Plant traits and their effect on fire and decomposition

Thesis by publication.Includes bibliographical references.1. General introduction -- Burn or rot : leaf traits explain why flammability and decomposability are decoupled across species -- 3. Towards a better understanding of fuel bed flammability ; scaling up from individual leaves -- 4. Bark fates explored : decomposition and flammability of 10 woody species from the Sydney region (south-eastern Australia) -- 5. Models for leaf ignitibility based on leaf traits -- 6. General discussion.Wildfires are a major disturbance worldwide with large effects on ecosystem functioning, species composition and nutrient cycling. A fundamental factor in wildfires is the fuel, namely, live and dead plant material. Plant species differ in their flammability, but the role of plant traits in this remains largely unknown. The decomposition rates of different plant materials (and species) can strongly affect the availability of fuel for potential wildfires.While the influence of leaf traits on litter decomposability is reasonably well studied, it has never been compared to the drivers of litter flammability. In this thesis I focused on these two important turnover processes of plant material, i.e., fire and decomposition. By comparing a wide range of species from south-eastern Australia, I investigated theexistence of general relationships between plant traits, flammability and litter decomposability.In experiments on individual leaves (Chapter 2) I found that morphological leaf traits (such as specific leaf area or dry mass) were most strongly correlated with interspecific variation in flammability, while decomposability was mainly driven by chemical traits. Similar results were found for bark, another important litter component of the Australian forests (Chapter 4). Bark ignitibility of smooth bark species was driven by bark mass per area, while decomposition was strongly associated with initial lignin concentration. Consequently, fire and decomposition, as two alternative fates for leaves or bark, were unrelated.Next, I demonstrated that leaf traits which affect the flammability of individual leaves (e.g. specific leaf area) continue to affect flammability when scaling up to fuel beds (Chapter 3). Can we use these findings on interspecific variation in leaf trait – flammability relationships to improve predictions of fire behaviour? In Chapter 5 I showed that the inclusion of leaf traits (especially leaf thickness) improved the prediction of individual leaf ignitibility.Altogether, this suite of studies increased our understanding of trait-effects on leaf and bark flammability and decomposability. Including plant traits in future analyses could improve the estimation of fuel loads and the prediction of wildfires.Mode of access: World wide web1 online resource (197 pages) illustrations (some colour

Leaf flammability and fuel load increase under elevated CO₂ levels in a model grassland

Fire is a common process that shapes the structure of grasslands globally. Rising atmospheric CO₂ concentration may have a profound influence on grassland fire regimes. In this study, we asked (1) does CO₂ and soil P availability alter leaf flammability (ignitibility and fire sustainability); (2) are leaf tissue chemistry traits drivers of leaf flammability, and are they modified by CO₂ and soil P availability?; (3) does CO₂ and soil P availability alter fuel load accumulation in grasslands; and (4) does CO₂ and soil P availability alter the resprouting ability of grassland species? We found that leaf flammability increased under elevated CO₂ levels owing to decreased leaf moisture content and foliar N, whereas fuel load accumulation increased owing to decreased foliar N (slower decomposition rates) and increased aboveground biomass production. These plant responses to elevated CO₂ levels were not modified by soil P availability. The increase in leaf flammability and fuel load accumulation under elevated CO₂ levels may alter grassland fire regimes by facilitating fire ignition as well as shorter fire intervals. However, the increased root biomass of grasses under elevated CO₂ levels may enhance their resprouting capacity relative to woody plants, resulting in a shift in the vegetation structure of grasslands.9 page(s

Grootemaat2017_Oikos_DryadData

This spreadsheet contains data on: (1) species name + growth form, (2) flammability parameters as measured in fuel beds (Maximum Temperature, Burning Time, Rate of Spread, Fuel Consumption), (3) trait measurements on fuel beds and individual leaves, and (4) flammability parameters on individual leaves from a previous study (Grootemaat et al. 2015, DOI: 10.1111/1365-2435.12449)

