year 12 microclimate & nutrient cycling

The microclimateThe microclimate

of a woodland of a woodland ecosystemecosystem

What is a Microclimate?

These are climates that exist over small areas, where the conditions of shelter, temperature, precipitation, humidity, winds, pressure and clouds are different to the general surroundings.

What abiotic factors affect the microclimate of a woodland

ecosystem?

SOLAR

RADIATION

WIND

HUMIDITYHUMIDITY

What abiotic factors affect the microclimate of a woodland

ecosystem?• Solar radiation

• Wind

• Humidity

What affects the amount of solar radiation in a woodland microclimate?The temperatures decrease downwards, owing to the shading effect of the trees.

The treetops of a high, dense forest can form an almost unbroken surface, which acts in a similar way to the ground.

Thus, the forest floor is generally cooler than the canopy and the surrounding countryside.

During the day the tree tops absorb solar radiation, resulting in high temperatures at canopy level.

What affects the amount of solar radiation in a woodland microclimate?Correct answer:

The treetops of a high, dense forest can form an almost unbroken surface, which acts in a similar way to the ground.

During the day the tree tops absorb solar radiation, resulting in high temperatures at canopy level.

The temperatures decrease downwards, owing to the shading effect of the trees.

Thus, the forest floor is generally cooler than the canopy and the surrounding countryside.

In the Summer the temperature difference can be as much as 5 degrees Celsius.

At night forests retain their heat and are generally warmer than their surroundings.

What affects wind in a woodland microclimate?

Above the canopy

The canopy

The trunk zone

Ground level

This is where the wind speeds are lowest. As the canopy is approached velocity falls rapidly.

Velocity falls due to friction and the effect of low lying plants.

This area is more open and there is less interference of airflow.

This is where wind speeds are greatest. There are no obstacles to interfere airflow

•Increased output of moisture - In a forest, leaves are continually losing moisture into the atmosphere by ___________. 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 ___________ moisture, so less of it reaches the forest floor. •Daytime temperatures within woodland are _______ than those outside - this makes the relative _________ of the air greater within a forest.

intercepting humidity cooler transpiration

What affects humidity in a woodland microclimate?

On a hot summer’s day it is noticeable that temperatures in a forest 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.

•Trees reduce temperature during the day, but retain heat during the night. Temperatures are thus more even (less extreme)

• Wind speed is reduced

• Evaporation is lower, especially in the day but also at night. Locally, air becomes saturated due to transpiration (and is not blown away); this reduces evaporation.

• Humidity levels remain high and constant due to transpiration and low evaporation rates. Mosses are common on the forest floor

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

Moisture in woodlands•Increased output of moisture - In a forest , leaves are continually transpiring 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

Winter 06

Winter 07

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

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)

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