Pitting fails to sustain increases in ecosystem structure in arid rangelands

Mechanized approaches to the rehabilitation of degraded rangeland have been extremely popular since the early 1930s but their effectiveness depends on climatic and environmental conditions (e.g. soil texture, pre-treatment plant cover). We evaluated the effects of pitting, a popular rehabilitation technique based on the creation of elongated soil depressions (pits), on ecosystem structure from 14 trials conducted at 10 sites across an extensive area (similar to 100,000 km(2)) of rangelands in eastern Australia. Averaged across all sites and rehabilitation times, pitting had a significant positive effect on the cover of perennial forbs and annuals, and suppressed bare ground compared with untreated sites. However, these treatment effects varied with different site conditions such as soil texture, and pre-treatment rainfall and plant cover among individual sites. Pre-treatment plant cover, and rainfall in the 3 months prior to measurements increased the effects of pitting on litter cover, and time since treatment increased the relative effect of pitting on annual plant cover. Negative effect of pitting on the cover of bare soil declined with increasing rainfall. Soil moisture was generally greater beneath pits than either control soils or soils between the pits (inter-pits). Despite some positive effects on annual plant and litter cover, pitting effects were generally short lived, suggesting that a single pitting treatment may fail to achieve long-term rehabilitation. Given that these field trials were conducted half a century ago under conditions of higher average rainfall, the prognosis for the success of pitting under current conditions of lower rainfall and higher temperature is generally poor.