Tropical phenology: functional change in ecosystems across space and time

Monitoring plant phenology pattern has a long history nonetheless most studies focused on a few species. In recent years, several forest sites, such as Barro Colorado Island (Panama), Pasoh (Malaysia), Fushan (Taiwan), applied seed trap method to monitor flower and seed production. This design contains a substantial number of seed traps and three seedling plots adjacent to each trap in large, stem-mapped forest plots. Weekly collection and sorting of samples captured by traps provides phenological information for many plant species in the forests. Flower/seed data with high temporal resolution and large spatial scale offer opportunities to investigate community-wide phenology patterns, its association with climate, and to quantify seed availability and seed dispersal distance. In addition, hypotheses regarding community assembly can be tested combining data from seed traps and adjacent seedling plots. However, trap efficiency and representation are yet examined. Professor Yu-Yun uses long-term seed trap data from three forest sites to address these questions. Preliminary results indicate that the rate of species accumulation in traps slows down quickly when number of traps increases. However, adding more traps largely increases average number of individual per species. Census interval greater than 2 weeks is not recommended due to disproportional loss of phenology information.

Phenological patterns represent the rhythms of plant production and as such play a central role in regulating access to resources for animals, many of which are now endangered. In biodiverse tropical forests, factors that influence phenology are complex, involving climatic, edaphic, and biotic variables. As such long-term data it needed to unravel the interactions among variables and many of the long-term data sets involve information derived from direct or indirect observation of trees made over decades. Thus, a critical question that must be asked to advance theory and conservation is: What does observational phenology data mean when addressing particular questions? Professor Chapman considers questions that have often been ignored in the past including; How can patterns differ if trees are considered as fruiting or not or if a magnitude of fruiting is considered? What is the magnitude of interobserver variation? How do the observation of trees vary with data collected with fruit traps? What do short-term data (i.e., a few years) that is often collected by researchers studying particular animal species, contribute to our knowledge of changing phenological patterns? When considering how change in phenological patterns drive population size of endangered species, what do we consider food? Addressing these questions over many geographical locations and different time scales, will help advance our quantification of phenological patterns and help comprehend how climate change will impact the future of tropical forests and the animals they support.

The application of digital cameras to monitor the environment is becoming global and changing the way of phenological data collection. Digital cameras monitoring vegetation phenology (“phenocams”) have an important role by filling the “gap of observations” between satellite monitoring and the traditional on-the-ground phenology. The technique of digital repeated photographs has increased due to its low-cost investment, reduced size, easy set up installation, and the possibility of handling high-resolution near-remote data. The use of imagery data over the traditional phenological observations allows simultaneous multi-sites and long-term monitoring, collecting high-frequency data (daily, hourly), and reduced human labor fieldwork for data acquisition. Phenocams have potential applications for conservation as to document disturbances and changes on vegetation structure, such as deforestation, fire events, flooding and the vegetation recovery. The association of a long-term imagery data with local sensors (e.g., meteorological stations and surface-atmosphere flux towers) allows a wide range of studies, especially linking phenological patterns to climatic drivers; and the impact of climate changes on plant responses. Phenocam networks are growing globally and represent a potential tool for monitoring tropical phenology, for conservation biology and foster networking, as it provides hourly to daily information of monitored systems spread over several sites, ecosystems, and climatic zones, aggregating invaluable information of wide use from phenology to ecosystem dynamics and changes over space and time.

Space offers a unique vantage point from which to observe the ‘timing’ of recurring phenological phases across Earth’s ecosystems, along with the biotic and abiotic drivers of their timing, and their responses and shifts to climate and environmental change. Satellite sensors are highly calibrated, sophisticated optical instruments that are launched into space to monitor the earth. Satellite data are available at hourly to monthly temporal frequencies; meter to kilometer spatial grids; and include measures of vegetation chlorophyll, fluorescence, air & canopy temperatures, laser scanning, total water storage, active radar and microwave emissions. Through synoptic views, access, and repetitive sampling they generate key measurements that are of immense value in understanding ecosystem functioning. In this talk, Professor Huete will discuss the key challenges and opportunities of satellite based phenological observations across tropical forests. Descriptions of satellite data products, algorithms, data compositing, and quality control/analysis (QA/QC) tools are presented to gain a better understanding of data complexities and improve their utilisation over tropical areas.  We further highlight past and current controversies in satellite phenology applications in the tropics and show how they've advanced our knowledge and improved utilisation of satellite data. Case studies of Amazon greening in the dry season and the confounding influences of seasonality in aerosol loadings from biomass burning, dry and wet season cloud contamination, and seasonal sun angle trajectories are emphasised, all of which can augment forest canopy phenology. Satellite phenology studies of tropical forests are optimised with the use of multiple sensors and in conjunction with ground measurements.  

There are many different ways to observe and record phenology and the current suite of established, long-term, tropical phenology datasets reflects this methodological diversity. Information on the functioning of tropical ecosystems is sparse, and therefore the data recorded in each of these long-term studies is highly valuable. However, the question remains: How can we combine phenology data from different studies to enable meta-analysis of tropical ecosystem function? In this wrap-up talk, Emma Bush will give a comparative assessment of four major methods of phenology data collection - litter-trapping, canopy observations, digital-photography and remote sensing – summarizing for each, the geographic spread across the tropics, the development of protocols and “best practices” for compatibility and the specific ecological information sampled. The major aims of this talk will be to assess which ecological hypotheses can be tested using which data and to identify both opportunities and challenges in combining data for cross-disciplinary, large-scale analyses of tropical ecosystems.

