Abstract
High severity wildfire events are a feature of forests globally and are likely to be more prevalent with climate change. As a disturbance process, fire has the potential to change important ecological functions, such as decomposition, through its impact on biodiversity. Despite the recognised importance of decomposition in terms of fuel loads and energy flow, little is known about the post-fire effects of fire severity on decomposition by litter-dwelling macroinvertebrate detritivores. We tested the hypotheses that: 1) increasing fire severity is associated with decreased rates of leaf litter decomposition by macroinvertebrate detritivores; and 2) the abundance and biomass of macroinvertebrate detritivores decreases with increasing fire severity, while body size increases. We used a litterbag experiment at long-unburnt, ground-burnt and crown-burnt sites (n = 7 for all treatments) to test the effect of fire severity on: a) macroinvertebrate-driven break-down of litter fuel loads; and b) the size and abundance of macroinvertebrate detritivores three years after fire. Microhabitat conditions differed among fire severity classes. Macroinvertebrate exclusion reduced litter decomposition by 34.7%. Macroinvertebrate detritivores were larger and less abundant following higher severity fires, possibly as a result of fire-induced changes in habitat structure. Opposing effects of fire severity on macroinvertebrate abundance and body size resulted in both similar detritivore biomass and, most interestingly, no differences in leaf litter decomposition under different fire severities. This suggests that the diversity of macroinvertebrates enhances functional resilience of litter decomposition to fire and that litter-breakdown is not inhibited within three years following a high severity fire in this forest type and where recolonisation sources are readily available. We found no support for the hypothesis that high severity fires reduce litter decomposition and therefore increase the likelihood of future fires.
Highlights
Fire is recognised globally as an important form of disturbance due to its widespread occurrence and potential to alter the structure and function of ecosystems [1]
We used a manipulative experiment to test the following hypotheses: 1) increasing fire severity is associated with decreased rates of leaf litter decomposition by macroinvertebrate detritivores; 2) the abundance and biomass of macroinvertebrate detritivores decreases with increasing fire severity, while body size increases
PC1 was positively correlated with moss cover and negatively correlated with foliage cover, moisture, relative humidity, litter cover and soil disturbance (Fig 1; Table 1)
Summary
Fire is recognised globally as an important form of disturbance due to its widespread occurrence and potential to alter the structure and function of ecosystems [1]. The Effects of Fire Severity on Detritivores and Litter Decomposition events occur in forests exposed to persistent high pressure system events that dry fuel [2]. At local scales, where single tree species often dominate, climate and litter quality are likely to vary less, increasing the relative importance of biota in decomposition. The role of other drivers, such as climate and leaf substrate quality may be far less predictive of litter decomposition than measures of the macroinvertebrate detritivore assemblage [22,25,26]. Two recent meta-analyses showed that litter quality and climate are important drivers of decomposition [25,26] These studies emphasised that macroinvertebrate detritivores had substantial effects on decomposition and that this third factor has been neglected and warranted emphasis in future studies.
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