Global trends in biodiversity with tree plantation age

Tree plantations are expanding globally to satisfy demands for wood, food, energy, oil and other ecosystem services, often replacing primary vegetation. Plantations are generally less biodiverse than primary vegetation, yet the effects of plantation age on biodiversity are not well understood. More accurate estimations of biodiversity within plantations over time could improve predictions of the ecological effects of tree planting, guiding more sustainable land use and management decisions. Here, we assess the effects of plantation age on the abundance and number of species of invertebrates, birds, plants, mammals, amphibians, reptiles and lichens, and on compositional similarity to minimally-used primary vegetation. We find that plantations usually support fewer species than both minimally-used primary vegetation and mature secondary vegetation, fewer individuals, and some novel species (i.e. species not also found in primary vegetation). We also find that, on a global scale, plantation age has positive effects on species richness, the abundance of individuals, and compositional similarity to primary vegetation. However, geographic realm, biome, management intensity and plantation type influence the biodiversity trends. We also include a case study for oil palm, showing that species richness increases with oil palm plantation age. Nevertheless, plantations typically remain less biodiverse than natural vegetation even thirty years after planting, especially in the tropics, where compositional similarity between plantations and minimally-used primary vegetation remains approximately 20% lower than the non-tropics. Our results highlight the negative ecological consequences of establishing new plantations in place of primary vegetation or restoration, yet we also reveal spatio-temporal differences in plantation biodiversity.