Climatic conditions affect shoot flammability by influencing flammability-related functional traits in nonfire-prone habitats.

Plant flammability is an important driver of wildfires, and flammability itself is determined by several plant functional traits. While many plant traits are influenced by climatic conditions, the interaction between climatic conditions and plant flammability has rarely been investigated. Here, we explored the relationships among climatic conditions, shoot-level flammability components, and flammability-related functional traits for 186 plant species from fire-prone and nonfire-prone habitats. For species originating from nonfire-prone habitats, those from warmer areas tended to have lower shoot moisture content and larger leaves, and had higher shoot flammability with higher ignitibility, combustibility, and sustainability. Plants in wetter areas tended to have lower shoot flammability with lower combustibility and sustainability due to higher shoot moisture contents. In fire-prone habitats, shoot flammability was not significantly related to any climatic factor. Our study suggests that for species originating in nonfire-prone habitats, climatic conditions have influenced plant flammability by shifting flammability-related functional traits, including leaf size and shoot moisture content. Climate does not predict shoot flammability in species from fire-prone habitats; here, fire regimes may have an important role in shaping plant flammability. Understanding these nuances in the determinants of plant flammability is important in an increasingly fire-prone world.

Shoot-level flammability across the Dracophyllum (Ericaceae) phylogeny: evidence for flammability being an emergent property in a land with little fire.

Plant flammability varies across species, but the evolutionary basis for this variation is not well understood. Phylogenetic analysis of interspecific variation in flammability can provide insights into the evolution of plant flammability. We measured four components of flammability (ignitability, sustainability, combustibility and consumability) to assess the shoot-level flammability of 21 species of Dracophyllum (Ericaceae). Using a macroevolutionary approach, we explored phylogenetic patterns of variation in shoot-level flammability. Shoot-level flammability varied widely in Dracophyllum. Species in the subgenus Oreothamnus had higher flammability and smaller leaves than those in the subgenus Dracophyllum. Shoot flammability (ignitability, combustibility and consumability) and leaf length showed phylogenetic conservatism across genus Dracophyllum, but exhibited lability among some closely related species, such as D. menziesii and D. fiordense. Shoot flammability of Dracophyllum species was negatively correlated with leaf length and shoot moisture content, but had no relationship with the geographic distribution of Dracophyllum species. Shoot-level flammability varied widely in the genus Dracophyllum, but showed phylogenetic conservatism. The higher flammability of the subgenus Oreothamnus may be an incidental or emergent property as a result of the evolution of flammability-related traits, such as smaller leaves, which were selected for other functions and incidentally changed flammability.

Shoot flammability of vascular plants is phylogenetically conserved and related to habitat fire-proneness and growth form.

Terrestrial plants and fire have interacted for at least 420 million years1. Whether recurrent fire drives plants to evolve higher flammability and what the evolutionary pattern of plant flammability is remain unclear2-7. Here, we show that phylogeny, the susceptibility of a habitat to have recurrent fires (that is, fire-proneness) and growth form are important predictors of the shoot flammability of 194 indigenous and introduced vascular plant species (Tracheophyta) from New Zealand. The phylogenetic signal of the flammability components and the variation in flammability among phylogenetic groups (families and higher taxonomic level clades) demonstrate that shoot flammability is phylogenetically conserved. Some closely related species, such as in Dracophyllum (Ericaceae), vary in flammability, indicating that flammability exhibits evolutionary flexibility. Species in fire-prone ecosystems tend to be more flammable than species from non-fire-prone ecosystems, suggesting that fire may have an important role in the evolution of plant flammability. Growth form also influenced flammability-forbs were less flammable than grasses, trees and shrubs; by contrast, grasses had higher biomass consumption by fire than other groups. The results show that shoot flammability of plants is largely correlated with phylogenetic relatedness, and high flammability may result in parallel evolution driven by environmental factors, such as fire regime.

Seed release by a serotinous pine in the absence of fire: implications for invasion into temperate regions.

In pines, the release of seeds from serotinous cones is primarily considered a response to the high temperatures of a fire. However, the naturalization of serotinous pines in regions where fires are rare highlights the need to quantify environmental conditions that determine seed release to allow accurate prediction of dispersal and spread risk. We investigated the conditions that break cone serotiny in Pinus radiata, a widely planted forestry species that has naturalized in temperate regions worldwide. We quantified the cone temperatures at which cones open in this species, while also assessing potential confounding effects of cone moisture and age on these temperature requirements. We compared our laboratory results with cone opening behaviour under typical field conditions during summer in Canterbury, New Zealand. Cones opened at a mean temperature of 45 °C, much higher than maximum ambient air temperatures recorded in New Zealand. We found no influence of cone age or moisture content on opening temperature. Under field conditions, cones opened upon reaching similar temperatures to those determined in the laboratory; however, passive solar heating caused cones to reach temperatures up to 15 °C higher than ambient conditions. This resulted in 50 % of cones opening in field conditions where maximum air temperatures never exceeded 30 °C. Our results highlight the need for complementary laboratory and field experiments for understanding seed release from serotinous cones. Our findings have important implications for weed risk assessments, showing that serotinous pines can release seed in temperate climates without fire.

Green firebreaks as a management tool for wildfires: Lessons from China.

