Abstract
‘Xanthorrhoea…is in habit one of the most remarkable genera of Terra Australis, and gives a peculiar character to the vegetation of that part of the country where it abounds’ Robert Brown (1814). Grasstrees (arborescent Xanthorrhoea, Dasypogon, Kingia), with their crown of long narrow leaves and blackened leafbase-covered trunk (caudex), are a characteristic growth form in the Australian flora. Xanthorrhoea is the most widespread genus, with 28 species that are prominent from heathlands to sclerophyll forests. While leaf production for X. preissii reaches a peak in spring–summer, growth never stops even in the cool winter or dry autumn seasons. Summer rain, accompanied by a rapid rise in leaf water potential, may be sufficient to stimulate leaf production, whereas root growth is confined to the usual wet season. Grasstrees are highly flammable yet rarely succumb to fire: while retained dead leaves may reach >1000°C during fire, the temperature 100 mm above the stem apex remains <60°C and the roots are insulated completely. Immediately following fire, leaf production from the intact apical meristem is up to six times greater than that at unburnt sites. For X. preissii, pre-fire biomass is restored within 40 weeks; the mass of live leaves remains uniform from thereon, whereas the mass of dead leaves increases steadily. Leaves usually survive for >2 years. In X. preissii, the post-fire growth flush corresponds to a reduction in starch storage by desmium in the caudex. Minerals, especially P, are remobilised from the caudex to the crown following a spring fire, but accumulate there following an autumn fire. At least 80% of P is withdrawn from senescing leaves, while >95% K and Na are leached from dead leaves. Most stored N and S are volatilised by fire, with 1–85% of all minerals returned as ash. Despite monthly clipping for 16 months, X. preissii plants recover, although starch reserves are depleted by 90%, indicating considerable resilience to herbivory. Analysis of colour band patterns in the leafbases of X. preissii shows that elongation of the caudex may vary more than 5–50 mm per annum, with 10–20 mm being typical. Exceptionally tall plants (>3 m) may reach an age of 250 years, with a record at 450 years (6 m). Fires, recorded as black bands on the leafbases, in south-western Australia have been decreasing in frequency but increasing in variability since 1750–1850. Some grasstrees have survived a mean fire interval of 3–4 years over the last two centuries. In more recent times, some grasstrees have not been burnt for >50 years. The band-analysis technique has been used to show a downward trend in plant d13C of 2–5.5‰ from 1935 to the present. Grasstrees are most likely to flower in the first spring after fire. A single inflorescence is initiated from the apical meristem, elongating at up to 100 mm day–1 and reaching a length up to 3 m, with one recorded at 5.5 m. This rapid rate of elongation is achieved through leaf (and inflorescence) photosynthesis and desmium starch mobilisation. The developing spike and seeds are vulnerable to a moth larva. Leaf production recommences from axillary buds and the trade-off with reproduction is equivalent to 240 leaves in X. preissii. Flowering and seed production are affected by time of fire. Grasstrees are mainly insect-pollinated. Up to 8000 seeds per spike are produced, although pre-dispersal granivory is common. Seeds are released in autumn and persist in the soil for <2 years. Most fresh seeds germinate in the laboratory but germination is inhibited by light. At any time, seedlings and juveniles may account for most plants in the population, although there may be up to an 80% reduction within 1 year of seedling emergence, often due to kangaroo herbivory. In the absence of fire, mortality of adults may be 4% per annum. Although few grasstree species are considered rare or threatened, their conservation requirements, especially in regard to a suitable fire regime, remain unknown. Grasstrees are particularly susceptible to the exotic root pathogen, Phytophthora cinnamomi, although recruitment among some species has been observed 20–30 years after pathogen invasion. Much remains to be known about the biology of this icon of the Australian bush.
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Claims 18
Claim · model-written summary
Xanthorrhoea has 28 species across heathland and sclerophyll forest.
- Taxon
- Xanthorrhoea
Xanthorrhoeae0 - Outcome
- Xanthorrhoea is the most widespread genus, with 28 species that are prominent from heathlands to sclerophyll forestse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Xanthorrhoea is the most widespread genus, with 28 species that are prominent from heathlands to sclerophyll forests”
Claim · model-written summary
X. preissii leaf production peaks in spring and summer but continues year round.
- Taxon
- X. preissii
Xanthorrhoea preissiie0 - Outcome
- leaf production for X. preissii reaches a peak in spring–summer, growth never stops even in the cool winter or dry autumn seasonse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“leaf production for X. preissii reaches a peak in spring–summer, growth never stops even in the cool winter or dry autumn seasons”
Claim · model-written summary
Summer rain may stimulate leaf production, whereas root growth is wet-season restricted.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Summer rain, accompanied by a rapid rise in leaf water potential, may be sufficient to stimulate leaf production, whereas root growth is confined to the usual wet seasone0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Summer rain, accompanied by a rapid rise in leaf water potential, may be sufficient to stimulate leaf production, whereas root growth is confined to the usual wet season”
t0“Grasstrees”
Claim · model-written summary
Grasstrees rarely die in fire despite hot retained dead leaves.
