Application. Clones of Eucalyptus grandis and E. grandis hybrids were naturally subjected to temperatures down to -6°C for 18 h in Florida. Locally adapted trees may be intensively screened to develop frost resilient candidates. Ortets must be further tested for vigor and frost resilience. Major commitments are needed to obtain satisfactory numbers of clones for operational use.Abstract. Eucalyptus grandis, E. grandis hybrid, and E. saligna hybrid trees, developed through as many as four generations of selection in southern Florida, were naturally exposed to exceptionally low winter temperatures. In a genetic base population and related field studies, 100 phenotypically superior cloning candidates were selected after an 8-h freeze with a low of -11 °C. Following propagation as rooted cuttings, 55 clones (typically 11-42 ramets per clone) were outplanted in a single-tree plot design and evaluated for 3.8 years which included two additional severe freezes. Significant clonal variation was observed in frost resilience, vigor, and quality. After composite evaluation for frost resilience, size, and form, only three clones were considered suitable for operational planting. Selection of further clones for outplanting requires major commitments to locate candidates and to test them. Field testing for frost resilience requires considerable investment, much beyond the requirements for developing fast-growing clones alone. Clones identified by testing will not be resistant to freezing conditions but will be resilient and greatly reduce the risks now associated with plantation culture in southern Florida.
The volume in merchantable trees (4 inches d.b.h. and larger) was about the same at spacings of 4 x 8, 8 x 8, 12 x 8, and 16 x 8 feet for Eucalyptus grandis trees at plantation age 7.4 years in Glades County, Florida. Total volume in all stems, however, was 1.7 times greater at the closest spacing than at the two widest spacings. Thus, in a conventional pulpwood system, merchantable yields equal to those from closer spacings could be obtained from the wider spacings at lower cost for establishment and harvest. However, if merchantability limits could be circumvented by field chipping small trees, volume yields 16 to 68 percent greater could be achieved by planting at close spacings. Neither wood quality nor tree height was appreciably affected by stand density over the range of spacings tested. If the harvesting system is unknown at planting time, a spacing of about 6 x 12 feet is probably best.
SYNOPSISAn international provenance trial of Eucalyptus grandis was established in southern Florida in 1980 and measured for growth and frost-tolerance through 8,8 years. The trial compared 20 Australian provenances 1) among themselves and 2) with seed orchard stock from Florida and South Africa. Florida orchard seedlots grew better than nearly all other material, including a South African clonal seed orchard bulklot. Provenance variability was significant for growth, survival. and frost-tolerance. with some provenances notably more frost-tolerant than provenances previously introduced into the Florida breeding population. Only the Herberton provenance was comparable to advanced-generation Florida seedlots in all critical traits. Importation of some provenances from the northern part of the species range may be warranted to broaden the genetic base of E. grandis in Florida. Further comparisons in a supplemental study and a Florida genetic base population also noted variation between relatively close provenances and provenances by site interaction for growth characteristics. Provenances superior as early as age one year in the field were usually best at 8,8 years, but the tallest seedlings in the nursery did not maintain superiority in the field. Soil types influenced growth significantly, and provenance x soil type interactions were common. Single-tree plots evaluated provenances much more efficiently than block plots.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.