A note to my Yarns from the Farm Readers—this is the fifth instalment of a series on biodiversity for our local newspaper. Earlier versions can be found in Yarns from the Farm on my website Nan
Why is there an image of a humpback whale’s ‘bubble net’ at the beginning of this article? Well, it’s a story about grazing and biodiversity, and such a cool one that I couldn’t resist using it as the lead-in. The image captures the line of bubbles the whale leaves as he creates an acoustic net to trap small fish and then scoop them up. This image was taken off Tasmania in 2020. Photo credit: Wild Ocean Tasmania. The full video of him setting the net and then fishing it is well worth watching!
Humpback whales were seen in the waters of eastern Australia last year in the largest pods recorded for decades—as many as 90 at a time. This is the reward for those decades of international collaborative action to provide protections for whale populations. The full story can be found in The Conversation, a free online site.
Coming back to solid ground, grazing in farmland and bush is, like chocolate and carbon dioxide, a good thing in moderation. Grazing helps more sensitive plants that might not be able to compete with the most robust plants in the system (e.g. cocksfoot grass, silver tussock native grass) by opening up the plant canopy to allow sunshine in for photosynthesis.
Without grazing to even the playing field, those dominant plants will gradually take over. Grazing can be by domesticated or wild animals—the plants don’t mind. The object is to get enough, but not too much, regular pruning of the full sward of plants in the system. This can be in a fully exotic (introduced pasture) system or a native ecosystem with hundreds of plant species. Both systems need grazing to maintain and enhance biodiversity.
As is usually the case when dealing with nature, though, too much grazing can tip the scales the other way. When grazing results in very short grass or bare ground, the loss of moisture from the soil starts to favour those drought-tolerant species over the more sensitive ones.
How do you know when you’ve got the porridge just right: not too much, not too little? It depends on a whole raft of factors, and it will vary from farm to farm and season to season. Is it a grassland system or bush? Is it a high or low rainfall year? What’s the pattern of rainfall—lots of winter rain, which helps the root reserves, or more spring and summer rain that favours rapid plant growth?
It’s a delicate balance and you won’t always get it right, but if you’re watching carefully, you’ll learn from each year’s lessons.
Some strategies I’ve found useful include: keep grazed plant length several inches high, to maintain good root health and ground cover; allow some fraction of your property to go to seed each year; and graze native areas in autumn and winter, in preference to spring when plants are reproducing.
If the all the plants in your system have the opportunity to reproduce successfully each year, they will be better able to withstand the challenges of weather and climate, and your grazing operation will be more resilient.
And since biodiversity is at the heart of good animal nutrition, it’s worth the effort to protect and enhance it.