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To determine the geographical variation in serotiny in a common New Zealand shrub as a contemporary indicator of past fire regimes. The distribution of serotiny could then be used to explore factors limiting the spread of fire-dependent vegetation. South Island, New Zealand. Serotiny was assessed as the proportion of closed capsules on a shoot of standard stem diameter for 5–35 plants in 45 widely scattered populations of Leptospermum scoparium. Site characteristics, including locality, altitude, rainfall, habitat type and minimum burnable area were recorded at sampling sites. Serotiny was distributed bimodally within and among populations with capsules either mostly closed or mostly open. There was considerable geographical variation in capsule behaviour, most of which we attribute to variation in fire history. In wetlands and other sites unsuitable for forest growth, populations were all serotinous above a minimum area of 30 km2 and nonserotinous below this threshold. In grassy habitats in the drier eastern areas, most populations were serotinous. The nonserotinous exceptions occurred in areas thought to have been cleared of forests by Polynesian settlers before the arrival of Europeans or in areas with numerous barriers to fire in the form of large rivers, floodplains, glaciers and barren mountain tops. We suggest that serotiny in L. scoparium is a reflection of a long history of fire in the South Island. As such, it provides a contemporary signature of a past fire regime. Landscape barriers to the spread of fire were major obstacles limiting the spread of serotiny and associated fire-dependent vegetation. Rivers, lakes, glaciers, and sparsely vegetated floodplains prevented the spread of fire in high rainfall regions more than the lack of dry weather. People, by igniting fires in small open areas seldom struck by lightning, could radically increase the importance of fire on islands. [ABSTRACT FROM AUTHOR]

Browsing by large vertebrates has been a major force in the evolution of terrestrial plants but Holocene extinctions of the browsers have left a legacy of broken biotic partnerships. Ratite birds were the largest herbivores in several regions, such as the moas of New Zealand. Many woody plants there have a distinct form of branching, described as “divaricate”, with thin, wide angled, branches intertwining to form a tangled canopy. Divaricate branching has been interpreted as a form of protection against climate extremes or as an anachronistic defense against the extinct moas. Here we report the first experimental evidence that many of these plants are defended against extant ratite browsers. In feeding experiments on two tree species with different (heteroblastic) juvenile and adult branch morphology, emus and ostriches obtained adequate feeding rates from adult shoots but sub-maintenance feeding rates from juvenile shoots with the ratite-resistant traits. Divaricate juvenile shoots suffered 30–70% less biomass removal to the birds than adult shoots. Ratites browse by a distinctive clamping and tugging action. Structural defence traits that exploit the limitations of this feeding mode include narrow, strong, elastic branches that resist being torn off, wide branching angle (“divaricate”) that makes shoots difficult to swallow, and small, widely spaced leaves. This novel plant architectural defence has developed in at least 20% of the native woody flora of New Zealand, including 10 heteroblastic tree species that exhibit the ratite-resistant strategy until they reach ca 3 metres height. It is also a major axis of variation amongst homoblastic woody shrub species. The defences are useless against mammalian browsers that shear shoots, contributing to marked decreases in the abundances of ratite-resistant species in New Zealand after the introduction of mammals. [ABSTRACT FROM AUTHOR]