A project undertaken at Western Sydney University, and supervised by Dr Kristine Crous.
While wildfires rarely occur in rainforests the areas of Nightcap and Dorrigo National Parks which feature species-rich subtropical rainforest were moderately to severely burnt in Nov-Dec. 2019. These subtropical rainforests are one of the most biodiverse regions of Australia and are the main refuge of ancient rainforest lineages with evolutionary links to Gondwana, as recognised by their listing in the Central Eastern Rainforest Reserves World Heritage property. However, almost no data exist on how these forests recover after fire and what controls their recovery rate. We now have a unique opportunity to quantify rainforest productivity and recovery after fire.
Building on earlier preliminary data of mortality, we seek to contrast the productivity and resilience of fire-affected and non-burnt rainforest communities growing on nutrient-poor and nutrient-rich soils because post-fire mortality can continue for some years in rainforests. The capacity to recover ecosystem productivity and normal ecosystem functioning is largely dependent on soil nutrients, which are important to the overall long-term resilience of rainforests but rarely studied. We will focus on the following questions (1) How do nutrients influence rainforest recovery after fire? (2) How do species on rich versus poor soils differ in their aboveground productivity? and (3) Do soil nutrients influence post-fire responses and species composition and colonisation after bushfire?
Rainforest species responses to fire include resprouting, re-seeding, and mortality, with slow recovery rates compared to other ecological communities (e.g. eucalypt-dominated forests) and species loss. While tree mortality and bushfire damage immediately recorded after fire ranged between 12 and 80%, we aim to quantify longer-term rainforest productivity in burnt and non-burnt plots with different soil fertility and test ecological ideas regarding species composition and long-term resilience over time. As bushfires may push rainforests to an alternative vegetation type and eliminate habitat for threatened and endangered species, we need to understand the longer-term recovery rate, vital to future bushfire management and securing conservation outcomes.
Sixteen 20 x 30 m plots will be established in the Nightcap NP: four burnt plots and four non-burnt plots on two soil types (rhyolite or basalt). We will build on previous monitoring measurements and further link ecosystem function with forest structure after fire by examining aboveground productivity and leaf litterfall differences since the fires between burnt and non-burnt plots related to rainforest recovery.
Plots on nutrient-rich basalt and nutrient-poor rhyolite soil will have different species assemblages with some species shared on both soil types and we expect different recovery trajectories on different soil types. We will quantify canopy health, ongoing mortality, stem growth, canopy expansion and leaf turnover both at species-level and stand-level over a period of 3 years in burnt and non-burnt plots. The contents of leaves and wood will be analysed for phosphorus for several of the more dominant species. These measurements are critical to learn how a broad set of rainforest species recover and to protect other rainforest refugia into the future.
We seek to understand the rate at which species composition approaches a mature-phase (with structure and functioning close to undisturbed plots) as part of their recovery, including how this recovery trajectory is different depending on nutrient availability. We aim to quantify post-fire changes in aboveground productivity and nutrient dynamics to link forest function with forest structure during rainforest recovery in one of the most diverse Australian ecosystems. Our insights into the resilience of rainforest species recovering after fire can inform strategies for future forest management and biodiversity conservation.