The dynamic regeneration niche of a forest following a rare disturbance event

Abstract

Aim Knowledge of how climate and fire regimes affect regeneration in foundation species is critical to the conservation of entire ecosystems. Different stages of regeneration often require different ecological conditions, but dynamic constraints on regeneration are poorly known for species that regenerate only after infrequent wildfires. Focussing on a long-lived, foundation tree species (Eucalyptus regnans), we tested the hypothesis that the relative importance of fire regime variables (fire severity and time since previous fire) and environmental gradients on post-fire regeneration would shift as seedlings developed.Location South-eastern Australia.Methods Following a large (> 59,000 ha) summer wildfire in 2009, we sampled 131 sites (61 burnt) annually for four years (2009)(2010)(2011)(2012), representing the range of environmental conditions in which E. regnans occurs. We analysed the effect of fire severity, time since fire and environmental variables on early regeneration processes critical for post-fire species distributions: seedling establishment, seedling density and growth through different height stages (10 cm, 25 cm, 50 cm and 200 cm). ResultsThe regeneration niche of E. regnans was defined by different factors at different stages of development. Initially, seedlings established prolifically on burnt sites, regardless of severity. Three years into the regeneration process, high-severity fire became the dominant driver of seedling persistence and growth over 25 cm. Growth over 50 cm was dependent on environmental conditions relating to elevation and precipitation.Main conclusions Our results describe how fire occurrence, fire severity and environmental gradients affected seedling establishment, persistence and growth. The dynamic constraints on regeneration likely reflect temporal changes in the biotic and abiotic environment and variation in resource requirements during the early post-fire years. Our findings will enable more accurate forecasts of species distributions to assist forest conservation in the face of global changes in climate and fire regimes.

Avoiding ecosystem collapse in managed forest ecosystems

“…For example, the regeneration niche is a critical part of the life cycle of all forest tree species and therefore to the maintenance of forest ecosystems. However, the regeneration niche of many forest trees can be sensitive to recurrent human and natural disturbances as well as to the impacts of exotic taxa that can greatly impair regeneration (Bhagwat et al 2012;Smith et al 2016). In the southwestern US, ponderosa pine (Pinus ponderosa) forests can be vulnerable to regeneration failure after high-severity fires (Friederici 2003).…”

From unburnt to salvage logged: Quantifying bird responses to different levels of disturbance severity

“…Rapid recovery in species richness on sites subject to high‐severity fire is, in part, a function of the substantial initial reduction in species richness at the time of disturbance, although overall richness still did not approach that of unburnt unlogged sites. Part of the explanation for relatively rapid recovery may be related to high‐severity fire that leads to dense natural regeneration around dead trees from the previous fire‐killed stand (Blair et al., ; Smith et al., ). Stands characterised by rapid regeneration in vegetation structure coupled with numerous dead and burned standing trees may, in turn, provide an array of suitable habitat niches for a range of bird species.…”

“…Our study area was the mountain ash forest in the Toolangi, Marysville and Powelltown districts of the Central Highlands of Victoria, south‐eastern Australia (Figure ). Stand‐replacing fire is one of the predominant forms of natural disturbance in mountain ash forests leading to stands of broadly uniform age (Smith et al., ). We constrained our study to one age class of forest—stands that were 70 years old at the time of the 2009 wildfires, having regenerated after previous wildfires in 1939.…”

The importance of managing and conserving large old trees: a case study from Victorian Mountain Ash forests

“…Many species of large old trees produce massive seed crops, with positive relationships between increasing tree size with allocation to reproduction being a widespread phenomenon globally (Wenk & Falster 2015). Mountain Ash appears to follow this pattern and recent work has indicated that, following wildfire, the prevalence of germinants and seedlings is significantly greater in burned old growth stands than in forests that were of younger age at the time of fire (Smith et al 2013;Smith et al 2016). …”