Development of a seedling quality control method in forest nurseries: a cypress (Cupressus lusitanica) case study

Abstract

In forest nurseries for tropical hardwood tree species there are no criteria or reference values for quality control procedures, nor proper sampling quality control procedure. A random sampling procedure using cypress (Cupressus lusitanica) seedling beds as strata was utilized. The sampling unit consisted in 28 seedlings where 11 quantitative and qualitative variables per seedling were registered. A 6% sampling intensity for production beds with 2000 seedlings is proposed, for a target sampling error below 5%. Sampling procedures registered 1.87% seedlings with forking problems, 0.51% with apical shoot damage, 2.21% with crocked stem, 15% in suppressed sociological position, 0.68% with mechanical damages, 0.51% with severe phytosanitary problems, 13.5% with low-quality roots, and 3.92% under quality 3 or rejection category. Roots registered a length growth of 1.39 cm week-1, 1.14 mm week-1 at neck-diameter and 1.3 cm week-1 for total height. The mortality rate was stabilized between the 12th and 15th week after transplanting and reached near 25%. Genetic (hereditary) and silviculture as possible causes of the cypress seedling quality in nurseries are discussed. In a quality index on a 1-3 scale (1 for best or ideal seedling), a general quality value of 1.59 was determined. Production beds with seedlings quality 1+2 <85%, height variation coefficients >15%, >10% suppressed seedlings, >15% severely diseased seedlings and mortality rates >10%, should be considered as rejection criteria and indicators for production units in cypress nurseries.