10.5061/DRYAD.1G1JWSTVX
Delpierre, Nicolas
0000-0003-0906-9402
University of Paris-Saclay
Chuine, Isabelle
0000-0003-3308-8785
Centre national de la recherche scientifique
Cole, Eleanor
University of Oxford
Tree phenology - observer intercalibration and individual tree
phenological scoring
Dryad
dataset
2021
leaf phenology
field observations
observer inter-calibration
within-population variability
2021-04-01T00:00:00Z
2021-04-01T00:00:00Z
en
https://doi.org/10.1111/1365-2745.13656
306758 bytes
6
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
We report data documenting (1) the dynamics of budburst and leaf
senescence in three European natural forest tree populations over the
period od 2012-2015 and (2) the variability among phenological observers
as documented from seven observer inter-calibration experiments conducted
in France over 2007-2017 for both the budburst and leaf senescence period.
We report three sets of ground phenological observations, conducted in
different forests: (1) observations of two species (Quercus petraea,
Carpinus betulus) in the Fontainebleau-Barbeau forest (France) from
2013-2017; (2) observations of three species (Quercus petraea, Carpinus
betulus, Castanea sativa) in the Orsay forest (France) from 2012-2015; (3)
observations of six species (Quercus robur, Fraxinus excelsior, Fagus
sylvatica, Betula pendula, Corylus avellana, and Acer pseudoplatanus) in
Wytham Woods (Oxfordshire, UK) in 2013 and 2014. The three datasets share
the particularity of documenting the whole sequence of spring budburst or
leaf senescence at the individual tree scale. This means that each tree
was monitored from winter state (all buds closed) to 100% budburst and
from mature green summer leaves to all leaves colored or fallen. In
Fontainebleau-Barbeau and Orsay, the same tree individuals were monitored
during spring and autumn. The three sets of observations were each
collected consistently by a small group (less than five) of observers who
have been trained and inter-calibrated before data collection, such that
the observer variability in this dataset is minimal. At the
Fontainebleau-Barbeau and Orsay forests, the percentage (on a 10%-step
scale) of open leaf buds (in the upper-third of the tree crown), leaf
coloration and leaf fall (over the whole tree crown) for individual trees
were monitored with binoculars 2-3 times a week from March to June and
once a week from September to December. At Wytham Woods, the development
of buds was scored over whole tree crowns using a key of phenological
stages different from BBCH, at a 3-day interval from March to May. A
seven-stage key (stage 1 = small dormant buds, 2 = larger, slightly
elongated buds, 3 = larger, loosened greenish brown buds, 4 = further
elongated buds with leaves starting to erupt, 5 = leaves emerging but
still tight, 6 = leaves loosening and extending outwards, 7 = leaves fully
emerged and unfurled) was used for Quercus robur and a five-stage key
(stage 1 = dormant bud, 2 = elongated/swollen buds, 3 = budburst, 4 =
leaves emerging and extending outwards, 5 = leaves fully emerged and
unfurled) used for the other species. The scale used for the observation
of budburst in the Fontainebleau-Barbeau and Orsay forests differed with
that used in Wytham Woods. Indeed, bud observations in the
Fontainebleau-Barbeau or Orsay forests started from the first signs of
buds opening (0% buds opened), and ended when 100% buds were open,
corresponding to the interval from stage 4 to stage 7 using the
seven-stage key and stage 3 to stage 5 using the five-stage key in Wytham
Woods. In order to homogenize protocols, we scaled the Wytham Woods
observations of budburst to a 0-100% scale similar to the one used in
Fontainebleau-Barbeau and Orsay, setting stage 3 (or 4 depending on the
species) of the Wytham Woods scale to 0% and setting stage 5 (or 7,
depending on the species) to 100%. We ensured that the tree individual
phenological sequences collected at Fontainebleau-Barbeau, Orsay and
Wytham woods were monotonically increasing with time. If a phenological
observation record was less than the previous record, we corrected it to
be equal to the previous record (affects 0.25% / 7.8% of all budburst/leaf
senescence data). The observer inter-calibration dataset was obtained
during seven inter-calibration sessions of observers conducted in France
during 2007-2017, three of which concerned budburst observations, and four
of which concerned observation of leaf senescence. The sessions took place
in different locations each year and concerned different tree species. An
average of 30 individual trees (from 12 to 49 trees) were observed by 10
to 37 observers each time following the same protocol and scoring scale
(BBCH scale). The observers were scientists, technicians and doctoral
students in biological sciences, and most of them participated all the
sessions, which lasted one and a half day each. The inter-calibration
sessions were organized as follows. At the first session, all participants
were trained to the BBCH scoring scale and protocol. At all sessions, all
participants first trained altogether on a set of tree individuals.
Participants subsequently also scored another set of tree individuals
independently. They used binoculars for observing tree crowns. Observers
were instructed not to exchange information or discuss during this scoring
in order to guarantee the independence of the scoring. The data obtained
with this independent scoring were used for this study.