Forest and Vegetation Propagation

Forest and Vegetation Propagation at 915 MHz

Vegetation is one of the most significant impairments to 915 MHz propagation. Forested terrain requires a fundamentally different planning approach from open or urban environments.

Foliage Attenuation

915 MHz is significantly absorbed by vegetation. Typical losses:

Even a few hundred meters of dense forest can consume the entire link margin of a typical LoRa deployment. This means ground-level range in dense forest may be only 200–500 meters even with the longest LoRa spreading factors.

Seasonal Variation

Deciduous forests have dramatically different propagation in summer (full leaf) versus winter (bare branches). A link that works reliably in December may fail completely in July when the leaves are out.

Always plan coverage for worst-case summer leafed-out conditions. Links that are marginal in winter will likely fail in summer. If your network must work year-round, design for July.

Elevation Above Canopy

The single most effective technique for improving range in forested terrain is getting the antenna above the tree canopy.

A node mounted at canopy level or just above it has near-line-of-sight to distant nodes that are also above the trees. Even 5–10 meters above the canopy dramatically improves range in forested areas.

This is a dramatic difference — the same hardware performs 10–20× better simply by being above the canopy.

Trail Corridor Effect

Trails create linear openings in the forest canopy. Range along a trail is significantly better than off-trail in the same forest. The open sky corridor above the trail allows near-LOS propagation along the trail axis.

This is useful for planning hiking or trail mesh coverage — nodes near trail intersections or high points along trails will have better coverage than nodes placed arbitrarily in the forest interior.

Mixed Terrain Path Budgets

When a link crosses both open and forested terrain, plan for the worst-case segment. A 10 km link that crosses 3 km of dense forest needs to be designed for the forest loss, not the open segments.

Use a simple approach: calculate the total forest path length in your link, apply 15 dB/100m as a conservative estimate for dense summer deciduous forest, and verify the total loss fits within your link budget. If it doesn't, raise antenna height, increase transmit power (where regulations permit), or use a higher-gain antenna.

Summary for Forest Deployments

• Mount antennas as high as practical — at or above canopy height
• Test and plan for summer worst-case conditions
• Use trail corridors for coverage where possible
• Account for every meter of forest in your path budget
• Consider tower or tall-tree mounting for backbone nodes