The superpowers of NZ moss: Dry shrubland and its moss ground cover

I love moss.

I have always loved mosses. They are so cute!

Moss is green, all kinds of green, every nuance.

Some of them are leafy, some of them flat, and some look like cushions.

They make the forest floor look like a fairyland.

Even better than simply being aesthetically pleasing, mosses have superpowers.

Like Spider-Man, they stick to vertical flat surfaces, decorating walls with adorable green spots. Moss also has another power. I remember walking through the dunes in my hometown of Calais (France), the sound of waves in the background. Suddenly, between the European beachgrass (Ammophilia arenaria) that keeps the sand and dunes in place, I spot a brown patch of dead moss. Dead? Not really. With just a few drops of water on it, the moss revives in a few seconds, turning the brownish-dead area into a bright green patch of life. Just amazing. Tiny dune zombies are coming back to life through water.

Consequently, moss brings joy to people, or at least to me. However, what role is moss playing in nature?

The study conducted by Rebecca Dollery, Mike Bowie, and Nicholas Dickinson in 2022 helps to answer this question. They were particularly focused on the importance of moss ground cover in a dry shrubland area of New Zealand. They found that moss could be represented as a collector that loves to hoard various things.

First into the hoard is water. Moss absorbs rainwater or humidity from the air. Moss is almost always wet when touched. The water is then used by the moss. The soil benefits from the waterlogged moss cover: in summer, soil is wetter under the moss carpet. The moss acts as a protective layer for the soil against the summer heat, allowing retention of water in the soil. The water is later used by the surrounding plants. In a dry shrubland environment, moss can have a positive effect on other native plants populating the area.

Second into the hoard are soil nutrients. All plants need them to grow. One of the most important nutrients is nitrogen (N). It can be found in soil and absorbed by the plants in two forms: nitrate (NO3) and ammonium (NH4+) molecules. With the ground covered by a moss carpet, the quantity of nitrate and ammonium in the soil decreased, up to 75% for the latter. In addition, the thicker the moss, the lower the amount of nitrate. Therefore, moss not only absorbs water but also sequesters essential nutrients. The nitrogen is trapped within the moss.

This sounds alarming: moss is taking away the necessary food source of all other plants. However, this is not a tragedy for the dry shrubland environment. Indeed, their soil is low in nutrients under normal circumstances. Consequently, the plants growing there are adapted to these conditions. On the contrary and surprisingly, they might even suffer from a large increase in soil nutrients. The moss carpet thus preserves the original composition of the soil, which is also the optimum growing condition for plants native to dry shrublands.

Third into the hoard are the seeds that fall and are stored within the moss layer. The researchers tested the impact of moss ground cover on the ability of some native species to germinate. Generally, moss cover prevents germination: fewer seeds germinate than on bare ground. The scientists supposed that the seeds did not germinate because they were in the dark, after falling into the depth of the moss layer. This was mostly observed with tauhinu (Pomaderris amoena) and kānuka (Kunzea serotina) (the species name was revised back to Kunzea ericoides in 2023). Both suffered a 60% reduction of their germination capacity.

The seeds of the common broom (Carmichaelia australis) can germinate in the dark. For this species, the high humidity within the moss could be the reason why seeds germinated up to 88% less often with moss ground cover. Nevertheless, some seeds germinated and became seedlings. Their next step was to have their roots access the soil to absorb nutrients. The scientists observed that more common broom seedlings survived on the bare ground than with ground moss cover. The moss layer probably acted as a barrier between the roots and the soil. Despite that, the seedlings of common broom and tauhinu that germinated with moss were up to 3 times heavier than the ones from bare soil. This indicates that the conditions provided by the moss cover have had a positive impact on their growth.

Rebecca and the team identified the moss as a plant that loves to stockpile things: first water, then nitrogen, and finally seeds. The various impacts of the collecting moss were in some ways beneficial for the native plants of the dry shrubland ecosystem. They were, however, detrimental towards exotic and invasive weeds. These invasive species suffer from the low nutrients in the soil and the difficulties of germinating within the moss layer. Moss, therefore, participates in the conservation of native plants in the dry shrubland ecosystem.

A very interesting name can be added to the “things collected by moss” list: carbon (C). Sphagnum moss are one of the main components of peatlands. In these ecosystems more vegetation is growing than is decomposing, thus vegetation, including moss, is gradually accumulated as layers of peat. Furthermore, when plants are growing, they absorb CO2 from the atmosphere, they keep the carbon to form sugar and release oxygen (O2). Therefore, peatlands are trapping carbon in their vegetation, in their moss. Larmola and colleagues (2014) calculated that one-third of the total amount of carbon stocked on land is trapped in peatlands!

After all those discoveries, I continue to love and admire moss. I will carry on watching the moss turn green again in the dunes and taking naps on forest moss. Those tiny superheroes decorate my city pavement and walls, promote native plant species in New Zealand’s dry shrublands and trap carbon from the atmosphere, as little fighters against global warming.

This article was prepared by Master of International Nature Conservation student Eva Saison as part of the ECOL608 Research Methods in Ecology course.

Dollery, R., Bowie, M. H., & Dickinson, N. M. (2022). The ecological importance of moss ground cover in dry shrubland restoration within an irrigated agricultural landscape matrix. Ecology and Evolution, 12(4).

Heenan, P. B., McGlone, M. S., Mitchell, C. M., McCarthy, J. K., & Houliston, G. J. (2023). Genotypic variation, phylogeography, unified species concept, and the ‘grey zone’ of taxonomic uncertainty in kānuka: Recognition of Kunzea ericoides (A.Rich.) Joy Thomps. sens. lat. (Myrtaceae). New Zealand Journal of Botany, 0(0), 1–30.

Larmola, T., Leppänen, S. M., Tuittila, E.-S., Aarva, M., Merilä, P., Fritze, H., & Tiirola, M. (2014). Methanotrophy induces nitrogen fixation during peatland development. Proceedings of the National Academy of Sciences, 111(2), 734–739.

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