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Wet storage of hickory pulpwood in the southern United States and its impact on bark removal efficiency

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True hickories (Carya sp.) cover a wide geographical range, from eastern Texas north to Minnesota and east to the Atlantic Coast. Twenty years ago, hickory comprised approximately 8.5 percent of the hardwood resource in this area (7). It has now grown to approximately 10 percent, with some local areas reaching 15 percent or more (2,6,12-16). Compared to other hardwood species, hickory is extremely difficult to debark for much of the year. Therefore, it has traditionally been excluded from the chip furnish of most mills because of past experience with the negative effects bark can have on the pulp and paper process (10).

Lack of knowledge and research about specific bark characteristics for relevant pulpwood species has contributed to the underutilization of hickory by the pulp and paper industry. Increasing wood costs, a shrinking resource base, and an increasing demand for fine paper products make it necessary to expand the use of this species. The hickory resource in the eastern half of the United States represents approximately $2.2 billion in standing timber (11). In addition, harvesting would be simplified through increased utilization, landowners would obtain more income from their land and would be able to apply better management techniques, and transportation costs would decrease because mills would not need to transport alternate species from further away.

The amount of published literature dealing with hickory debarking is very limited. Often it is only mentioned as an example of one of the hardest tree species to debark. One study quantified this by measuring the strength of the bark-to-wood bond of 42 hardwood species, including hickory. According to Einspahr et al. (1), the dormant season bark-to-wood adhesion for hickory is greater than 3000 kPa, which is a tenfold difference from the growing season and nearly three times as great as the dormant season wood/bark...