logging on the reconstitution of the timber stock. This information now allows us to simulate the trajectories of exploited tropical rainforests according to the harvesting intensity, but also other variables – including rainfall and soil type.

Using this information, we calculated the reconstitution of a forests’s biomass, the commercial volume of timber and the evolution of biodiversity within the Amazon basin to highlight significant differences within the same region.

We found that, in general, the rotation times of 25-35 years in force in most tropical countries are insufficient to fully reconstitute the timber volume removed. On the other hand, biodiversity and biomass seem to recover fairly quickly within 20-25 years, after which more than 80% of biodiversity remains at the level of the pre-harvest level.

Unsustainable production

In the Brazilian Amazon, current forest protection legislation is based on a 35-year cycle, with an harvesting intensity of 15-20 m3 per hectare and an initial proportion of commercial species of 20%. At this rate, and considering a harvesting area of 35 million hectares, the level of production cannot be maintained beyond one harvesting cycle of 35 years, and will then decline each year until the resources are depleted.

Only by reducing harvesting intensity by half and a 65-year cutting cycle would ensure sustainable and constant timber production; however, in this situation, only 31% of current demand could be met.

In Southeast Asia, the cutting cycle period is 20 to 30 years, and logging intensities in primary forest, on average 80m3 per hectare, can exceed 100m3 per hectare. But data from forest dynamics monitoring indicate that only an intensity of 60m³ per hectare every 40 years would ensure sustainable and consistent production over time.

Finally, in Central Africa, the recovery of the stock of timber removed 25 years after logging is only 40%, suggesting a recovery of barely 50% over a 30-year rotation.

A new system for harvesting timber

The idea behind tropical silviculture, designed more than half a century ago, is that natural tropical forests are capable of producing timber in a sustained manner. In light of our results, this position must be completely revised.

The monitoring of tropical forests dynamics after logging shows that, in most tropical countries, they will not be able to meet the growing market demand for timber within 30 years, according to the rules established by forestry legislation.

In the vast majority of cases, true sustainability would require a considerable reduction in the harvesting intensity and a significant increase in the duration of logging cycles, which compromises the economic sustainability of selective logging in the current legislation system.

Natural tropical forests can no longer be perceived as a simple source of timber: the environmental services they produce should also be taken into account. For example, we could consider pricing timber from natural forests higher than that from plantations, with intended use linked to the higher quality of their wood. This higher price would increase the economic profitability of timber harvesting in natural forests, while plantation wood could be used for less noble purposes.

There is an urgent need to promote diversified tropical forestry now, combining timber production from natural forests, mixed plantations, agroforests (human-created forest systems with a multi-level vegetation structure similar to natural forests), and secondary forests (those regenerated on deforested areas left to be abandoned).

The rising international interest in tropical forest restoration under the Bonn Challenge – a plan to restore 350 million hectares of deforested land by 2030 – or the very recent proclamation of the UN Decade of Ecosystem Restoration (2021-2030), are both opportunities to implement this new approach in the tropics.

But no new system aimed at sustainable timber production will be successful without also introducing effective policies to combat illegal logging and deforestation, which continue to supply the timber market at lower costs and compete with any logging system aimed at long-term sustainability.

By Plinio Sist, member of the FTA Management Team

Originally posted on The Conversation »


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  • Silviculture techniques help farmers improve incomes, develop more productive agricultural systems

Silviculture techniques help farmers improve incomes, develop more productive agricultural systems


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Staff measure timber volume in a demonstration plot in Gunung Kidul. Photo by Riyandoko/ICRAF
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Staff measure timber volume in a demonstration plot in Gunung Kidul. Photo by Riyandoko/ICRAF

Two new studies reveal the importance of silviculture for increasing farmers’ incomes in Java and East Nusa Tenggara, Indonesia.

Planting timber in agricultural systems is a common practice in Indonesia. Farmers often cultivate timber together with other crops to diversify and increase their incomes. Timber acts as a savings bank, only being harvested when large funds are needed. To ensure the best growth of timber, experts recommend that farmers practise silvicultural techniques, which, despite the numerous benefits, are still not widely adopted.

In Gunung Kidul in the province of Yogyakarta and in Sumbawa and South-central Timor in East Nusa Tenggara province, researchers in the Developing and Promoting Market-based Agroforestry Options and Integrated Landscape Management for Smallholder Forestry in Indonesia project explored the factors that encouraged farmers to adopt silvicultural techniques.

Their findings have been published in Agroforestry Systems: Adoption of silvicultural practices in smallholder timber and NTFPs production systems in Indonesia. The project is funded by the Australian Centre for International Agricultural Research and is linked to the CGIAR Research Program on Forests, Trees and Agroforestry (FTA).

“At the research sites, timber and non-timber forest products contributed significantly to the economy,” said Gerhard Manurung, research leader and agroforestry scientist with the World Agroforestry Centre (ICRAF) in Indonesia. “We found that the most important factors affecting whether farmers would use silvicultural techniques or not were ease of access to the knowledge found in forestry extension services and farmers’ groups, how well they understood government policies on timber and non-timber forest products [NTFPs], the number of land parcels held by each farmer, and the number of tree and other species that the farmer managed.”

