Management strategies for pitch canker infected Año Nuevo stands of Monterey pine

Abstract

The future resilience of Pinus radiata D. Don (Monterey pine) is dependent upon the development of a silviculture program inclusive of either preventative or management techniques for the potentially fatal pitch canker disease (Fusarium circinatum Nirenberg and O’Donnell (=F.subglutinans (Wollenw and Reinking) Nelson et al. f. sp. Pini). As an ecologically and commercially valued species of limited natural range, a number of factors threaten to reduce the Monterey pine gene pool potentially impacting its long-term resilience. This study evaluated the effectiveness of uneven-aged forest management for regeneration success applied in the native, pitch canker infested Año Nuevo stands at Swanton Pacific Ranch in Davenport, California. The impact of gap size (0.20-ha (0.50 acre), 0.10-ha (0.25 acre), and 0.05-ha (0.125 acre)), site-preparation treatment (pile and burn, lop and scatter), and parent tree (13 local seed sources) on seedling survival and growth response (height, diameter) were addressed. Pitch canker symptoms were quantified to conclude if there is indeed a range of expressed resistance according to parent tree. The above independent variables were also examined for being correlated with branch tip incidence of pitch canker and western gall rust disease.A generalized linear mixed model estimated that the odds of seedling survival varied by site treatment and parent, but not by gap size. Pile and burn sites were estimated to have higher survival rates than lop and scatter sites. Linear mixed models estimated that gap size was associated with average seedling growth, both in terms of height and diameter. Parent and site treatment were not found to be significantly associated with the growth outcome measures. The 0.05-ha sites had smaller average height and diameter than the 0.20-ha sites. The 0.10-ha site also had smaller average diameter than the 0.20-ha sites. The presence of pitch canker disease on branch tips was found to be correlated only with gap size, with 0.10-ha sites having higher pitch canker incidence than the 0.05- and 0.20-ha sites. Though gall rust presence on branch tips was not associated with any of the hypothesized independent variables, there was an association between gall rust presence and pitch canker presence on branch tips. Site treatment and parent tree were associated with seedling survival, while gap size was found to be associated with seedling growth and disease resistance.