Relative neighbour effect (RNE) at eleven subalpine (hatched bars) and alpine (solid bars) sites, respectively (after Callaway et al., 2002)
 

Whereas the relative neighbour effect was negative at many of the subalpine sites, it was positive at all high altitude sites. Note that this is an overall effect, and that for particular species such as some cushion plants negative interactions may prevail.

Interactions among plants were assessed by the removal of all neighbouring species within 10 cm of a target individual, and comparison of the performance after two growing seasons of target plants with neighbours removed to that of control plants around which neighbours were left intact.
RNE was calculated for biomass of target plants at all sites except for the Caucasus and the Andes sites, where RNE was calculated using the difference in leaf number between control and target pairs.
RNE_biomass = (biomass _target - biomass _control) / biomass _target
RNE_leaf = (final leaf number/initial leaf number_target - final leaf number/initial leaf number_control) / (final leaf number/initial leaf number_target)