The current default world generation settings are a maximal map height of 30 and a snow line height of 15, while tropical tree line height is calculated automatically based on the maximal map height and can not be set, afaik.
In effect in sub-arctic there is no snow and in sub-tropic there are no tropical trees except at the coast-line, when using the default settings.
For sub-arctic setting the snow line height to 5 provides sufficient snow and
for sub-tropic setting the maximal map height to the historic value 15 gives tropical forests.
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