Plant Growth on North vs. South Slopes by Hemisphere

A question about growth differences between north- and south-facing slopes in northern and southern hemispheres, assuming light is the primary driver.

The key factor is heat load, not just light quantity:

• Northern Hemisphere: South-facing slopes receive more intense afternoon sun → higher soil/air temperatures, faster evaporation, greater drought stress. North-facing slopes get morning sun → cooler, moister, longer growing season for heat-sensitive species.
• Southern Hemisphere: Reversed. North-facing slopes get afternoon sun → hotter, drier. South-facing slopes are cooler, moister.

Plants adapted to cooler, moister conditions (many woodland species) thrive on north slopes (NH) / south slopes (SH). Heat-tolerant, drought-adapted species (many Mediterranean, prairie, succulent plants) favor south slopes (NH) / north slopes (SH).

Light duration also differs: south slopes (NH) have longer daily insolation in winter, shorter in summer; opposite in SH. This affects phenology—bud break, flowering, dormancy.

Slope angle, soil depth, wind exposure, and cold-air drainage modify these patterns. But heat load is the primary ecological driver of slope-aspect vegetation differences worldwide.