There is a wide range of literature on failure of tropical trees in forming clearly visible annual growth rings especially where there is extended rainy season. Most southern parts of Ethiopia have bimodal rainfall with varying degrees of distinction between rainy seasons. We targeted to check growth periodicity of trees in such climate. We used Cupressus lusitanica which is the second most important plantation species in Ethiopia and has not been targeted by many dendrochronological studies so far. We evaluated if its growth rings are annual and dependence of its growth on temperature and precipitation seasonality. We hypothesized as the Cupressus lusitanica trees form clearly visible annual growth rings even if the study area has two not clearly distinct rainy seasons with a short dry season between them and their widths are proportional to the amount of rainfall received. This study is aimed at evaluating the relationship between the annual growth of Cupressus lusitanica and the various regimes of temperature and precipitation at Wondo Genet. Twelve trees were sampled by simple random sampling and one disc from each tree was collected at stump height and its rings were identified, marked, widths measured, cross-dated and chronology of 30 radiuses was developed. The association with climate was investigated over the 30 years long available meteorological records from Wondo Genet. Cross-dating ensured that the trees were absolutely dated and that the growth rings were annual. The standardized ring-width index was significantly correlated ( r = 0.59; p < 0.05) with the amount of precipitation and poor correlation with the temperature at Wondo Genet. Even though the distribution of precipitation was not clearly unimodal, this study demonstrates that exotic species growing in far from optimal dendrochronological conditions still have the potential for dendrochronological studies by forming clearly visible annual growth rings with satisfactory response to climate variability.

Keywords: Tropical dendrochronology; Climate-growth relationship; Annual rings of conifer; Rainy seasons; short dry season.