Higher tree transpiration due to road-associated edge effects in a tropical moist lowland forest

• Roads significantly affect the microclimate at forest edges in the Central Amazon.
• Tree water use was higher at forest edges compared to the forest interior.
• This could be due to a species effect and/or changes in microclimate conditions.
• High water consumption makes disturbed forests more susceptible to water stress.

Newly created forest edges have significant ecophysiological effects on bordering trees. We studied edge effects on microclimate and tree transpiration rates during wet and dry seasons along a 250 m transect spanning the edge of an unpaved road into an old growth tropical lowland forest in the Central Brazilian Amazon. Canopy openness decreased only minimal from the road (3.68%) towards the forest interior (1.69%). Vapor pressure deficit (measured at 2.2 m height above ground) was lower in the forest interior. The edge effect on microclimate penetrated deeper into the forest (>100 m) during the dry season compared to the wet season (<100 m). Overall, sap flux, and therefore transpiration rate, was 54% higher in trees adjacent to the road compared to forest interior trees. Higher transpiration rates at the forest edge can be explained by higher turbulences and energy exchange of the canopy boundary layer and by a shift in species composition to high water using secondary forest species 25 years after the road construction. Similar changes might be expected for other disturbances affecting local relative humidity and in situations that favor plants with water use traits differing from those found in the forest interior.