MODULE 5. VEGETATION PHENOLOGY

Phenology is the study of seasonal biological events (e.g. leaf budburst, flowering and leaf fall) that are sensitive to variability in climate. In this particular exercise, you will be learning how temperature affects the timing of leaf budburst in the spring. Research studies show that trees in urban areas had earlier spring growth than those trees in the rural areas. Earlier leaf budburst is a direct response to warm temperature in the spring. Budburst, as defined, occurs when tiny leaves emerge from the bud.

If global warming continues, what happens to the length of growing season in temperate region? What are the ecological consequences of this phenomenon? Think about the growth requirements of plants and how the demand for these resources (water and nutrients) can be affected by prolonged growing season.

Phenology data from Tokyo, Japan

Let us examine the relationship of temperature and timing of budburst of a native deciduous tree species in Tokyo, Japan. Tokyo is the capital city and is considered the largest city in Japan with a population of 12 M. Phenology data (Table 6) was collected in Spring 2005 by the GLOBE teachers and students in Tokyo, Japan through the GLOBE Urban Phenology Year project. The study was conducted to determine the effect of urbanization, particularly the heat island effect on the timing of leaf budburst. Trees observed were categorized into urban and rural sites within the city. Surface temperature (°C) (temperature emitted by the object on earth as detected by satellite sensors) was derived from satellite image and date of budburst was based on the day of the year (DOY).

Table 5. Date of budburst (BUD, 2005) of Zelkova serrata trees and surface temperature (°C) in urban and rural areas of Tokyo, Japan. BUD is expressed as day of the year (DOY).

Using t-test (two-sample assuming unequal variance) – following the Data Analysis and Interpretation module – determine if surface temperature and date of budburst are significantly different between urban and rural sites in Tokyo, Japan. Calculate the mean surface temperature and mean budburst date for both urban and rural sites. Record the means and p-values of the t-test in Table 6.

Table 6. Mean surface temperature (°C) and date of burdburst (DOY) of Zelkova serrata trees located in urban and rural sites in Tokyo, Japan.

What can you conclude from the data? Were the results significant? Note that if p-value is ≤ 0.05, the mean surface temperature or mean budburst date difference between urban and rural sites are statistically significant otherwise surface temperature or budburst date in both urban and rural sites are the same.

Between urban and rural sites, which one had higher surface temperature? Which site had earlier budburst date? Note that a lower number of budburst date means that budburst occurred earlier.

Create a scatter plot of temperature (x-axis) and budburst date (y-axis) and indicate the regression model and r2 value. Based on the regression model, what is the relationship of budburst date and temperature?

Phenology data from West Virginia

Let us now examine the relationship of elevation and budburst date of yellow (tulip) poplar (Liriodendron tulifipera) trees. Yellow poplar is a native species in West Virginia and a valuable timber species that grows throughout the state. You have learned previously that as elevation increases, temperature decreases. This is the reason why temperature is cooler up in the mountains than in the lowlands. What would then be the effect of elevation on budburst date? Do you expect budburst to occur earlier or later in the mountains with cooler spring temperature?

Field observations of budburst were conducted in 2007 by Glenville State College students, and GLOBE teachers and students in different cities in West Virginia and Mt. Morris, Pennsylvania. The data is provided in Table 7.

Table 7. Budburst date (BUD, 2007) of yellow poplar trees in different cities in West Virginia and Mt. Morris, Pennsylvania (Morris). BUD is expressed as day of the year (DOY)

Before analyzing the budburst data for yellow poplar trees, let us create a map showing the locations of yellow poplar trees using ArcExplorer Java Edition for Education (AEJEE). Use elevation map (3 m resolution) on AEJEE as the background map. Follow the module on Exploring Budburst Data using GIS (Lessons 1b-d). Map should appear like the one below. Note that the location label can be done later once you have inserted the image file (created in AEJEE) in MS Word.

Calculate the mean budburst date, mean elevation and total number of trees observed for each city and record results in Table 8.

Table 8. Results of budburst observation of yellow poplar in different cities in West Virginia and Mt. Morris, Pennsylvania.

Based on Table 8, what can you conclude about the data? Create a scatter plot of elevation (x-axis) and budburst date (y-axis) and indicate the regression model and r2 value. How is date of budburst affected by elevation? Which city had the earliest budburst date? latest budburst date? Note that a lower number of budburst date means that budburst occurred earlier.