A plant that seems to defy biogeographical and evolutionary rules: Dodonaea viscosa (Sapindaceae), part 2: wood density

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...continued from https://www.inaturalist.org/journal/milewski/99976-a-plant-that-seems-to-defy-biogeographical-and-evolutionary-rules-dodonaea-viscosa-sapindaceae-part-1#

INTRODUCTION

We have seen that Dodonaea viscosa is a fast-growing tall shrub or short tree (up to 10 m high, https://books.google.com.au/books/about/Trees_of_Southern_Africa.html?id=jtvZAAAAMAAJ&redir_esc=y), that is capable of colonising bare ground.

Based on this biological profile, D. viscosa might be expected to have light wood, economical for a rapid succesional turnover (https://www.researchgate.net/publication/381698504_Wood_Density_Functional_Trait_in_Plants).

In this Post, I point out the following:

Perhaps the most remarkable - and underappreciated - aspect of the biology of Dodonaea viscosa is the extreme density of its wood.

The exceptional nature of D. viscosa is shown, for example, by a comparison with the many other taxa of trees indigenous to New Zealand (see data at the end of this Post, with D. viscosa marked by ***).

RESULTS

Most trees in New Zealand have wood densities (specific gravity when air-dry) of about

• 0.6 (gymnosperms), or
• 0.7 (angiosperms).

The latter value is in line with typical 'hardwoods', e.g. English oak, which has a density of 0.72 (https://en.wikipedia.org/wiki/Quercus_robur).

In order to visualise what the range of values means:
In water, any wood with values < 1.0 floats, whereas any wood with values > 1.0 sinks.

Somewhat exceptional in the flora of New Zealand are the following trees.

Species with unusually light wood are

• Entelea arborescens about 0.22 (https://www.inaturalist.org/taxa/343580-Entelea-arborescens)
• Ceodes brunoniana 0.23 (https://www.inaturalist.org/taxa/400629-Ceodes-brunoniana)
• Libocedrus spp. about 0.38 (https://www.inaturalist.org/taxa/135820-Libocedrus-bidwillii and https://www.inaturalist.org/taxa/135819-Libocedrus-plumosa).

Species with unusually heavy wood are

• Dodonaea viscosa 1.18 (https://www.inaturalist.org/observations?place_id=6803&subview=map&taxon_id=83637)
• Olearia paniculata 1.12 (https://www.inaturalist.org/taxa/336338-Olearia-paniculata)
• Leptospermum scoparium 1.08 (https://www.inaturalist.org/taxa/54699-Leptospermum-scoparium)
• Metrosideros umbellata about 1.04 (https://www.inaturalist.org/taxa/403879-Metrosideros-umbellata)
• Nestegis montana 1.01 (https://www.inaturalist.org/taxa/409655-Nestegis-montana)
• Vitex lucens about 0.97 (https://www.inaturalist.org/taxa/338187-Vitex-lucens)
• Metrosideros excelsa 0.91 (https://www.inaturalist.org/taxa/122905-Metrosideros-excelsa)
• Leucopogon fasciculatus 0.90 (https://www.inaturalist.org/taxa/409552-Leucopogon-fasciculatus)

Other references state the density for D. viscosa to be

• 1.10 (https://keys.lucidcentral.org/keys/v3/arid/key/Key%20to%20arid%20Australian%20hardwoods/Media/Html/Taxa%20factsheets/Dodonaea.htm)
• 1.2-1.25 (https://prota.prota4u.org/protav8.asp?g=pe&p=Dodonaea+viscosa).

The basic wood density (https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.1175#:~:text=While%20wood%20density%20has%20been,biomass%20from%20living%20tree%20volume. and https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/wood-density) of D. viscosa is

• 0.814 (https://hrcak.srce.hr/clanak/415414)
• 0.93 (https://link.springer.com/article/10.1007/S11632-013-0109-X)
• 0.95 (https://www.fs.usda.gov/nrs/pubs/gtr/gtr-nrs200-2021_appendixes/gtr_nrs200-2021_appendix11.pdf).

For comparison, the basic wood density of English oak (Quercus robur) is 0.646.

