[
Root Disease Management Guidebook Table of Contents]

Disease assessment and stratification survey methods

This section provides descriptions of root disease survey procedures along with an overview on the suitability and application of each method.

Procedure – intersection length method survey

Overview

The intersection length survey method is an area-based survey most commonly used in coastal stands for laminated root rot (Phellinus weirii), primarily because of the disease’s tendancy to form discrete, well-defined infection centers. There are two options for setting up the survey transect grids (random or systematic), and both can be run using a mapping option if desired (see section on sketch mapping survey). Root disease incidence estimates of the intersection length method (ILM) survey can be done by hand calculation. There is also a computer model (RRSAMP) available to estimate statistical reliability of the random ILM survey. This model is also used for estimating infection center size class frequencies and for computer-assisted mapping.

Field procedure

Douglas-fir leading species survey variant (the default ILM survey).

  1. Stratify the selected area by tree cover, using aerial photos, biogeoclimatic and forest cover maps, and available history records.

  2. Determine the laminated root rot hazard rating and survey priority for each stratum, based on species composition.

  3. Establish a base line and place survey grid transects 40 to 70 m apart. Identify above-ground visible infection center boundaries using disease signs and symptoms.

  4. Use metric grid field sheets (or FS 1061 form) to record all intercept lengths. Optionally, one may map all infection centers and stratum boundaries. Summarize disease intercept and transect lengths per stratum.

  5. Determine the disease incidence by summing the disease intercept lengths and transect lengths of each stratum (or all strata) using the following formula:

  6. Summarize the root disease incidence and risk rating for each stratum.

  7. Determine the appropriate site treatment required, if any, using the results obtained and threshold levels for treatment described in section on “Evaluation and final prescription.”

Procedure – sketch mapping survey

Overview

This method is recommended for use only in coastal stands with Phellinus.

Field procedure

One hundred per cent of the prescription area is mapped at a scale of 1:2–5000 by walking along lines spaced 40–60 m apart and sketching in all infection centres to an accuracy of ±5 m. Following the field mapping, treatment buffers are added around each infection center (10 m for pre-harvest stands, and 5 m for pre-stand tending stands). Treatment units are then delineated on the basis of root disease incidence and distribution.

Procedure – line transect survey

Overview

A line transect survey is a tree-based survey suitable for almost all stand types and all root diseases. This survey is designed to function as a simple method for observing and tallying disease incidence by pathogen and host. Depending upon the interval selected, this method also provides a fair estimate of disease location for stratification purposes.

Field procedure

  1. Obtain an overview map of the area and create a large scale map of the stand (i.e., 1:5000 or better). Layout the location of the transects within the stand, prior to conducting the field portion of the survey, with the assistance of aerial photographs and walkthrough reconnaissance data (if available).

  2. The line transect is a continuous 2 to 5 m wide strip. The point-of-commencement should be placed 50 m from the edge of the stand and a transect should not come closer than 10 m to any stand boundary. Transect lines should be spaced, in parallel, over the entire survey area. The distance between transects should not be >100 m; 50 m is the recommended interval.

  3. Transect line notes can be recorded on FS 310, FS 375, or other suitable form. Transect lines should be flagged so the lines can be easily relocated for inspection. On each line, flag the beginning of the line with a ribbon marked with the date, survey title (e.g., “root rot survey”), and bearing of the line.

  4. Along each transect line the following information should be collected:

    a. location of susceptible tree species and their estimated dbh (if >7.5 cm)

    b. location along the transect of any dead or infected tree regardless of species or diameter

    c. status of tree (i.e., healthy, standing-infected, standing-dead, windthrown)

    d. presence and extent along transect of infection centres.

    Trees down due to windthrow should be noted only if root disease can be identified as contributing to the cause of windthrow.

  5. If the stand is to be harvested using partial cut methods or is to be thinned, no physically damaging examination should be conducted on any live standing tree (i.e., no removal of bark at tree base or excavation of roots) unless the tree is clearly designated for removal. All symptoms leading to diagnosis of a living tree must be externally detectable.

  6. Total the number of infected trees and the total number of examined trees and determine the disease incidence of each stratum using the following formula:

    This calculation may also be modified to calculate the amount of infected trees by species, root disease and stratum.

  7. Determine the appropriate site treatment required, if any, using the results obtained and the threshold levels for treatment described in section on “Evaluation and final prescription.”

Procedure – pixel survey

Overview

The pixel survey is an area-based survey suitable for use in mature interior stands only where Armillaria and Phellinus root diseases are expressed in centers, scattered patches or as individual tree mortality.

Pixel definition

A pixel is 25 m long and 3 m wide and has one lengthwise edge along the compass line. A pixel survey is, essentially, a transect survey divided into short plots (Figure 9).

Figure 9. Example of pixels. Each lettered area is one 3 m x 25 m pixel.

Field procedure

The following procedure for a systematic pixel survey can either be incorporated into a pre-harvest evaluation or used as a separate survey of root disease. To calculate the number of pixels required for sampling at a certain intensity, use the following guide.

One hectare contains 133 possible pixels (thus, a 10% sample would be 14 pixels or seven pairs). Knowing the area and the pixel size, one can compute spacing between lines. These must be distributed systematically over the entire area.

To obtain the recommended 5% sample, insert 0.05 for sampling intensity.

