I have monitored dates of leaf-out over a woodland in northeast England, and have noticed substantial variation with some tree species. Sycamore (Acer pseudoplatanus L.) composes one of the selected plots, where 20 trees (all Sycamore) were assessed, and dates of leaf-out differed by over one month within this plot. Because these 20 individuals (same species, uneven age) grow in very close proximity (
That's a very observation. In perennial trees this is very common.This happens simply because of preferential vascular connection between roots and shoots at certain sites but does not happen at other sites...
Dear Elias, that is an interesting observation. Do you have information about the sociological positions of the trees (which trees are dominant, co-dominant,.. suppressed)? Could it be that the trees in the understorey leaf-out earlier as they want to benefit from the incoming radiation before the dominant trees close the upper canopy?
Did you observe similar variation in leaf-out dates for other species as well?
http://wiki.awf.forst.uni-goettingen.de/wiki/index.php/Tree_sociological_position
Dear Elias, Have a look on physiological control mechanism from this interesting paper. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2011.03803.x/full.
Though there are multiple site and community specific interactions/reasons for such phenomenons. If you may explain little more of your observation then there may be some specific answer. like, is difference horizontal or vertical. (understory or upper story?)
Dear Elias,
what I can tell you on basis of my experiments is that individuals, even if at the same age, show huge variation in day length and chilling requirements, which ultimately leads to huge variations in leaf-out dates. Why this is the case we don't know. In addition, age differences of course play a role
Dear Elias,
From my experience, among the different tree species I monitored for spring phenology, sycamore maple was the most variable within a same forest stand and show the largest age effect (with much earlier leaf-out for youngest trees). It really looks like that both early and late flushing strategies may provide benefits for this species (disruptive selection) but as Constantin said we don't know why individuals with lower or higher chilling/forcing requirements have been selected in the understory (perhaps connected to late frosts events that may select late flushing saplings during a couple of years when actual late frosts have occurred and competition that may select for earlier flushing saplings during years showing no occurrence of late spring frost...). It would be nice to determine the exact age of each monitored tree... I also noticed for this species a very large phenological variation within the same individual tree (among the different twigs), which makes it harder to define an average date of leaf-out...
Soil substrate features, vascular connection between above ground plant portion to under ground root system, variation in microclimate with regard to orientation 9f slope side to sun orientation, many factors candidly contribute to such variation..
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