Tree phenological monitoring is of immense significance because it provides a potential tool to address critical questions related to climate change. The tropical dry forests constitute a mosaic composed of several phenological functional types adapted to seasonal drought in different ways. These functional types differ with respect to phenological timing and triggering factors, water relations, extent of deciduousness (~ leaflessness), etc. Deciduousness reflects interacted effect of seasonal drought, tree characteristics and resource use rates. Dry tropical forest tree species show functional diversity in deciduousness, stem wood density (SWD), leaf mass area (LMA) and leaf strategy index (LSI, reflecting resource use rate) to overcome water limitations. Leaf-exchanging short-deciduous species  (having higher SWD and LMA and low LSI) show  flowering coinciding with leaf transitional state when vegetative growth is at its minimum, and both fruit formation and leaf flushing being supported at the same time. In contrast, long-deciduous species (with lowest SWD and LMA, higher LSI) show predominantly dry season flowering, subsequent fruiting on leafless shoots and distinct separation of vegetative and flowering phenophases. Intermediate species show wider flowering range through summer, rainy, autumn or winter seasons. The ability of tree species to withstand (leaf-exchange) or avoid (deciduousness) drought stress and varying seasonal flowering timings appear to be the principal mechanism for successful survival and reproduction under extremely dry and seasonal climate. There is a need to develop capabilities to detect and predict the impact of climate change on deciduousness through long-term phenological network in tropics. This talk will explore the ecological significance of deciduousness in tropical trees with emphasis on inter- and intra-species plasticity in deciduousness, various capacity adaptations related with the duration of deciduousness, and the relationship between tree stem water status and deciduousness. The impending environmental change (i.e. temperature and precipitation) in dry tropics are likely to affect deciduousness and other phonological traits significantly.

Unprecedented opportunities are now at hand to bridge the gap between forest seasonal dynamics, flux tower data and apparent temporal signals in vegetation indices. They pass through progress in observational systems at different scales: UAV and ground based LiDAR and multispectral sensors (phenocams) and growing constellations of (nano)satellites. These systems provide detailed structural and temporal information complementing more traditional destructive data collection campaigns, permanent forest plots and tree climbing. The unprecedented amounts of data obtained allow documenting detailed foliage dynamics at tree to landscape levels, and hence in turn to quantify the budget of matter and energy exchange between plants and the atmosphere. This budget can potentially become so resolute as to allow characterizing plant-plant or even within-plant interactions, and thus feed into next generation individual plant growth models (FSPMs). This talk will present some results of ongoing collaborative work in Central Africa and French Guyana, highlight some difficulties as well as intended research directions.

The Joint UK Land-Environment Simulator (JULES) is the land surface component of the Met Office’s Unified Model. It is a community model that is co-developed by both the Met Office and NERC science community (particularly the Centre for Ecology and Hydrology), and forms a key part of the UK’s contribution to the global model inter-comparison projects (e.g. CMIP6). JULES can be run as a standalone model or as the fully integrated land surface component of the Unified Model for weather forecasts and/or climate and earth system simulations. This presentation will give a brief overview of how vegetation, in particular phenology, is modelled within JULES. It will demonstrate key strengths and weaknesses in the modelling of vegetation phenology using recent results comparing Leaf Area Index (LAI) derived from satellite observations (Copernicus Global Land Service 1km LAI product) with JULES modelled LAI across global biomes and climate zones, and will finish with ideas on how to improve phenological modelling within JULES. A major aim of this presentation is to encourage greater collaboration between ecological experts and climate modellers to ensure the most up-to-date ecological science and observations are included in model developments.

The Food and Agriculture Agency of UN has as mission to achieve food security for all. FAO’s three main goals are: the eradication of hunger, food insecurity and malnutrition; the elimination of poverty and the driving forward of economic and social progress for all; and, the sustainable management and utilization of natural resources, including land, water, air, climate and genetic resources for the benefit of present and future generations. In the framework of supporting developing countries in their fight against emergencies (diseases, disasters, etc.), FAO Forestry helps to develop adoptable, adaptable and feasible tools based on satellite data to help in forecasting of tropical human, and livestock disease as well as nature emergences. Moreover in order to help countries, FAO Forestry assists developing countries to prepare and implement national strategies for global policies (as e.g. REDD+). For the monitoring, reporting and verification, FAO supports the countries to develop national satellite forest monitoring systems that allow for credible measurement, reporting and verification (MRV) of REDD+ activities. These are among the most critical elements for the successful implementation of any REDD+ mechanism. The UN-REDD Programme is supporting countries to develop cost- effective, robust and compatible national monitoring and MRV systems, providing tools, methodologies, training and knowledge sharing that help countries to strengthen their technical and institutional capacity for effective MRV systems. To develop strong nationally-owned forest monitoring systems, technical and institutional capacity building is key. The UN-REDD Programme, through FAO, has taken on intensive training together with other partners (e.g. INPE, USAID, Silvacarbon), and has provided technical help and assistance for in-country training and implementation for national satellite forest monitoring. In this talk, some concrete examples of incorporation of phenology in environmental applications for the global climate change policy will be presented.