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Further publications

Your Gardens Feb 2015

When Graeme Errington started work as a garden labourer at the Australian Botanic Garden Mount Annan, he had no idea that his new-found career would ignite a passion and fascination with plants that would set him on a path to a PhD in rainforest seed conservation some 15 years later.

Offord CA, Meagher PF and Zimmer HC (2014) AoB Plants Volume 6

Seedling growth rates can have important long-term effects on forest dynamics. Environmental variables such as light availability and edaphic factors can exert a strong influence on seedling growth. In the wild, seedlings of Wollemi Pine (Wollemia nobilis) grow on very acid soils (pH ∼4.3) in deeply shaded sites (∼3 % full sunlight). 

To examine the relative influences of these two factors on the growth of young W. nobilis seedlings, we conducted a glasshouse experiment growing seedlings at two soil pH levels (4.5 and 6.5) under three light levels: low (5 % full sun), medium (15 %) and high (50 %). Stem length and stem diameter were measured, stem number and branch number were counted, and chlorophyll and carotenoid content were analysed. 

In general, increased plant growth was associated with increased light, and with low pH irrespective of light treatment, and pigment content was higher at low pH. Maximum stem growth occurred in plants grown in the low-pH/high-light treatment combination. However, stem number was highest in low pH/medium light. We hypothesize that these differences in stem development of W. nobilis among light treatments were due to this species' different recruitment strategies in response to light: greater stem growth at high light and greater investment in multiple stem production at low light. 

The low light levels in the W. nobilis habitat may be a key limitation on stem growth and hence W. nobilis recruitment from seedling to adult. Light and soil pH are two key factors in the growth of this threatened relictual rainforest species.

G. Errington, P. Cuneo, C. Offord (2013) Australasian Plant Conservation 21(3)

The aim of the Rainforest Seed Conservation Program of the Royal Botanic Gardens & Domain Trust is to identify species that can be seed banked and those with ‘bad’ seed storage behaviour that require alterative ex situ germplasm conservation techniques.

The exploration of the seed storage behaviour of seeds can be complicated and there is much to learn about how seeds from rainforests response to seeds storage treatments and how we should approach alternative for germplasm conservation. 

K. Hamilton, C. Offord, P. Cuneo, M. Deseo (2013) Plant Species Biology 28 (1)

Seed characteristics were measured in 71 Eastern Australian rainforest species representing 30 families. Sensitivity to desiccation to low moisture contents (< 10%) occurred in 42% of species. We estimate, based on findings from 100 species from this present study and previously published reports, that 49% of Eastern Australian rainforest species have non-orthodox seeds. 

Germination level and time to 50% germination were not significantly different between desiccation sensitive (DS) and desiccation tolerant (DT) seeds.

The estimation of seed desiccation sensitivity based on predictors is an important tool underpinning ex situ conservation efforts. 

Seed characteristics differed significantly between DS and DT seeds; that is, DS seeds had: (i) larger fruits (19 949 mg vs 8322 mg); (ii) larger seeds (1663 mg vs 202 mg); (iii) higher seed moisture contents (49.7% vs 35.5% fresh weight); (iv) lower oil content (7.3% vs 24.8% yield); and (v) less investment in seed coats (0.19 vs 0.48 seed coat ratio). Only 25% of DS seeded species had oily seeds compared with 87% of DT seeded species. Most green embryos were DS. Seed coat ratio was the best predictor of seed DS (80% correctly predicted). Seed moisture content at maturity was also related to germination time. Mean seed size was correlated (-0.657, P = 0.01) with mean seed oil content in 46 species. 

Further research on seed storage physiology of possible oily and/or DS seeded species is crucial to ensure future long-term security of this biodiversity, particularly for species currently threatened in situ and/or of socioeconomic importance in Eastern Australian rainforests.


The estimation of seed desiccation sensitivity based on predictors is an important tool underpinning ex situ conservation efforts


C. Offord (2011) Annals of Botany 108(2)

Under predicted climate change scenarios, increased temperatures are likely to predispose trees to leaf and other tissue damage, resulting in plant death and contraction of already narrow distribution ranges in many relictual species. The effects of predicted upward temperatures may be further exacerbated by changes in rainfall patterns and damage caused by frosts on trees that have been insufficiently cold-hardened. The Araucariaceae is a relictual family and the seven species found in Australia have limited natural distributions characterized by low frost intensity and frequency, and warm summer temperatures. The temperature limits for these species were determined in order to help understand how such species will fare in a changing climate.

Experiments were conducted using samples from representative trees of the Araucariaceae species occurring in Australia,Agathis (A. atropurpurea, A. microstachya and A. robusta), Arauacaria (A. bidwilli, A. cunninghamii and A. heterophylla) andWollemia nobilis. Samples were collected from plants grown in a common garden environment. Lower and higher temperature limits were determined by subjecting detached winter-hardened leaves to temperatures from 0 to -17 °C and summer-exposed leaves to 25 to 63 °C, then measuring the efficiency of photosystem II (F(v)/F(m)) and visually rating leaf damage. The exotherm, a sharp rise in temperature indicating the point of ice nucleation within the cells of the leaf, was measured on detached leaves of winter-hardened and summer temperature-exposed leaves.

