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The effects of a woodland on microclimate
On a hot summer’s day it is noticeable that temperatures in a forest or woodland are much lower than those outside. You are no longer walking under a hot, baking sun. It feels sheltered and it may feel slightly more humid. The light reaching the ground is reduced to small patches amid the shadows.

A microclimate is created when there are variations in a small area or a locality. There may be changes in temperature, precipitation, wind speed and evaporation rates because of the local environment. In a woodland the trees themselves help to create these changes.

Chapter 8 of Lenon & Cleves Fieldwork Techniques includes suggestions for studying local climate. Towns, woods and lakes all create their own climate.

Sun flecks at the Braidburn, Edinburgh.
 

Radiation exchanges in woodland
diagram radiation excahnge
  • Examples of tree albedos: Scots pine 9%; Oak (summer) 15%, Oak (spring) 12%; Sitka spruce 12%; Norway spruce 12%; Orange trees 32%; Tropical forest 13%.

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The effects of woodland type
diagram woodland type

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diagram winds in woods
Temperature in woodlands
  • Woodlands are normally cooler in summer and slightly warmer in winter.

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Moisture in woodlands
  • Increased output of moisture - In a forest , leaves are continually transpirating moisture into the atmosphere. As winds inside a woodland area are usually light, this moisture is not easily dispersed.
  • Interception of moisture input - On the other hand, vegetation is continually intercepting moisture, so less of it reaches the forest floor.
  • The net effect on humidity levels within a woodland is small.
  • Daytime temperatures within a woodland are cooler than those outside - this makes the relative humidity of the air greater within a forest (even if the forest atmosphere contains the same absolute amount of water vapour as outside it).
  • Experiments suggest a 5% difference, although much depends on the time of year and weather conditions.

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Difference of relative humidity (per cent) between the inside and outside of a forest

Forest type

January

April

July

October

Year
Deciduous broad leaf

3.4

3.2

-0.8

1.1

2.2
Needle tree conifer

4.8

4.8

6.5

9.5

6.8
Japanese cedar

1.6

-1.1

1.5

0.5

0.8
Positive values indicate that the inside of the forest was more humid. The research was undertaken by the University of Tokyo, Japan. (Briggs & Smithson p140)

References: David Briggs and Peter Smithson (1985) Fundamentals of Physical Geography pub Hutchison, chp 9.

  • Chapter 8 of Lenon & Cleves Fieldwork Techniques includes suggestions for studying local climate. Towns, woods and lakes all create their own climate.

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