Concept · keystone idea · Ch 9
Why the poorest ground grows the richest flora
On desperately poor soil no single plant can grow fast enough to dominate, so the field falls open to hundreds of specialists — the poverty is the cause of the richness.
First, meet: The nitrogen–phosphorus asymmetryPodzolisation (how sand goes bankrupt)
It looks like the poorest country on the coast, and in a sense it is: bleached, bottomless sand, leached so hard that barely a trace of nutrient survives. It is also one of the richest gardens in Australia — hundreds of species packed where you would expect almost nothing — and the second fact is true because of the first.
The mechanism is almost a parable. Where soil is rich, a few fast, greedy plants grab the abundant nutrients, shoot up, and shade and crowd everyone else into oblivion; abundance, perversely, narrows the field to a handful of bullies. Where soil is desperately poor, no plant can grow fast enough to lord it over the others, so the door is thrown open to hundreds of specialists, each scratching a living a slightly different way.
Poverty is a great leveller and a greater diversifier. It is what a landscape looks like when no one is allowed to win — and the wallum is where you get to watch it happen.
In depth
The paradox has two mechanisms working together. (1) Competitive release: on fertile ground a few fast growers monopolise abundant nutrients and shade competitors into oblivion, so richness is low; on phosphorus-depleted ground no species can achieve the growth rate needed to dominate, competitive exclusion relaxes, and many species coexist. (2) Niche multiplication: as available phosphorus falls, the number of distinct nutrient-acquisition strategies rises — mycorrhizal symbioses, cluster roots in the Proteaceae that exude carboxylates to mobilise sorbed P, carnivory (Drosera, Utricularia) for nitrogen, and N-fixation in legumes and wattles — and this strategy diversity underpins the species diversity.
The evidence, stated honestly. The strongest demonstration that strategy diversity rises as phosphorus declines is Zemunik et al. (2015), on the Jurien Bay chronosequence in Western Australia — a principle, not a Cooloola measurement. For the Sunshine Coast the wallum-diversity claim is kept at the regional level: Cooloola is the classic chronosequence (Thompson 1981 for the giant podzols; Chen et al. 2015 for the measured P decline), and the richest-on-the-poorest pattern is read against that regional backdrop rather than a site-specific richness curve. Higher resolution never means looser facts.
Primary sources & further reading — the doorway
- Zemunik, G., Turner, B.L., Lambers, H. & Laliberté, E. (2015). Diversity of plant nutrient-acquisition strategies increases during long-term ecosystem development. Nature Plants 1: 15050. (Jurien Bay chronosequence, WA — the principle of rising strategy diversity; NOT a Cooloola study. Earlier draft mis-cited as "Laliberté et al., Cooloola".) — Nutrient-acquisition strategy diversity rises as P declines — the mechanism (Jurien Bay, WA; NOT Cooloola).
- Walker, T.W. & Syers, J.K. (1976). The fate of phosphorus during pedogenesis. Geoderma 15: 1–19. — Why the ground gets, and stays, poor — the phosphorus arc beneath the paradox.
- Thompson, C.H. (1981). Podzol chronosequences on coastal dunes of eastern Australia. Nature 291: 59–61. — The Cooloola giant podzols the regional pattern is read against.