Direct and higher-order interactions in plant communities under
increasing weather persistence
Abstract
Climate change is increasing the weather persistence in the
mid-latitudes, prolonging both dry and wet spells compared to historic
averages. These newly emerging environmental conditions destabilize
plant communities, but the role of species interactions in this process
is unknown. Here, we tested how direct and higher-order interactions
(HOIs) between species may change in synthesized grassland communities
along an experimental gradient of increasing persistence in
precipitation regimes. Our results indicate that species interactions
(including HOIs) are an important determinant of plant performance under
increasing weather persistence. Out of the 12 most parsimonious models
predicting species productivity, 75 % contained significant direct
interactions and 92 % significant HOIs. Inclusion of direct
interactions or HOIs respectively tripled or quadrupled the explained
variance of target species biomass compared to null models only
including the precipitation treatment. Drought dominated the plant
responses, with longer droughts increasing direct competition but also
HOI-driven facilitation. Despite these counteracting changes, drought
intensified net competition. Grasses were generally more involved in
competitive interactions whereas legumes had a stronger affinity for
facilitative interactions. Under longer drought, species affinity for
nutrient rich or wet environments resulted in more negative direct
interactions or HOIs, respectively. We conclude that higher-order
interactions, crucially depending on species identity, only partially
stabilize community dynamics under increasing weather persistence.