- Taxon
- GrasstreesXanthorrhoeae0
- Outcome
- Grasstrees are highly flammable yet rarely succumb to fire: while retained dead leaves may reach >1000°C during fire, the temperature 100 mm above the stem apex remains <60°C and the roots are insulated completelye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grasstrees are highly flammable yet rarely succumb to fire: while retained dead leaves may reach >1000°C during fire, the temperature 100 mm above the stem apex remains <60°C and the roots are insulated completely”
Claim · model-written summary
Leaf production after fire reaches six times unburnt levels.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Immediately following fire, leaf production from the intact apical meristem is up to six times greater than that at unburnt sitese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Immediately following fire, leaf production from the intact apical meristem is up to six times greater than that at unburnt sites”
t0“Grasstrees”
Claim · model-written summary
X. preissii restores biomass within 40 weeks.
- Taxon
- X. preissiiXanthorrhoea preissiie0
- Outcome
- For X. preissii, pre-fire biomass is restored within 40 weekse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“For X. preissii, pre-fire biomass is restored within 40 weeks”
Claim · model-written summary
Leaves usually survive more than two years.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Leaves usually survive for >2 yearse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Leaves usually survive for >2 years”
t0“Grasstrees”
Claim · model-written summary
Post-fire growth flush corresponds with reduced caudex starch.
- Taxon
- X. preissiiXanthorrhoea preissiie0
- Outcome
- In X. preissii, the post-fire growth flush corresponds to a reduction in starch storage by desmium in the caudexe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In X. preissii, the post-fire growth flush corresponds to a reduction in starch storage by desmium in the caudex”
Claim · model-written summary
Minerals move from caudex to crown after spring fire but accumulate following autumn fire.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Minerals, especially P, are remobilised from the caudex to the crown following a spring fire, but accumulate there following an autumn firee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Minerals, especially P, are remobilised from the caudex to the crown following a spring fire, but accumulate there following an autumn fire”
t0“Grasstrees”
Claim · model-written summary
Senescing leaves withdraw at least 80% P; dead leaves leach more than 95% K and Na.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- At least 80% of P is withdrawn from senescing leaves, while >95% K and Na are leached from dead leavese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At least 80% of P is withdrawn from senescing leaves, while >95% K and Na are leached from dead leaves”
t0“Grasstrees”
Claim · model-written summary
Fire volatilizes most stored N and S and returns minerals as ash.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Most stored N and S are volatilised by fire, with 1–85% of all minerals returned as ashe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Most stored N and S are volatilised by fire, with 1–85% of all minerals returned as ash”
t0“Grasstrees”
Claim · model-written summary
X. preissii recovered after clipping while starch reserves fell 90%.
- Taxon
- X. preissiiXanthorrhoea preissiie0
- Outcome
- Despite monthly clipping for 16 months, X. preissii plants recover, although starch reserves are depleted by 90%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Despite monthly clipping for 16 months, X. preissii plants recover, although starch reserves are depleted by 90%”
Claim · model-written summary
Exceptionally tall grasstrees can reach 250 years with a record of 450 years.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Exceptionally tall plants (>3 m) may reach an age of 250 years, with a record at 450 years (6 m)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Exceptionally tall plants (>3 m) may reach an age of 250 years, with a record at 450 years (6 m)”
t0“Grasstrees”
Claim · model-written summary
Fire frequency decreased and variability increased since 1750–1850.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Fires, recorded as black bands on the leafbases, in south-western Australia have been decreasing in frequency but increasing in variability since 1750–1850e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Fires, recorded as black bands on the leafbases, in south-western Australia have been decreasing in frequency but increasing in variability since 1750–1850”
t0“Grasstrees”
Claim · model-written summary
Post-fire flowering is most likely in the first spring.
- Taxon
- GrasstreesXanthorrhoeae0
- Outcome
- Grasstrees are most likely to flower in the first spring after firee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grasstrees are most likely to flower in the first spring after fire”
Claim · model-written summary
Flowering spikes reach up to 3 m and can produce 8000 seeds.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Up to 8000 seeds per spike are producede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Up to 8000 seeds per spike are produced”
t0“Grasstrees”
Claim · model-written summary
Light inhibits laboratory germination of fresh seeds.
- Taxon
- GrasstreesXanthorrhoeat0
- Outcome
- Most fresh seeds germinate in the laboratory but germination is inhibited by lighte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Most fresh seeds germinate in the laboratory but germination is inhibited by light”
t0“Grasstrees”
Claim · model-written summary
Grasstrees are susceptible to Phytophthora cinnamomi, though recruitment can occur decades later.
- Taxon
- GrasstreesXanthorrhoeae0
- Outcome
- Grasstrees are particularly susceptible to the exotic root pathogen, Phytophthora cinnamomi, although recruitment among some species has been observed 20–30 years after pathogen invasione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grasstrees are particularly susceptible to the exotic root pathogen, Phytophthora cinnamomi, although recruitment among some species has been observed 20–30 years after pathogen invasion”