e in size or biomass, but this time light would be the limiting factor.
The following, illustration, Relative Plant Size and Biomass Per Unit Area, uses APST, latitude and various biological limiting factors to assist in developing a feeling for plant height and /or biomass per unit area, for various latitudes across a planet’s surface.
Also, remembered that gravity affects height, so that the largest or tallest plants on a 3.0 Earth mass planet will be considerably shorter than the tallest plants on a 1.0 or 0.5 Earth mass planet—that is, if all parameters are equal except planetary mass.
The 0ºC APST’ model in the illustration shows short plants growing at around 30º latitude, this planets tundra zone. This biologically limiting, cold environment, rapidly gives way to a cool forest which extends from about 25º ‘north (and south’) latitude to the equator. With the sun passing nearly over the habitable equatorial zone, we would expect to find the plant communities of the cool temperature forest well developed into vertical light gathering strata.
Illustration: Relative Plant Size and Biomass Per Unit Area
The 60ºC APST (140ºF average planetary surface temperature) model has short, ‘shade loving’ plants in the biologically limiting, dimly lit, twilight like polar region. With a decrease in latitude and subsequent increase in elevation of the mid day sun, the cool temperature forests develop a fierce competition for light. Around 60º latitude, the damp. Warm and fairly well illuminated conditions produce a tropical type forest canopy which carries the tallest plants on the planet. Below 60º latitude, increasing temperatures tend to overcome moisture availability where upon plant size or biomass per unit area must be reduced to thwart starvation.
Approaching 30º latitude, the high pressure system creates arid conditions. This area is not only arid, but extremely hot, with air temperatures 10ºF above that required to destroy protein. From about 30º latitude and down to the equator, temperatures tend to become the biologically limiting factor. (Note: For comparison, its recommended that we turn adjust the water temperature in our home hot water tank from 140ºF to about 120ºF to reduce the chance of being scalded).
On a planet with a large mass, i.e. 2.0 to 3.0 Earth mass, the dry land area is quite small compared with the area covered by water, therefore, at 60ºC APST, a dry land area located at 30º latitude would not be arid, it would be for us, an environment of extreme heat and severe humidity. On such a world, at 30º latitude, our bodies would feel like they were in a 140ºF sauna. We wouldn’t feel comfortable until we relocated to 70º latitude where 70ºF air temperatures would be found; equivalent to being above our ‘Arctic Circle’, in Finland, Alaska, northern Russia, northern Canada, Greenland.
Continued in Chapter 9: Data Correlation