Climate change

 Are you covered? – Native perennial grasses provide the best insurance against all weather challenges

Keep your cool – on the role of land management in influencing
local climate

Are you covered?

February 2020

If you’ve been thinking that the heat, fires and smoke have been all too much, it’s time now to brace yourself for the inevitable next thing – the rain.  With luck this will start very gently and persistently, gently wetting up the soil profile over a number of weeks with little disturbance to the ground cover.  However, it is unlikely that we will be that fortunate, and in any case who has a dam that does not need filling?  Only overland flow will rectify that; and with summer storms a possibility, a rush of water may be heading for the dams and creeks any time soon.

If you have those fertilized, annual-dominated pastures that I so frequently despair of, the ground cover is likely to be minimal, with lots of bare ground, loose plant fragments, and plenty of dung.  The next heavy rain is when the ecological chickens will come home to roost.  Overland water flows will carry organic matter (dung, plant parts, fine mulch, soil organic matter) and mineral soil into the dams and drainage lines, effectively exporting nutrients into the Murray-Darling. What was your paddock’s productive potential has now become a source of pollution in waterways, promoting algal growth and killing aquatic life with algal toxins and oxygen deprivation.  This is what ecologists call a leaky system, and because there is poor conservation of water, soil, nutrients and organic matter, it is reducing productivity and accelerating the aridity that our district is facing.

Although at one level, soil conservation is well understood both scientifically and practically, it seems that erosion and soil degradation is actually a normalized process, judging from the general state of our landscapes and waterways. Tough perennial grasses are needed to protect priceless soil.  Native perennials will grow, even in a drought….

After the hottest, driest year on record, this ungrazed plot still supports dense grass cover in mid-January 2020.  The reddish grass in the foreground is Kangaroo grass (Themeda triandra).  There is excellent cover, despite the dry spring.

What about the grazed situation?  All those kangaroos.  We certainly have our share on Gang Gang, but unless they are literally starving, they will avoid the most nutrient-poor plants, as these require more energy to digest than they give up.  Hence, the nearby grazed areas have short patches of the more nutritious grasses (here Kangaroo and Wallaby Grasses), but the less digestible species remain.

This area nearby has been grazed by an uncontrolled kangaroo population.  Note the reddish-coloured Themeda has been eaten to lawn, but the paler Wire Grass (Aristida ramosa) has not.
The soil protection insurance provided by dense Wire Grass includes the bonus of excellent rainfall infiltration.

Wire Grass is one of many native herbaceous species of low palatability that can offer this kind of resilient cover (others locals include Joycea, Dianella, Lomandra, Poa, Carex, Juncus).  But they can offer even more.  In the dry spring, I  was surprised by the degree to which Wire Grass  shaded and nurtured nutritious forbs and annuals. In summer, the Wire Grass patches are bursting with insects while the short patches are bereft.  This is habitat for wildlife even in the harshest conditions.

From a pasture production point of view, what I am extolling what might be considered a nightmare.  Wire Grasses, and their ilk, are hated because, like kangaroos, livestock find them unpalatable.  Even management of grassland for conservation should be aiming for a diversity of  native species, inclusive of both the soft edible types and the hard, indigestible guardians of the soil. In a later column, I will discuss how these otherwise-maligned ‘tough’ species can be balanced up in a grassland so as to benefit from their special qualities, as well as support species that provide nutritious forage.

Keep your cool
May 2018

Whether it is “just” another 20 year drought or part of the current warming trend, this autumn has been a sober warning of what is to come: unseasonal heatwaves, downpours of rain and severe drought. I recall reading predictions that these events would intensify as far back as the 1980s. Thirty years later, the populace is still struggling to come to terms with the reality of climate change. Acting on it at a global-scale seems a step too far for our species at the moment.  But beyond ceasing fossil fuel burning to stem CO2 emissions there are additional things we can do to directly influence the local climate. And these are things very much in your control.

A Czech scientist Jan Porkorný has devoted his career to pointing out just how important local landscape management is to keeping the planet cool. I knew Jan when he worked for a few years at CSIRO in the early 80s.  Later I visited the Institute of Landscape Ecology in Třeboň, stayed in his family’s 700 year old house in Bohemia and saw the amazing cultural landscape of meadows and ponds where the local delicacy, European carp, is raised. It was in this landscape that Jan came to understand the vital role of vegetation and water in keeping the land surface and surrounding air cool. In a recent review Jan summarized what is known about this topic[1]. The mechanisms are complicated, and I am happy to send copies of the paper to anyone interested.

However, the message is simple. Retaining vegetation and rainwater in the landscape, both directly and indirectly, keeps the landscape cool and promotes local rainfall.

Seeing hills bared of all perennial vegetation in our district is very, very scary.  Apart from the well-understood risk of losing soil into the Yass River, bare ground absorbs more radiant heat from the sun. With no plants converting this sunlight into biomass, bare ground instead heats up, creating fluctuating temperature conditions and reducing relative humidity. The greener and wetter the vegetation, the greater the cooling effect. Water evaporates from the plants’ leaves which contributes to cooling and greater moisture. Water begets water it seems. In Western Australia, researchers concluded that the sharp decline in rainfall that has been experienced in the south-west inland was due to vegetation clearance rather then global-scale changes to atmospheric conditions[2].

Returning native perennial grasses, trees and shrubs to our land is a positive move that is within the capacity of most landholders. It has the added benefit of helping our wildlife. Not having houses, air conditioning or a means of diverting more resources for their survival (e.g. no irrigated crops), much of our fauna is going to suffer from the heat and dryness even more than ourselves. More habitat will mean greater survival opportunities. Moreover, we have the know-how and institutions to make serious revegetation little more demanding than a ramping-up of business as usual.

I am not sure what it reveals about our ability to forget the past, but what I am saying here was not news in the 19th century. A Polish immigrant to South Australia, Johann Tepper, wrote an article published in the Agricultural Gazette of New South Wales in 1896 about the role of trees in ameliorating the local climate and promoting rainfall.

His words were are follows:

Even in countries with such deep rich soils, moist and temperate climate, and extremely favourable constitution for continued cropping as central and eastern Europe, it is considered by those who have studied the whole question that one-third of the area should be kept under forest or heath vegetation; for the drier parts of Australia one-half would not be too much.

I am not sure that our landscape can be left exposed and vulnerable, and stay as productive as it currently is, if we ignore the warnings for another 100 years.
Time to act.

[1] Huryna, H. & Porkorný, J. (2016) The role of water and vegetation in the distribution of solar energy and local climate: a review. Folia Geobotanica, 51, 191-208.

[2] Andrich, M.A. & Imberger, J. (2013). The effect of land clearing on rainfall and fresh water resources in Western Australia: a multi-functional sustainability analysis. International Journal of Sustainable Development and World Ecology, 20, 549-63.