Do multiple fires interact to affect vegetation structure in temperate eucalypt forests?

Abstract

Fire plays an important role in structuring vegetation in fire-prone regions worldwide. Progress has been made towards documenting the effects of individual fire events and fire regimes on vegetation structure; less is known of how different fire history attributes (e.g., time since fire, fire frequency) interact to affect vegetation. Using the temperate eucalypt foothill forests of southeastern Australia as a case study system, we examine two hypotheses about such interactions: (1) post-fire vegetation succession (e.g., time-since-fire effects) is influenced by other fire regime attributes and (2) the severity of the most recent fire overrides the effect of preceding fires on vegetation structure. Empirical data on vegetation structure were collected from 540 sites distributed across central and eastern Victoria, Australia. Linear mixed models were used to examine these hypotheses and determine the relative influence of fire and environmental attributes on vegetation structure. Fire history measures, particularly time since fire, affected several vegetation attributes including ground and canopy strata; others such as low and sub-canopy vegetation were more strongly influenced by environmental characteristics like rainfall. There was little support for the hypothesis that post-fire succession is influenced by fire history attributes other than time since fire; only canopy regeneration was influenced by another variable (fire type, representing severity). Our capacity to detect an overriding effect of the severity of the most recent fire was limited by a consistently weak effect of preceding fires on vegetation structure. Overall, results suggest the primary way that fire affects vegetation structure in foothill forests is via attributes of the most recent fire, both its severity and time since its occurrence; other attributes of fire regimes (e.g., fire interval, frequency) have less influence. The strong effect of environmental drivers, such as rainfall and topography, on many structural features show that foothill forest vegetation is also influenced by factors outside human control. While fire is amenable to human management, results suggest that at broad scales, structural attributes of these forests are relatively resilient to the effects of current fire regimes. Nonetheless, the potential for more frequent severe fires at short intervals, associated with a changing climate and/or fire management, warrant further consideration.

Effects of a large wildfire on vegetation structure in a variable fire mosaic

“…Our finding that many aspects of the invisible mosaic influenced forest and woodland vegetation structure contrasts with the results of Haslem et al. (), who found the effects of long‐term fire history on vegetation structure of foothills Eucalyptus forests was limited compared with the effects of the most recent fire (severity, time since fire), and environmental variables (e.g., rainfall; Haslem et al. ).…”

“…In contrast, Haslem et al. (, mixed eucalypt forest) found that properties of a recent severe wildfire overrode most effects of previous fire history on vegetation structure. There is therefore a need to better understand the extent to which wildfire modifies the effects of the previous fire history on habitat structure, and hence, whether it is important for post‐wildfire management, and attempts to re‐instate variation in time‐since fire, to account for the established invisible mosaic.…”

Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

“…); however, interactive effects of multiple fires, particularly under high‐severity conditions, remain largely unquantified (Haslem et al. ).…”

Effects of time since fire on frog occurrence are altered by isolation, vegetation and fire frequency gradients

“…For example, different animal taxa often show variable—or even opposite—responses to time since fire (Barton et al., ; Driscoll & Henderson, ; Smith et al., ; Watson et al., ). Further, while time elapsed since the last fire in an environment is a strong predictor of species abundance in many instances (Haslem et al., ; Kelly et al., ), some species also respond to other aspects of the fire regime, such as the frequency of past fires (Lindenmayer et al., ; Lindenmayer, Blanchard, et al., ). Finally, the effects of fire on biota can vary markedly between locations with distinct vegetation, climate or topography (Nimmo et al., ).…”