Mechanisms of competition: thermal inhibition of tree seedling growth by grass

Abstract

The relative importance of thermal interference and competition for below-ground resources in the inhibition of tree seedling growth by grass was determined under field conditions. Snow gum (Eucalyptus pauciflora) seedlings were grown in bare soil or soil covered with either live grass or straw. Covering soil with straw produced thermal conditions in soil and air that were indistinguishable from those associated with live grass. In contrast, seedlings grown in bare soil experienced more rapid increase in soil temperatures during late winter and spring, less frequent and less severe frosts, and temperature maxima that more closely followed those of the atmosphere than seedlings growing in live grass or straw. After 1 year, seedlings in bare soil had four times the biomass of those grown in grass or straw. Inhibition of seedling growth by grass was attributed to alteration of the thermal environment which caused (1) seedlings to have a short growing season largely restricted to summer, (2) temporal separation in competition for resources with consumption of below-ground resources by grass in spring reducing availability of resources to support tree seedling growth in early summer, and (3) seedlings to be more subject to stress from temperature extremes. These results show that thermal interference plays a major role in interactions between plants.

The role of below-ground competition during early stages of secondary succession: the case of 3-year-old Scots pine (Pinus sylvestris L.) seedlings in an abandoned grassland

“…This thermal effect may be more beneficial to seedlings grown in bare soil than in the grass vegetation treatment, but we did not observe aerial phenology delay between both treatments nor differences in growth in 2001. These findings contrast with those obtained by Ball et al (2002) who reported, in Eucalyptus pauciflora seedlings, stress from temperature extremes induced by grass vegetation. The importance of these cold temperatures in tree growth and development could be species-dependant (Dang and Cheng 2004) as we know that pines exhibit ecophysiological adaptations to minimise the effect of frost and cold temperature (Rundel and Yoder 1998).…”

“…In fertile grasslands characterised by a tall and dense grass canopy, competition for light is more conspicuous (Soussana and Lafarge 1998). Others have also suggested that extreme temperature fluctuations, aboveground and below-ground, induced by grass vegetation, may have or not dramatic consequences for seedlings survival and growth depending on the considered species and climate (Ball et al 1997(Ball et al , 2002Provendier and Balandier 2004). From these examples, we can conclude that in many cases exploitative grasses are probably unfavourable to tree establishment and growth, but the determinants need to be identified.…”

Scale-dependent relationships between the spatial distribution of a limiting resource and plant species diversity in an African grassland ecosystem

“…Plant cover alters microclimatic conditions in ways that can further influence nutrient availability (Ball et al 2002). It is well known that the experimental alteration of nutrient availability in a sward changes plant species composition and richness (Tilman 1984;Barnes et al 1987;Gough et al 2000).…”

Effects of management techniques on the establishment of eucalypt seedlings on farmland: a review

“…The only study that considered more than one species found similar responses (George and Brennan 2002). Ellis (1990) x Ellis et al (1985) x Chingaipe (1985) x Fagg (1988) x x x x Fagg (1988) x x x Postplanting weed control Ball et al (2002) x Dalton (1992) x x Fagg (1988) x x x Fagg (1988) x x x x Little and van den Berg (1999) x Soil cultivation Ellis (1990) x McKimm and Flinn (1979) x x Measki et al (1998) x Lacey et al (2001) x ? ?…”