3. Micro climate
Microclimate data (including soil temperature, humidity and light levels) can be used to support investigations into differences in vegetation. If carried out carefully, your results will provide a snapshot of the environmental stresses experienced by plants. All measurements should be made at the same time of day, with the same technique at each site. Ideally measurement could be collected at the same location at the same time of day over the course of a year.
Temperature (air and soil)
A simple glass analogy non-mercury filled thermometer can be used, however extreme care must be taken when using glass apparatus in the field. Digital temperature probes are much better and can be purchased cheaply.
It is sometimes useful to find the temperature range over a particular time period, such as 24 hours. Maximum/minimum thermometers are widely available. Try as much as you can to standardise the temperature reading between sample sites.
An digital anenometer will measure wind speed directly. Take readings at the same height above the ground each time.
The most practical way of measuring humidity in the field is a digital hygrometer. Hand-held whirling hygrometers are also often used. This piece of equipment compares the temperatures recorded by wet and dry thermometer bulbs. The bulb surrounded by a wet fabric sleeve usually shows a lower temperature than the other because of the cooling effect of evaporation. The bigger the difference recorded by the two bulbs, the lower the relative humidity. There are standard tables for the conversion.
- Light levels at ground level often vary throughout a woodland so a large number of readings need to be taken at fixed points.
- Light conditions constantly change e.g. with seasons, the time of day and changes in cloud cover. If two areas being compared readings must be taken simultaneously.
- Different light meters vary in what they measure and their accuracy. Matched calibrated meters should always be used.
Because of these difficulties it is often simpler and more meaningful to obtain an indirect measure of how much light might reach the ground community (e.g. by assessing the amount of open sky which can be seen through the canopy at a number of fixed points, or by recording whether the ground at these points is in shade or sun at set time intervals during the day).