Abstract
Imperata cylindrica is a perennial grass that often proliferates in fire-affected forests. Recent fire events have been consistently associated with a lowering of soil nitrogen (N) to phosphorus (P) ratios. Thus, I. cylindrica might have a tendency toward P-limited growth and/or tolerance for low soil N availability that confers a competitive advantage post-fire. We contrasted soil and I. cylindrica chemistry between recently burned and unburned areas in eastern Australia. Imperata cylindrica foliar N:P ratios were 21% lower in burned areas than in unburned areas, reflecting an increase in the uptake of P, but not N, post-fire, consistent with P-limitation. We then grew I. cylindrica seedlings in soils with differing fire-exposure histories and subjected them to various resource amendments (including N and P addition). Survival of I. cylindrica seedlings was not affected by the fire-exposure history of soil, but was reduced by 66% through N-addition. Soil fire history did not significantly affect I. cylindrica growth, but addition of P greatly enhanced I. cylindrica growth, particularly on unburned soils. Our results indicate that the association between I. cylindrica and forest fire regime could be facilitated, in part, by the short-term positive effect of fire on soil phosphorus and the long-term positive effect of fire-exclusion on soil nitrogen, particularly on well-weathered soils.
Highlights
Periodic fire events are a normal and necessary feature of many terrestrial ecosystems [1,2]
The recent and/or frequent burning (RFB) and no recent fires (NRF) contrasts at Toohey Forest and White Rock-Spring Mountain Conservation Estate (WRSMCE) yielded few effects that were quantitatively or qualitatively consistent across the three sites
We found that increases in soil P levels likely benefit I. cylindrica, while increases in soil N levels appear to be detrimental, such that the lowering of soil N:P
Summary
Periodic fire events are a normal and necessary feature of many terrestrial ecosystems [1,2]. The species is established on every vegetated continent [18], and research published in 1998 estimated that the global extent of I. cylindrica ‘infestation’ was over 500 million hectares [16] Much of this extent is in tropical and subtropical Asia [26], where repeated burning, along with logging and other land-use changes, has facilitated the invasion and subsequent monodominance of I. cylindrica across vast areas of previously highly biodiverse forested landscapes [18,27,28]. There is a need to understand the mechanisms through which I. cylindrica gains a competitive advantage in recently and/or frequently burned forest ecosystems and is likewise potentially disadvantaged by the long-term absence of burning [21]
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