Original scientific paper
Simulation model of the effect of air temperature on the leaves phenophases of the pubescent oak on the island of Pag
Ljiljana Šestan
; Hrvatske šume, Šumarija Pag
Abstract
The impact of climate change has been observed in case of occurrence and duration of seasons which in deciduous forest manifest through changing of the leaves. Monitoring changes in the development of leaves was carried out through phenological observations, where specific change corresponds to a particular phenophase. In researching this issue, despite numerous studies, phenophases have not been studied as a system, but individually and then compared (e.g. Ahas et al., 2002; Menzel, 2000). Most previous studies of this issue were related to classical statistical methods, such as descriptive statistics, linear regression, correlation, multiple regression (e.g. Ahas et al., 2002; Chmielewski and Rőtzer, 2001; Menzel, 2000). The most commonly used method, the method of linear regression, assumes a linear relationship between phenomena. However, as relations between elements of complex natural system are not always linear, the application of the linear regression method is not sufficient for the development of a model of the entire process, without losing specific components and including the environmental influence (Šestan 2010). Therefore, in this study, to model and study the effect of air temperature on the system of phenophases, the system-dynamic principle was applied.
The research of the impact of the most important climatic factor – air temperature, on the phenophases, was conducted on experimental plot in the pubescent oak forest (Quercus pubescens) on the island of Pag (Adriatic Sea). Systematic phenological observations were carried out there during period 1993–2005. Six phenophases marked as F0, F1...F5, were distinguished:
1. Dormant vegetation, all the leaves have fallen (F0),
2. Leaves begin to develop (F1),
3. Leaves are fully developed (F2),
4. Leaves begin to change colour (F3),
5. Leaves have completely changed colour (F4),
6. The leaves begin to fall (F5).
The relevant indicators of the dynamics of phenophases were obtained by collecting and organizing data through phenological observations: average time of appearance in the annual cycle, the average duration of the annual cycle and the frequency of certain phenophases (table 1). Based on systematic observations of phenological data, the frequency of crossing between phenophases was determined as the neighbouring phenophases state differences (table 2). Data on the dynamics of air temperature were obtained from the State Meteorological and Hydrological Institute. The process of determining the characteristic distribution was carried out for the weekly mean air temperature for all phenophases when they are present, or when the state of phenophase is greater than 0 (table 5).
Gathered and processed data have allowed the building of the simulation model of the system of phenophases. Simulation model was based on system-dynamic approach (figure 1). In order to determine whether the model represents the real system satisfactorily, the process of model validation was carried out (table 6 and table 7).
The research of the influence of air temperature on leaf phenophases was conducted with the developed model, through different scenarios from 1 to 6. The results of the simulated scenarios (table 8, 9 and 10) confirmed the crucial influence of temperature on the leaves phenophases. The results of these studies have shown that on average, phenophases F1, F4 and F0, are the most sensitive on the fluctuations in air temperature, but above all F1 as first that reacts to change. However, they also showed that all phenophases are not equally responsive to temperature changes. It is interesting that phenophases F3 and F5 showed the least sensitivity to temperature changes, in terms of average time of occurrence. Such result of the simulation experiments indicates that those phenophases are significantly influenced by other factors.
Keywords
climate changes; modelling; phenology; phenophases; pubescent oak; simulation; system-dynamic approach
Hrčak ID:
84710
URI
Publication date:
30.6.2012.
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