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

Abstract

Management guidelines for many fire-prone ecosystems highlight the importance of maintaining a variable mosaic of fire histories for biodiversity conservation. Managers are encouraged to aim for fire mosaics that are temporally and spatially dynamic, include all successional states of vegetation, and also include variation in the underlying "invisible mosaic" of past fire frequencies, severities, and fire return intervals. However, establishing and maintaining variable mosaics in contemporary landscapes is subject to many challenges, one of which is deciding how the fire mosaic should be managed following the occurrence of large, unplanned wildfires. A key consideration for this decision is the extent to which the effects of previous fire history on vegetation and habitats persist after major wildfires, but this topic has rarely been investigated empirically. In this study, we tested to what extent a large wildfire interacted with previous fire history to affect the structure of forest, woodland, and heath vegetation in Booderee National Park in southeastern Australia. In 2003, a summer wildfire burned 49.5% of the park, increasing the extent of recently burned vegetation (<10 yr post-fire) to more than 72% of the park area. We tracked the recovery of vegetation structure for nine years following the wildfire and found that the strength and persistence of fire effects differed substantially between vegetation types. Vegetation structure was modified by wildfire in forest, woodland, and heath vegetation, but among-site variability in vegetation structure was reduced only by severe fire in woodland vegetation. There also were persistent legacy effects of the previous fire regime on some attributes of vegetation structure including forest ground and understorey cover, and woodland midstorey and overstorey cover. For example, woodland midstorey cover was greater on sites with higher fire frequency, irrespective of the severity of the 2003 wildfire. Our results show that even after a large, severe wildfire, underlying fire histories can contribute substantially to variation in vegetation structure. This highlights the importance of ensuring that efforts to reinstate variation in vegetation fire age after large wildfires do not inadvertently reduce variation in vegetation structure generated by the underlying invisible mosaic.

Fire as a key driver of Earth's biodiversity

“…() also noted that species diversity should be greatest with a mixture of patches at different fire frequencies as the extremes were quite different in species composition (although any effect of patch size on S was not considered). Others have observed no effect (Davis et al, ) or a negative effect (Bassett et al, ; Foster et al, ). The extent to which this fails to support intermediate P as maximizing biodiversity due to ( i ) testing an inadequate range of P , thus observing only part of the ‘hump’, ( ii ) not using a fixed reference area, thus not appreciating that increasing patch type is at the expense of patch area and thus species—area limitations come into play, or ( iii ) using different indices of P and diversity, requires further investigation.…”

Fire season modifies the perennial plant community composition through a differential effect on obligate seeders in eastern Mediterranean woodlands

“…This idea has served as the basis for development of the variable mosaic concept, implying that managers should aim to promote variability in both the visible fire mosaic (i.e., time since fire, fire size, fire severity, fire patchiness) and the underlying invisible mosaic (i.e., lengths of past inter‐fire intervals, fire frequencies; Bradstock et al., ; Ponisio et al., ; Tingley, Ruiz‐Gutierrez, Wilkerson, Howell, & Siegel, ). More recent work has shown that translating this concept into a system‐specific management plan may be challenging (Driscoll et al., ; Foster, Barton, MacGregor, Robinson, & Lindenmayer, ; Kelly, Brotons, & McCarthy, ; Parr & Andersen, ). Nevertheless, our findings may have important implications for conservation and management of the eastern Mediterranean ecosystem.…”

Bridging the Divide: Integrating Animal and Plant Paradigms to Secure the Future of Biodiversity in Fire-Prone Ecosystems

“…The time between fires sets the window for growth and reproduction in many plants. Studies of animals and plants that explore combinations of fire regime characteristics are increasing [11] and represent an important development in fire ecology.…”

“…One reason is that data on plants, animals, and spatio-temporal mosaics has been lacking [11]. In part, this is being addressed by a surge of new studies on fire regimes and biodiversity [3].…”