DISCUSSION

It is noteworthy that the spp. with the heaviest wood in New Zealand

• belong to various families (Sapindaceae, Asteraceae, Oleaceae, Ericaceae, Myrtaceae), and
• are small-bodied enough, in several cases, to be described as shrubs rather than trees.

Furthermore, in the Myrtaceae:
Metrosideros contains both

• the only trees (always larger-bodied than shrubs) with wood of density >1.01, and
• a shrubby species (Metrosideros angustifolia, https://www.inaturalist.org/taxa/428239-Metrosideros-angustifolia) occurring - by partial biogeographical analogy with D. viscosa - in South Africa (https://www.inaturalist.org/journal/milewski/81613-metrosideros-angustifolia-myrtaceae-the-pacific-face-of-fynbos#).

There is a clear finding that the wood of D. viscosa - despite this species being usually shrubby and short-lived, and functioning as a pioneer in the succession of vegetation - is the heaviest of any plant indigenous to New Zealand.

The wood of D. viscosa is also remarkably consistent worldwide, regardless of climate (https://bsapubs.onlinelibrary.wiley.com/doi/10.3732/ajb.90.4.532).

These findings are all the more puzzling considering the following:
Dodonaea viscosa is the only indigenous plant in New Zealand, capable of growing into a tree, that has a cosmopolitan distribution.

What emerges is the following new perspective on the nature of D. viscosa:
This species has

• a 'weedy' ecological strategy, unspecialised in most respects,
• fairly generalised growth-form, foliage, flowers, fruits, and seeds,
• variable sexuality/mating system (dioecious with hermaphroditism, plus other aberrations, https://www.publish.csiro.au/BT/BT22062 and https://www.anbg.gov.au/gnp/interns-2007/dodonaea-viscosa.html),
• versatile anti-herbivore defences,
• an ambivalent relationship to fire, with regeneration partly germinative ('hardseeded', with dormancy alleviated by scorching) and partly vegetative (with new shoots sometimes producing from the base of the shrub/tree), and
• a seed-dispersal syndrome that is 'non-committal', being partly anemochorous, partly myrmecochorous (https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1442-9993.1995.tb00573.x), and partly (presumably) hydrochorous.

In D. viscosa, the real specialisation is in:

• unpredictable intraspecific variation - vaguely described by an 'ochlospecies' concept - that is incongruent with subspeciation, ecotypy, or raciality, and
• extreme density of wood.

This raises two basic questions about the natural history of D. viscosa, viz.

• What is the natural lifespan in this species? and
• How has the extreme lignification of its stems contributed to its unique success in colonising the world during the Pleistocene?

MY COMPILATION OF THE DATA

Reference: Kennedy et al. (2023) Wood density and stiffness of New Zealand native trees and shrubs. New Zealand Journal of Forestry Science 53: 13 (https://nzjforestryscience.nz/index.php/nzjfs/citationstylelanguage/get/acm-sig-proceedings?submissionId=315&publicationId=286&issueId=8).

The values are for density (specific gravity) of air-dry wood, for species of trees indigenous to New Zealand.

Conifers:

Araucariaceae:
Agathis australis 0.468-0.630

Cupressaceae:
Libocedrus bidwillii 0.344-0.416
Libocedrus plumosa 0.380

Podocarpaceae:
Dacrycarpus dacrydioides 0.429-0.492
Dacrydium cupressinum 0.455-0.754
Halocarpus biformis 0.554
Halocarpus kirkii 0.627
Lepidothamnus intermedius 0.766
Manoao colensoi 0.515-0.788
Pectinopitys ferruginea 0.625-0.658
Podocarpus laetus 0.619
Podocarpus totara 0.435-0.559
Prumnopitys taxiflora 0.534-0.787

Phyllocladaceae:
Phyllocladus toatoa 0.675
Phyllocladus trichomanoides 0.553-0.645

Monocotyledons:

Arecaceae:
Rhopalostylis sapida 0.401

Asparagaceae:
Cordyline australis 0.522
Cordyline indivisa 0.626

Dicotyledons:

