Flammability trajectories following destocking and forestation: a case study in the New Zealand high country

Abstract

New forests can bring many benefits; however, public concern over wildfires can create a dilemma for restoration ecologists, managers, and policy makers advocating for forestation. In southern montane New Zealand, destocking following pastoral tenure review and forestation incentives have resulted in an increase in woody vegetation, raising concerns over fire risk. We used abundance-weighted community flammability metrics to investigate changes in the flammability of montane grassland within Mahu Whenua Ecosanctuary following destocking, and the relative flammability of woody communities likely to establish naturally in this area. While woody species cover increased following destocking, a decrease in highly combustible graminoids and shrubs, and increased abundance of non-flammable herbaceous species meant community flammability metrics reduced or showed no change. Woody communities that could potentially develop in the area varied substantially in structure and composition. Open, species-rich, shrublands showed lower flammability metrics for both understorey and canopy than mixed dense shrubland/forests or species-poor beech (Nothofagaceae) forests. For active forestation projects where fire is undesirable, a low-flammability herbaceous understorey can reduce fire risk. Where desirable forest species are highly combustible but fire-intolerant, e.g. New Zealand beech, fire risk could be reduced by maintaining buffer zones of low-flammability vegetation or applying planting strategies such as nucleation that accelerate the development of closed canopy forest patches more likely to have moisture-retentive ground layers. However, in historically burnt landscapes, additional information will be needed to define the wider pool of low-flammability species appropriate for forestation programs.

Trophic facilitation in forest restoration: Can Nothofagus trees use ectomycorrhizal fungi of the pioneer shrub Leptospermum?

“…The benefits gained from trophic facilitation occurring throughout the successional process are also complemented by physical benefits, such as the shade and shelter that early‐successional species provide for later‐successional ones (Crouzeilles et al., 2017 ; Davis et al., 2013 ; Tulod & Norton, 2020a ). Focusing restoration purely on the establishment of early‐successional plants like Leptospermum comes with risks because pioneer species can sometimes inhibit the development of more diverse later‐successional communities (Tulod & Norton, 2020b ), or create fire‐prone early‐successional states that self‐perpetuate (Lord et al., 2022 ). However, by stimulating succession, trophic facilitation lowers such risks, allowing late‐successional plants to benefit from both shelter and the mycorrhizal symbionts available.…”