Post‐Fire Litter Microsites: Safe for Seeds, Unsafe for Seedlings

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Abstract
We explore the effect of post—fire microsites on seed and seedling distribution and hence their potential role in community restoration. A summer wildfire and control burn in a sclerophyll shrubland in mediterranean Australia produced mosaics of physically and chemically contrasting microsites of litter and sand. Most seeds (>75%) of all species released from the burnt canopies fell, or were redispersed by wind, into the litter patches after both fires. Data on microsite characteristics and wind exposure (fire intensity), height of fruits, time of release, and seed properties were required to interpret relative distribution between the litter and sand patches. Seeds remained equally viable (up to 100%) over summer—autumn in the litter and sand and had equally high rates and levels (up to 100%) of subsequent winter germination. However, seedlings were 2—3 times less likely to survive in the litter and survivors were 35% smaller than those in the sand by the end of the first summer. Banksia hookeriana was particularly vulnerable to microsite properties, whereas the needle—leaved Hakea polyathema showed only minor responses. Pre—summer thinning of seedlings in the litter increased survival of the remainder by 2 times and size of the survivors by 31%. The fire—sensitive, small—seeded B. hookeriana had 17 times more seeds in the backburn litter than the resprouting, larger—seeded B. attenuata, which more than compensated for its 3 times greater seedling mortality levels over the dry summer. Recruitment of species prone to density—dependent mortality in the litter was enhanced by the retention of some seeds in the sand where competition for water was minimal, as indicated by the 2.2 times greater stomal conductance of their seedlings in early summer.

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