Australian Rangeland Systems and Grazing Management

Introduction to Australian Rangeland Systems and Fragility

• Rangeland systems in Australia encompass a diverse range of environments from dense forests to small grasslands and intermediate pastures.

• These ecosystems are relatively fragile and are governed primarily by natural ecosystem processes rather than intensive human intervention.

• Environmental Importance:

  • Rangelands are critical for maintaining biodiversity.

  • They serve as a significant carbon source and storage area due to the volume of trees.

  • Management must consider a holistic global perspective on environmental benefits rather than focusing solely on production benefits.

• Woody Thickening:

  • A historical trend of "woody thickening" has been observed across rangelands.

  • This phenomenon is largely attributed to the removal of traditional indigenous land management practices.

  • Specifically, the cessation of regular fire management, which was essential to the evolution of these ecosystems, has allowed woody vegetation to proliferate.

  • Modern grazing production systems often lack the consistent fire regimes necessary to maintain the tree-grass balance.

• Productivity vs. Biodiversity:

  • Managing rangelands involves a delicate balance between optimizing production and maintaining biodiversity.

  • There is no "perfect number" for the ratio of trees to feed for any specific paddock, making precise management a significant challenge.

Land Condition Assessment (The ABCD System)

• Land condition is driving the assessment of whether landscapes are being degraded using a specific class system: A, B, C, and D.

• Criteria for Assessment:

  • Coverage of 3P Species: Perennial, productive, and palatable grasses are the primary indicators of health.

  • Soil Condition: Assessments look for signs of soil degradation and erosion.

  • Woody Weed Thickening: This includes the encroachment of shrubs and the formation of thickets that overtake the landscape.

• Sensitivity to Stocking Rates:

  • Rangelands are extremely sensitive to even minor changes in animal density per square kilometer.

  • Case Example: Shifting from $1.9$ to $1.4$ or $1.6 \text{ animals/km}^2$ may appear miniscule given the scale of large stations, but these changes have significant impacts on overall land condition and degradation.

• Recommendation for Producers: The primary management strategy is to stock at the Long-Term Carrying Capacity (LTCC).

Challenges in Assessing Long-Term Carrying Capacity (LTCC)

• Assessing LTCC is complex; the Northern Territory Department of Primary Industry (NT DPI) employs dedicated teams to assess carrying capacity across individual stations and specific landscape units.

• Goal of Assessment: To define a level of "safe utilization" based on rainfall and soil fertility, providing a margin for error during dry seasons.

• Historical Rainfall Context:

  • Over the last $30-40$ years, Northern Australia has experienced a period of higher-than-average rainfall compared to records dating back to the mid-1800s.

  • This consistency of high rainfall leads to anxiety among experts that current assessments of "sustainable" carrying capacity may be overestimated.

  • Assumptions made over a single human career ($20-30$ years) might not remain valid for the next several decades.

• Climate Change Impacts:

  • Global warming is driving temperatures above average and increasing sea temperatures.

  • It remains uncertain if specific rangeland environments will become wetter or significantly drier in the next $30-50$ years.

The Jones and Sandland Model in Rangelands

• The Jones and Sandland model describes the interaction between stocking rate, productivity per head, and productivity per hectare.

• Temperate/Intensive Systems:

  • As stocking rates increase, animals compete for high-quality feed, leading to a marginal reduction in per-head liveweight gain.

  • Overall productivity per hectare increases as more animals are added, eventually reaching a maximum before declining as animals reach a "maintenance only" level of feed intake.

• Rangeland Deviations:

  • In rangelands, the model rarely completes the full curve. While per-head productivity does decrease with increased stocking, the per-hectare productivity peak is often never reached in a way that signals a decline to the manager.

  • Productivity per hectare appears to increase constantly with higher stocking rates (occupying only the "yellow part to the left" of the model's graph).

  • This leads to a trap: land degrades faster than the livestock productivity signals the problem.

• Economic vs. Ecological Optima:

  • Short-term economic optimum stocking rates are often a long way from ecological optimum stocking rates.

  • Business-logical decisions in the short term often conflict with the long-term sustainability of the ecosystem.

Constraints on Reactive Stocking and Management

• Managers often fail to see the benefits of conservative stocking within a $12$-month or even contextually multi-year window because rangeland productivity per head is not immediately responsive to minor rate reductions.

• Seasonal Variability:

  • Rangelands have short, fixed growing seasons ($2-4$ months) followed by long dry periods ($8+$ months) with zero growth.

  • Reducing stocking rates during a dry season does not result in immediate regrowth or increased per-head weight gain because the plants are dormant.

