Patterns and drivers of natural regeneration on old-fields in semi-arid floodplain ecosystems

Abstract

Socio-economic and environmental drivers are causing large scale abandonment of agricultural land worldwide. Simultaneously, there is growing recognition that urgent and widespread revegetation is required in our agricultural landscapes to restore biodiversity, ecosystem services and promote carbon sequestration. The design of effective revegetation strategies, however, can be limited by a lack of knowledge regarding patterns and processes of regeneration. Here, we examine naturally regenerating woody vegetation on 12 old-fields and compare this to paired remnant vegetation across four regions of a semi-arid agricultural area in eastern Australia. We found that naturally regenerating vegetation on old-fields exhibited similarities to remnant vegetation in terms of composition but varied substantially with respect to key structural attributes. Woody vegetation tends to regenerate in these old-fields with relatively high density given sufficient time (~ 30–40 years), but prior to this, very limited structural recovery occurs at all. The composition and richness of tree seedling and shrub assemblages did not differ between remnant and old-field areas. However, tree assemblages in remnant areas differed in composition and had higher species richness. Old-fields had extremely low numbers of exotic trees and shrubs. Simultaneously, most dominant native species present in the remnant vegetation were also observed in regenerating old-fields, contributing to a low degree of compositional difference between old-fields and remnant areas overall. The abundance of paddock trees, time since abandonment and mean annual rainfall are key drivers influencing natural regeneration of these old-fields. We recommend that natural regeneration is a viable form of restoration of old-fields in the northern Murray-Darling Basin given sufficient time.