Lower temperature limits (indicated by FT(50), the temperature at which PSII efficiency is 50 %, and LT(50) the temperature at which 50 % visual leaf damage occurred) were approx. -5·5 to -7·5 °C for A. atropurpurea, A. microstachya and A. heterophylla, approx. -7 to -9 °C for A. robusta, A. bidwillii and A. cunninghamii, and -10·5 to -11 °C for W. nobilis. High temperature damage began at 47·5 °C for W. nobilis, and occurred in the range 48·5-52 °C for A. bidwillii and A. cunninghamii, and in the range 50·5-53·5 °C for A. robusta, A. microstachya and A. heterophylla. Winter-hardened leaves had ice nucleation temperatures of -5·5 °C or lower, with W. nobilis the lowest at -6·8 °C. All species had significantly higher ice nucleation temperatures in summer, with A. atropurpurea and A. heterophylla forming ice in the leaf at temperatures >3 °C higher in summer than in winter. Wollemia nobilis had lower FT(50) and LT(50) values than its ice nucleation temperature, indicating that the species has a degree of ice tolerance.

While lower temperature limits in the Australian Araucariaceae are generally unlikely to affect their survival in wild populations during normal winters, unseasonal frosts may have devastating effects on tree survival. Extreme high temperatures are not common in the areas of natural occurrence, but upward temperature shifts, in combination with localized radiant heating, may increase the heat experienced within a canopy by at least 10 °C and impact on tree survival, and may contribute to range contraction. Heat stress may explain why many landscape plantings of W. nobilis have failed in hotter areas of Australia.


K. Hamilton, S. Ashmore, C. Offord (2008) Australasian Plant Conservation 17(1)

Crop wild relatives are native taxa that are close relatives of commercial crop plants and represent the wider genetic diversity of the crop gene pool. They are a valuable source of functional traits (e.g. disease resistance, flood tolerance and medicinal properties) for improvement of food, forestry and medicines. Thus, continuing access to the existing crop wild diversity is important. Some of the nationally and internationally significant crop wild relatives and bush foods of Australia include rainforest genera that contain commercially cultivated species 

One of the key risks of projected climate change is its effect on Australian rainforests, which are one of five natural systems predicted to be vulnerable to damage. Climate change is predicted to interact with other threats, such as weeds and habitat fragmentation, in some of the most vulnerable environments including the Wet Tropics. 

The seed of many species can be routinely stored ex situ in seed banks using standard desiccation (5% moisture content) and freezing (-20°C) protocols; such species have 'orthodox' seeds. However, not all species are amenable to these procedures (i.e. they have 'non-orthodox' seeds) and require the development of alternative conservation technologies. International and national partnerships have been established to develop alternative technologies for the conservation of Australian species with non-orthodox seeds. These include the Millennium Seed Bank Project (Royal Botanic Gardens Kew, UK), the Queensland Seeds for Life project and the Rainforest Seed project (Botanic Gardens Trust, Mount Annan, NSW).

There is growing recognition of the national and international importance of crop wild relatives as a vital source of genetic diversity, and of the increasing threat to these from habitat destruction and climate change. Thus there is an urgent need to develop alternative ex situ conservation technologies, especially for rainforest fruits and crop wild relatives which currently cannot be stored by standard seed banking methods.

Crop wild relatives… are a valuable source of function traits…for improvements of food, forestry and medicines

C. Offord, C. Porter, P. Meagher, G. Errington (1999) Annals of Botany 84(1)

The two known populations of the recently discovered rare and threatened Wollemi Pine (Wollemia nobilis Jones, Hill and Allen) consist of a small number of large multi-stemmed adult trees and small seedlings. Female and male cones are produced on adult trees with pollen release occurring in spring (October–November). Seed cones mature 16–19 months later in late summer and autumn and appear to be produced annually. Approximately 10% of seed produced in two consecutive years was viable, 25% of which was damaged by animals. 

Glasshouse studies showed that seed germination at 25 °C (day) 16 °C (night) proceeded slowly but steadily at approx. 4% per week until, after 6 months, 88% of apparently viable seed had germinated with the remainder of the seed rotting. Growth of potted seedlings in this temperature regime was continuous (after a lag period of 4–6 months) with the monopodial axis growing 0±05–0±25 m in the first year, 0±5–0±6 m in the second year and 0±25–0±35 m in the third year, attaining a total height of 0±8–1±2 m. Multiple orthotropic shoots developed on some plants at this stage, some of which outgrew the primary shoot in height. The diameter of the stem below the cotyledon (just above the soil) grew 3–7 mm in the first year, 10–14 mm in the second and 15–20 mm in the third at which time it was 25–34 mm. The average number of lateral branches produced was five–17 in the first year, 25–36 in the second year and 24–30 in the third year giving a total of 60–77. 

The establishment of Wollemi Pine in the wild does not appear limited by the inherent viability of seed and potential for early growth of seedlings.