• The Forage Budgeting Challenge:

  • Forage supply is assessed at the end of the wet season.

  • While managers know how much feed is available, they do not know how long it must last (the timing of the next wet season "break").

  • Managers often overestimate the seasonal outlook or react too slowly to signs of overgrazing.

• Logistics of Reaction:

  • Mustering in rangelands is a massive undertaking involving helicopters and teams of stockmen, taking weeks of effort.

  • By the time cattle are visibly consuming feed too quickly, the land is already under stress and contributing to long-term degradation.

• Profitability Finding: Studies over a $25$-year period indicate that steady stocking at LTCC is more profitable than highly reactive stocking because it avoids the costs of land degradation and excessive labor.

Utilization Rates and Patch Grazing

• Utilization Rate Benchmarks:

  • Temperate beef: $\sim 40\%$

  • Dairy systems: $50-60\%$

  • Australian rangelands: $20-30\%$ of annual herbage (can be as low as $10-20\%$ for poor condition land).

• High Selectivity:

  • Rangelands have low stocking rates but high plant species diversity. Managers must allow high selectivity so animals can find the "dessert" (high-protein bits) to maintain productivity on low-quality forage.

  • Plant density is low, changing the "angle of attack"; animals can graze from the sides or the base of plants rather than mowing from the top down.

• Water Point Effects:

  • Sparse watering points create "radial" grazing patterns. Cattle trails are dense near the water source and spread out as distance increases.

  • Sacrifice Zones: The area within a $\sim 500\,m$ radius of a water source is typically completely overgrazed and depleted of feed.

  • Utilization drops significantly by $2\,km$ and is nearly zero at $3\,km$ away from water.

  • Behavioral Habituation: Animals are habitual and may stay near a familiar water point even if the feed is gone, sometimes refusing to move to new bores because the area is "novel" or "scary."

Evaluation of Strategic Management Tools

• Fencing and Paddock Size:

  • Decreasing paddock size allows for better control over soil types and grazing pressure, but it is expensive to implement in low-input systems.

  • Rangelands often require a mix of soil types within one paddock (e.g., red soils for quick response, black soils for bulk during the main wet season) to buffer against environmental variability.

• Water Point Infrastructure:

  • Installing more watering points can spread utilization and prevent "over-utilization" patches without forcing animals to eat low-quality diet (preserving selectivity).

  • It is often necessary to sequentially turn water points on and off to force animals to move, though cattle may risk perishing beside a turned-off bore if not actively herded.

• Rotational Grazing Systems:

  • Philosophies like those from RCS (Resource Consulting Services) promote intensive rotation, but research (e.g., Douglas Daly region study in the Northern Territory) has partially debunked its benefits for rangelands.

  • Findings from Douglas Daly Study:

    • Intensive rotational grazing consistently resulted in lower per-head productivity because animals were forced to consume low-quality, non-preferred feed.

    • It resulted in a moderate loss of soil carbon compared to continuous grazing at LTCC.

  • The Soil Carbon Hypothesis: Australian soils are fragile and did not evolve with cloven-hoofed animals (unlike Africa with wildebeest). High-intensity hoof traffic disturbs the soil bio-crust and biology more than the system can handle.

• The Utility of "Rest":

  • In systems with infrequent, unpredictable rainfall, short rest periods during dry months are "useless" because no biomass accumulation occurs.

  • Intensive grazing pressure during a rotation is not offset by a rest period if that period lacks plant growth.

Wet Season Spelling: The Key Recovery Tool

• Wet season spelling is the most effective tool for rehabilitating rangelands.

• Mechanism: Animals are removed during the growing season to allow 3P grasses to reach the reproductive phase and set seed.

• Recovery Timeline:

  • Because plant density is low, recovery requires new perennials from seed, not just regrowth of existing leaf.

  • Improving land condition by one ABCD class typically requires two consecutive seasons of back-to-back wet season spelling.

• Long-term Impact:

  • Cycling "year on, year off" grazing and spelling can eventually lift a class C landscape to class A/B, but this requires decades of conservative management.

  • Continuous grazing at even moderate rates usually results in stagnant or declining percentages of 3P grasses.

Recommended Readings

• Ash and Stafford Smith: Detailed paper on stocking rates in rangeland systems.

• Chardat et al. (2015): Paper discussing Douglas Daly study results and rotational grazing.

• MLA Grazing Land Management Handbook: A comprehensive guide covering rangeland management and fire.

• Acker and Dickman Paper: Reference regarding sacrifice zones around water sources.