MANUAL Part II Visual Assessment of Crown Condition - ICP Forests

14 II. CROWN CONDITION ASSESSMENTS
9.3 Data plausibility
It is strongly recommended that plausibility checks are included in hand-held data gathering
devices (if used) and/or in the early stages of data evaluation. Plausibility checks should also be
integrated into any national data analysis system and NFC’s are responsible for the quality of
national data reported.
Field checks
Aims:
1. improve data completeness
2. improve consistency between teams
3. improve data consistency regarding Level II combined indices
4. document variability
5. provide information to improve training
An independent check survey should re-measure a proportion (e.g. 5-10%) of the sample plots
assessed by each survey crew and this should be done very close to the actual survey date to
avoid differences due to crown development. In case of significant discrepancies, adjustments or
clarification of instructions and their application must be arranged immediately to avoid serious
systematic errors.
National Focal Centres should compare the control data with the original observations and take
action as appropriate. A summary of the data comparisons, together with details of any action
taken, should be documented for potential evaluations.
9.4 International Quality Control
ICCs are field exercises aimed to
(i) document the relative position of individual National Reference Teams (NRTs)
within the international context,
(ii) monitor the consistency of NRTs’ position through time,
(iii) improve the traceability of the data by establishing a direct connection with the data
collected at national level. This will also help to explain anomalous year-by-year
fluctuations, and
(iv) explore the relationships between the performance of the various NRTs and the major
site and stand characteristics
by using field estimates and photo methods.
Detailed methodology see Annex 4.
updated 06/2006