When to mow a meadow? Ecological challenges in threatened grasslands
Updated: Aug 23, 2021
Canberra, in the Australian Capital Territory, is known as ‘the bush capital’. Relatively new by city standards, at just over 100 years old, strategic planning saw the protection of significant areas of natural vegetation within the bounds of the city.
Foresight by early town planners has preserved vegetation types in the Canberra region that are now nationally threatened. One of these is a Natural Temperate Grassland community that is relatively common in the Canberra region, so it is too easy to forget the real threats at a national scale. Grasses provide most food for both people and livestock. Natural grasslands around the world have often been highly altered through grazing or other land management practices. Also, grasslands are often preferentially utilised for broad-scale agriculture as there are usually few trees to remove.
Grasslands and the Molonglo River corridor provide rich habitats for a large numbers of animals. These include larger animals such as echidnas, which feed on termites.
Echidna_3128 Echidna_2735s Termites_6421s
Many birds feed in grasslands and nest in denser vegetation, or in trees along the river.
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A large array of spiders and even the occasional scorpion can be found making webs among the grass or under rocks.
Spider_3088 Spider_3002 Spider_5682s Spider_5326s Spider_9941s Spider_0009s Spider_5531s Spider_0095s Scorpion_6528s
Grasshoppers are common, often blending very well into their surroundings. If you are lucky, you might spot the endangered Peranga Grasshopper, with a distinctive 'X' on its back (last two images below).
Grasshopper_2512s Grasshopper_0368s Grasshopper_2936 Grasshopper_2926s Perunga_Grasshopper_0150s Perunga_Grasshopper_1759s
Beetles are found everywhere, and grasslands are no exception.
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Butterflies and moths are common too, starting out as caterpillars and often feeding on very specific plant hosts (see Bond et al. 2016).
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Bees and bee-flies can be very important for the pollination of native flowers.
Bee_on_Eryngium_2716 Convolvulus_angustissimus_9170 Solanum_cinereum_2590 Chrysocephalum_apiculatum_0404
Many other insects can be found, the preying mantis showing quite an attitude if disturbed. The rare Mungarda can also be found in old spider burrows (last photo).
Preying_Mantis_9522s2 Ant_8317s Eryngium_ovinum_2739 Hoverfly_0080s Damselfly_7143s Mungarda_2997s
A number of lizard species are found in grasslands or along the river, including the rare Pink-tailed Worm Lizard, which has no legs and spends its time in ant burrows. It is most often found under rocks. Rocks should not be disturbed as these small lizards are easily injured, or their small homes destroyed when rocks are moved.
Pogona__2719s Skink_8441s Ctenotus_6043 Tiliqua_skinkoides_4952s Legless_Lizard_0810s Worm_Lizard_6162s
Maintaining good condition for these threatened grasslands is however a more serious matter. With a long history of grazing and weed invasion, combined with close proximity to housing and subsequent high fire risks, current management practices can be complex. It is well understood that reduced fire fuel loads close to houses significantly increase the ability to control fires in emergency situations, the best way to control fuel loads in natural vegetation, and especially a threatened community, is less certain.
Grasslands are commonly shaped by disturbance events such as fire and grazing, so excluding these natural processes can lead to changes in structure and composition, especially an increase in biomass (the physical quantity of vegetation).
Grazing by kangaroos, wallabies and wombats can influence the density of natural species, but grazing levels are rarely high enough to reduce the level of introduced species that often grow more rapidly than natives. Grazing with cattle and even goats is still practiced in some areas, but has its limitations.
Cattle_0650s Kangaroo_0948s Kangaroos_1210s Rabbit_3052 Kangaroos_1232s Kangaroos_1289
As an alternative to fire and grazing, biomass levels can be reduced by mowing. However, many land managers are reluctant to use mowing due to concerns over weed invasion and changes to species responses. We used extensive mown firebreaks in Natural Temperate Grasslands in the Canberra region to examine the effects of long-term mowing on both native and introduced species.
High natural variability in Natural Temperate Grassland species diversity is reflected by the relatively few species that re-occurred in sufficient frequency across the 200 sample sites to allow statistical analyses to be undertaken. The tedious nature of documenting the presence and abundance of every species in 200 plots limits the number of sites that can be scored in a year by a pair of botanists (important for consistency). It would be interesting to see if larger-scale sampling or measurements across multiple years enabled the analysis of a larger proportion of species.
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We found increased richness for 16 out of 24 functional groups (differing in various ecological responses), and no reduction in species richness. In most cases, mowing had a positive effect on natives species, and had little or no influence on introduced species. Overall, consistent mowing increased both the cover of native perennial grasses and naturally bare earth (important for new seedling recruitment), corresponding to a reduction in introduced perennial grasses.
Clear positive effects of mowing were demonstrated for six native species, and species complexity was maintained. Mowing may lower the abundance of some species, including the highly invasive Chilean Needlegrass (Nassella neesiana).
We conclude that mowing can be an effective tool for the management of Natural Temperate Grasslands, provided high standards of vehicle hygiene are maintained. The best management results are likely to be gained from a variable mowing regime, combined with targeted management of invasive weeds (e.g. direct herbicide application).
With ongoing management, the Natural Temperate Grasslands around Canberra should continue to delight visitors for generations to come.
Leucochrysum_albicans_5412 Acaena_novaezelandiae_3846 Arthropodium_fimbriatum_1017 Dianella_longifolia_6316 Lotus_australis_7600 Wurmbea_dioica_2879 Thysanotus_patersonii_2861 Wahlenbergia_communis_0056 Stylidium_graminifolium_1513 Rutidosis_leptorrhynchoides_0687 Dawsonia_sp_3460 Eryngium_ovinum_2976
Further reading:
Barrett, R.L., Cosgrove, M. & Milner, R.N.C. (2018). Field guide to plants of the Molonglo Valley: natural temperate grassland, box gum woodland, riparian vegetation. (ACT Government, Territory and Municipal Services, Parks and Conservation Service: Canberra.)
Bond, S., Holliday, S. & Stein, J. (2016). Field guide to butterflies of the Australian Capital Territory. (National Parks Association of the ACT: Canberra.)
Cosgrove, M. (2014). Photographic guide to native plants of the Australian Capital Territory. (Meadow Argus: Canberra.)
Eddy, D., Mallinson, D., Rehwinkel, R. & Sharp, S. (2011). Grassland flora: a field guide for the Southern Tablelands (NSW & ACT). 2nd edition. (Environment ACT, NSW National Parks and Wildlife Service, World Wide Fund for Nature Australia, Australian National Botanic Gardens, Department of Land and Water Conservation, Environment Australia: Canberra.)
Sharp, S., Rehwinkel, R., Mallinson, D. & Eddy, D. (2015). Woodland flora: a field guide for the Southern Tablelands (NSW & ACT). (Friends of Grasslands: Canberra.)
Smith, A.L., Barrett, R.L. & Milner, R.N.C. (2018). Annual mowing maintains plant diversity in threatened temperate grasslands. Applied Vegetation Science 21: 207–218. http://onlinelibrary.wiley.com/doi/10.1111/avsc.12365/full
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