Slow rate of secondary forest carbon accumulation in the Guianas compared with the rest of the Neotropics

Abstract

Secondary forests are a prominent component of tropical landscapes, and they constitute a major atmospheric carbon sink. Rates of carbon accumulation are usually inferred from chronosequence studies, but direct estimates of carbon accumulation based on long‐term monitoring of stands are rarely reported. Recent compilations on secondary forest carbon accumulation in the Neotropics are heavily biased geographically as they do not include estimates from the Guiana Shield. We analysed the temporal trajectory of aboveground carbon accumulation and floristic composition at one 25‐ha secondary forest site in French Guiana. The site was clear‐cut in 1976, abandoned thereafter, and one large plot (6.25 ha) has been monitored continuously since. We used Bayesian modeling to assimilate inventory data and simulate the long‐term carbon accumulation trajectory. Canopy change was monitored using two aerial lidar surveys conducted in 2009 and 2017. We compared the dynamics of this site with that of a surrounding old‐growth forest. Finally, we compared our results with that from secondary forests in Costa Rica, which is one of the rare long‐term monitoring programs reaching a duration comparable to our study. Twenty years after abandonment, aboveground carbon stock was 64.2 (95% credibility interval 46.4, 89.0) Mg C/ha, and this stock increased to 101.3 (78.7, 128.5) Mg C/ha 20 yr later. The time to accumulate one‐half of the mean aboveground carbon stored in the nearby old‐growth forest (185.6 [155.9, 200.2] Mg C/ha) was estimated at 35.0 [20.9, 55.9] yr. During the first 40 yr, the contribution of the long‐lived pioneer species Xylopia nitida, Goupia glabra, and Laetia procera to the aboveground carbon stock increased continuously. Secondary forest mean‐canopy height measured by lidar increased by 1.14 m in 8 yr, a canopy‐height increase consistent with an aboveground carbon accumulation of 7.1 Mg C/ha (or 0.89 Mg C·ha−1·yr−1) during this period. Long‐term AGC accumulation rate in Costa Rica was almost twice as fast as at our site in French Guiana. This may reflect higher fertility of Central American forest communities or a better adaptation of the forest tree community to intense and frequent disturbances. This finding may have important consequences for scaling‐up carbon uptake estimates to continental scales.

Forest aboveground biomass stock and resilience in a tropical landscape of Thailand

“…Thus, the accumulation of AGB with age follows different trends across sites, as already highlighted in previous studies (Kennard et al, 2002;Poorter et al, 2016a;Ray and Brown, 2006;Ruiz et al, 2005;Silver et al, 2000;Toledo and Salick, 2006). Understanding how these trends vary according to abiotic factors (e.g., soil type, rainfall), species assemblage and diversity, and prioritizing effects such as types of land use and land management existing before forest recolonization, constitute an important avenue of research (Chazdon, 2014;McMahon et al, 2019).…”

“…Tropical forest disturbances and subsequent biomass recovery through time significantly affect the global carbon cycle (Harris et al, 2012). Although secondary forests in the tropics could constitute a major global carbon sink, the magnitude of such a sink remains poorly known (Chazdon, 2014;Lugo and Brown, 1992). A previous study estimated that 40 years of carbon storage in regenerating tropical forests from Latin America offset the past 19 years of carbon emissions from fossil fuels and industrial production in this region (Chazdon et al, 2016).…”

Secondary forests offset less than 10% of deforestation‐mediated carbon emissions in the Brazilian Amazon

“…Many of the plots (~60%) also began growing before 1985 (Requena Suarez et al., 2019), when large‐scale deforestation had not yet substantially reduced forest cover (Fearnside, 2005) and before mechanized agriculture had intensified land use. Recent studies from other regions have shown much lower carbon accumulation rates of 2.25 Mg ha −1 year −1 in Paragominas and Santarém‐Belterra (Lennox et al., 2018), 1.08 Mg ha −1 year −1 in Bragança (Elias et al., 2019) or as low as 0.89 Mg ha −1 year −1 in the Guiana Shield (Chave et al., 2020).…”

“…While the carbon balance of undisturbed forests has been well studied (Brienen et al, 2015;Hubau et al, 2020;Pan et al, 2011;Saatchi et al, 2011), estimates of the rate of carbon sequestration in secondary forests remain highly variable (Elias et al, 2019;Grace et al, 2014;Pan et al, 2011;Saatchi et al, 2011 (Elias et al, 2019) or as low as 0.89 Mg ha −1 year −1 in the Guiana Shield (Chave et al, 2020).…”

Resource availability and disturbance shape maximum tree height across the Amazon

“…The sheer size of the Amazon, its environmental heterogeneity, and species diversity pose challenges and practical difficulties to understand general ecological relationships and biogeographical patterns (Tuomisto et al, 2019). Forest inventory plots provide many valuable insights to investigate the influences of the environment on tree height but they only represent a minuscule fraction of the total forest area (Chave et al, 2020). Currently, a network of 5,351 forest inventory plots established across the Brazilian Amazon, of known and published sites recently compiled by Tejada et al (2019), represents only 0.0013% of the total forest area in this region.…”