SUMMARYThe mature length of the second internode (which was undergoing rapid vacuolation at the time of treatment with ABA) was not appreciably affected by doses of ABA below 20 jig per plant although the rate of elongation was depressed for the first 2 days after treatment, the depression being as much as 50% in tall varieties. Doses of ABA in excess of 20 ^g not only depressed elongation rate immediately, but resulted in shorter internode length at maturity. Etiolated seedlings showed a stimulation of elongation rate and mature length in the dwarf 'Meteor', hut no statistically significant differences in the tall variety 'The Pilot' with doses below 20 jxg ABA. Higher doses of ABA caused immediate cessation of elongation in vacuolating internodes, but only postponed the onset of vacuolation in younger internodes. Lighted plants also showed this postponement of the onset of vacuolation in the younger internodes at higher doses; in both lighted and etiolated seedlings the normal growth rate was resumed after a delay of between 3 and 7 days.Decapitation reduced elongation rate during the subsequent 48 hours either with or without ABA. In the absence of ABA there was a subsequent recovery in growth rate of the dwarf variety so that the final length of the second internode was the same for both intact and decapitated plants. But decapitation of the tall variety produced a marked reduction in mature length of the second internode, as it did in all ABA treated plants both dwarf and tall, intact and decapitated. The only significant interaction between decapitation and ABA on elongation rate occurred in the tall variety: during the first 24 hours all doses of ABA produced approximately the same big reduction in elongation rate in intact plants but had no statistically significant effect on decapitated plants; during the second day only the higher doses of ABA reduced the elongation rate of intact plants while all three levels produced the same big reduction in elongation rate of the decapitated plants. In the dwarf variety there was no significant interaction between the decapitation and ABA effects. Lateral bud outgrowth in decapitated plants was inhibited by ABA, and 100 [ig per plant achieved inhibition comparable to that produced by the apex in intact plants. Hence ABA may possibly be the inhibitory substance demonstrated to be responsible for the phenomena of correlative inhibition.

This paper reviews the most recent work conducted by scientists and engineers of the Forest Service of the US Department of Agriculture (USDA) in the areas of forest operations and woody biomass logistics, with an emphasis on feedstock supply for emerging bioenergy, biofuels, and bioproducts applications. This work is presented in the context of previous research in this field by the agency and is measured against the goals and objectives provided by several important national-level initiatives, including the USDA Regional Biomass Research Centers. Research conducted over the past 5 years in cooperation with a diverse group of research partners is organized in four topic sections: innovative practices, innovative machines, sustainability, and integration. A wide range of studies in operations and logistics address advances in harvest and processing technology, transportation systems, scheduling and planning, feedstock quality, biomass conversion processes, and environmental impacts, including greenhouse gas emissions. We also discuss potential future research to address persistent knowledge gaps, especially those in fire and fuel management. Overall, the research reviewed here aligns well with broad national goals of providing the USA with sustainable and efficient forest biomass management and production systems, specifically including:(1) improved harvest, collection, handling, and transportation systems for woody biomass; (2) cost and equipment information and options for field processing biomass to improve efficiency and mitigate impacts; and (3) forest biomass management systems and technologies to offset impacts and enhance environmental outcomes. However, as needs evolve, professionals in this field must strive to adapt research, development, and dissemination to address relevant future challenges and strengthen capabilities to solve critical problems in the forest sector.

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