Growth variability in a Senegalese provenance of Acacia nilotica ssp. tomentosa E. WOLDE-MESKEL 1, * and F. L. SINCLAIR 2 1 Department of Plant Production and Dryland Farming, Awassa College of Agriculture, P.O. Box 5, Awassa, Ethiopia; 2 School of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd, LL57 2UW, UK (*Author for correspondence: Agricultural University of Norway, Department of Biotechnology, P.O. Box 5040, 1432 Ås, Norway; E-mail: ikbewm@ikb.nlh.no) Key words: biomass, provenance, sample size, seed size Abstract. Growth variability and effect of seed size on growth of seedlings of Acacia nilotica ssp. tomentosa of a Senegalese provenance were studied in a greenhouse experiment. Seedlings were raised from a sample of 52 seeds with a seed weight range of 0.070 g to 0.258 g; and a range of growth variables were measured on seedlings harvested 11 weeks after planting. Based on the sample mean and variance, the sample size required to estimate the parameter (mean) of the growth variables was determined. Seedlings showed a large variability in growth. There were five-fold and three-fold differences between seedlings in leaf area and total dry weight, respec- tively. Seed weight has little effect on seedling growth. The number of replications required to estimate a parameter mean of the different growth variables, within ±20% margin of error at P = 0.05, ranged from nine to 24. The observed growth variability was indicated to be an important biological variable which could be used to improve growth and yield in A. nilotica. Introduction Less variability in seedling growth parameters is desirable for establishment of managed plantations and when conducting experiments. In experiments, fewer replications will be required; and experimental differences can be more easily related to treatment effects if inherent differences in seedling growth are less. Conversely, trees useful in agroforestry are often wild and undo- mesticated, exhibiting high variability. Large within and between provenance variation in seed and seedling growth have been observed in different agroforestry tree species (Salazar, 1986; Ernst, 1988 Ngulube, 1989; Sniezko and Stewart, 1989; Joly et al., 1992; Wanyancha et al., 1994). Contrary to the need for uniformity in intensively managed plantations, there may be advantages in maintaining variability in agroforestry, especially in semi-arid areas where there is large and uncontrollable variation in environmental conditions. The extant variability provides ample biological resources to improve agroforestry trees with respect to growth and yield, nitrogen fixation, or canopy structure. Little experimental work has been done on wild species, such as A. nilotica, utilised in traditional agroforestry systems. It is desirable, therefore, to know the variability in growth so as to indicate their potential for future improve- Agroforestry Systems 48: 207–213, 2000.  2000 Kluwer Academic Publishers. Printed in the Netherlands.