Taking the pulse of Earth's tropical forests using networks of highly distributed plots☆
Introduction
As the most diverse and productive ecosystems on Earth, tropical forests play essential roles in the carbon and water cycles and maintenance of global biodiversity. Tropical forest lands are also home to more than a billion people and thousands of cultures. Having first provided the environments and germplasm that sustained foragers and farmers since the earliest days of humanity, today they underpin a large fraction of our globalized diet and intense demand for water, food and clean air. They also affect our health in multiple ways, providing rich pharmacopoeias to traditional and modern societies, and capable of changing the course of history when pandemic zoonotic pathogens emerge as forests and wildlife are exploited. Tropical forests are also critical to determining the degree and impact of anthropogenic climate change. Because of their extent, carbon density and productivity, they may both slow global heating by absorbing carbon into their biomass and soils, or accelerate it as deforestation and high temperatures damage forests and release carbon to the atmosphere.
Tropical carbon and biodiversity are therefore critical targets for environmental measurement and monitoring. While vital to our past and future, efforts to measure and monitor them have until recently been localised and largely disconnected. Although aspects of their ecology can be sensed remotely, on-the-ground, tree-by-tree measurement is essential. Indeed ground measurements are irreplaceable – whether to address a plethora of ecological questions (e.g., Wright, 2021), inform and validate ecosystem models (e.g., Malhi et al., 2021), or assist with interpreting remotely acquired data (e.g., Chave et al., 2019; Duncanson et al., 2019; Phillips et al., 2019). Yet the very features that enhance tropical forests' ecological value, such as remoteness, diversity and high rainfall, make fieldwork challenging. Tropical forest science and scientists from forest-rich countries are often under-resourced and academically marginalised. Often colonized from afar and distant from economic centres, tropical nature and many who explore it remain peripheral to national and global academic and political priorities.
The focus of this paper is specifically about the power of new collaborative networks to transform tropical forest science – what we do, how we do it, and eventually who does it - to understand tropical forest functioning and dynamics over large temporal and spatial scales. Conceived and funded starting in South America in 1999 (RAINFOR, Malhi et al., 2002) and later adapted to Africa (AfriTRON, Lewis et al., 2009) and Southeast Asia (T-FORCES, Qie et al., 2017) our approach encourages international grassroots initiatives and links them with standardized field methods and data management. Now, with ForestPlots.net (López-Gonzalez et al., 2011, López-Gonzalez et al., 2015) we support multiple networks with cyber-infrastructure that enables tropical scientists to do together what was previously impossible alone. Providing tools to ensure tropical scientists can manage, share and analyse their data themselves, ForestPlots.net is a global platform where data originators are in control and free to collaborate, support, or lead as much as they like. However, while much has been accomplished the wider challenges still run deep. Our aim of supporting the best possible science within a model of equitable access to data and other resources remains as much an aspiration as a claim of achievements already made.
Here we first review how the continental networks and ForestPlots.net emerged, in terms of collaborators, institutions, people and plots. Next we focus on key scientific achievements of the combined networks, including a comprehensive understanding of the variation in biomass carbon stock, growth rates, and carbon residence time among continents. We also review multiple discoveries concerning large-scale changes over time, with insights emerging from highly distributed permanent plots that have transformed our understanding of the role that tropical forests play in the biosphere. Finally, we return to the challenges of building and sustaining long-term science networks in the tropics and outline key priorities for the future.
Section snippets
Network development
Tropical research plots that tag, measure, identify and follow forests tree-by-tree have existed for decades. They long precede any continental or global network, but no plot survives since before 1939 and few predate 1970. The earliest efforts were closely connected to the imperial and post-imperial projects of European nations. As such, these were largely motivated by questions of timber inventory and wood production, and only later diversity and wider ecological questions. The very first
Environmental representation
While it is not possible to intensively sample the whole tropical forest extent, in practice RAINFOR, AfriTRON and T-FORCES have managed to cover almost the entire climatic and geographic space across the humid tropics with permanent plots (Fig. 4a) as well as extensively sample the biome space of the terrestrial tropics except for semi-arid biomes (Fig. 4b). Within each continent coverage has been focused on the moist tropical lowlands with sampling extending into montane and drier forest
Discovery: forest ecology across the tropical continents
RAINFOR, AfriTRON and T-FORCES plots have generated ecological and biogeographical insights that have only been achievable via large-scale collaboration. RAINFOR has revealed that Amazonian forests differ substantially from one another, even those that share essentially identical climates. For example, basal-area weighted wood density of northeastern forests is 50% greater than that of southern and western forests. This reflects floristic differences (Baker et al., 2004a, Baker et al., 2009;
Discovery: tropical forest change
The single most significant scientific impact of these multiple permanent plot networks has been to transform our understanding of how tropical forests function in the Earth system.
As the most diverse and carbon-rich tropical biome, the fate of humid tropical forests will impact the future of all life on Earth. Until quite recently it was axiomatic that old-growth tropical forests are at equilibrium when considered over sufficiently large scales, and that any changes observed at smaller scales
Challenges and the future of tropical forest monitoring
Large-scale plot networks have not only made a series of crucial scientific discoveries and advances, but even more profoundly the Social Research Network model pioneered by RAINFOR since 2000 has influenced how the science itself is being done. Tropical ecology has undergone a remarkable shift from a small cadre of researchers working in one or two sites to a more globalized and decentralised process with greatly increased contributions from tropical scientists. This has been made possible by
Achievements, impact and potential
Despite the challenges, tropical forest science has come a very long way. Until recently, tropical ecology suffered from a massive data deficit. We had plenty of theory and conjecture, but few comparable observations over time and space to deductively put these ideas to the test or inductively generate new ones. Networks such as ForestGEO, RAINFOR, AfriTRON, and the wider ForestPlots community have contributed much to resolving this. By leveraging a remarkably old technology, forest plot
CRediT authorship contribution statement
All authors have contributed to ForestPlots.net-associated networks by leading, collecting or supporting field data acquisition, or implementing and funding network development, data management, analyses and outputs. O.L.P. wrote the manuscript with initial contributions from S.L.L., M.J.S. contributed new analyses, M.J.S., G.L.P. and A.L. helped prepare the figures, and all authors reviewed the manuscript with many suggesting valuable edits. O.L.P., T.R.B., G.L.-G. and S.L.L. conceived //www.forestplots.net
Declaration of competing interest
There is no conflict of interest.
