Appendix S1 Determination of the length (years) for the recent floristic survey from the
DIGITALE database to improve completeness of the recent floristic list
2500
120
100
2000
80
1500
60
1000
40
500
0
1900
20
0
1920
1940
1960
1980
Number of visited 4 by 4 km grid squares (bars)
Total number of records of species last recorded
in 4 by 4 km grid squares (line)
Botanical recording in the Thiérache during the second half of the 20th century has known
periods with little botanical activity and periods with high botanical activity (Figure C.1).
It was our goal to compare the historical floristic data with a recent period of reliable
length in order to avoid that some areas in the Thiérache were less recorded than others.
2000
Year
Figure C.1: The total number of records of last recorded species in any given 4 km square and the number
of visited 4 km squares in each year.
We looked at increasingly longer periods, starting from 2005 and going backwards, using
the year of last recording of a species in a 4 x 4 km grid square. To make sure that all 4
km squares (n = 129) were visited, at least a 1971-2005 or longer period had to be taken
into account. Shorter periods resulted in some 4 km squares with no species.
The period was subsequently lengthened until in each 4 km square at least 50 species
were recorded. This resulted in 1958-2005 as the recent period for comparison with the
historical floras. The cumulative number of records (i.e. last recorded species - 4 km
square combinations) equalled 24 226. The number of species per 4 km square ranged
between 77 and 365 (mean = 188, median = 178, standard deviation = 60). Further
extending the period did not substantially increase the number of species sited in a 4 km
square.
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