Working with nature: tropical
forest regrowth and its potential for mitigating climate change

The Bonn challenge aims to restore 350 million hectares of
degraded land by 2030 of which currently almost 100 million hectares has been
committed through various initiatives. Restoration is a global priority; not
only to restore the productivity of degraded and unproductive land, but also
because promoting tree cover will increase carbon uptake from the air into
vegetation biomass and soil, contributing to climate change mitigation. The
land area designated for restoration is huge and shows global commitment for
the cause. But how does one go about restoring such vast areas, and, isn’t that
very expensive?

As part of an international group of researchers, called
2ndFOR, we recently stressed the vital role of second-growth forest for land
restoration and climate change mitigation. Second-growth forests are forests
that regrow after nearly complete removal of forest cover for agricultural use.
Second-growth forest has previously been put forward as a potential carbon sink
but their potential for carbon sequestration has never been quantified at large
scale. It turns out that these forests may teach us how to restore the land and
take up vast amounts of carbon while working with nature, instead of against it.
Our results were recently published in the prestigious journals Nature and Science Advances.

We reported on the enormous grow-back potential of tropical
forests in Nature.
From the analysis on 1500 forest plots from
45 sites across Latin America we concluded that carbon uptake is surprisingly
fast in these second-growth forests: After 20 years, these forests had recovered
122 tons of aboveground biomass per hectare. This corresponds to an uptake of
3.05 tons of carbon per ha per year, which is 11 times the uptake rate of old-growth
forests. We also found that the rate of regrowth differed dramatically
across the study sites and that this rate is larger in areas with higher rainfall.
A map is provided of the grow-back potential of second-growth forests across
the Latin American tropics.

Biomass resilience map of the Latin American tropics showing
the predicted aboveground forest biomass (AGB) attained 20 years after
abandonment of agricultural use. Picture credits: Nature
Publishing Group.

In Science Advances
we reported what this regrowth potential implies for climate change
mitigation. The area of second-growth forests in Latin America is substantial: 240
million ha, which is 28% of the lowland forest area. Assuming that 100% of this
second-growth forest is able to persist and grow over the coming 40 years, there
will be an additional 31.1 petagrams of CO₂ stored over that time
period, which is enough of offset the carbon emissions from fossil fuel use and
industrial processes in these countries in the past 21 years. What is
remarkable is that this huge amount of carbon uptake does not require any
costly tree planting or loss of farmlands. This is exclusively based on natural
forest regrowth and only requires protection of the second-growth forests
present.

So, working with nature provides us with a low-cost and
effective solution for restoring large areas of land and mitigating climate
change. To do so, second-growth forests should be left to regrow, which only
works if there is some form of protection (e.g. fencing, fire-breaks). Forest
regrowth is not a quick fix, it takes many decades and the carbon benefits
accumulate over long time scales. At the same time, adequately protecting mature
forests is vital for climate change mitigation. Mature forests do not take up
carbon as fast as second-growth forest but they have large amounts of carbon
stored in both biomass and soils. If mature forests are not adequately protected,
carbon-uptake gains by second-growth forest may be in vain.

As the
world looks for efficient and affordable ways to restore degraded land and combat
climate change these findings tell us that forest regrowth clearly deserves
more attention among (inter)national policy makers than it has received so far.
Rather than working against nature we should work with nature; natural regrowth
is a cheap and nature-based solution with a tremendous carbon mitigation
potential.

By Madelon Lohbeck

World Agroforestry Centre (ICRAF), Nairobi, Kenya 

Wageningen University, Wageningen, the Netherlands

Based on the publications:

Chazdon, R. L., E. N. Broadbent, D. M. A. Rozendaal, F. Bongers, A. M. A.
Zambrano, T. M. Aide, P. Balvanera, J. M. Becknell, V. Boukili, P. H. S.
Brancalion, D. Craven, J. S. Almeida-Cortez, G. A. L. Cabral, B. d. Jong, J. S.
Denslow, D. H. Dent, S. J. DeWalt, J. M. Dupuy, S. M. Durán, M. M.
Espírito-Santo, M. C. Fandino, R. G. César, J. S. Hall, J. L. Hernández-Stefanoni,
C. C. Jakovac, A. B. Junqueira, D. Kennard, S. G. Letcher, M. Lohbeck, M.
Martínez-Ramos, P. Massoca, J. A. Meave, R. Mesquita, F. Mora, R. Muñoz, R.
Muscarella, Y. R. F. Nunes, S. Ochoa-Gaona, E. Orihuela-Belmonte, M.
Peña-Claros, E. A. Pérez-García, D. Piotto, J. S. Powers, J.
Rodríguez-Velazquez, I. E. Romero-Pérez, J. Ruíz, J. G. Saldarriaga, A.
Sanchez-Azofeifa, N. B. Schwartz, M. K. Steininger, N. G. Swenson, M. Uriarte,
M. v. Breugel, H. v. d. Wal, M. D. M. Veloso, H. Vester, I. C. G. Vieira, T. V.
Bentos, G. B. Williamson, and L. Poorter. 1016. Carbon sequestration potential
of second-growth forest regeneration in the Latin American tropics. Science
Advances 2. e1501639. DOI:
10.1126/sciadv.1501639

Poorter, L., F. Bongers, T. M. Aide, A. M. Almeyda Zambrano, P. Balvanera,
J. M. Becknell, V. Boukili, P. H. S. Brancalion, E. N. Broadbent, R. L.
Chazdon, D. Craven, J. S. de Almeida-Cortez, G. A. L. Cabral, B. H. J. de Jong,
J. S. Denslow, D. H. Dent, S. J. DeWalt, J. M. Dupuy, S. M. Durán, M. M.
Espírito-Santo, M. C. Fandino, R. G. César, J. S. Hall, J. L.
Hernandez-Stefanoni, C. C. Jakovac, A. B. Junqueira, D. Kennard, S. G. Letcher,
J.-C. Licona, M. Lohbeck, E. Marín-Spiotta, M. Martínez-Ramos, P. Massoca, J.
A. Meave, R. Mesquita, F. Mora, R. Muñoz, R. Muscarella, Y. R. F. Nunes, S.
Ochoa-Gaona, A. A. de Oliveira, E. Orihuela-Belmonte, M. Peña-Claros, E. A.
Pérez-García, D. Piotto, J. S. Powers, J. Rodríguez-Velázquez, I. E.
Romero-Pérez, J. Ruíz, J. G. Saldarriaga, A. Sanchez-Azofeifa, N. B. Schwartz,
M. K. Steininger, N. G. Swenson, M. Toledo, M. Uriarte, M. van Breugel, H. van
der Wal, M. D. M. Veloso, H. F. M. Vester, A. Vicentini, I. C. G. Vieira, T. V.
Bentos, G. B. Williamson, and D. M. A. Rozendaal. 2016. Biomass resilience of
Neotropical secondary forests. Nature 530:211-214. DOI:10.1038/nature16512

Download
the papers at Researchgate:

Biomass
resilience of Neotropical secondary forests

Carbon
sequestration potential of second-growth forest regeneration in the Latin American
tropics