Acknowledgments
This paper is a product of the RAINFOR, AfriTRON and T-FORCES networks and the many other partner networks in ForestPlots.net which support long-term forest science and monitoring across tropical countries. These initiatives have been supported by numerous people and grants since their inception. We are particularly indebted to more than one thousand four hundred field assistants for their essential help in establishing and maintaining the plots, as well as highly distributed rural communities
References (152)
- et al.
Maximising synergy among tropical plant systematists, ecologists, and evolutionary biologists
Trends in Ecology & Evolution
(2017) Forest turnover, diversity, and CO2
Trends in Ecology & Evolution
(1997)- et al.
Changing trends and persisting biases in three decades of conservation science
Global Ecology and Conservation
(2017) - et al.
Estimating net biomass production and loss from repeated measurements of trees in forests and woodlands: Formulae, biases and recommendations
Forest Ecology and Management
(2019) - et al.
The Global Ecosystems Monitoring network: monitoring ecosystem productivity and carbon cycling across the tropics
Biological Conservation. Biological Conservation
(2021) - et al.
Forests and their canopies: achievements and horizons in canopy science
Trends in Ecology & Evolution
(2017) - et al.
Drier tropical forests are susceptible to functional changes in response to a long-term drought
Ecology Letters
(2019) - et al.
Long-term droughts may drive drier tropical forests towards increased functional, taxonomic and phylogenetic homogeneity
Nature Communications
(2020) - et al.
Forest biomass density across large climate gradients in northern South America is related to water availability but not with temperature
PloS One
(2017) - et al.
Influence of landscape heterogeneity on spatial patterns of wood productivity, wood specific density and above ground biomass in Amazonia
Biogeosciences
(2009)
Remote sensing detection of droughts in Amazonian forest canopies
New Phytologist
CTFS-Forest GEO: a worldwide network monitoring forests in an era of global change
Global Change Biology
Environmental change and the carbon balance of Amazonian forests
Biological Reviews
An integrated pan-tropical biomass map using multiple reference datasets
Global Change Biology
Variation in wood density determines spatial patterns in Amazonian forest biomass
Global Change Biology
Increasing biomass in Amazonian forest plots
Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences
Do species traits determine patterns of wood production in Amazonian forests?
Biogeosciences
Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years
Nature
Tropical forest wood production: a cross-continental comparison
Journal of Ecology
Anthropogenic disturbance in tropical forests can double biodiversity loss from deforestation
Nature
Impacts of selective logging on tree diversity across a rainforest landscape: the importance of spatial scale
Landscape Ecology
Opportunities and challenges for an Indonesian forest monitoring network
Annals of Forest Science
Long-term decline of the Amazon carbon sink
Nature
sPlot–A new tool for global vegetation analyses
Journal of Vegetation Science
Forest Inventory and Analysis Fiscal Year 2018 Business Report
Ground data are essential for biomass remote sensing missions
Surveys in Geophysics
Carbon sequestration potential of second-growth forest regeneration in the Latin American tropics
Science Advances
Prediction of neotropical woody plant diversity from soil and climatic data
Biodiversity and Conservation
Evolutionary diversity is associated with wood productivity in Amazonian forests
Nature Ecology & Evolution
Tropical Rain Forests: An Ecological and Biogeographical Comparison
The vegetation of Moraballi Creek, British Guiana: an ecological study of a limited area of tropical rain forest. Part I
Journal of Ecology
Tropical moist forest silviculture and management: a history of success and failure
Weighing trees with lasers: advances, challenges and opportunities
Interface Focus
Drought impact on forest carbon dynamics and fluxes in Amazonia
Nature
Sixty-two years of change in subtropical wet forest structure and composition at El Verde
Puerto Rico. Interciencia
Plant diversity patterns and their conservation implications in neotropical dry forests
Science
The importance of consistent global forest aboveground biomass product validation
Surveys in Geophysics
Assessing the growth and climate sensitivity of secondary forests in highly deforested Amazonian landscapes
Ecology
Size and frequency of natural forest disturbances and the Amazon forest carbon balance
Nature Communications
Seasonal drought limits tree species across the Neotropics
Ecography
Compositional response of Amazon forests to climate change
Global Change Biology
Widespread but heterogeneous responses of Andean forests to climate change
Nature
Drought‐induced shifts in the floristic and functional composition of tropical forests in Ghana
Ecology Letters
Hyperdominance in Amazonian forest carbon cycling
Nature Communications
Height-diameter allometry of tropical forest trees
Biogeosciences
Tree height integrated into pantropical forest biomass estimates
Biogeosciences
Amazon forest response to repeated droughts
Global Biogeochemical Cycles
Carbon-focused conservation may fail to protect the most biodiverse tropical forests
Nature Climate Change
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The article is attributed collectively as ForestPlots.net et al., with individual authors listed alphabetically first by country of institution and secondly by family name.