Revegetation with Australian native grasses - a reassessment of the importance of using local provenances

Abstract

Many restoration guidelines strongly recommend the use of local sources of seed in native plant revegetation projects. These recommendations are based on assumptions that the species used for revegetation are cross-pollinated and woody, as they were developed for overstorey vegetation from the northern hemisphere. Their validity is challenged with respect to replacing or enhancing the native Australian grass component of degraded ecosystems. First, far from being the dominant pollination mechanism, obligatory cross-pollination has not been recorded in any Australian native grasses except for a few dioecious species. Indeed, the common Australian native grasses so far studied have revealed complicated breeding systems that provide the evolutionary resilience necessary for coping with the variable Australian climate as well as with future climate change. It is suggested that a key feature of this flexibility is polyploidy and its implications for sourcing seed are discussed. Second, it is argued that the genetic dissimilarity among populations of a species is not proportional to the distance between them but is more related to the environmental stresses that have been placed on those populations in the past. This is illustrated by different scales of ecotypic variation that are often trait-dependent. Evidence for this can be found in several translocation experiments, where populations of native grasses from a great distance away survive and often perform better than local populations. It is concluded that there is little justification for the recommendation that only local sources of seed of Australian native grasses should be used for revegetation projects, and particularly in large-scale programs. Instead, it is argued that studies on Australian native grasses provide clear evidence that distinct adaptive advantages may be gained by sourcing non-local provenance seed, which is matched to the environment of the revegetation site, and which contains appropriate stress tolerance genes, or by mixing populations from several locations to increase the genetic diversity of seed sources. Some general guidelines are provided for deciding whether or not to use local provenances depending on the purpose of the revegetation, the degree of environmental modification of the site and the characteristics of the species of choice.