The Effects of Rehabilitation Treatments on Landscape Function Within a Softwood Plantation After Fire: Implications for Catchment Management

There is global interest in enhancing the ecosystem services provided by landscapes and catchments dominated by plantation (monoculture) forestry. Partial reversion of plantations to locally native species (reforestation) is one option. However, the ecological outcomes of this kind of plantation reversion are poorly known. The partial reforestation of a pine plantation (Pinus radiata D. Don 1836) in the Australian Capital Territory with native species following a wildfire provides a rare case study of the environmental consequences of such a reversion. We estimated changes in landscape functionality by measuring indices of water infiltration, nutrient cycling, and soil surface stability across five landscape-scale treatments after the 2003 Lower Cotter Catchment bushfire: (1) natural regeneration of a native forest burned in 2003, (2) burned pine plantation replanted to pines, (3) burned plantation replanted to native trees and shrubs, (4) burned plantation allowed to naturally regenerate, and (5) forest roads rehabilitated by planting native trees and shrubs. At 14 years after the fire, we found that the regenerating native forest had the highest indices of water infiltration, nutrient cycling, and soil surface stability. The burned pine plantation that was replanted to pines in 2005 had indices of functionality that were higher than the burned plantation areas that were either allowed to naturally regenerate to native eucalypt forest or were planted with native forest species. These two types of native forest rehabilitation treatments had only minor differences in functionality. The rehabilitated closed roads were the least functional. We found that a pine plantation at the closed canopy stage can supply regulating services of water infiltration, nutrient cycling, and soil surface stability comparable to a native forest at a similar stage postfire; however, a significant limitation of the plantation was its low ecosystem resilience. It required massive soil disturbance to replant postfire and long-term maintenance of an extensive unpaved road network. The active or passive rehabilitation of native forest is justified to improve the natural resilience to wildfire. However, this rehabilitation of a native forest following use as a pine plantation is a multidecade process in this relatively low-rainfall environment. The 2003 Canberra bushfire destroyed the entire pine plantation at Lower Cotter Catchment, a water catchment in Australian Capital Territory, but also provided an opportunity to examine and quantify changes in ecosystem functions with different restoration treatments. Landscape Function Analysis, including three indices (water infiltration, nutrient cycling, and soil surface stability), was used in this study. Findings suggest that both native eucalyptus forests and pine plantations recovered to relatively high levels of functionality within just 15 years after the bushfire, compared with all other restoration treatments, but plantations of Pinus radiata are not resilient to wildfire from a commercial perspective. These results help to justify the controversial decision to restore the majority of the catchment with native species in 2005. However, long-term monitoring is needed to determine how long it will take for the replanted and natural regeneration treatments to approach the functionality of the native forest.