He pointed out that most available research on silvicultural practices was usually done in the context of natural forests, whereas this study offered a fresh perspective because it focused on agroforestry systems, or trees on farms.

Silviculture helps farmers develop more productive systems and reap greater benefits. For example, pruning leads to knot-free timber, which attracts premium prices; thinning young trees so that the remaining trees do not have as much competition for light and nutrients generates the highest percentage of heartwood volume, meaning bigger trees for harvest and more timber to sell; and intercropping teak with nitrogen-fixing shrubs helps to increase the trees’ diameter while at the same time improving soil conditions, which facilitates faster and stronger growth and bigger trees.

A staff member prunes a teak tree. Photo by Riyandoko/ICRAF

Timber and NTFPs contributed more than 60 percent to household incomes at the three sites, which was greater than that from agricultural and plantation crops, yet the adoption of silviculture remained low. The researchers found that a lack of resources and access to information stopped farmers from adopting better practices. In Sumbawa and South-central Timor, when there was more access to forestry extension services and farmers’ groups where knowledge was exchanged, the likelihood of farmers adopting better silvicultural practices rose 2–4 times.

The researchers recommended that policymakers, researchers and extension providers should collaborate more robustly, using approaches that put farmers’ livelihoods at the forefront. Research and training should incorporate participatory techniques, which are renowned for their success in fostering problem-solving skills and speeding learning. Additionally, government research centres should provide on-farm support, such as demonstration plots, that allowed farmers to observe changes brought about by improved techniques.

In terms of policies, the researchers proposed that governments encourage intensification of smallholders’ tree products through intercropping, which escalates the rate of adoption. Regulations on the sale of tree products should be simplified and information provided about grading and pricing mechanisms.

The other study, The significance of planted teak for smallholder farmers, focused on Gunung Kidul, where teak is a valuable investment and an important part of cultural heritage. When grown together with other commercial crops, teak agroforestry systems in Gunung Kidul contributed 40 percent of household income.

Typically, teak produced by smallholders has a diameter of 30 centimeters, which is considered suboptimal by the industries in Jepara in Central Java that produce much of the nation’s teak furniture. Thinning trees helps to improve the size and quality of those that remain but often farmers are unwilling to thin because they fear they will lose income. Also, most farmers use wildlings, sourced from forests or natural regrowth on farms, instead of high-quality seedlings or seeds produced in nurseries. Wildlings typically do not grow as well as those produced by skilled nursery operators.

In Indonesia, the value chain for teak consists of smallholders, local traders, wholesalers and processors. Farmers typically sell logs at prices based on information from other farmers. There is a general lack of knowledge about market prices and grading systems, resulting in sales often below market value. Because traders bear the major risk in the transaction, they lower their offers to farmers so as to cover the cost of the risk.

Echoing Manurung and team’s findings, the researchers recommended the use of on-farm trials as a way of stimulating farmers’ interest in improvements. Further, silviculture needed to be aligned with farmers’ needs for short-, medium- and long-term income. For example, by thinning trees farmers could plant short-rotation tree species, which could be harvested in 5–8 years, in between the teak.

The researchers also urged the development of win-win partnerships between farmers and industry, with governments providing incentives and simplifying timber regulations. Information about price and quality needed to be widely disseminated along with silvicultural extension programs. Research centres and industries could provide access to high-quality seeds and seedlings.

By Enggar Paramita, originally published at ICRAF’s Agroforestry World


This work is linked to the CGIAR Research Program on Forests, Trees and Agroforestry, which is supported by CGIAR Fund Donors


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  • Eighteen institutions sign up to Tropical managed Forests Observatory

Eighteen institutions sign up to Tropical managed Forests Observatory


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It is estimated that only a quarter of tropical forests are pristine. Photo by TmFO
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The DR Congo has the second largest tropical forest area in the world. Photo by Ollivier Girard/CIFOR

The Tropical managed Forests Observatory (TmFO) was recently formalized by a collaboration agreement signed by 18 institutions, including Agricultural Research for Development (CIRAD).

The confirmation of this unique network will enable it to continue monitoring the world’s logged tropical forests and drafting recommendations for sustainable silviculture. This is a crucial challenge in the light of biodiversity erosion and climate change.

Some 75 percent of the world’s tropical forests have been disrupted by human activity. It is vital to understand the ecology and resilience of these managed ecosystems in order to determine their future role in mitigating global warming and conserving biodiversity in the territories concerned. The TmFO network is the only organization working on logged tropical forests, as the other existing structures (Rainfor and CTFS) are limited to so-called primary forest.

“The network, which is now official, will benefit from greater visibility,” said the CIRAD researcher coordinating the network, Plinio Sist, also of the CGIAR Research Program on Forests, Trees and Agroforestry (FTA). “What we have to do now is to sustain it by developing projects.”

