Using morphological characteristics for assessing seedling vitality in small-scale tree nurseries in Kenya

摘要

Small-scale tree nurseries are important in fulfilling the goals of reforestation and agroforestry implementation schemes in Kenya and other developing countries. The focus in seedling production has been on quantity, instead of quality, but a change can be seen in recent tree nursery manuals. These manuals are emphasising morphological characteristics as tools for assessing potential field performance of seedlings. However, morphological criteria are debatable and their value is questioned. A survey was carried out among tree nursery operators in the Meru area, in the Eastern province of Kenya, to determine how operators perceived seedling vitality, and how they separated acceptable seedlings from those of poor vitality. Based on the survey, 3 pairs of criteria were chosen, size (tall versus small), colour (green versus yellowish), and sturdiness quotient (sturdy versus lanky). These criteria were tested on survival and growth in a field trial, a controlled bench trial, and in a root growth potential test. The results showed that the nursery operators were aware of quality differences in seedlings, but they did not cull accordingly. The results from the field trial showed that mango (Mangifera indica L.) performed poorly compared to grevillea (Grevillea robusta A. Cunn. ex. R. Br.), probably due to the high altitude. The altitudinal range for mango and grevillea are 0-1,200 m and 0-2,300 m, respectively, and the trial site was located on an altitude of 1,725 m. In grevillea, small seedlings grew better than tall in the field trial, but no differences could be found in the other trials. In mango, sturdy seedlings grew better than lanky ones in the field trial, while in the controlled trials tall seedlings grew better than small ones. The results showed that morphological characteristics as seedling quality assessment criteria could be unreliable as the effect differs with species and planting site.