Scaling up flammability from individual leaves to fuel beds

Wildfires play an important role in vegetation composition and structure, nutrient fluxes, human health and wealth, and are interlinked with climate change. Plants have an influence on wildfire behaviour and predicting this feedback is a high research priority. For upscaling from leaf traits to wildfire behaviour we need to know if the same leaf traits are important for the flammability of 1) individual leaves, and 2) multiple leaves packed in fuel beds. Based on a conceptual framework, we hypothesised that fuel packing properties, through airflow limitation, would overrule the effects of individual leaf morphology and chemistry. To test this hypothesis we compared the results of two experiments, respectively addressing individual leaf flammability and monospecific fuel bed flammability of 25 perennial species from eastern Australia. Across species, fuel bed packing ratio and bulk density scaled negatively with fire spread and positively with maximum temperature and burning time. Species with 'curlier' leaves, higher specific leaf area, lower tannin concentrations and lower tissue density promoted faster fire spread through fuel beds. We found that species with shorter individual leaf ignition times had a faster fire spread, shorter burning times and lower temperatures in fuel beds. Leaf traits that affect the flammability of individual leaves (e.g. specific leaf area), continue to do so even when packed in fuel beds. While previous studies have focused on either flammability of individual plant particles or fire behaviour in fuel beds, this is the first time that an overarching combination of the two approaches was made for a wide range of species. Our findings provide a better understanding of fuel bed flammability based on interspecific variation in morphological and some chemical leaf traits. This can be a first step in linking leaf traits to fire behaviour in the field

Bark traits, decomposition and flammability of Australian forest trees

Bark shedding is a remarkable feature of Australian trees, yet relatively little is known about interspecific differences in bark decomposability and flammability, or what chemical or physical traits drive variation in these properties. We measured the decomposition rate and flammability (ignitibility, sustainability and combustibility) of bark from 10 common forest tree species, and quantified correlations with potentially important traits. We compared our findings to those for leaf litter, asking whether the same traits drive flammability and decomposition in different tissues, and whether process rates are correlated across tissue types. Considerable variation in bark decomposability and flammability was found both within and across species. Bark decomposed more slowly than leaves, but in both tissues lignin concentration was a key driver. Bark took longer to ignite than leaves, and had longer mass-specific flame durations. Variation in flammability parameters was driven by different traits in the different tissues. Decomposability and flammability were each unrelated, when comparing between the different tissue types. For example, species with fast-decomposing leaves did not necessarily have fast-decomposing bark. For the first time, we show how patterns of variation in decomposability and flammability of bark diverge across multiple species. By taking species-specific bark traits into consideration there is potential to make better estimates of wildfire risks and carbon loss dynamics. This can lead to better informed management decisions for Australian forests, and eucalypt plantations, worldwide

Leaf and flammability traits (individual leaves)

This data set contains the leaf traits and flammability parameters as measured on individual leaves. The first sheet displays the MEAN values per species, which were mainly used for the publication. The second sheet holds the RAW data and the third sheet holds the species list. Abbreviations are explained in the overview

Data from: Burn or rot: leaf traits explain why flammability and decomposability are decoupled across species

