Mixed-species plantations of Eucalyptus with nitrogen-fixing trees: A review

Abstract

Mixed-species plantations of Eucalyptus with a nitrogen (N 2 ) fixing species have the potential to increase productivity while maintaining soil fertility, compared to Eucalyptus monocultures. However, it is difficult to predict combinations of species and sites that will lead to these benefits. We review the processes and interactions occurring in mixed plantations, and the influence of species or site attributes, to aid the selection of successful combinations of species and sites. Successful mixtures, where productivity is increased over that of monocultures, have often developed stratified canopies, such that the less shade-tolerant species overtops the more shade-tolerant species. Successful mixtures also have significantly higher rates of N and P cycling than Eucalyptus monocultures. It is therefore important to select N 2 -fixing species with readily decomposable litter and high rates of nutrient cycling, as well as high rates of N 2 -fixation. While the dynamics of N 2 -fixation in tree stands are not well understood, it appears as though eucalypts can benefit from fixed N as early as the first or second year following plantation establishment. A meta-analysis of 18 published studies revealed several trials in which mixtures were significantly (P < 0.001) more productive than monocultures, and no instances in which mixtures were less productive than monocultures. Regression analyses of such data were more informative than indices of relative yield, and were more informative in trials that contrasted four or more different species compositions. Thus replacement series examining compositions of 100:0, 67:33, 33:67, and 0:100 were more informative than minimalist 100:0, 50:50 and 0:100 series. #

Soil carbon and nitrogen in pasture soil reforested with eucalyptus and guachapele

“…The tolerance of eucalyptus to soil acidity and high Al contents, its adaptability to low soil fertility, and the ability to absorb N from different sources (Neves et al, 1990;Grespan et al, 1998) suggest that the use of this species in mixed plantations with N 2 -fixing leguminous trees could improve soil fertility and contribute to a more sustainable land use. Recent studies showed that intercropping eucalyptus with tree legumes was not detrimental to timber yield and resulted in increased soil N availability for eucalyptus (Binkley et al, 1992;Forrester et al, 2006). These results suggest that the implementation of such mixed forests may result in significant economical and ecological advantages due to the N input through biological nitrogen fixation (Forrester et al, 2006).…”

“…Recent studies showed that intercropping eucalyptus with tree legumes was not detrimental to timber yield and resulted in increased soil N availability for eucalyptus (Binkley et al, 1992;Forrester et al, 2006). These results suggest that the implementation of such mixed forests may result in significant economical and ecological advantages due to the N input through biological nitrogen fixation (Forrester et al, 2006).…”

“…This land use calls for new management techniques that would lessen impacts on biodiversity and processes of soil fertility exhaustion (Novais & Barros, 1997;Paschoal, 2005;Forrester et al, 2006). The tolerance of eucalyptus to soil acidity and high Al contents, its adaptability to low soil fertility, and the ability to absorb N from different sources (Neves et al, 1990;Grespan et al, 1998) suggest that the use of this species in mixed plantations with N 2 -fixing leguminous trees could improve soil fertility and contribute to a more sustainable land use.…”

“…Since eucalyptus litter degrades very slowly, it seems to contribute little to SOM replenishment (Resh et al, 2002). However, the lower C/N ratio of the legume combined with eucalyptus litter results in a material with a higher turnover rate that could influence eucalyptus production (Balieiro et al, 2004;Forrester et al, 2006) and SOM contents (Resh et al, 2002;Resende et al, 2006) positively.…”

Species-site matching in mixed species plantations of native trees in tropical Australia

“…Size-asymmetric competition appears as the dominant structuring factor in both monoculture and mixed species plantations (Potvin and Dutilleul 2009) and only when these competitive effects are minimised, by matching species with compatible height growth and shade tolerances, can the positive interactions of facilitation and complementarity drive mixtures to out-yield monocultures (Forrester et al 2006). Competition for light is often asymmetrical between species, especially in mixtures that include rainforest trees with different shade tolerances .…”