7.18 Optional subprogramme BI: Tree bioelements and tree indication

• 7.18.1 Introduction
• 7.18.2 Methods
• 7.18.2.1 Selection of plots
• 7.18.2.2 Observations
• 7.18.3 Frequency of observations
• 7.18.4 Quality assurance/Quality control
• 7.18.5 Data pre-treatment
• 7.18.6 Data reporting
• 7.18.7 References
• BI Annex

7.18.1 Introduction

The chief purpose of the BI subprogramme is to estimate the state and change in amount of chemical elements that is contained in the tree biomass, including roots, and the dead wood of a catchment. In the forest ecosystem this is one of the most important pools of elements and is sometimes more sub-stantial than the soil pool.

Other aims are:

• to keep record of the trees as influencing deposition (subprogramme Throughfall (TF)), overall transport, internal circulation (subprogrammes Foliage chemistry (FC) and Litterfall (LF)) and ion balance of elements in the catchment
• to monitor tree populations as biological indicators of pollutional and other atmospheric changes.

This subprogramme is complemented with the vegetation structure monitoring of subprogramme VS, Vegetation structure and species cover.

The BI subprogramme can not be applied meaningfully where forest stands are missing or so sparse as not to contribute significantly to the biomass of the site. Its full application is impaired where functions for biomass calculation and values of element concentrations are missing. However, in such cases it is acceptable to use simpler functions or functions established in other regions, if not too dissimilar to the actual one.

Tree biomass estimate should be complemented with a biomass estimate of the field and bottom layers after suitable methods have been developed.

7.18.2 Methods

7.18.2.1 Selection of plots

Data are collected by a combination of tree stand mapping and sampling of tree characteristics on plots representing each stand in the catchment.

Measurements are performed on plots, preferably circular of 10 m radius, on or near those established for subprogramme VS, i. e. in a quadratic network (BI Annex Figure 1). After mapping the stands it is decided how many plots in each stand type are needed. It is recommended that the largest stand (up to 1 km²) should have no more than 20 sample plots and the smallest stand (minimum 0.25 ha) should have at least two plots.

Reject plots where more than one stand is represented! If this rule leads to too great a loss of plots for meaningful monitoring, accept plots with two stand types and measure only those trees which clearly belong to the dominant one. Plots with more than two different stand types are rejected in any case. Plots that are regarded as "impossible" with respect to topography, heterogeneity etc. are also excluded.

7.18.2.2 Observations

Measurements of trees, logs and stumps (clearly not connected with logs) may be performed at two levels of ambition. The higher level includes measuring the position of each individual tree on the plot while at the lower level this is not done. In the former case the biomass change through time is better estimated and the population dynamics can be followed more in detail.

Defoliation, discolouration and damage according to the subprogramme Forest damage (FD) preferably should be observed on the BI plots.

Living trees

• Measure the diameter at breast height (dbh; at 1.3 m above ground) of all living trees on the plot above a minimum dbh and determine the species. Which minimum size to choose depends on the character of the tree stands at the site. 5 or 10 cm are recommended for tall forest. If small trees make up a substantial part of the stands a smaller dbh should be chosen.
• Measure the heights of living sample trees objectively selected from each diameter class. For example, take the first tree in each 5 or 10 cm dbh class of each species encountered when moving clockwise round the plot starting from the north (Figure 7.18.1). This procedure ensures that all diameter classes are represented.
• Measure the height to the lower crown limit and the crown diameter of the sample tree (the two latter if necessary for bio mass functions or for calculation of canopy cover and crown volume).
• Classify the vitality of all trees as follows:  
  1 - healthy,  
  2 - generally weak,
  3 - dying
• At the higher level of ambition measure the position of each tree-base centre (core) as to direction and distance from the plot centre.

Dead trees, logs and stumps

• Measure dbh of dead standing trees and diameter at 1.3 m from the base on logs (windthrows). On tall stumps dbh is measured, on low ones the diameter of the upper surface. Apply the same minimum diameter as for living trees.
• Stage of decomposition of wood may be classified as follows (use a sharp knife to test the penetrability of the wood):  
  0 - fresh, bark left,  
  1 - bark gone, all wood hard,
  2 - <10% by volume of wood soft (=penetrable),
  3 - 10-50% of wood soft,  
  4 - 50-75% of wood soft,
  when >75% of wood is soft the windthrow is not observed
• At the higher ambition level measure the position of each object as to direction and distance from the plot centre. The position and length of a log can be inferred from coordinates for its base and top ends on those parts of the log that are within the plot circumference.

Stand areas

• Measure the area of the whole site and of each stand on the map.

7.18.3 Frequency of observations

Observations are repeated every five years.

7.18.4 Quality assurance/Quality control

Train the field crew for accuracy in measurements! Check the field data for "impossible" figures both when collecting them and before and after storing into computer! The chance of storing correct data is increased if an electronic field data storer is used. There is a great risk to make mistakes and get faulty data in the many operations of biomass and bioelement calculations unless ready-made and controlled programmes are used.

7.18.5 Data pre-treatment

Estimate height, crown diameter and crown limit of all trees from the regression between dbh/height, dbh/crown diameter and dbh/crown limit on the sample trees, thus ensuring an acceptably accurate estimate of the biomass with little extra input of time in the field.

It is recommended that each country makes its own calculations of bioelements since the functions and parameters are more or less locally limited. An example of functions and parameters based on Scandinavian measurements are presented in the BI Annex. Some of them are based on small samples, especially as regards deciduous trees. There is a full account of the steps needed for calculation included in the BI Annex.

If functions for biomass estimate and data on element concentrations are missing only the number of trees and their sizes per stand type are reported. As a complement either a stand map or data on the area of each stand should be reported.

7.18.6 Data reporting

Example files

BI example Excel file
BI example ASCII file

• File identifier SUBPROG states the subprogramme.   
• Station number SCODE is given as 9999 to represent the whole IM site (or use a SCODE of your choise) . 
• Report stand type code as MEDIUM. Enclose a separate list of those (full) stand type names and codes that are used. The country code is given as the list name (LISTSPE), e.g. SE for a Swedish code list. (List codes will be unified by the Programme Centre).   
• Report which minimum dbh classes is applied in the measurements.
• Report area of stand type, necessary for calculation of biomass etc. as SIZE.   
• Spatial pool (SPOOL) gives the number of plots representing the stand.  
• Tree species is reported as SPECIES, using NCC codes (list code B4, see Annex 6, for the most common species see throughfall subprogramme, TF).   
• Report dbh, height, vitality and decomposition classes as CLASS.  
• Sampling year and month are given as YYYYMM.   
• General information on flags is given in Chapter 4.

7.18.7 References

van Ek, R. & Draaijers, G.P.J., 1991. Atmospheric Deposition in Relation to Forest Stand Structure. Inst. of Geographical Research, Dept of Physical Geography, Univ. of Utrecht.

BI Annex

Procedure for calculating biomass and bioelements