Carbon accumulation in agroforestry systems is affected by tree species diversity, age and regional climate: A global meta‐analysis

Abstract

Aim Agroforestry is a globally practised system of land use for achieving greater and more diverse biomass production, but it has other ecological benefits, such as mitigation of climate change. Despite this, long‐term carbon (C) accumulation in different components of agroforestry systems, the drivers for C accumulation and the linkages between tree biomass and soil C stocks remain unclear. Location Global. Time period From 1989 to 2019. Major taxa studied Trees. Methods Here, we report on a global meta‐analysis based on 141 studies to identify patterns of C accumulation in tree‐based agroforestry systems compared with sole cropland and pasture. Results We found that agroforestry systems had, on average, 46.1 Mg/ha (95% confidence interval, 36.4–55.8 Mg/ha) more C in tree biomass compared with sole cropland‐ or pasture‐based land uses without trees. Furthermore, agroforestry systems with multiple tree species contained greater biomass C stocks and accumulated biomass C faster than systems with a single tree species. The effect of agroforestry practices on soil C stock increased with tree age, although such increases varied among climatic zones. Agroforestry systems in tropical zones had the ability to increase soil C to peak levels quickly, whereas soil C in temperate zones increased at a slower rate but peaked at a greater overall soil C level. Our structural equation model did not detect a direct linkage between biomass C and changes in total soil C stock in agroforestry systems. Main conclusions Our results demonstrate that planting multiple tree species in agroforestry systems is an important strategy to increase biomass C sequestration, with regional climate affecting the temporal change of soil C in response to agroforestry practices.

Changes in soil carbon and nitrogen stocks following degradation of alpine grasslands on the Qinghai‐Tibetan Plateau: A meta‐analysis

“…Since most collected studies focused on the change in SOC or STN stock in topsoil (0–30 cm) after grassland degradation, the data of soil properties such as SOC stock, STN stock, and soil BD were compiled from 0 to 30 cm soil layer. If one study reported SOC or STN stocks at different depths (e.g., 0–10 cm, 10–20 cm, and 20–30 cm), only stocks measured across the whole sampling depth were used to avoid interdependence of observations (Ma, Chen, Bork, Carlyle, & Chang, 2020). For the same purpose, only soil BD in the uppermost soil layer was collected (Jian et al, 2016).…”

“…In general, the effect sizes were unweighted (Shi et al, 2016), weighted by the inverse of pooled variances (Jian et al, 2016; Zhang et al, 2019) or replications (Dlamini et al, 2016; Lam et al, 2012; Ma et al, 2020; Xia et al, 2018) from previous meta‐analyses. Since not all the compiled studies presented the standard deviations of the means, and variance‐based weighting function might cause extreme weights (van Groenigen, Osenberg, & Hungate, 2011), the effect sizes were thus weighted by a function of replications in this study: Where: W is the weight; N nd and N d are the numbers of replications at non‐degraded sites and degraded sites, respectively.…”

“…Given that most compiled studies did not report sampling variance, the funnel plots were plotted as the effect sizes against their sample sizes (Ma et al, 2020). Begg's rank test and Egger's regression test were applied to evaluate the potential asymmetry of the funnel plots (Ma et al, 2020; McDonald, Lawrence, Kendall, & Rader, 2019). The results showed that there was no publication bias in the present meta‐analysis (Table S3 and Figure S1).…”

Agroforestry: An Appropriate and Sustainable Response to a Changing Climate in Southern Africa?

“…Luedeling et al [30] compiled C sequestration rates of AFS located in Mozambique, Zambia and Tanzania (on sites with mean annual rainfall ranges from 500 to 1200 mm) and found values ranging from 0.22 to 5.8 Mg C ha −1 yr −1 ; rotational woodlots stored more C than other AFS in the studied regions. Ma et al [167] in a global meta-analysis of C storage within AFS reported an average of 46.1 Mg Ha −1 more C than tree-less land-use systems with systems consisting of multiple tree species storing a higher C in their collective biomass.…”

“…In SSA, tree intercropping systems have the highest potential to sequester C (1.5 to 3.0 Mg C ha −1 yr −1 ), followed by silvopastoral systems (1.0 to 2-5 Mg C ha −1 yr −1 ) and protective systems like shelter belts (0.4 to 1.0 Mg C ha −1 yr −1 ). All estimates are highly variable, depending on agroecological distribution [2]; nevertheless, a conversion of cropland to AFS has the potential to increase SOC [167]. More research is needed in order to get consistent and reliable data [53].…”