A tropical dry forest in Central Western Mexico, close to my hometown and which I visit during the October 12-24, 2021.
The main steps followed in our methodology to derive predictions of plant functional traits across tropical forests using Sentinel-2 satellite spectral data.
Pantropical modelling of canopy functional traits using Sentinel-2 remote sensing data
Remote Sensing of Environment volume 252, Article number: 112122 (2021)
Tropical forest ecosystems are undergoing rapid transformation as a result of changing environmental conditions and direct human impacts. However, we cannot adequately understand, monitor or simulate tropical ecosystem responses to environmental changes without capturing the high diversity of plant functional characteristics in the species-rich tropics. Failure to do so can oversimplify our understanding of ecosystems responses to environmental disturbances. Innovative methods and data products are needed to track changes in functional trait composition in tropical forest ecosystems through time and space. This study aimed to track key functional traits by coupling Sentinel-2 derived variables with a unique data set of precisely located in-situ measurements of canopy functional traits collected from 2434 individual trees across the tropics using a standardised methodology. The functional traits and vegetation censuses were collected from 47 field plots in the countries of Australia, Brazil, Peru, Gabon, Ghana, and Malaysia, which span the four tropical continents. The spatial positions of individual trees above 10 cm diameter at breast height (DBH) were mapped and their canopy size and shape recorded. Using geo-located tree canopy size and shape data, community-level trait values were estimated at the same spatial resolution as Sentinel-2 imagery (i.e. 10 m pixels). We then used the Geographic Random Forest (GRF) to model and predict functional traits across our plots. We demonstrate that key plant functional traits can be accurately predicted across the tropicsusing the high spatial and spectral resolution of Sentinel-2 imagery in conjunction with climatic and soil information. Image textural parameters were found to be key components of remote sensing information for predicting functional traits across tropical forests and woody savannas. Leaf thickness (R2 = 0.52) obtained the highest prediction accuracy among the morphological and structural traits and leaf carbon content (R2 = 0.70) and maximum rates of photosynthesis (R2 = 0.67) obtained the highest prediction accuracy for leaf chemistry and photosynthesis related traits, respectively. Overall, the highest prediction accuracy was obtained for leaf chemistry and photosynthetic traits in comparison to morphological and structural traits. Our approach offers new opportunities for mapping, monitoring and understanding biodiversity and ecosystem change in the most species-rich ecosystems on Earth.
Fig. 1: The distribution of vegetation plots (green dots) in Ghana, West Africa.
Fig. 2 The relationship between functional diversity, species diversity and phylogenetic diversity with the long-term water availability (MCWD) in Ghana West Africa.
Long-term droughts may drive drier tropical forests towards increased functional, taxonomic and phylogenetic homogeneity
Jesús Aguirre-Gutiérrez, Yadvinder Malhi, Simon L. Lewis, Sophie Fauset, Stephen Adu-Bredu, Kofi Affum-Baffoe, Timothy R. Baker, Agne Gvozdevaite, Wannes Hubau, Sam Moore, Theresa Peprah, Kasia Ziemińska, Oliver L. Phillips & Imma Oliveras
Nature Communications volume 11, Article number: 3346 (2020)
Tropical ecosystems adapted to high water availability may be highly impacted by climatic changes that increase soil and atmospheric moisture deficits. Many tropical regions are experiencing significant changes in climatic conditions, which may induce strong shifts in taxonomic, functional and phylogenetic diversity of forest communities. However, it remains unclear if and to what extent tropical forests are shifting in these facets of diversity along climatic gradients in response to climate change. Here, we show that changes in climate affected all three facets of diversity in West Africa in recent decades. Taxonomic and functional diversity increased in wetter forests but tended to decrease in forests with drier climate. Phylogenetic diversity showed a large decrease along a wet-dry climatic gradient. Notably, we find that all three facets of diversity tended to be higher in wetter forests. Drier forests showed functional, taxonomic and phylogenetic homogenization. Understanding how different facets of diversity respond to a changing environment across climatic gradients is essential for effective long-term conservation of tropical forest ecosystems.
Fig. 3: Climatic and soil drivers of observed rates of change in the three facets of diversity.
Image 3. Tree climber sampling a tree in one of the vegetation plots in Ghana, West Africa. ©Yadvinder Malhi