Wildfire is a widespread natural hazard that is expected to increase in areal extent, severity and frequency with ongoing changes in climate and land-use. One tool that has been used in an effort to reduce the damage caused by wildfires is green firebreaks: strips of low-flammability vegetation grown at strategic locations in the landscape. Green firebreaks are increasingly being recommended for wildfire management and have been implemented in many countries. The approach is particularly widely used in China, where more than 364,000 km of green firebreaks have been planted and a further 167,000 km are planned for construction before 2025. China is not only a world leader in the implementation of green firebreaks but has also led the way in testing the effectiveness of green firebreaks and in providing guidelines for green firebreak construction. However, most of this research has been reported in the non-English literature, and so is inaccessible to many readers. Here we review the extensive research on the construction and effectiveness of green firebreaks in China and examine how the lessons learned from this research could contribute to the effective implementation of green firebreaks globally. Chinese studies suggest that the ideal species for green firebreaks should meet trait requirements from three perspectives: ecological, silvicultural and economic. Green firebreaks with a multi-layered structure and a closed canopy have the potential to be an effective, long-term, biodiversity-friendly and low-cost tool for fire suppression, although they complement rather than replace other more traditional fire suppression approaches.

Taxonomic affinity, habitat and seed mass strongly predict seed desiccation response: a boosted regression trees analysis based on 17 539 species.

Background and Aims: Seed desiccation response plays an important role in plant regeneration ecology, and has significant implications for species conservation. The majority of seed plants produce desiccation-tolerant (orthodox) seeds, whilst comparatively few produce desiccation-sensitive (recalcitrant) seeds that are unable to survive dehydration, and which cannot be conserved in traditional seed banks. This study develops a set of models to predict seed desiccation response in unstudied species. Methods: Taxonomy, trait, location and climate data were compiled to form a global data set of 17 539 species. Three boosted regression trees models were then developed to predict species' seed desiccation responses based on habitat and trait information for the species, and the seed desiccation responses of close relatives (either members of the same genus, family or order, depending on the model). Ten-fold cross-validation was used to test model predictive success. The utility of the models was then demonstrated by predicting seed desiccation response for two floras: Ecuador, and Britain and Ireland. Key Results: The three models had varying success rates for identifying the desiccation-sensitive species: 89 % for the genus-level model, 79 % for the family-level model and 60 % for the order-level model. The most important predictor variables were the seed desiccation responses of a species' relatives, seed mass and annual precipitation. It is predicted that 10 % of seed plants from Ecuador and 1.2 % of those from Britain and Ireland produce desiccation-sensitive seeds. Due to data availability, prediction accuracy is likely to be higher for the British and Irish flora, where it is estimated that a desiccation-sensitive species had a 96.7 % chance of being correctly identified, compared with 80.8 % in the Ecuador flora. Conclusions: These models can utilize existing data to predict species' likely seed desiccation responses, providing a gap-filling tool for global studies of plant traits, as well as critical decision-making support for plant conservation activities.

Exploiting interspecific olfactory communication to monitor predators.

Olfaction is the primary sense of many mammals and subordinate predators use this sense to detect dominant species, thereby reducing the risk of an encounter and facilitating coexistence. Chemical signals can act as repellents or attractants and may therefore have applications for wildlife management. We devised a field experiment to investigate whether dominant predator (ferret Mustela furo) body odor would alter the behavior of three common mesopredators: stoats (Mustela erminea), hedgehogs (Erinaceus europaeus), and ship rats (Rattus rattus). We predicted that apex predator odor would lead to increased detections, and our results support this hypothesis as predator kairomones (interspecific olfactory messages that benefit the receiver) provoked "eavesdropping" behavior by mesopredators. Stoats exhibited the most pronounced responses, with kairomones significantly increasing the number of observations and the time spent at a site, so that their occupancy estimates changed from rare to widespread. Behavioral responses to predator odors can therefore be exploited for conservation and this avenue of research has not yet been extensively explored. A long-life lure derived from apex predator kairomones could have practical value, especially when there are plentiful resources that reduce the efficiency of food-based lures. Our results have application for pest management in New Zealand and the technique of using kairomones to monitor predators could have applications for conservation efforts worldwide.

Species assemblage patterns around a dominant emergent tree are associated with drought resistance.

Water availability has long been recognized as an important driver of species distribution patterns in forests. The conifer Agathis australis (D. Don) Lindl. (kauri; Araucariaceae) grows in the species-rich forests of northern New Zealand. It is accompanied by distinctive species assemblages, and during summer the soil beneath A. australis is often significantly drier than soils beneath surrounding broadleaved angiosperm canopy species. We used a shade house dry-down experiment to determine whether species that grow close to A. australis differed in drought tolerance physiology compared with species that rarely grow close to A. australis. Stomatal conductance (g(s)) was plotted against leaf water potential (ψ) to identify drought tolerance strategies. Seedlings of species that occur in close spatial association with A. australis (including A. australis seedlings) were most resistant to drought stress, and all displayed a drought avoidance strategy of either declining gs to maintain ψ or simultaneous declines in g(s) and ψ. The species not commonly occurring beneath A. australis, but abundant in the surrounding forest, were the most drought-sensitive species and succumbed relatively quickly to drought-induced mortality with rapidly declining gs and ψ values. These results were confirmed with diurnal measurements of g(s) and assimilation rates throughout the day, and leaf wilting analysis. We conclude that the varied abilities of the species to survive periods of drought stress as seedlings shapes the composition of the plant communities beneath A. australis trees. Furthermore, forest diversity may be impacted by climate change as the predicted intensification of droughts in northern New Zealand is likely to select for drought-tolerant species over drought-intolerant species.