Does flushing date vary with seed origin?

 

Background

There is evidence that seed origins from warmer or more southerly locations flush earlier and are therefore, statistically, more frost tender. A series of provenance trials has been established by Ecology Division to identify superior planting material for timber production. These trials also provide the opportunity to assess the relationship between flushing date and seed origin or provenance. It should be noted that seed origin relates to the location that a genotype has adapted to in the long term, while provenance refers to the location from which the seed was collected; thus if a non-native seed origin was planted, it would produce seed of a local, and possibly assumed native, provenance after only one generation.

Experimental details

Flushing date was assessed for 21 provenances of oak (both Quercus robur and Q. petraea) at a trial site on the South Downs in West Sussex in 2004. The experimental plan is a randomised block design, with three replicate blocks and 36 trees per block. Flushing was assessed in the four central trees in each plot. Provenances from England, Scotland, Wales, Ireland, Holland, Germany and France were included. Three separate phases were identified: 

Phase 2
Initiation of flushing - green leaf material visible

Phase3
Leaf form visible

Phase4
Leaves fully expanded

Results

There is a clear tendency for the more southerly provenances to flush earlier with, for example, the French provenances flushing, on average, six days before the British provenances. Although this seem a small difference, it can have a dramatic effect on tree form and thus timber quality. The earliest flushing UK provenance is, in fact, the central belt of Scotland and at a trial site in central England has been repeatedly frosted; the conclusion drawn from this observation is that its origin is likely, in reality, to be France or southern Germany. This highlights the difference between origin and provenance, and the difficulty in ensuring that locally sourced material is of local origin. There is also some indication that those provenances flushing earliest taking the longest to complete leaf expansion and development.

Phenological development (spring 2004) of 25 provenances of oak at Chiddingfold,
grouped by country of origin

Country of origin	Number of provenances	Developmental phase (DOY)			Duration (days)
		Phase 2	Phase 3	Phase 4
UK	9	117.1	126.0	134.9	17.8
Germany	4	118.4	126.6	134.8	16.4
Ireland	3	119.1	127.8	136.4	17.3
France	8	111.1	121.5	130.6	19.5
Netherlands	1	123.0	130.0	137.3	14.3

Conclusions

It is clear that genetic origin influences flushing date and, thus, frost sensitivity. Where climate change adaptation includes the planting of more southerly provenances, there is therefore an increased risk of frost damage under the current climate; adaptation must balance current and future risks and the planting of mixed provenances may thus represent the best adaptation measure against climate change, providing some insurance against an uncertain future.