Early recovery signs of an Australian grassland following the management of Parthenium hysterophorus L.

Abstract

HighlightsWe quantified the impact of parthenium weed upon species diversity in grassland.We assessed the resulting shifts in plant community composition following management.High infestations of parthenium weed significantly affected species diversity and native species abundance.Herbicide applications were beneficial to the recovery of the grassland with grazing exclusion.Productivity of these grasslands increased, being a key step in determining an environmentally stable management strategy. Page 2 of 24A c c e p t e d M a n u s c r i p t ABSTRACT Parthenium weed (Parthenium hysterophorus L.) is believed to reduce the above-and belowground plant species diversity and the above-ground productivity in several ecosystems. We quantified the impact of this invasive weed upon species diversity in an Australian grassland and assessed the resulting shifts in plant community composition following management using two traditional approaches. A baseline plant community survey, prior to management, showed that the above-ground community was dominated by P.hysterophorus, stoloniferous grasses, with a further high frequency of species from Malvaceae, Chenopodiaceae and Amaranthaceae. In heavily invaded areas, P. hysterophorus abundance and biomass was found to negatively correlate with species diversity and native species abundance. Digitaria didactyla Willd. was present in high abundance when P. hysterophorus was not, with these two species, contributing most to the dissimilarity seen between areas. The application of selective broad leaf weed herbicides significantly reduced P. hysterophorus biomass under ungrazed conditions, but this management did not yet result in an increase in species diversity. In the above-ground community, P. hysterophorus was partly replaced by the introduced grass species Cynodon dactylon L. (Pers.) 1 year after management began, increasing the above-ground forage biomass production, while D. didactyla replaced P. hysterophorus in the below-ground community. This improvement in forage availability continued to strengthen over the time of the study resulting in a total increase of 80% after 2 years in the ungrazed treatment, demonstrating the stress that grazing was imposing upon this grassland-based agroecosystem and showing that it is necessary to remove grazing to obtain the best results from the chemical management approach.

Managing an Invasive Weed Species, Parthenium hysterophorus, with Suppressive Plant Species in Australian Grasslands

“…However, both pasture mixtures were able to maintain a stable biomass production over time and even after simulated grazing had been applied ( Figure 2 ). The high abundance of species with good drought tolerance in both pasture mixtures probably contributed to this response [ 16 ].…”

“…Positive species interactions, such as an improvement in the abundance of native species with grazing value, were expected to occur. However, three months of field evaluation might have limited these kinds of observations as in sub-tropical Queensland, changes in community composition due to a sown pasture may take 10 or more years [ 6 , 16 ]. In the longer term, nitrogen fixation by the legume component, better nutrient recycling and a more balanced usage of the available resources might result in obtaining positive responses in yield, forage quality and community species diversity.…”

“…However, the large scale weed infestations and the environmental concerns rule out the continuous and frequent use of chemicals. Ecologically based approaches have been proposed as more sustainable to manage this species [ 16 , 17 , 18 ]. In Queensland, a biological control program for parthenium weed was started in the late 1970s and since then, nine insect and two fungi biocontrol agents have been released into that state [ 19 , 20 ].…”

Feasible or foolish: Attempting restoration of a Parthenium hysterophorus invaded savanna using perennial grass seed

“…The weed then bolts, maturing rapidly and producing an abundance of flowers and subsequently seed, often in excess of 30 000 per plant, until it senesces during mid-autumn (Strathie et al, 2011;Cowie et al, 2020a). These P. hysterophorus invasions are particularly troublesome in grazed or disturbed savannas/rangelands, where the weed forms recurring and dense monospecific stands, with extensive and persistent seedbanks (Nigatu et al, 2010;Belgeri et al, 2014;Nguyen et al, 2017). The dense stands commonly outcompete and chemically exclude (allelopathy) native flora and are toxic and unpalatable to any domestic or wild herbivores, reducing available pasture and furthering agricultural and conservation concerns (Strathie et al, 2011;Adkins and Shabbir, 2014).…”

“…The limited control of P. hysterophorus in South Africa, suggests that additional or supplementary, site-specific management approaches will be required to attain control in certain areas (Khan et al, 2013(Khan et al, , 2014Cowie, 2020). In the case of invaded savannas/rangelands, reducing grazing herbivore numbers and subsequently grazing pressure, has been shown to allow the recovery of pastures along with reductions in P. hysterophorus density and impact (Dhileepan and Strathie, 2009;Belgeri et al, 2014). However, reducing grazing pressure alone, to allow the natural recovery of pastures, may take prolonged periods of time, and depending on the severity of invasion, can have limited success (O'Conner, 2015).…”