AusTraits, a curated plant trait database for the Australian flora

We introduce the AusTraits database - a compilation of values of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 448 traits across 28,640 taxa from field campaigns, published literature, taxonomic monographs, and individual taxon descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological attributes (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual- and species-level measurements coupled to, where available, contextual information on site properties and experimental conditions. This article provides information on version 3.0.2 of AusTraits which contains data for 997,808 trait-by-taxon combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data, which also provides a template for other national or regional initiatives globally to fill persistent gaps in trait knowledge.

Trees use more non-structural carbohydrate reserves during epicormic than basal resprouting

Non-structural carbohydrates (NSCs) are crucial to support tree resprouting after disturbances that damage the crown or stem. Epicormic resprouting (from stem) could demand more from NSC reserves than basal resprouting (following top-kill), since epicormically resprouting trees need to maintain a greater living biomass. Yet, little is known about NSC use during epicormic resprouting, particularly the relative importance of stem and below-ground NSC reserves. We compared the distribution and magnitude of NSC decreases during epicormic and basal resprouting by experimentally removing crowns or stems of 14-year-old Eucalyptus obliqua L'Hér. trees in native forest, then harvesting these trees over a 10-month period (start, sprouts emerged, sprouts expanded) to measure changes in NSC concentration and mass by organ (stem, lignotuber, roots). We hypothesized that (i) NSC depletion during resprouting is primarily due to decreases in starch rather than soluble sugars concentrations; (ii) during epicormic resprouting, stem NSC concentrations are decreased irrespective of any decreases in roots; and (iii) absolute decreases in NSC mass are greater for epicormic than basal resprouting during the leafless period due to the carbon demands associated with maintaining greater living biomass. Results confirmed our hypotheses; starch was the primary storage carbohydrate, stems were an important source of starch during epicormic resprouting and carbon demands of maintenance functions were greater for epicormic resprouting, leading to greater decreases in NSC reserves. Roots were a more important starch storage organ than the lignotuber for both epicormic and basal resprouting. The proportional decrease in starch was severe for both modes of resprouting due to a long leafless period, after which trees resprouting epicormically relied on starch reserves for longer than those resprouting basally. It remains to be seen how the timing of disturbance affects the timing and vigour of resprouting, and how long-term NSC recovery differs for epicormic and basal resprouting.

Whole-tree distribution and temporal variation of non-structural carbohydrates in broadleaf evergreen trees

Non-structural carbohydrates (NSCs) form a fundamental yet poorly quantified carbon pool in trees. Studies of NSC seasonality in forest trees have seldom measured whole-tree NSC stocks and allocation among organs, and are not representative of all tree functional types. Non-structural carbohydrate research has primarily focussed on broadleaf deciduous and coniferous evergreen trees with distinct growing seasons, while broadleaf evergreen trees remain under-studied despite their different growth phenology. We measured whole-tree NSC allocation and temporal variation in Eucalyptus obliqua L'Hér., a broadleaf evergreen tree species typically occurring in mixed-age temperate forests, which has year-round growth and the capacity to resprout after fire. Our overarching objective was to improve the empirical basis for understanding the functional importance of NSC allocation and stock changes at the tree- and organ-level in this tree functional type. Starch was the principal storage carbohydrate and was primarily stored in the stem and roots of young (14-year-old) trees rather than the lignotuber, which did not appear to be a specialized starch storage organ. Whole-tree NSC stocks were depleted during spring and summer due to significant decreases in starch mass in the roots and stem, seemingly to support root and crown growth but potentially exacerbated by water stress in summer. Seasonality of stem NSCs differed between young and mature trees, and was not synchronized with stem basal area increments in mature trees. Our results suggest that the relative magnitude of seasonal NSC stock changes could vary with tree growth stage, and that the main drivers of NSC fluctuations in broadleaf evergreen trees in temperate biomes could be periodic disturbances such as summer drought and fire, rather than growth phenology. These results have implications for understanding post-fire tree recovery via resprouting, and for incorporating NSC pools into carbon models of mixed-age forests.

