ForestGEO: Understanding forest diversity and dynamics through a global observatory network

Highlights

• ForestGEO - a global network of large long-term forest dynamics plots

• 71 plots, 27 countries, 7.3 million trees include 20% of tree species diversity

• sampling more than trees is needed to capture drivers of forest diversity & change

• knowledge gaps constrain predictions on future forest change

• funding, training and collaborations are needed to sustain long-term forest research

Abstract

ForestGEO is a network of scientists and long-term forest dynamics plots (FDPs) spanning the Earth's major forest types. ForestGEO's mission is to advance understanding of the diversity and dynamics of forests and to strengthen global capacity for forest science research. ForestGEO is unique among forest plot networks in its large-scale plot dimensions, censusing of all stems ≥1 cm in diameter, inclusion of tropical, temperate and boreal forests, and investigation of additional biotic (e.g., arthropods) and abiotic (e.g., soils) drivers, which together provide a holistic view of forest functioning. The 71 FDPs in 27 countries include approximately 7.33 million living trees and about 12,000 species, representing 20% of the world's known tree diversity. With >1300 published papers, ForestGEO researchers have made significant contributions in two fundamental areas: species coexistence and diversity, and ecosystem functioning. Specifically, defining the major biotic and abiotic controls on the distribution and coexistence of species and functional types and on variation in species' demography has led to improved understanding of how the multiple dimensions of forest diversity are structured across space and time and how this diversity relates to the processes controlling the role of forests in the Earth system. Nevertheless, knowledge gaps remain that impede our ability to predict how forest diversity and function will respond to climate change and other stressors. Meeting these global research challenges requires major advances in standardizing taxonomy of tropical species, resolving the main drivers of forest dynamics, and integrating plot-based ground and remote sensing observations to scale up estimates of forest diversity and function, coupled with improved predictive models. However, they cannot be met without greater financial commitment to sustain the long-term research of ForestGEO and other forest plot networks, greatly expanded scientific capacity across the world's forested nations, and increased collaboration and integration among research networks and disciplines addressing forest science.

Introduction

Forests store about half of the world's carbon, take up 25% of all new anthropogenic carbon emissions (Keenan and Williams, 2018), and control climatic and hydrological cycles (Immerzeel et al., 2020). They house about 50% of the world's known species, providing medicines, food, and fuel for a huge fraction of humanity. Forests are in the midst of the greatest transformation since the last great extinction through the combined anthropogenic effects of deforestation, forest degradation through overexploitation, the deposition of pollutants, invasive pests, and climate and atmospheric change. How forests respond to the Anthropocene has profound consequences for life on Earth, yet understanding these responses has proved challenging due to the diversity and complexity of forest ecosystems and the long timeframes over which forests develop and change. The current state of knowledge of the underlying processes regulating species distributions, population and community dynamics, and the resistance and resilience of forests to perturbations provides an incomplete basis from which to predict the future of the world's forest biomes. Even the fundamental biology of many forest species is unknown, yet is essential to predicting and mitigating anthropogenic impacts on forests at a global scale.

The diversity, structure and functioning of forests vary across a wide range of spatial and temporal scales and involve a plethora of interacting species beyond trees. In other words, while trees make up forests, forests are more than trees. Tree species can persist across diverse climatic conditions, and forests vary by orders of magnitude in species diversity across the Earth. The same area that supports roughly ten tree species in a Sequoia forest can support over a thousand in Borneo or the Amazon (Lee et al., 2002; Duque et al., 2017). Yet, we remain ignorant of how the ecological niches and demographic characteristics of the vast majority of tree species determine their specific geographic and environmental distributions, which underpin patterns of diversity. The dynamics of tree growth, mortality, and recruitment vary dramatically among forests and through time. Abiotic environmental drivers, like climate, soil, and disturbances, and biotic drivers, involving interactions with other taxa, shape the vital rates of trees, which ultimately determine carbon, water, and nutrient storage and fluxes. Yet, these processes and interactions remain obscure. Nowhere is this more true than in tropical forests, where knowledge of the myriad ways in which animals and microbiota interact with trees, and consequently forests, is in its infancy. A challenge for defining these interaction networks is not only identifying which taxa live in forests, but also quantifying what ecological roles they play and when, and with what impact. Integrating the entire forest biota into a holistic understanding of forest ecosystem function is daunting, yet is key to predicting the resilience or vulnerability of forests to change.

The enormous challenge for forest science is determining the controls on the structure, function, and diversity of forests across large spatial and temporal scales and linking these processes to the functioning of the Earth system. Meeting this challenge requires integration across levels of organization from the molecular to the ecosystem levels using detailed standardized data collected around the world and over decades to centuries. While ambitious, this knowledge is essential for building better predictive models and improving space-borne observation platforms that can be used to monitor and predict the future of forested biomes globally. Such advances cannot be accomplished by a single research group, institution, or even country, but rather require a distributed network of scientists, representing many disciplines, and engaging in long-term collaborations, who are committed to capacity-strengthening in forest science globally and to seeking long-term financial support for these essential endeavors. The mission of the Forest Global Earth Observatory (ForestGEO) is to advance these fundamental and pressing research and training needs.