The Big Grass Years

Themeda 2

How did the Big Wet years of 2010-2011 affect your local vegetation? Many readers sent in their observations when I asked this question in an earlier blog. Last week I summarized all of the observations from wetlands and floodplains. In the post below I summarize observations about grasses, herbs and weeds from the ‘dry’ hills and plains. Once again, the phrases in italics are from readers’ comments, and the normal text is mine. All of the original observations can also be read on the initial blog. I hope you enjoy reading everybody’s observations.

* * * * *

When you get a lot of rain, you get a ton of grass, as many readers observed across south-east Australia. On the northern plains, 2009-2010 [was] the most amazing summer/autumn period I’ve ever seen, with tremendous growth of C4 grasses and other nice summer growing things (Sida, Euphorbia etc). It was also fantastic for regeneration of chenopod shrubs like Rhagodia, which suddenly seemed to be everywhere. Further south, grasslands in west Melbourne had a productivity surge and many sites required burning over successive years to maintain open swards.

Native grasses thrived from the plains to the hills. Many of the hills and slopes that seemed bare dirt from a distance in late 2009 quickly covered up with… native grasses and improved over 2010 and 2011 with the continued wet summers.

The big wet had a significant impact on native grasses which predominantly remain on the upper slopes (too steep to cultivate) of the hills, either in isolation or understorey to open grassy woodlands. As the start of the big wet in this region was summer, with major rainfall starting in February 2010, the perennial warm season grasses were the first to respond – and they responded vigorously. There were areas where the Microlaena seeded for 4-5 months, with Red grass going even longer. Surprisingly, in some areas Kangaroo grass did not seem to go so well until much later, virtually not til the next spring/summer.

Weeping Grass (Microlaena stipoides) was a big winner in many regions: I recall Weeping Grass flowering continuously for about 6 months. Of note is that our paddock has been free of stock since 2007-08, and so grass was presumably free to grow at will once rain arrived.

Not all species prospered in the thick grass and wet soils. Within the grasslands, Chenopodiacae and other dry loving plants like Ptilotus hated the continuous wet 2010-2011 period, and showed quite dramatic declines, probably due to the increased competition with grasses, but also increased fungal disease and insect activity.

Big wet weeds

Unfortunately, the Big Wet also promoted many exotic plants, as many readers lamented. Hundreds of briar rose and blackberry have appeared and, especially under gum trees, huge numbers of thistles have become established…. In our area (around Albury), Night-shade (Solanum nigrum) and Red Ink Weed (Phytolacca octandra) both appeared abundantly beneath trees during the wet period…. Dianella tarda is being displaced by the exotic spiny rush, Juncus acutus, in a gully on my road and the Big Wet has hastened this process…. In another area, exotic pasture grasses have spread significantly and are crowding out the more diminutive native grasses, for instance on my acreage much of the fibrous spear grass (Austrostipa semibarbata) has given way to exotic grasses.

pattersons curse

On roadsides and Government owned blocks containing mainly native vegetation, tens of thousands of bridal creeper seedlings have suddenly appeared. This includes a block that my Landcare group has been working on. Unless some action is taken, I expect bridal creeper will wipe out vast tracts of roadside and small reserve native vegetation remnants over the next few years…. The blackberries and particularly St John’s Wort also recovered, with areas suffering major infestations of Wort that had not shown any for years – it does not seem to enjoy drought. The advantage is that many farmers now are really interested in managing to protect these native grasslands after this.

A flood of Beauty-heads

It wasn’t all bad though: the wet years and abundant grass were great for thinning out the Romulea minutiflora (one of the worst weeds in the grasslands). Romulea seemed to be getting steadily worse through the dry period prior. And many native plants loved the Big Wet. 

On one particular site in Deer Park where forbs are relatively abundant, I casually observed an increase in forb frequency that I suspect related to a combination of high seed availability and an extended period of wet conditions conducive to recruitment (rather than just seasonal regeneration from root-stock)…. The most successful regenerating plants were Calocephalus citreus, Eryngium ovinum and Chrysocephalum sp.1 and… most of these plants have persisted despite the dry conditions of 2012-13.

Lomandra longifolia presented synchronous seed germination over 5 or 6 sites. This seemed to occur post heavy rain around December 2010 (I think). The seed must have been stored in the seed bank…. Some herbaceous natives have also done very well, with Lemon Beauty-heads popping up along many roadsides. Restoration works gave some natives a helping hand: at sites that were regularly maintained using a mix of hand removing and spraying, many Senecio species (including S. quadridentatus, S. minimus, S. bipinnatisectus and others) all responded favourably.

* * * * *

The big pulse of thick grass after the Big Wet is interesting in itself. But it’s also very important ecologically, because thick grass affects many other species, from seedling plants to ground-dwelling birds. In the next blog, we’ll look at how the Big Wet affected regeneration of trees and shrubs. Many readers reported lots of tree regeneration in some area but none in others. What caused this difference? For that story, stay tuned next week.

Thanks again to everyone for sending in so many great observations. Please leave a note below if the observations above remind you of other changes you saw in the Big Wet.

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7 thoughts on “The Big Grass Years

    • Hello TB, thank you for your comment and for the link to the post on fleabane. Phytolacca was common in the wet years in NE Vic, especially under trees, where I assume the birds had spread the seeds. Hopefully it will decline in drier years, although I assume it will re-emerge next time we have a big wet year. best wishes Ian

    • Hi Tarra, Ian and others,
      Just to share a past memory of mine;
      I recall driving west to Orange (via Crookwell, NSW) and seeing a few hillsides covered in a type of thistle (either Scotch or Illyrian thistles (Onopordum species)). I remember the seeds blowing off in the wind and thought how far could they travel? I was (sadly) impressed by the amount of seed. I wondered if they could travel to some of the sites I was looking after (~100km east of that area). With some of the winds (especially a strong westerly) I guessed they could.
      Then I remembered the dust storm that blew soil from central South Australia/NSW. It was thought that some of the soil was even transported to New Zealand!
      I now think that weeds from the family such as Asteraceae could build up in numbers somewhere west of an area for a decade or so and then get picked up in a wind (if seeding at the time) and end up in a brand new area!
      Just a thought on how Fleabane could arrive one year after never being seen before.
      Thanks,
      Rus

      • Hi Rus

        I think in our case, Fleabane was definitely around as a background weed but went largely unnoticed, in the past few years it has been highly visible (it seems) all of a sudden with large colonies dominating disturbed sites and roadsides, but also noticeably popping up more in native vegetation, especially where it borders grazing land. Inkweed seemed to really emerge in areas burnt by the 2009 fires.

  1. Hello Rus and TB, thanks again for your comments. There’s an interesting PhD thesis on Conyza ecology on the web – http://www.cottoncrc.org.au/files/13da4c24-e53f-4d0b-b4c4-a05a00b9f9e6/10154_Green_PhD_Thesis_Cotton_CRC.pdf – And it shows that Conyza seeds don’t last very long in the soil, with 99% of shallowly-buried seeds germinating within 2 years. Thus, it seems most likely that the huge flush of Conyza in Gippsland was due to very high seed production after the rains, rather than because the wet prompted lots of establishment from a long-term seed bank. The thesis has heaps of great info on Conyza ecology and is well worth a look. Best wishes Ian

  2. In addition to the blog comments above, two readers sent their observations via Twitter, as follows.

    Thanks again to everyone for taking the time to send in an observation.

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