Karen Sommerville and Cathy Offord (2015) Acta Horticulturae 1101

Seedbanking is an effective ex situ conservation technique for species with seeds that tolerate drying to 3-7% moisture content and long term storage at -20ºC. However, it has been estimated that as many as 50% of rainforest species may produce seeds that do not tolerate desiccation; the remainder may tolerate desiccation but may not tolerate freezing or may be comparatively short-lived in storage at -20ºC. We investigated freezing tolerance and comparative longevity in storage for 5 Australian rainforest trees with desiccation-tolerant seeds.

Seeds stored at -20ºC for 2 to 7 years were removed from storage, thawed and germinated on 0.7% agar at 20 or 25ºC with a 12 h photoperiod. Seeds that had retained their viability following freezing (germination ≥ 84%) were rehydrated for two weeks at 20ºC and 47% relative humidity then artificially aged at 43±2ºC and 60% relative humidity. Seeds were withdrawn from the aging environment at intervals of 1, 2, 5, 9, 20 and 30 days and tested for their ability to germinate. Species found to be comparatively short-lived were further tested for their ability to tolerate cryopreservation (storage in LN vapour at -192ºC) with no pre-treatment.

Of the five species tested, only Archirhodomyrtus beckleri failed to germinate following freezing. Abrophyllum ornans tolerated freezing but storage for 7 years at -20ºC reduced its germinability from 100% to 41%. The remaining three species – Caldcluvia paniculosa, Cuttsia viburnea and Quintinia verdonii – had retained viability following storage at -20ºC for 2-3 years but proved to be comparatively short-lived under artificial aging conditions (p50 < 5 days) and therefore also likely to be short-lived in storage at the standard seedbanking temperature of -20ºC. All three species tolerated storage for 1 week at -192ºC with no significant reduction in germination percentage.

Cryopreservation is likely to be the best option for long-term storage of both desiccation-sensitive and desiccation-tolerant seeds from rainforest regions.

G. Errington, C. Offord and C. Catterall (2015) Acta Horticulturae 1101

Seed collection and processing can be a costly and time-consuming element of plant production and germplasm conservation. Understanding seed set, viability and germination, and responses to handling and storage conditions might provide information for decision-making relating to both horticultural plant production and long-term seed conservation. In this study, two species, Backhousia citriodora and B. myrtifolia were used to model how seed characteristics should be assessed. Commonly used in horticulture and readily available from Australian seed suppliers, anecdotal industry information suggested seed viability was an issue for both species.

It was found that low seed set rather than seed viability was the reason for apparent low germination. Although seeds were found only in a small percentage of capsules, for B. citriodora 8-16.5% and for B. myrtifolia 20 and 35%, the extracted seed had relatively high germination rates; B. citriodora 74% and B. myrtifolia 94%.

This finding underlines the importance of implementing ongoing seed quality assessment to maximise effectiveness of seed collection. In addition, an examination of storage options and seed longevity indicated that an alternative seed storage method such as cryopreservation should be considered to ensure long-term conservation of germplasm of these two species.

H. Zimmer, P. Meaher, T. Auld, and C. Offord - 2015

Seed production varies from year-to-year in most species. Factors influencing this variation can include pollination and dispersal mechanisms, seed predation and resource availability. Here we examine a long-term (12-year) photographic record of seed cone production for the Australian endemic conifer Wollemia nobilis (Araucariaceae).

Coefficient of variation (a commonly used measure of variation in seed production) was low for the two trees analysed, compared with published values for other polycarpic plants. Nevertheless, cone production decreased with increasing spring minimum temperatures (during pollination) and increased with summer total rainfall (during cone initiation). Hence, Wollemia nobilis cone production was correlated with weather, in line with the resource-matching hypothesis.

Impacts of variation in cone production on the Wollemia nobilis population are likely to be buffered by the shade-tolerant, slow-growing juvenile life stage of Wollemia nobilis

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Dr Karen Sommerville was award a scholarship to attend the National Center for Genetic Resource Preservation in Colorado USA, to learn new skills in the handling and storage of dessication sensitive seeds.

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H. Zimmer, T. Auld, L. Hughes, and P. Baker - 2015

Historically, rainforests have been considered vulnerable to fire. Recent research, however, has shown that many rainforest species can survive fire by resisting burning and by resprouting and seeding post-fire. We investigated the response of a warm temperate rainforest community to fire by burning juveniles of the dominant canopy tree species (Doryphora sassafras, Syzygium smithii and Wollemia nobilis) and examining litter flammability in a controlled environment.

The three species resprouted after the experimental burn, predominantly from buds on the stem that were below the soil surface. Higher fire temperatures resulted in reduced overall plant height and resprouting from buds lower on the stem. Increasing proportions of W. nobilis litter generated fires with higher intensities and fuel consumption compared with rainforest angiosperm litter. Moreover, fuel moisture content decreased with increasing W. nobilis litter proportions.

Higher litter flammability may result in increased likelihood of fire ignition and fire severity near W. nobilis trees, which would negatively impact the juveniles of all three rainforest species. Alternatively, after lower-temperature fires (e.g. in rainforest angiosperm litter), W. nobilis may have an advantage over the other species because of faster growing resprouts occurring higher on the stem. 

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