Forest Farming and Aspect: regional differences in site suitability recommendations

It’s easy to assume the east-facing slopes of a mountain would be wetter because they get the gentle morning sun, but in the Rocky Mountains and Sierra Nevada the opposite is usually true: the west-facing slopes are significantly wetter and more densely forested. This is driven by the prevailing westerly winds. When moist Pacific air hits the range, it’s forced upward in a process called orographic lift. As the air rises, it cools, condenses, and drops most of its moisture as rain or snow on the windward (western) side. By the time the air crests the ridge and descends the eastern slope, it has lost much of its moisture, creating a drier “rain shadow” on the leeward side. This pattern flips the usual planting advice you hear in the East: -In the Appalachians (where winds are less consistently from one direction and summer humidity is high), forest farmers growing ramps (wild leeks) and other spring ephemerals prefer north- and east-facing slopes. Those aspects stay cooler and moister through spring, giving shade-loving, moisture-dependent plants a longer growing window before the canopy closes. -In the Rockies and Sierra Nevada, however, if you’re forest-farming osha (Ligusticum porteri)—a high-elevation medicinal herb that thrives in cool, moist woodlands under and around aspen especially but also fir, spruce, Douglas fir, and oak—you’d do better to plant on west- or southwest-facing slopes at the appropriate elevation (5,000 to 11,500 feet). That’s where the orographic effect delivers the most consistent soil moisture that osha needs. -So the same ecological preference—a cool, moist, forested landscape—leads to opposite slope-aspect recommendations depending on which side of the continent you’re farming.