Figure 55.14 Positive Plant Interactions Are More Common at Higher Elevations The species interactions of alpine plants were experimentally measured (using the relative neighbor effect [RNE], defined as the growth of the target plant species with neighboring plants present minus its growth with neighboring plants removed) in 11 mountain ranges worldwide. RNE values greater than zero (in blue) indicate that neighbors increased the growth of target species; RNE values less than zero (in red) indicate that neighbors decreased the growth of target species. Plants generally benefited from neighbors at high elevations where temperatures were colder and competed with them at lower elevations where temperatures were warmer.