Using thermal time models to predict germination of five provenances of silver birch (<i>Betula pendula</i> Roth) in southern England

Abstract

Using thermal time models to predict germination of five provenances of silver birch (Betula pendula Roth) in southern England Midmore E. K., McCartan S. A., Jinks R. L., Cahalan C. M. (2015). Using thermal time models to predict germination of five provenances of silver birch (Betula pendula Roth) in southern England. Silva Fennica vol. 49 no. 2 article id 1266. 12 p. Highlights• Using cumulative germination data, thermal time models were developed for Betula pendula.• Models indicated varying degrees of dormancy and pre-chill requirements among provenances.• Thermal time parameters were used with climatic data to predict germination times under mild and cold winters in southern England.• Predictions suggest that pre-chilled French seeds would germinate about six weeks later than the fastest germinating provenance. AbstractClimate predictions indicate that growing conditions may become unfavourable for certain tree species in parts of Britain. Guidelines suggest some planting of seed sources from regions between 2° and 5° south of those currently used as part of a climate change adaptation strategy. However, there has been little research on the benefits and risks associated with the use of planting stock from more southerly seed sources. Seeds of five provenances of the 'relatively' dormant Betula pendula were germinated over a range of temperatures both with and without a pre-chill. Subsequently, a thermal time model was used to predict the impact of migrating these provenances to southern England. Results identified geographical differences in germination response; those from higher latitude were more sensitive to pre-chill.

Genetic variation in early fitness traits across European populations of silver birch (Betula pendula)

“…Differences in germination rates among populations of B. pendula have been previously reported, even at smaller geographical scales ( Holm 1994a ). Similar to our results, Midmore et al (2015) predicted markedly high differences in germination rates among populations, ranging between 0 and 100 % among populations from 47°N to 60°N. Similar patterns of population-level variation have been found in other Betula species (e.g.…”

“…S1 ] . Midmore et al (2015) showed that, on average, southern populations had a higher percentage of empty seeds (~77 %) than northern populations (~28 %). Southern B. pendula populations are generally more isolated, have smaller size, lower density and lower levels of genetic variation, which could have limited ovule fertilization rates because of more irregular pollen availability and/or inbreeding depression ( Holm 1994a ; Palmé et al 2003 ).…”

“…Differences in germination among populations could have also resulted from differences in dormancy duration or different environmental requirements to break their dormancy. For instance, Midmore et al (2015) showed that populations of B. pendula from higher latitudes were more sensitive to pre-chilling compared to populations from lower latitudes, particularly under colder temperatures. In our study, in contrast, germination rates were largely unaffected by pre-chilling.…”

“…Betula pendula typically exhibits high proportions of unviable (empty) seeds, with substantial variation among populations (e.g. 30–70 % in Midmore et al 2015 ). Reliably separating full and empty Betula seeds is a very time-consuming process, unfeasible for the large amounts used in this study.…”

“…Differences among populations in dormancy, germination, growth and phenology traits associated with latitudinal and altitudinal clines have already been found in northern populations (e.g. Myking and Heide 1995 ; Viherä-Aarnio and Velling 2008 ; Midmore et al 2015 ), but there is little information on range-wide genetic variation at early fitness traits assayed under natural conditions, especially for southern and mid-low latitude populations.…”