Growth of second rotation Pinus patula stands: effect of intercropping with Leucaena diversiforlia legume at Shume Forest Plantations Project, Tanzania.

Abstract

This study was carried out to investigate the effect of Leucaena diversifolia on the growth of second rotation Pinus patula stands as one of the options for increasing growth and yield. The trial was conducted at Shume Forest Plantations Project, Lushoto, Tanga, Tanzania. Site preparation was done through clearing of the harvested first rotation stands, burning of the logging slash, followed by complete cultivation. Nursery raised potted seedlings of the Pinus patula were planted in 1997 at a spacing of 3 m × 3 m within each plot, while those of Leucaena diversifolia were interplanted in alternating rows in 1998, followed by complete weeding twice a year. A Completely Randomized Block Design (CRBD) with three replications was adapted. Total tree height and diameter at breast height (dbh) were measured in 1999, 2000, 2001 and 2002 and analyzed for growth. Within the limits of the present study, the results on the cumulative growth performance of the second rotation pine plantations in their pure stands were, generally superior to those recorded in the mixtures with Leucaena trees - mainly resulting from the underground competition for limited nutrient resources. The mean cumulative heights were 3.67, 4.82, 5.58 and 7.77 m in pure stands and 3.64, 4.71, 5.55 and 7.60 m in the mixtures while the corresponding diameters were 4.74, 6.95, 9.78, 12.39 cm and 4.65, 6.69, 8.64, 11.41 cm for the 1st, 2nd, 3rd and 4th years of assessment respectively. The corresponding 1st, 2nd and 3rd annual height increments were 1.15, 0.76, 2.19 m and 1.07, 0.84, 2.05 m with annual diameter increments being 2.21, 2.83, 2.61 cm and 2.04, 1.95, 2.77 cm respectively. Although, within the time limits of the present study, the anticipated beneficial effects of the Leucaena legumes in promoting the growth of none leguminous plantation trees were not indicated in terms of cumulative growth, they were clearly manifested in the fourth year of annual increment trends. These results should, therefore, be treated as preliminary and an extended monitoring protocol is recommended to give room for the observed emergence of favorable effects, through the annual increment trends, to translate into positive cumulative growth expected to manifest within the first half of the pine\'s 25-30 years rotation age.

TJFNC Vol. 76 2007: pp. 110-117