Read more: Tropical Production Forests Observatory

Fine-tuning recommendations concerning sustainable silviculture 

TmFO has existed informally since 2012. At the time, CIRAD decided to use funding from FTA to federate several experimental sites on three continents (in Amazonia, the Congo Basin and Southeast Asia). Those sites are monitoring forest dynamics after logging and silviculture. Some have existed for more than 30 years, such as Paracou (French Guiana), Mbaiki (Central African Republic) and Tapajos in the Brazilian Amazon.

It is estimated that only a quarter of tropical forests are pristine. Photo by TmFO

“The aim is to have a regional and pantropical picture of the resilience of these forests,” Sist explained. In effect, “the forests of the northeastern Amazon do not react to logging in the same way as others in the South of the forest basin. The observatory’s data are placed within a regional context, and are thus more useful for adapting sustainable silviculture recommendations.”

Exceptional opportunity to study forest resilience  

The TmFO network has already enabled a degree of progress. For instance, it has demonstrated that Amazon forests recover their carbon stock in 20 years. This result shows that sustainably logged forests play a fundamental role in C02 capture, hence in mitigating climate change.

Read more: Diversity, commitment, challenges and shared goals: How CIRAD looks at FTA

The general agreement specifies four main structures: a steering committee, in which each of the 18 member institutions will be represented by a member, and three regional technical committees, for Amazonia, the Congo Basin and Southeast Asia. CIRAD is coordinator for the next two years.

The TmFO network in figures:

  • 22 experimental sites encompassing 517 forest plots covering a total of 1134 ha
  • 18 forestry research institutions are monitoring those sites, all of which have signed the agreement
  • 9 countries are home to those sites: Bolivia, Brazil, Guyana, France (French Guiana), Surinam, Central African Republic, Gabon, Malaysia and Indonesia
  • 40 researchers are involved in the network.

Originally published on CIRAD.fr.


This work forms part of the CGIAR Research Program on Forests, Trees and Agroforestry (FTA), which is supported by CGIAR Fund Donors


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  • Eighteen institutions sign up to Tropical managed Forests Observatory

Eighteen institutions sign up to Tropical managed Forests Observatory


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It is estimated that only a quarter of tropical forests are pristine. Photo by TmFO
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FTA COMMUNICATIONS TEAM

The DR Congo has the second largest tropical forest area in the world. Photo by Ollivier Girard/CIFOR

The Tropical managed Forests Observatory (TmFO) was recently formalized by a collaboration agreement signed by 18 institutions, including Agricultural Research for Development (CIRAD).

The confirmation of this unique network will enable it to continue monitoring the world’s logged tropical forests and drafting recommendations for sustainable silviculture. This is a crucial challenge in the light of biodiversity erosion and climate change.

Some 75 percent of the world’s tropical forests have been disrupted by human activity. It is vital to understand the ecology and resilience of these managed ecosystems in order to determine their future role in mitigating global warming and conserving biodiversity in the territories concerned. The TmFO network is the only organization working on logged tropical forests, as the other existing structures (Rainfor and CTFS) are limited to so-called primary forest.

“The network, which is now official, will benefit from greater visibility,” said the CIRAD researcher coordinating the network, Plinio Sist, also of the CGIAR Research Program on Forests, Trees and Agroforestry (FTA). “What we have to do now is to sustain it by developing projects.”

Read more: Tropical Production Forests Observatory

Fine-tuning recommendations concerning sustainable silviculture 

TmFO has existed informally since 2012. At the time, CIRAD decided to use funding from FTA to federate several experimental sites on three continents (in Amazonia, the Congo Basin and Southeast Asia). Those sites are monitoring forest dynamics after logging and silviculture. Some have existed for more than 30 years, such as Paracou (French Guiana), Mbaiki (Central African Republic) and Tapajos in the Brazilian Amazon.

It is estimated that only a quarter of tropical forests are pristine. Photo by TmFO

“The aim is to have a regional and pantropical picture of the resilience of these forests,” Sist explained. In effect, “the forests of the northeastern Amazon do not react to logging in the same way as others in the South of the forest basin. The observatory’s data are placed within a regional context, and are thus more useful for adapting sustainable silviculture recommendations.”

Exceptional opportunity to study forest resilience  

The TmFO network has already enabled a degree of progress. For instance, it has demonstrated that Amazon forests recover their carbon stock in 20 years. This result shows that sustainably logged forests play a fundamental role in C02 capture, hence in mitigating climate change.

Read more: Diversity, commitment, challenges and shared goals: How CIRAD looks at FTA

The general agreement specifies four main structures: a steering committee, in which each of the 18 member institutions will be represented by a member, and three regional technical committees, for Amazonia, the Congo Basin and Southeast Asia. CIRAD is coordinator for the next two years.

The TmFO network in figures:

  • 22 experimental sites encompassing 517 forest plots covering a total of 1134 ha
  • 18 forestry research institutions are monitoring those sites, all of which have signed the agreement
  • 9 countries are home to those sites: Bolivia, Brazil, Guyana, France (French Guiana), Surinam, Central African Republic, Gabon, Malaysia and Indonesia
  • 40 researchers are involved in the network.

Originally published on CIRAD.fr.


This work forms part of the CGIAR Research Program on Forests, Trees and Agroforestry (FTA), which is supported by CGIAR Fund Donors


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