Changing patterns of pasture production in south-eastern Australia from 1960 to 2015

Abstract

The seasonal pattern of pasture production and its variability from year to year are important for pasture-based livestock production systems in south-eastern Australia because they influence key strategic decisions such as stocking rate and timing of the reproductive cycle. In this study, the effects of observed climate variations over the period 1960–2015 on pasture growth patterns were investigated by using a biophysical modelling approach. Pasture growth rates were simulated using DairyMod biophysical software at five sites ranging from high-rainfall, cool temperate at Elliott in Tasmania to medium-rainfall, warm temperate at Wagga Wagga in southern New South Wales. Annual pasture yields showed a small increasing rate of 50 kg DM/ha.year at Elliott and 40 kg DM/ha.year at Ellinbank (P < 0.05), whereas other sites showed no significant trend over time. A cross-site analysis of seasonal average pasture growth rates predicted under four different discrete periods of 14 years each showed that winter growth has increased steadily through time (P = 0.001), and spring pasture growth rate has decreased (P < 0.001) in 2002–15 compared with the earlier periods. Year-to-year pasture yield variability (coefficient of variation) during autumn and spring seasons has also increased (P < 0.05) across sites in the period 2002–15 compared with 1998–2001. At each site, the number of spring days with water stress (growth limiting factor_water <0.7) was ~10 times greater than the number of days with temperature stress (growth limiting factor_temperature <0.7). There was an increase in the number of days with water stress at Wagga Wagga, and increased heat stress at Wagga Wagga and Hamilton (P < 0.05) in the most recent period. These results highlight the importance of incorporating more heat-tolerant and deep-rooting cultivars into pasture-based production system. Although previous studies of climate-change impact have predicted increasing winter growth rates and a contraction of the spring growing season in the future (2030), this study provides clear evidence that these changes are already occurring under the observed climate in south-eastern Australia.

Using Leaf Temperature to Improve Simulation of Heat and Drought Stresses in a Biophysical Model

“…Climate data for each site (solar radiation in MJ/m −2 , maximum and minimum temperatures in • C, rainfall in mm, evaporation in mm and RH%) were obtained from the SILO database service [62]. Soil type details of the two sites were extracted from [5]. Simulations were managed as a cutting trial where pastures were harvested to a residual level of 1.4 t DM/ha at the end of each month.…”

“…Climate change projections for Australia indicate increasing frequency and magnitude of extreme climate events such as heat waves, droughts, extreme precipitation and frost occurrences in the coming decades [1], which are likely to reduce productivity and profitability of pasture-based systems [2]. A recent study conducted in southeastern (SE) Australia showed that the anticipated changes to the pasture growth patterns under future climate change reported by [3,4] are already occurring under current climate change, including increased pasture yield variability over the major growing seasons (autumn and spring) and a decreased spring season growth leading to shorter growing season lengths [5]. These changes were more prominent in the most recent period (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) compared to the periods before and were mainly caused by the increased occurrences of heat and drought stress [5].…”

Productivity and nutritional value of 20 species of perennial legumes in a low‐rainfall Mediterranean‐type environment in southern Australia

“…Characteristics that are desirable for new species and varieties for the rain‐fed Mediterranean‐type climate and dry temperate zone of southern Australia include persistence through 5–7 months of dry weather, tolerance of soil constraints, high feeding value (a function of biomass availability, nutritional value and voluntary intake by ruminants), ability to produce quantities of inexpensive seed, ease of establishment and management, rapid recovery after defoliation, high water use through deep roots and well‐adapted and effective root nodule rhizobia (Cocks, 2001; Edwards et al., 2019). Climate change will have a range of impacts on perennial forage systems due to factors such as increasing variability in autumn rainfall, declining growing season rainfall and an increase in spring moisture stress days (Perera et al., 2020).…”

Pasture legumes differ in herbage production and quality throughout spring, impacting their potential role in fodder conservation and animal production

“…In both Mediterranean and temperate environments of Australia, the timing of opening season rainfall and rainfall received throughout the growing season are the major factors impacting herbage production (Black, 1964; Chapman et al., 2009). Recent modelling has shown increasing variability in autumn rainfall, declining growing season rainfall and tripling (from 20 to 60 days) in the number of spring moisture stress days in the period 2002–2015 compared to 1988–2001 for medium rainfall areas of south‐eastern Australia (Perera et al., 2020). Despite variability in seasonal conditions, a common feature of both Mediterranean and temperate environments in extensive livestock production systems, such as those in southern Australia, is an excess of spring production relative to direct utilization by livestock.…”