Acanthaceae
Avicennia marina 0.701

Araliaceae
Meryta sinclairii 0.462
Neopanax arboreus 0.677
colensoi 0.722
Pseudopanax crassifolius 0.757
lessonii 0.674
Raukaua edgerleyi 0.581
simplex 0.576
Schefflera digitata 0.559

Asteraceae:
Brachyglottis repanda 0.681
Olearia furfuracea 0.783
ilicifolia 0.663
lacunosa 0.748
paniculata 1.120
rani 0.850
virgata 0.776

Atherospermataceae:
Laurelia novae-zelandiae 0.382-0.465

Chloranthaceae:
Ascarina lucida 0.500

Coriariaceae:
Coriaria arborea 0.618

Corynocarpaceae:
Corynocarpus laevigatus 0.791

Cunoniaceae:
Ackama rosifolia 0.485
Pterophylla racemosa 0.572-0.639
sylvicola 0.627-0.680

Elaeocarpaceae:
Aristotelia serrata 0.575-0.593
Elaeocarpus dentatus 0.562-0.708
hookerianus 0.514-0.568

Ericaceae:
Archeria traversii 0.688
Dracophyllum latifolium 0.779
traversii 0.615
Leucopogon fasciculatus 0.901

Fabaceae:
Sophora microphylla 0.766-0.804
tetraptera 0.884-0.961

Griseliniaceae:
Griselinia littoralis 0.763
lucida 0.655

Lamiaceae:
Vitex lucens 0.959-0.980

Lauraceae:
Beilschmiedia tarairi 0.591-0.888
tawa 0.637-0.761
Litsea calicaris 0.502-0.603

Loganiaceae:
Geniostoma rupestre 0.562

Malvaceae:
Entelia arborescens 0.137-0.281
Hoheria angustifolia 0.738
lyallii 0.747
populnea 0.793
Plagianthus regius 0.506

Meliaceae:
Dysoxylum spectabile 0.491-0.678

Monimiaceae:
Hedcarya arborea 0.584

Myrtaceae:
Kunzea ericoides about 0.760 (0.731-0.943)
Leptospermum scoparium 1.076
Lophomyrtus bullata 0.694
Metrosideros excelsa 0.915
robusta 0.710-0.915
umbellata about 1.040 (0.968-1.140)
Neomyrtus pedunculata 0.741
Syzygium maire 0.637

Nothofagaceae:
Nothofagus cliffortioides 0.596-0.661
fusca about 0.600 (0.490-0.780)
menziesii 0.419-0.700
solandri 0.609-0.790
truncata 0.615-0.782

Nyctaginaceae:
Ceodes brunoniana 0.226

Oleaceae:
Nestegis cunninghamii 0.790-0.995
lanceolata 0.825
montana 1.013

Onagraceae:
Fuchsia excorticata 0.788

Pararyphiaceae:
Quintinia serrata 0.620

Pennantiaceae:
Pennantia corymbosa 0.526

Piperaceae:
Macropiper excelsum 0.519

Pittosporaceae:
Pittosporum eugenioides 0.796
tenuifolium 0.807-0.955
umbellatum 0.827

Plantaginaceae:
Veronica parviflora 0.768
salicifolia 0.822

Primulaceae:
Myrsine australis 0.805-0.991
salicina 0.844

Proteaceae:
Knightia excelsa 0.721-0.785
Toronia toru 0.836

Rhamnaceae:
Discaria toumatou 0.819

Rousseaceae:
Carpodetus serratus 0.742-0.822

Rubiaceae:
Coprosma arborea 0.654
linariifolia 0.835
lucida 0.674
repens 0.599
robusta 0.664

Rutaceae:
Melicope ternata 0.808

Santalaceae:
Mida salicifolia 0.733

Sapindaceae:
Alectryon excelsus 0.854-0.916
***Dodonaea viscosa 1.179

Scrophulariaceae:
Myoporum laetum 0.630

Strasburgeriaceae:
Ixerba brexioides 0.648-0.675

Violaceae:
Melicytus lanceolatus 0.597
ramiflorus 0.654

Winteraceae:
Pseudowintera axillaris 0.643
colorata 0.645

Posted on October 15, 2024 10:25 PM by milewski