Environmental effects on germination phenology of co-occurring eucalypts: implications for regeneration under climate change

Germination is considered one of the important phenological stages that are influenced by environmental factors, with timing and abundance determining plant establishment and recruitment. This study investigates the influence of temperature, soil moisture and light on the germination phenology of six Eucalyptus species from two co-occurring groups of three species representing warm-dry and cool-moist sclerophyll forests. Data from germination experiments were used to calibrate the germination module of the mechanistic model TACA-GEM, to evaluate germination phenology under a range of climate change scenarios. With the exception of E. polyanthemos, the optimal niche for all species was characterised by cool-moist stratification, low light, cool temperatures and high soil moisture. Model results indicated that of the warm-dry species, Eucalyptus microcarpa exhibited greater germination and establishment under projected changes of warmer drier conditions than its co-occurring species Eucalyptus polyanthemos and Eucalyptus tricarpa which suggests that E. microcarpa could maintain its current distribution under a warmer and drier climate in southeastern Australia. Among the cool-moist species, Eucalyptus radiata was the only species that established under projected climate change of the 2080s but at such a low probability that its persistence compared to Eucalyptus obliqua and Eucalyptus sieberi cannot be posited. For all cool-moist species, germination did not benefit from the phenological shifts they displayed. This study successfully demonstrated environmental effects on germination phenology and how a shift in climate can influence the timing and success of recruitment.

Environmental effects on growth phenology of co-occurring Eucalyptus species

Growth is one of the most important phenological cycles in a plant's life. Higher growth rates increase the competitive ability, survival and recruitment and can provide a measure of a plant's adaptive capacity to climate variability and change. This study identified the growth relationship of six Eucalyptus species to variations in temperature, soil moisture availability, photoperiod length and air humidity over 12 months. The six species represent two naturally co-occurring groups of three species each representing warm-dry and the cool-moist sclerophyll forests, respectively. Warm-dry eucalypts were found to be more tolerant of higher temperatures and lower air humidity than the cool-moist eucalypts. Within groups, species-specific responses were detected with Eucalyptus microcarpa having the widest phenological niche of the warm-dry species, exhibiting greater resistance to high temperature and lower air humidity. Temperature dependent photoperiodic responses were exhibited by all the species except Eucalyptus tricarpa and Eucalyptus sieberi, which were able to maintain growth as photoperiod shortened but temperature requirements were fulfilled. Eucalyptus obliqua exhibited a flexible growth rate and tolerance to moisture limitation which enables it to maintain its growth rate as water availability changes. The wider temperature niche exhibited by E. sieberi compared with E. obliqua and Eucalyptus radiata may improve its competitive ability over these species where winters are warm and moisture does not limit growth. With climate change expected to result in warmer and drier conditions in south-east Australia, the findings of this study suggest all cool-moist species will likely suffer negative effects on growth while the warm-dry species may still maintain current growth rates. Our findings highlight that climate driven shifts in growth phenology will likely occur as climate changes and this may facilitate changes in tree communities by altering inter-specific competition.

Edge type affects leaf-level water relations and estimated transpiration of Eucalyptus arenacea

While edge effects on tree water relations are well described for closed forests, they remain under-examined in more open forest types. Similarly, there has been minimal evaluation of the effects of contrasting land uses on the water relations of open forest types in highly fragmented landscapes. We examined edge effects on the water relations and gas exchange of a dominant tree (Eucalyptus arenacea Marginson & Ladiges) in an open forest type (temperate woodland) of south-eastern Australia. Edge effects in replicate woodlands adjoined by cleared agricultural land (pasture edges) were compared with those adjoined by 7- to 9-year-old eucalypt plantation with a 25m fire break (plantation edges). Consistent with studies in closed forest types, edge effects were pronounced at pasture edges where photosynthesis, transpiration and stomatal conductance were greater for edge trees than interior trees (75m into woodlands), and were related to greater light availability and significantly higher branch water potentials at woodland edges than interiors. Nonetheless, gas exchange values were only ∼50% greater for edge than interior trees, compared with ∼200% previously found in closed forest types. In contrast to woodlands adjoined by pasture, gas exchange in winter was significantly lower for edge than interior trees in woodlands adjoined by plantations, consistent with shading and buffering effects of plantations on edge microclimate. Plantation edge effects were less pronounced in summer, although higher water use efficiency of edge than interior woodland trees indicated possible competition for water between plantation trees and woodland edge trees in the drier months (an effect that might have been more pronounced were there no firebreak between the two land uses). Scaling up of leaf-level water relations to stand transpiration using a Jarvis-type phenomenological model indicated similar differences between edge types. That is, transpiration was greater at pasture than plantation edges in summer months (most likely due to greater water availability at pasture edges), resulting in significantly greater estimates of annual transpiration at pasture than plantation edges (430 vs. 343lm(-2)year(-1), respectively). Our study highlights the need for landscape-level water flux models to account for edge effects on stand transpiration, particularly in highly fragmented landscapes.