Conservation of tropical forest tree species in a native timber plantation landscape

Tropical terrestrial environments are becoming dominated by anthropogenic land-uses, making retention of biodiversity in production landscapes of critical conservation importance. Native timber plantations may represent a land-use capable of balancing production and conservation by potentially supporting understorey plant and tree species otherwise restricted to old-growth forests, with little impact on yield. In this study we investigated the conservation value of native plantation forests in the lowlands of New Britain, Papua New Guinea. We compared the composition of tree species (≥10. cm DBH) of unlogged forest to those of different aged native Eucalyptus deglupta plantations and intervening (historically logged) secondary forests. We found a high capacity for biodiversity conservation within plantations, with 70% of forest tree species persisting in mature plantations (13-15. years old). However, compositional analyses revealed lower numbers of large individuals (≥10. cm DBH) in both late-successional and non-vertebrate-dispersed species in the plantations, indicating the difficulty of retaining mature old-growth forest trees in production land-uses. Secondary forest protected by conservation reserves was compositionally indistinct to unlogged forest. Our results demonstrate the potential for tropical native timber plantations to contribute to the retention of biodiversity. However, appropriate management is required to ensure the persistence of source populations of old-growth forest tree species. With careful planning a balance between production and conservation can be achieved in lowland tropical regions.

The dynamic regeneration niche of a forest following a rare disturbance event

Aim: Knowledge of how climate and fire regimes affect regeneration in foundation species is critical to the conservation of entire ecosystems. Different stages of regeneration often require different ecological conditions, but dynamic constraints on regeneration are poorly known for species that regenerate only after infrequent wildfires. Focussing on a long-lived, foundation tree species (Eucalyptus regnans), we tested the hypothesis that the relative importance of fire regime variables (fire severity and time since previous fire) and environmental gradients on post-fire regeneration would shift as seedlings developed. Location: South-eastern Australia. Methods: Following a large (> 59,000 ha) summer wildfire in 2009, we sampled 131 sites (61 burnt) annually for four years (2009-2012), representing the range of environmental conditions in which E. regnans occurs. We analysed the effect of fire severity, time since fire and environmental variables on early regeneration processes critical for post-fire species distributions: seedling establishment, seedling density and growth through different height stages (10 cm, 25 cm, 50 cm and 200 cm). Results: The regeneration niche of E. regnans was defined by different factors at different stages of development. Initially, seedlings established prolifically on burnt sites, regardless of severity. Three years into the regeneration process, high-severity fire became the dominant driver of seedling persistence and growth over 25 cm. Growth over 50 cm was dependent on environmental conditions relating to elevation and precipitation. Main conclusions: Our results describe how fire occurrence, fire severity and environmental gradients affected seedling establishment, persistence and growth. The dynamic constraints on regeneration likely reflect temporal changes in the biotic and abiotic environment and variation in resource requirements during the early post-fire years. Our findings will enable more accurate forecasts of species distributions to assist forest conservation in the face of global changes in climate and fire regimes.