Radial permeability of the hybrid pine (Pinus elliottii × Pinus caribaea) in Australia

The radial permeability (gas and liquid) of the hybrid pine (Pinus elliottii var. elliottii [PEE] × Pinus caribaea var. hondurensis [PCH]) was investigated for wood samples collected from 30 trees that were 19 years of age and represented various genotypes and stocking rates. The PEE × PCH hybrid is now a very important resource for the Australian forestry industry, producing logs used to manufacture a diverse array of wood products. The permeability of wood influences many important wood properties and industrial processes. For all data combined from all radial sampling positions, there was no significant effect of genotype and stocking rate on radial permeability. Both gas and liquid permeability increased from pith to bark positions within the tree. Conversely, resin content decreased from pith to bark positions. Gas and liquid permeability were significantly positively correlated, and a highly significant negative relationship was also found between permeability (gas and liquid) and resin content.

Comparison of biomass partitioning and transpiration for water-stressed shortleaf, loblolly, and shortleaf × loblolly pine hybrid seedlings

Hybridization between shortleaf pine (Pinus echinata Mill.) and loblolly pine (Pinus taeda L.) has dramatically increased and may threaten the genetic integrity of shortleaf pine. Shortleaf pine is presumed to be more drought tolerant than loblolly pine, but the drought hardiness of the hybrid pine is not known. We determined biomass partitioning in response to water stress and measured whole-plant transpiration of shortleaf, loblolly, and hybrid pine seedlings. Water stress decreased total seedling biomass, increased biomass partitioning to foliage, and decreased biomass partitioning to coarse roots. Shortleaf pine seedlings partitioned more biomass to coarse roots than loblolly pine, and hybrid pine was intermediate between the parent species. We found no differences in the level of soil moisture at which seedlings of different species began to limit transpiration. Our results suggest that the transpiration response of shortleaf pine and hybrid pine is similar to that of loblolly pine when exposed to water stress. However, greater partitioning to coarse root may allow shortleaf and hybrid pines to better withstand drought due to greater potential belowground carbohydrate supply.

Impact of future climate change on a genetic plantation of hybrid pine

European black pine (Pinus nigra Arnold) and Japanese red pine (Pinus densiflora Siebold & Zucc.) are nonnative conifers that have been introduced into the United States and have the ability to hybridize with each other and can potentially become an invasive threat. Interspecific hybridization is an important component of applied genetic tree improvement programs. This study retrospectively examined the influence of climate on interannual growth patterns of 12 full-sib families of hybrid pine that were derived from the hybridization of European black pine and Japanese red pine. The hybrids (Pinus nigra × Pinus densiflora) were initially planted in 1982 in southern mid-Michigan at Michigan State University (MSU) Sandhill Research Area. Tree-ring analysis methods (dendrochronology) were used to quantify the influence of climate (i.e., mean temperature and moisture index) on interannual basal area growth rates of the hybrid pine over an 18 year period (1991–2008). The productivity of the 12 full-sib families of hybrid pine were also projected under future climate change in the 21st century based on the IPCC A1B emission scenario. Climatic sensitivities that were identified in the hybrid pine families included high temperature stress in the summer and fall, moisture stress in the summer, winter harshness, and the timing of the start of the growing season. According to projections, by the end of the 21st century, 8 out of the 12 pine families will show significant decreases in growth outside of the historical norm under the temperature-based dendrochronology models, while 4 families will show significant declines under the moisture index models. The results indicate that the hybrid pine families appear to be generally resilient to future changes in moisture, but will likely be extremely vulnerable to future climatic warming, and thus do not appear to be a future invasive threat. This study represents the first dendrochronological examination of hybrid pine in North America.