Water relations and growth of shrubs before and after fire in a semi-arid woodland

Abstract

Plant water relations and shoot growth rate of shrubs resprouting after fire or unburnt were measured in a semi-arid poplar box (Eucalyptus populnea) shrub woodland of eastern Australia. In vegetation unburnt for about 60 years, the dawn xylem water potential (ψ) of the dominant shrub species was about-1.0 MPa when the soil was wet and-8.0 MPa when the soil was very dry. At any one time, the dominant shrub species,Eremophila mitchellii, E. sturtii, Geijera parviflora andCassia nemophila, were similar in ψ butAcacia aneura andDodonaea viscosa were consistently higher in ψ than this group when the soil was moist and lower when the soil was dry. The dominant tree species,Eucalyptus populnea andE. intertexta, appeared to have access to additional water beneath the hardpan which is located 60-80 cm below the surface. When shrubs were under extreme water stress (ψ of-8 MPa), the trees had a ψ of-3 to-3.6 MPa. Following a fire, both ψ and leaf stomatal conductance (g ) of resprouting shrubs were higher for about 5 years than comparable-aged unburnt vegetation, with relative differences in ψ increasing with drought stress. Elongation rate of resprouts was positively linked to prefire shrub height in 3 of 4 species. However, shrubs resprouting after high intensity fires had substantially higher rates of shoot elongation than after low intensity fires which were in turn higher than for foliar expansion of unburnt shrubs. It is concluded that the growth rate of resprouting shrubs is primarily determined by physiological/ morphological factors associated with plant size but is also assisted by greater availability of water and possibly nutrients for a period after fire.

Investigating the vulnerability of an African savanna tree (Sclerocarya birrea ssp. caffra) to fire and herbivory

“…Marula stems within the fire trap are therefore extremely resilient to damage by fire. Hodgkinson (1992) found a higher resprouting response in eucalypts in Australia after a more intense fire, similar to marula in this study. A higher fire intensity could cause loss of apical dominance because of an increase in the damage to tissues, and thus result in a faster basal resprout response.…”

“…Marula stems thicker than 3.4 cm would be able to maintain their prefire height by resprouting epicormically (from the stem rather than the rootstock), and hence have an advantage over other species which would have to resprout basally. Even for stems that have to resprout basally after a fire, experimental evidence suggests that resprouts grow 3-40 times faster than an unburnt stem (Hodgkinson 1992). Indeed, topkilled marula stems less than 3.4 cm in basal diameter were able to regain their prefire height within one growing season.…”

Sprouting success of shrubs after fire: height-dependent relationships for different strategies

“…As plants grow and age, the size and extent of their root systems expand. The acquisition and loss of sprouting ability may therefore re¯ect a change in the ability of plants to supply nutrients and water to sprouts from erratic and spatially variable sources (Hodgkinson 1992;Tongway and Hodgkinson 1992).…”

Prospects for subsistence livelihood and environmental sustainability along the Kalahari Transect: The case of Matsheng in Botswana's Kalahari rangelands

“…within the Wildlife Management Areas), there is almost no interference from livestock, hence fire fuel loads can at regular times be very high depending on rainfall. The removal of fire in vegetation communities (as is the case at 4.0 and 18-km) that evolved with fire has mixed effects (Noble, 1989;Hodgkinson, 1991). For example, fire enhanced the germination of two of the seven principal shrub species in semi-arid shrub-invaded woodland in eastern Australia.…”