Report - ICP Forests

3. Intensive Monitoring 45
3. INTENSIVE MONITORING
3.1 Introduction
Intensive Monitoring data (Level II) for the survey year 2007 were submitted from 21 countries.
In comparison to the 2006 data submission, the number of submitting countries decreased by 7.
The numbers of plots with data submission per survey are given in Table 3.1-1. As not all
surveys are conducted continuously or annually, the plot numbers vary from year to year.
Nevertheless, compared to the 2006 data submission the number of plots decreased for most
surveys. The reduction of countries and plot numbers is mostly due to the fact that for the year
2007 the assessments were not co-financed by the European Commission. The methods for
intensive monitoring of forest ecosystems are laid down in the “Manual on methods and criteria
for harmonized sampling, assessment, monitoring and analysis of the effects of air pollution on
forests” (ICP Forests, 2010).
Table 3.1-1: Surveys, numbers of Level II plots and assessment frequencies.
Survey Number of plots Assessment frequency
Installed Data submitted
for 2007
Crown condition 836 462 Annually
Foliar chemistry 904 200 Every two years
Soil condition 615 0 Every ten years
Soil solution chemistry 302 169 Continuously
Tree growth 811 70 Every five years
Deposition 657 353 Continuously
Ambient air quality (active) 84 27 Continuously
Ambient air quality (passive) 254 167 Continuously
Ozone induced injury 114 43 Annually
Meteorology 265 191 Continuously
Phenology 186 58 Several times per year
Ground vegetation 777 67 Every five years
Litterfall 262 105 Continuously
3.2 Sulphur and nitrogen deposition and its trends
3.2.1 Data and Methods
Deposition data are collected on Level II plots in the open field (“bulk deposition”) and under
canopy (“throughfall”). Whereas bulk deposition is a basis for estimates of total atmospheric
deposition rates in open fields, throughfall deposition typically differs from bulk deposition due
to a) wash off of dry deposition from the forest canopy, b) element “leaching” from the tree
crowns, and c) absorption of elements by the foliage, so-called “canopy uptake”. The first two
effects lead to increased throughfall rates, the latter one, canopy uptake of elements by the
crown foliage, reduces throughfall deposition compared to bulk deposition. Thus, throughfall
deposition does not reflect total deposition but reflects the results of total deposition plus net
canopy exchange. In addition, throughfall deposition may have been underestimated especially