In fire-prone ecosystems, two important alternative fates for leaves are burning in a wildfire (when alive or as litter) or they get consumed (as litter) by decomposers. The influence of leaf traits on litter decomposition rate is reasonably well understood. In contrast, less is known about the influence of leaf traits on leaf and litter flammability. The aim of this study was twofold: (a) to determine which morphological and chemical leaf traits drive flammability; and (b) to determine if different (combinations of) morphological and chemical leaf traits drive interspecific variation in decomposition and litter flammability and, in turn, help us understand the relationship between decomposability and flammability. To explore the relationships between leaf traits and flammability of individual leaves, we used 32 evergreen perennial plant species from eastern Australia in standardised experimental burns on three types of leaf material (i.e. fresh, dried and senesced). Next, we compared these trait-flammability relationships to trait-decomposability relationships as obtained from a previous decomposition experiment (focusing on senesced leaves only). Among the three parameters of leaf flammability that we measured, interspecific variation in time to ignition was mainly explained by specific leaf area and moisture content. Flame duration and smoulder duration were mostly explained by leaf dry mass and to a lesser degree by leaf chemistry, i.e. nitrogen, phosphorus and tannin concentrations. The variation in the decomposition constant across species was unrelated to our measures of flammability. Moreover, different combinations of morphological and chemical leaf properties underpinned the interspecific variation in decomposability and flammability. In contrast to litter flammability, decomposability was driven by lignin and phosphorus concentrations. The decoupling of flammability and decomposability leads to three possible scenarios for species’ influence on litter fates: (I) fast-decomposing species for which flammability is irrelevant because there will not be enough litter to support a fire; (II) species with slow-decomposing leaves and a high flammability; and (III) species with slow-decomposing leaves and a low flammability. We see potential for making use of the decoupled trait – decomposition – flammability relationships when modelling carbon and nutrient fluxes. Including information on leaf traits in models can improve the prediction of fire behaviour. Herbivory is another key fate for leaves, but this study was focused on fire and decomposition

Effects of plant diversity and structural complexity on parasitoid behaviour in a field experiment

1. In natural ecosystems, plants containing hosts for parasitoids are often embedded within heterogeneous plant communities. These plant communities surrounding host-infested plants may influence the host-finding ability of parasitoids. 2. A release-recapture-approach was used to examine whether the diversity and structural complexity of the community surrounding a host-infested plant influences the aggregation behaviour of the leaf-miner parasitoid Dacnusa sibirica Telenga and naturally occurring local leaf-miner parasitoids. Released and locally present parasitoids were collected on potted Jacobaea vulgaris Gaertn.plants infested with the generalist leaf-miner Chromatomyia syngenesiae Hardy. The plants were placed in experimentally established plant communities differing in plant diversity (1–9 species) and habitat complexity (bare ground, mown vegetation, and tall vegetation). Additionally, parasitoids were reared out from host mines on the trap plants. 3. Plant diversity did not influence the mean number of recaptured D. sibirica or captures of other locally present parasitoids but the number of recaptured parasitoids was influenced by habitat complexity. No D. sibirica parasitoids were recaptured in the bare ground plots or plots with mown vegetation. The mean number of recaptured D. sibirica generally increased with increasing complexity of the plant community, whereas locally present parasitoids were captured more frequently in communities with more bare ground. There was a unimodal relationship between the number of reared out parasitoids and diversity of the surrounding vegetation with the highest density of emerged parasitoids at intermediate diversity levels. 4. The present study adds to the thus far limited body of literature examining the aggregation behaviour of parasitoids in the field and suggests that the preference of parasitoids to aggregate in complex versus simple vegetation is association specific and thus depends on the parasitoid species as well as the identity of the plant community.11 page(s

Are litter decomposition and fire linked through plant species traits?

Contents I. II. III. IV. V. VI. VII. References Summary: Biological decomposition and wildfire are connected carbon release pathways for dead plant material: slower litter decomposition leads to fuel accumulation. Are decomposition and surface fires also connected through plant community composition, via the species' traits? Our central concept involves two axes of trait variation related to decomposition and fire. The 'plant economics spectrum' (PES) links biochemistry traits to the litter decomposability of different fine organs. The 'size and shape spectrum' (SSS) includes litter particle size and shape and their consequent effect on fuel bed structure, ventilation and flammability. Our literature synthesis revealed that PES-driven decomposability is largely decoupled from predominantly SSS-driven surface litter flammability across species; this finding needs empirical testing in various environmental settings. Under certain conditions, carbon release will be dominated by decomposition, while under other conditions litter fuel will accumulate and fire may dominate carbon release. Ecosystem-level feedbacks between decomposition and fire, for example via litter amounts, litter decomposition stage, community-level biotic interactions and altered environment, will influence the trait-driven effects on decomposition and fire. Yet, our conceptual framework, explicitly comparing the effects of two plant trait spectra on litter decomposition vs fire, provides a promising new research direction for better understanding and predicting Earth surface carbon dynamics