Dear Gerry Hawkes:
I've read your recent many informative reports on tree decline with much
interest.
Leaf curling has been also observed in Japan, significantly since last
year, though is not sure whether it is the same phenomenon you observed
or not.
The leaf curling in Japan increases in rain and is obvious in thin-leaved
deciduous species such as Enkianthus, Acer, and Prunus. Increases of curling
during rain were confirmed by my observation using time-lapse video. The leaf
curling does not significantly recover after rain and the curling increases
as months pass. The curling is more significant in leaves in outer part of
the crown that receive more rain. From these observations, I suppose the leaf
curling in Japan is related to acid rain, though experimental proof has not
been obtained yet.
Best regards.
Gerry Hawkes <ghawkes@sover.net> wrote $B!' (J
> I wanted to add to Roy Hagen's observations on forest health problems in
Vermont. He did not have the opportunity to observe the episodic leaf curling
which has been occurring since the middle of last summer.
>
> The curling in the upper portions of the canopy resembles drought stress (but
there has been no drought). This curling is often visible simultaneously in
several species of hardwoods and is particularly evident in sugar maple. Most
commonly the curling is visible in the early morning, but also can be seen at
times in late afternoons. So far I have detected no predictable pattern other
than the curling episodes becoming more frequent and occasionally more severe,
sometimes affecting leaves down to the mid canopy level. I would estimate that
approximately 20 curling episodes occurred last summer (beginning in mid-summer)
while this year curling began as soon as the leaves were fully out and is now
occurring to varying degrees on the average of more than once every two days for
up to several hours at a time. There seems to be no correlation with weather.
>
> Also starting in mid-summer of last year there has been a light, but steady
fall of leaves. From leaf fall counts taken last year, it is estimated that a
60 foot tall sugar maple may be losing from 20-150 leaves per day. The leaves
that are falling are in a wide variety of conditions: yellow and shriveled, dry
and crisp, brown and wilted, green with a portion missing, full and healthy in
appearance - no one type of leaf condition dominates. Also the leaves appear to
be falling as much if not more from the lower crown as from the upper crowns.
The leaf fall is being noticed in many hardwood species as is steady, light
needle fall in all species of conifers. Numerous twigs with missing leaves can
be seen by closely observing a tree crown from various vantage points.
>
> Has anyone else been observing leaf curling and abnormal leaf and needle fall?
If so when, where, and to what extent? Does anyone have a plausible
explanation.
>
> - Gerry Hawkes
> Forest Management & Utilization Consultant
> Woodstock, Vermont
>
-----------------------------------------------------
Hisao Fujii (fujiihi@ffpri.affrc.go.jp)
Forestry and Forest Products Research Institute
P.O.Box16, Tsukuba Norin Kenkyu Danchi-nai,
Ibaraki, 305, Japan TEL 0298-73-3211(ext475)
$B!!?9NSAm9g8&5f=j!&4k2hD4@0It!!F#0f5WM: (J
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