Long-term growth performance of Cordia africana and Grevillea robusta trees in the Mount Kenya region

Abstract

This study examined the long-term growth performance of Cordia africana and Grevillea robusta, which are the most common indigenous and exotic trees, respectively, associated with crops in the Mount Kenya region. Local farmers prefer G. robusta to C. africana as on-farm trees because they believe that G. robusta grows faster. Measurements of height and diameter at breast height were made of 47 C. africana and 89 G. robusta trees for which the age was established based on interviews with farmers. The oldest G. robusta and C. africana trees were 55 and 46 years old, respectively. The apical growth rate for G. robusta was greater than that for C. africana in Katheri (a humid area). The differences between the two species were less remarkable in Ruiri (a dry-subhumid area). There was no notable difference in the radial growth performance of the two species in Katheri and Ruiri. These comparisons suggest that the longterm growth performance of C. africana is not necessarily inferior to that of G. robusta.

Promoting native trees in shade coffee plantations of southern India: comparison of growth rates with the exotic Grevillea robusta

“…However, in Rwanda, G. robusta diameter growth rates were higher, ranging from 0.9 to 3.4 cm yr -1 in monoculture plantations and from 1.1 to 3.7 cm yr -1 in multispecies farms (Kalinganire 1996). Another study in Africa also calculated higher growth rates of 2.15-2.64 cm yr -1 for juvenile G. robusta stems in multispecies farms (Takaoka 2008).…”

“…Similar studies have been carried out elsewhere with the aim of recommending native species for afforestation and agroforestry (Jama et al 1989;Okorio et al 1994;Dhyani and Tripathi 1999;Yamada and Gholz 2002;McDonald et al 2003;Takaoka 2008;Park et al 2010). However, whereas most previous comparisons used sapling cohort growth trials, we studied growth in established standing trees with a large range of diameters.…”

“…(family Proteaceae, commonly known as ''silver oak''), was the most dominant species in coffee plantations of Kodagu, constituting 20% of all trees censused (unpublished data). The most commonly cited advantages of using G. robusta in agroforestry plantations worldwide are its fast growth rate and minimal competitiveness with crops (Harwood 1989;Jama et al 1989;Okorio et al 1994;Kalinganire 1996;Baggio et al 1997;Lott et al 2000a;Takaoka 2008; but see Lott et al 2000b regarding competition with crops). In Kodagu, there are additional incentives to plant G. robusta, such as the absence of administrative constraints on marketing its timber and easy availability of saplings.…”

Why do farmers plant more exotic than native trees? A case study from the Western Ghats, India

“…In some countries, the introduction of fast growing exotic species has been promoted by governmentsupported agricultural extension workers who expect exotic species to be more efficient than native species in improving farm productivity and reducing poverty (Dunn, 1991;Dewees, 1995;Schneider et al, 2014). In addition, the exotic tree species themselves often possess (or may be perceived to possess) more useful attributes than native species, such as faster growth rates, higher economic value, fewer pests, and reduced competition with the main crop (Kalinganire, 1996;Tavares et al, 1999;Lott et al, 2000;Takaoka, 2008b;Anglaaere et al, 2011;Tefera et al, 2014). Finally, the local legal frameworks may also play a role in promoting exotic species by withholding farmers' rights of ownership over native trees, thus making the latter trees less attractive to propagate for the future (Van Noordwijk et al, 2003;Ruf, 2011;Schroth et al, 2011).…”

A Comparison of the Utility and Agronomic Traits of Indigenous and Exotic Trees in the Mount Kenya Region

“…The lower growth performance and relative difficulty of establishment of C. africana, as compared to G. robusta, can be compensated for by its higher timber quality and greater ability to produce stump sprouts. In fact, the long-term growth performance of C. africana is not necessarily inferior to that of G. robusta even though farmers believe that G. robusta grows faster (Takaoka 2008). Further studies are needed to obtain a comprehensive understanding of the long-term contributions of indigenous species to farmers.…”