School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemNutrient uptake and use efficiency in co-occurring plants along a disturbance and nutrient availability gradient in the boreal forests of the southwest Yukon, Canada(Wiley, 2017-01-01)Aim In boreal forest ecosystems plant productivity is typically constrained by mineral nutrient availability. In some boreal regions changes in nutrient availability have led to limited changes in productivity but large changes in plant composition. To determine the impact that a change in nutrient availability has on the plant communities it is important to understand how species use nutrients. Here we explore how plant species and functional types in a cold‐dry boreal forest community use available nutrients by quantifying their respective nutrient utilization and response efficiency. Location Boreal forests in the southwest corner of the Yukon Territory, Canada. Methods We collected soil samples and total plant biomass from 29 plots from nine locations subjected to fire, harvesting or bark beetle disturbances. Nutrient analysis of all vegetation and soil samples were conducted to determine the concentration of macro‐ and micronutrients from both plant biomass and soils collected. Nutrient pools between stands with different disturbance histories are compared. Nutrient uptake, use and response efficiencies were then calculated and nutrient response profiles were developed for each species/functional type. Results We found few differences between nutrient pools in plots with different disturbance histories. A clear separation of species and functional groups in elemental hyperspace suggesting divergent nutrient use in co‐occurring species was identified. The use efficiency analysis highlighted that the species with the highest uptake efficiency have lowest use efficiency and vice versa. Species showed either a monotonic or constant relationship between nutrient response efficiency and N, P, K, reflecting a lack of relationship between plant productivity and resource availability or a linear increase in productivity with increasing nutrient availability, respectively. Conclusions Our findings indicate that species are maximizing nutrient use along different parts of the resource gradient, which has implications for understanding how species respond to changes in nutrient availability. Our findings also show that nutrient use by some species may be governed more by uptake efficiency than use efficiency, allowing them to respond to increases in resource availability by increasing uptake rather than use.
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ItemEnvironmental effects on growth phenology of co-occurring Eucalyptus species(SPRINGER, 2014-05)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.
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ItemStructural diversity underpins carbon storage in Australian temperate forests(WILEY, 2020-05)Abstract Aim Forest carbon storage is the result of a multitude of interactions among biotic and abiotic factors. Our aim was to use an integrative approach to elucidate mechanistic relationships of carbon storage with biotic and abiotic factors in the natural forests of temperate Australia, a region that has been overlooked in global analyses of carbon‐biodiversity relations. Location South‐eastern Australia. Time period 2010–2015. Major taxa studied Forest trees in 732 plots. Methods We used the most comprehensive forest inventory database available for south‐eastern Australia and structural equation models to assess carbon‐storage relationships with biotic factors (species or functional diversity, community‐weighted mean (CWM) trait values, structural diversity) and abiotic factors (climate, soil, fire history). To assess the consistency of relationships at different environmental scales, our analyses involved three levels of data aggregation: six forest types, two forest groups (representing different growth environments), and all forests combined. Results Structural diversity was consistently the strongest independent predictor of carbon storage at all levels of data aggregation, whereas relationships with species‐ and functional‐diversity indices were comparatively weak. CWMs of maximum height and wood density were also significant independent predictors of carbon storage in most cases. In comparison, climate, soil, and fire history had only minor and mainly indirect effects via biotic factors on carbon storage. Main conclusions Our results indicate that carbon storage in our temperate forests was underpinned by tree structural diversity (representing efficient utilisation of space) and by CWM trait values (representing selection effects) more so than by tree species richness or functional diversity. Abiotic effects were comparatively weak and mostly indirect via biotic factors irrespective of the environmental range. Our study highlights the importance of managing forests for functionally important species and to maintain and enhance their structural complexity in order to support carbon storage.