Abstract
A plus-tree progeny test of full- and half-sib “superior” loblolly pine (Pinus taeda) was installed in 1969 on the Crossett Experimental Forest (CEF) to consider the performance of 28 improved families with unimproved planting stock from the CEF (family W29). Performance was evaluated using data from young (3-year-old; early 1970s), maturing (25-year-old; 1994), and mature (48-year-old; 2017) trees. With the exception of a single improved family, early survival was high (>80%), with most families exceeding 90%. Three years post-planting, fusiform rust infection rates were also low, with most families having less than 1% of seedlings infected. At this early stage, the unimproved CEF family W29 only slightly underperformed the best full- and half-sib superior families. By 1994, W29 had slightly higher than average merchantable volume. This trend continued for W29 when remeasured in 2017, with the average merchantable volume yield for W29 statistically similar to the most productive families. This study found only limited volume performance gains from crossing plus-trees. However, it was important to note that several of the best height growth-performing families in 1972 were not the highest merchantable volume producers at 25 or 48 years, and some of the worst early performers moved into the upper tiers by the later remeasurements. These outcomes suggest that depending solely on early height performance to select families for long-term (>50 year) volume (especially if adjusted for wood density) or biomass yields may not be the best approach for forest managers seeking to increase carbon sequestration.
Highlights
Forest genetics and tree improvement programs have greatly benefited forestry in the southern United States (Borders and Bailey, 2001; Allen et al, 2005; White et al, 2014; Wheeler et al, 2015)
Further study of loblolly pine has led to new approaches to the propagation of certain preferred traits using somatic embryogenesis (Gupta and Durzan, 1987), genomic selection (e.g., Resende et al, 2012; Isik, 2014), and new analysis approaches based on mate selection algorithms derived from other breeding programs (Isik and McKeand, 2019)
While best known for silviculture of naturally regenerated southern pine, tree improvement and forest genetics studies were conducted on the Crossett Experimental Forest (CEF) from 1951 until 1975 (Bragg et al, 2016)
Summary
Forest genetics and tree improvement programs have greatly benefited forestry in the southern United States (Borders and Bailey, 2001; Allen et al, 2005; White et al, 2014; Wheeler et al, 2015). Driven by the desire to increase productivity, disease resistance, seedling survival, and shorten harvest rotations, decades of increasingly sophisticated efforts have resulted in extensive plantations of improved loblolly pine (Pinus taeda), helping the South to become the most productive timber region in the world (Allen et al, 2005). By identifying rust-resistant loblolly pine families and selectively breeding them, tree improvement efforts greatly decreased the occurrence and economic impact of fusiform rust The recent sequencing of the loblolly genome (Zimin et al, 2014) offers promise for additional gains. These successes do not mean that there have not been failures, or at least undesired outcomes. Even the successful deployment of improved, shortrotation southern pine plantations has come with significant and often negative social and environmental consequences following the widespread conversion of natural-origin pine, pinehardwood, and hardwood forests (Wear and Greis, 2002, 2013; McGrath et al, 2004)
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