Picking from the Past in Preparation for a Pest: Seed Banks Outperform Herbaria as Sources of Preserved 'Ōhi'a Seed.

Seed banks serve the purpose of maintaining germplasm for ex situ species preservation. Herbarium vouchers may be a viable source of unique and/or additional seeds for restoration as they can sometimes be from larger and more representative populations compared with seed banks. Rapid 'ohi'a death (ROD) has emerged as a serious threat against Hawaii's most iconic and foundational forest tree (Metrosideros spp.), and seed banking has been identified as an important strategy in preserving the genetic diversity of 'ohi'a. With respect to 'ohi'a we ask the following: (1) what is the long-term viability of 'hi'a seeds stored in herbarium conditions, (2) how do herbarium curation practices affect seed viability, and (3) how long do seeds survive using conventional storage methods? We placed fresh 'ohi'a seeds in a herbarium dryer (57 degrees C/5% relative humidity) for 5 days, freezer (-18 degrees C/95% RH) for 2 weeks, and dryer then freezer, and compared against fresh control seeds. Seeds were harvested from a chronosequence of herbarium specimens, withdrawn from conventional storage conditions up to 3.75 and 6.5 years before experiments began, and germination assessed. There was no difference in the proportion germinated among treatments and control testing for herbarium entry (p = 0.56). Although no seeds from herbarium specimens germinated, freshly collected dried and frozen seeds germinated at a level equivalent to the control (p = 0.76). For seeds stored using conventional storage methods at 3.75 and 6.5 years, germination was equivalent to freshly harvested seeds. This suggests that seeds can survive the extreme climate conditions necessary to enter herbaria, but lose viability after storage at ambient conditions in 4 years or less. Although 'hi'a seeds may be plentiful in herbaria, we recommend using seeds deposited into seed banks using conventional storage methods for orthodox seeds for postdisturbance restoration, and to combat ROD.