Effect of tree density on competition between Leucaena leucocephala and Chloris gayana using a Nelder Wheel trial. I. Aboveground interactions

Abstract

Silvopastoral systems with the tree legume leucaena (Leucaena leucocephala (Lam.) de Wit) and grass pastures are widely used for ruminant feeding in subtropical and tropical regions. Different densities and planting configurations of leucaena will influence relative yields of both species because of intra- and interspecific competition. With the aim to describe the effects of competition between leucaena and Rhodes grass (Chloris gayana Kunth), a Nelder Wheel trial with 10 different leucaena tree densities (100–80 000 trees ha–1) growing with and without Rhodes grass was established in a subtropical environment at Gatton, south-east Queensland, in November 2013. From 2014 to 2016, the biomass of leucaena (six harvests) and Rhodes grass (seven harvests) was measured by using allometric equations and the BOTANAL sampling procedure over 742 and 721 days, respectively. No complementary or facilitative aboveground interactions were observed between the leucaena and Rhodes grass components of the pasture system. Increasing leucaena tree density resulted in greater aboveground intra- and interspecific competition. Average maximum individual tree yield (38.9 kg DM tree–1 year–1) was reached at 100 trees ha–1 without grass competition and was reduced by 60% with grass competition. Rhodes grass biomass yield was negatively affected by shading from the leucaena canopy, with negligible grass yield at tree densities ≥8618 trees ha–1. Therefore, there was effectively no grass competition on individual tree yield at higher leucaena densities. Accordingly, edible leucaena biomass per unit area was positively related to log10 leucaena density (R2 = 0.99) regardless of grass competition, reaching 21.7 t DM ha–1 year–1 (2014–15) and 27 t DM ha–1 year–1 (2015–16) at the highest leucaena density of 80 000 trees ha–1. By contrast, the yield of Rhodes grass was linearly and inversely correlated with log10 tree density (R2 = 0.99). Practical implications for the design and management of commercial leucaena–grass pastures are discussed.

Silvopastoral systems improve carbon stocks at livestock ranches in Tabasco, Mexico

“…The physiology of grass production seems to be inversely related to litter, tree abundance and coverage (Table 4). This is attributed to the crown size and, particularly, the high density of trees, and coincides with that reported by Yépez et al (2018) and Pachas et al (2018) who demonstrated that the level of intensity of the shade caused by the trees is one of the main factors that affect the production of grasses. However, when total biomass production (living tree biomass growth + litterfall + grass production) was compared between the two livestock systems evaluated, carbon input in STP was higher than in GM.…”

Initial spacing of teak (Tectona grandis) in northern Lao PDR: Impacts on the growth of teak and companion crops

“…wider spacing) had larger diameter compared to those grown at the higher initial stocking rates, a trend that starting after the fourth year of growth. The experiment confirmed that the diameter of teak is adversely affected by high stocking rates, in common with other tree species, as a result of increasing competition for light and water and to a lesser extent nutrients (Cameron et al, 1989;Eastham and Rose, 1990;Lamb and Borschmann, 1998;Kuehne et al, 2013;Pachas et al, 2018). There is relatively little information in the published literature about the diameter response of Tectona grandis grown at initial stocking rates of 600 trees ha −1 and lower, with most studies established at initial stockings of 833 to -2,000 trees ha −1 (Ola-Adams, 1990; Kanninen et al, 2004;Passos et al, 2006, Zahabu et al, 2015Noda and Himmapan, 2014).…”

A method for assessing sustainability, with beef production as an example

“…Semi‐intensive silvopastoral systems are used in thousands of farms in Colombia, Mexico and Brazil, and increasingly in Argentina, Australia and other countries. Some are in temperate regions or at altitude in subtropical countries (Peri, Dube & Varella, 2016; Pachas et al ., 2018; Radrizzani et al ., 2019). The term ‘intensive silvopastoral’ is not used here as the system is not intensive farming per se ; the term ‘semi‐intensive’ reflects the higher density of animals than in pasture‐only systems.…”