2ndFOR
Secondary Forests Research Network
2ndFOR is a collaborative research network focusing on understanding the ecology, dynamics, and biodiversity of tropical secondary forests and the ecosystem services they provide in human-modified tropical landscapes.
2ndFOR study published in Philosophical Transactions of the Royal Society B
14th November 2022
The recovery of soil conditions is crucial for successful ecosystem restoration and, hence, for achieving the goals of the UN Decade on Ecosystem Restoration. Here, we assess how soils resist forest conversion and agricultural land use, and how soils recover during subsequent tropical forest succession on abandoned agricultural fields. Our overarching question is how soil resistance and recovery depend on local conditions such as climate, soil type and land-use history. For 300 plots in 21 sites across the Neotropics, we used a chronosequence approach in which we sampled soils from two depths in old-growth forests, agricultural fields (i.e. crop fields and pastures), and secondary forests that differ in age (1–95 years) since abandonment. We measured six soil properties using a standardized sampling design and laboratory analyses. Soil resistance strongly depended on local conditions. Croplands and sites on high-activity clay (i.e. high fertility) show strong increases in bulk density and decreases in pH, carbon (C) and nitrogen (N) during deforestation and subsequent agricultural use. Resistance is lower in such sites probably because of a sharp decline in fine root biomass in croplands in the upper soil layers, and a decline in litter input from formerly productive old-growth forest (on high-activity clays). Soil recovery also strongly depended on local conditions. During forest succession, high-activity clays and croplands decreased most strongly in bulk density and increased in C and N, possibly because of strongly compacted soils with low C and N after cropland abandonment, and because of rapid vegetation recovery in high-activity clays leading to greater fine root growth and litter input. Furthermore, sites at low precipitation decreased in pH, whereas sites at high precipitation increased in N and decreased in C : N ratio. Extractable phosphorus (P) did not recover during succession, suggesting increased P limitation as forests age. These results indicate that no single solution exists for effective soil restoration and that local site conditions should determine the restoration strategies.
Conceptual diagram showing how nutrient (nitrogen, phosphorus) flows (arrows) change during three different phases: (1) slash and burn, (2) use as cropland (left) and pasture (right) and (3) young forest regrowth. Flows are indicated as inputs (blue arrows) and losses (orange arrows) to the soil system. Flows can be determined by different processes, e.g. decomposition, nitrogen fixation, mycorrhizal activity and dust trapping. Erosion can lead to nutrient input or loss, depending on the topographic position of the plot. Other processes affecting soil structure and chemistry (e.g. compaction, liming) are indicated by gears (or wheels). The magnitude of the flow is indicated by the size of the arrow. Most processes occur in all stages, and asterisks (*) indicate that the process is unique to a stage. The soil layers consist of bedrock (hatched), mineral soil (dotted) and the accumulation of organic matter in the top mineral soil layer (greyscale). Dashed lines and numbers refer to the two layers studied: (1) topsoil (0–15 cm depth) and (2) subsoil (15–30 cm depth); (3) refers to deep soil (not studied). The shifting cultivation cycle is affected by a hierarchy of external drivers (indicated on top) that operate from regional to local spatial scales, and from long to short temporal scales. Drivers included in this study are indicated in parentheses. CC BY
2ndFOR study published in Science today
10th December 2021
Tropical forests are converted at an alarming rate through deforestation, but also have the potential to regrow naturally on abandoned lands. A study published in Science shows that regrowing tropical forests recover surprisingly fast, and can attain after 20 years nearly 80% of the soil fertility, soil carbon storage and tree diversity of old-growth forests. The study concludes that natural regeneration is a low-cost, nature-based solution for climate change mitigation, biodiversity conservation, and ecosystem restoration.
We identified a set of three attributes – maximum tree size, overall variation in tree size and the number of tree species in a forest – that, viewed together, provide a reliable snapshot of how well a forest is recovering. These three indicators are relatively easy to measure, and managers can use them to monitor forest restoration. It is now possible to monitor tree size and forest structure over large areas and time scales using data collected by satellites and drones.
This graphic shows how four groups of forest attributes – soil, ecosystem functioning, forest structure and tree biodiversity – recover as tropical forests regrow on former farm and pasture lands. For each category, the image shows the average percentage of recovery compared with old-growth forests after 20, 40, 80 and 120 years. Percentages in black squares show average recovery for the whole forest at each interval. Pixels&Ink, CC BY-ND
New 2ndFOR article published in PNAS
29th November 2021
This continental-wide study entitled Functional recovery of secondary tropical forests shows that regrowing tropical forests are quite diverse in their recovery; dry and wet forests differ initially strongly in their functional composition, follow different successional pathways, but become more similar in functional characteristics over time when forests grow older. The study, published today in the Proceedings of the National Academy of Sciences provides insights on which type of tree species should be selected for restoration plantings, thereby enhancing tropical forest restoration success.
Picture by L. Poorter
2ndFOR beyond the Neotropics
Picture by R. Chazdon
Secondary forests
are forests that regrow naturally after nearly complete removal of forest cover for anthropogenic use (usually for shifting cultivation, conventional cropping or cattle ranching). Currently over half of the world’s tropical forests are not old-growth, but naturally regenerating forests of which a large part is secondary forest. In tropical Latin America, secondary forests cover as much as 28% of the land area.
Picture by F. Bongers
Tropical forests are home to more than 53,000 tree species, accounting for 96% of global tree diversity. These hyperdiverse forests are threatened by high levels of deforestation, mostly driven by agricultural expansion. Once agricultural fields are abandoned, they can be rapidly colonized by naturally regrowing forests, which are called “secondary forests”. Could these regrowing forests help reverse species loss and bring native species back?
Read our brief on the study published on march 2019 in the journal Science Advances
Watch the video made by IIES, Mexico, on our study Biomass resilience of Neotropical secondary forests published in the scientific journal NATURE in 2016