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Experiments Are Necessary in Process-Based Tree Phenology Modelling

2018; Elsevier BV; Volume: 24; Issue: 3 Linguagem: Inglês

10.1016/j.tplants.2018.11.006

1878-4372

Heikki Hänninen, Koen Kramer, Karen Tanino, Rui Zhang, Jiasheng Wu, Yongshuo H. Fu,

Plant and animal studies

Studies addressing spring phenology of trees are increasingly topical because of the ongoing climate change. Spring phenology of trees is often studied with process-based mathematical models, which simulate physiological processes underlying the timing of phenological events, such as vegetative bud burst. Process-based tree phenology models are often used in computer simulations for projecting the effects of future climate warming on trees and forest ecosystems. Traditionally models have been developed with the aid of growth chamber and greenhouse experiments, which have facilitated the determination of environmental responses of the physiological processes. However, nowadays models are often developed without experimental research, using observational long-term phenological records, or remote-sensed data, gathered in natural conditions as the only biological information. In boreal and temperate trees, air temperature is a major environmental factor regulating the timing of spring phenological events, such as vegetative bud burst, through underlying physiological processes. This has been established by experimental research, and mathematical process-based tree phenology models have been developed based on the results. The models have often been applied when assessing the effects of climate change. Currently, there is an increasing trend to develop process-based tree phenology models using only observational phenological records from natural conditions. We point out that this method runs a high risk of producing models that do not simulate the real physiological processes in the trees and discuss experimental designs facilitating the development of biologically realistic process-based models for tree spring phenology. In boreal and temperate trees, air temperature is a major environmental factor regulating the timing of spring phenological events, such as vegetative bud burst, through underlying physiological processes. This has been established by experimental research, and mathematical process-based tree phenology models have been developed based on the results. The models have often been applied when assessing the effects of climate change. Currently, there is an increasing trend to develop process-based tree phenology models using only observational phenological records from natural conditions. We point out that this method runs a high risk of producing models that do not simulate the real physiological processes in the trees and discuss experimental designs facilitating the development of biologically realistic process-based models for tree spring phenology. exposure of the bud to chilling temperatures. the duration of chilling required for rest completion. The duration often depends on the chilling temperature. any temperature causing rest break in the buds. Exact temperature range depends on the species studied. Usually temperatures a few degrees below and above +5°C are most effective as chilling temperatures. the state when no visible growth or bud burst is observed in an overwintering bud of a tree, regardless of the reason for the inactivity. a mathematical model simulating the progress of a process over time. any temperature above a specific threshold causing ontogenetic development towards bud burst. The threshold depends on the tree species. the duration of forcing temperature exposure required for bud burst. The duration depends on the forcing temperature. in this study, a technique where process-based tree phenology models are developed based on observational data of air temperature and timing of bud burst in natural conditions. More generally, a modelling technique where the cause is inferred from the effect. the degree to which the predictions of a model fit observations. the degree to which the relationships described by a model correspond to real ecophysiological relationships in real trees. a relative quantitative measure of the bud’s ability to respond to high forcing temperatures by microscopic anatomical development towards bud burst. With zero ontogenetic competence no such development takes place (red curve in Figure 1D), whereas with full ontogenetic competence the development progresses at the maximum rate in each temperature (black curve in Figure 1D). in this study, the microscopic anatomical development inside the bud, leading to the visible bud burst. More generally, the irreversible development of any biological structure. a model assuming that ontogenetic development already takes place during rest period in forcing temperatures, but the rate of development is lower than during quiescence. study of the timing of seasonally recurring developmental phenomena, such as vegetative bud burst of trees during spring. a computer model addressing explicitly the physiological processes affecting a given phenomenon being observed at the whole-tree level, such as bud burst. a phase of dormancy when the growth onset is prevented by unfavourable environmental conditions of the tree, usually low temperatures. Ontogenetic development towards visible bud burst occurs whenever air temperature rises above the forcing temperature threshold. Synonymous to ecodormancy. Ro, a model variable showing the percentage of the ontogenetic development towards bud burst taking place during 1 day (Figure 1D). Rr, a model variable showing the percentage of the processes of rest break required for rest completion taking place during 1 day (Figure 1C). a phase of dormancy when the growth onset is prevented by physiological factors inside the bud. Synonymous to endodormancy. the process of removing the internal growth-arresting physiological conditions in the bud. the event during dormancy when the internal growth-arresting physiological conditions are entirely removed in the bud. a model assuming that ontogenetic development takes place only after rest completion. a model variable showing the percentage of the ontogenetic development towards bud burst having taken place at a given moment. It is obtained by summing the previous daily values of the rate of ontogenetic development (Figure 1D). a model variable showing the percentage of the processes of rest break required for rest completion having taken place at a given moment. It is obtained by summing the previous daily values of rate of rest break (Figure 1C).