Land Care

Birdwood Downs is located in the coastal ecosystem of the Kimberley region in the semi arid
tropical pseudo monsoonal climatic region of North Western Australia. Due to the region’s severe environmental conditions, and a history of poor pastoral practices such as overgrazing with sheep and cattle, coupled with over burning has lead to widespread desertification, land degradation and marginal economics.

The climate has some extremes. Temperature ranges from 4 degrees centigrade at night during the April to August cool dry season to 47 degrees during the day during the September to November hot dry season. The high humidity of the wet season of December to March moderates these extremes to in the thirties.

Rainfall patterns are highly erratic both in quantity and frequency, with an average precipitation
of 625 mm which falls between December and April. Rainfall extremes range between 100 mm and 1500 mm per year. This rain can come in flooding downpours followed by weeks of dry, or in some low rainfall years fall in such small amounts that its effectiveness falling onto non wetting soils is vastly reduced. Evaporation rates can be higher than the annual precipitation. Winds particularly in the hot dry season before the wet, whipping up denuded soils, prepare the scene for the rains. These rains, often torrential, are driven by cyclonic winds during the wet season to scour and erode. Winds fan frequent and extensive hot fires. When fires come too frequent it further reduces the species diversity which contributes to degradation of vegetation and soils.

Birdwood Downs is situated on a series of stabilized sand dune ridges roughly a kilometer apart with sandy loam in the valleys on the ecotone with the coastal marsh. In the areas bordering the marsh in the transition zones yellow clays and silts predominate in the valleys between the dunes. These old weathered tropical soils are extremely low in macronutrients such as phosphorus and nitrogen, and micronutrients. A high level of iron and aluminum in the soils ensure that what phosphorus is in the soil is bound to the iron and unavailable for uptake by the plants. Due to the overgrazing, vast areas have been overrun by secondary succession and increaser species- Acacia scrub and annual grasses such as Spear grass (Heteropogan contortus). This pindan wattle country which covers almost half of the Kimberley region is considered of the lowest potential for development. The carrying capacity of such pindan was amongst the lowest of any land types in the Kimberley, especially since Birdwood Downs includes no river country or billabongs.

After the initial mechanical clearing of the invasive woody weed invasion, around half the property has been planted with improved grasses and legumes to restore productivity. Around four hundred acres are kept free from re-invasion by Acacia wattle through manual uprooting. This “wattle chopping” pasture maintenance while ongoing also provides first hand opportunity to observe at close quarters the changes in the ecology, the interface of soil and root systems and vegetative, insect and animal relationships, while being a more ecologically-friendly means of control compared to the use of herbicides. Over the years, Birdwood Downs has demonstrated that as the improved pasture spreads and the native vegetation recovers from the overgrazing and compaction, fewer man-hours are needed to keep invasive weeds under control.

The half of the property which was not originally cleared of invasive wattle nor directly seeded benefits from the spread of the better pasture species through ecological management of horses and cattle. They are the “weeders and seeders” – keeping undesirable species from seeding and spreading valuable species through their rotation. To make this possible Birdwood Downs invested in creating smaller paddocks and laneways to make the frequent moving of livestock easier. A control paddock is kept fenced and ungrazed as a long-term control to the other land uses at Birdwood Downs, so the impacts of pasture improvement and livestock can be gauged.

In the course of this environmental experimentation, methods of minimizing soil erosion and regeneration techniques appropriate to the challenging conditions of the Kimberley region have been developed.

Our major challenges were to keep invasive woody weeds from regrowing and overtaking the improved pasture. Deciding against the use of broad-scale herbicides as expensive and dangerous for people and the environment, we followed initial bulldozer and tractor chain clearing and stick-raking/burning of windrows, with hand removal using adzes. “Wattle chopping” at first seemed an almost impossible task since Acacia seeds can number 20,000 per hectare, and have a long life (20-25 year viability) till their hard seeds are activated by bushfire. With time, we began to beat the seed-bank to a stage where most of the 400 hectares of prime improved pasture at Birdwood Downs is kept under wattle control with just 0.5-1 hour labour per hectare. Pastures are “wattle-chopped” either once or twice per year depending on labour availability on the station. In the process, staff get a ground-truth view of the health of the pastures and other invasive species such as South Australian mint, Sida acuta, and Calytrix.

The improved pasture developed at Birdwood Downs increases sustainable stocking capacity over ten times that of native pasture in the Kimberleys, which leads to abundant production of cattle fodder. Cattle are also used for selective grazing to assist seed production and for pasture upgrade, and to serve as a demonstration of the increased weight gains possible with developed savannah pasture.