The effects of fire on the soil in a degraded semiarid woodland .I. Cryptogam cover and physical and micromorphological properties

Abstract

The effects of fire on the cryptogam cover and physical and micromorphological properties of a massive red earth soil were studied in a semi-arid eucalypt woodland, heavily invaded by shrubs, near Coolabah, N.S.W. Fire reduced the cryptogam cover and concomitantly increased the depositional material produced by erosion and the area of bare surface. Annual fires for 7 years completely destroyed the cryptogamic crusts, but they recovered slowly in the absence of fire to reach the same cover as unburnt areas after about 4 years. A single fire also caused a major decline in aggregate stability of the 0-1 cm horizon, possibly because of alteration of organic cementing materials which consist of gels secreted by algae. Micromorphological observations of surface crusts showed that, as the frequency of fire increased, there was more depositional material produced by erosion coupled with the presence of thin laminated deposits. There was also less surface irregularity, fewer algal gels and less evidence of soil mixing by soil fauna. There was a significant negative relationship between the saturated infiltration rate and the number of fires (r2 = 0.63, P = 0.05). However, there was no effect of fire treatment on the unsaturated infiltration rate measured at a supply pressure of -40 mm, at which pores >0.75 mm diameter are excluded from water flow. In our burned plots, the rate of recolonization by cryptogams was relatively fast and, with approximately 4 years recovery, cryptogam cover reached the level of unburned controls. This cryptogam cover is critical in maintaining the physical properties of the soil. It is concluded, therefore, that irregular fires in this land system will not result in a permanent decline in the physical properties of the soil.

Microbiotic soil crusts - a review of their roles in soil and ecological processes in the rangelands of Australia

“…There are many accounts in the literature of reduced water erosion due to microbiotic crusts (e.g. Mucher et al 1988;Campbell et al 1989;Chartres and Mucher 1989;Kinnell et al 1990;Greene et al 1990;Eldridge 1993a;Eldridge and Greene 1994). In the semi-arid woodlands of eastern Australia, microbiotic crusts have been found to be quite effective at reducing sediment loss from red earth soils.…”

“…They are reputed to play a major role in ecosystem functioning, landscape and soil stability (West 1990), and in processes such as nitrogen fixation (Rogers et al 1966), biomass production (Isichei 1990), and the regulation of infiltration in localized areas (Eldridge l993b). Microbiota are known to be susceptible to fire (Greene et al 1990), and trampling by livestock Lange 1971, Andrew andLange 1986a) and are poorly developed on areas which are frequently cultivated (West 1990). An understanding of their role in ecosystem functioning and how they are affected by management is desirable if ecologically sustainable development in the rangelands is to be achieved.…”

Bromus tectorum litter alters photosynthetic characteristics of biological soil crusts from a semiarid shrubland

“…Moreover, an increased fire return period from about once per century to once every four to five years induces positive feedback processes on B. tectorum and ultimately destabilization of shrubland structure by removing shrubs and other native vegetation (Brooks et al, 2004). Similarly, fires damage the crust biota and frequent fires may prevent biocrust reestablishment to pre-disturbance levels (Greene et al, 1989;Johansen, 2003;Hilty et al, 2004). Given the negative effects of B. tectorum litter on sagebrush communities, the development of practices that prevent its accumulation seems crucial to the maintenance and restoration of these communities.…”

A Field Guide to Biological Soil Crusts of Western U.S. DrylandsA Field Guide to Biological Soil Crusts of Western U.S. Drylands

“…Lichen-dominated crusts in Utah showed decreased hydraulic conductivity (Loope and Gifford 1972). Lichen and algal crusts in Australia were associated with high conductivity (Greene et al 1990). Three-year-old algal crusts in Utah and non-disturbed crusts in Nevada showed no discernible influence on conductivity (Williams 1993;Dobrowolski 1994 …”

“…3.3). In hot deserts, disturbance to smooth and rugose lichen-or cyanobacterial-crusted surfaces can increase overall infiltration rates (Greene et al 1990;Eldridge et al 2000). However, this increase in infiltration may negatively affect nearby vascular plants that depend on interspace runoff for survival (see Section 3.6).…”