1. In the office, lay out the transect lines for a root disease survey on a scale map of the operational area. Use an access road to or through the area for a baseline as shown in Figure 10. Start the first line 50 m inside one boundary and lay out the remaining lines parallel to the first at 100 m intervals, covering the whole area.

Figure 10. Layout of root disease survey transect lines over a proposed cutblock.

2. Establish a tie point for the survey. On an aerial photo, select a geographic point clearly visible on both the ground and the photo.

3. On each line, flag the beginning of the line with a ribbon of at least 30 cm length marked with the date, survey title (e.g., “root rot survey”), crew chief surname, and bearing of the line. Mark or ribbon each line at intervals so that it can be followed easily, and mark the ends of each line at the cutblock boundary. If the traverse is closed, a pre-marked baseline will be required. If these strips or lines are to be used to locate operational cruise plots, the pixel survey could easily be integrated.

4. Record on compass sheets (FS 374) essential notes, including baseline position, infection centers and important topographic features such as rock outcrops and wet areas. If a sub-unit of the area is to be treated separately, these notes should be sufficient to prepare a map of the treatment area(s).

5. For each pixel, record the presence or absence of root disease.

6. Calculate the percentage area infected using the following formula:

The resulting root disease incidence is an estimate of the proportion of area exhibiting disease expression.

7. On a scale map, indicate infected areas. Designate any large centers or other units which should be treated. It is desirable to delineate separate treatment strata.

8. Determine the appropriate site treatment required, if any, using the results obtained and threshold levels for treatment described in section on “Evaluation and final prescription.”

Procedure – intensity measuring pixel survey (IMPS)

Overview

This tree-based survey method is being tested to detect, assess, and stratify Armillaria and Phellinus root disease in the interior. The survey uses a variable-width pixel that samples a target of ten trees per pixel, grouping trees into four diameter classes, and as either healthy or infected. Tree counts are weighted relative to tree diameter within each pixel (i.e., small, infected trees represent less inoculum than large, infected trees) and, therefore, provide a weighted per cent estimate of infection for each stratum. This survey provides an estimate of the area affected by root disease as well as some indication of disease intensity.

The advantage of IMPS is that it reflects the differing contribution to total on site inoculum load by varying size of infection source. An infected 30 m tree and an infected 30 cm seedling do not represent equal contributions to the total disease on site. This difference is not recognized in some other root disease surveys. In addition, the variable width of the plots allows the survey to be used in different forest types, as a similar sample size is always used.

The IMPS survey is adaptable for use in conjunction with other surveys (i.e., pre-stratification, pre-harvest, timber cruise).

IMPS plot definition

An IMPS plot is 25 m long and of variable width. The width of each plot is determined at the start of that plot, and is recorded. The surveyor looks ahead for the length of the plot and estimates what width would be required to sample 6–10 trees over 12.5 cm dbh. Once the width has been estimated, it remains fixed for that plot. At the start of the next plot, a new width is estimated. Hence, each plot within the survey has an independently determined width.

Once the plot width has been determined, each living or dead tree within the plot is tallied as either infected or healthy by the following diameter classes:

  1. Regeneration (<1.3 m tall – only infected trees are tallied in this class)

  2. <12.5 cm dbh (all stems >1.3 m tall and <12.5 cm dbh)

  3. 12.5–30 cm dbh

  4. >30 cm dbh.

Snags or broken stems >1.3 m tall are tallied by their respective diameter class. Stumps which are visibly infected are tallied in the regeneration class regardless of their diameter class. Dead stems which are too decayed to determine their infection status are not tallied. Windthrown trees which have been uprooted are not tallied as either healthy or infected.

Field procedure

  1. In the office, choose a tie point and lay out the transect lines for a root disease survey on a scale map of the operational area. Place transect lines at systematic intervals over the survey area. The following intervals are recommended:

    These intervals may be modified depending upon the objectives of the survey. Start the first line at 50 m inside a stand boundary and lay out the remaining lines parallel to the first at the indicated interval covering the whole area.

  2. Establish a tie point for the survey. On an aerial photo, select a geographic point clearly visible on both the ground and the photo.

  3. On each line, flag the beginning of the line with a ribbon of at least 30 cm length marked with the date, survey title (i.e., “IMPS survey”), crew chief surname, and bearing of the line. Ribbon each line at intervals so that it can be followed easily, and mark the end of each line at the cutblock boundary. If the traverse is closed, a pre-marked baseline will be required. If these strips or lines are to be used to locate operational cruise plots, the IMPS survey could easily be integrated.

  4. Record on the IMPS field card essential notes including baseline position, infection centers and important topographic features such as rock outcrops and wet areas. If an area is to be treated separately, the notes should be sufficient to create a map of the treatment stratum.

  5. Upon completion of the survey, data is compiled using the IMPS compilation program which is available from regional forest health specialists. The program is user friendly and will compile the data, create a map of the survey, and allow the user to stratify the block.

    In the compilation phase, each of the four classes is given a weighted value:

    The per cent infection for each IMPS plot is determined as the total value of the infected points divided by the sum of the infected and healthy points. The per cent infection for the stratum is simply the average of infection values for all IMPS plots in that stratum.

  6. It is desirable to delineate separate treatment strata. Determine the appropriate site treatment required, if any, using the results obtained and threshold levels for treatment described in the section on “Evaluation and final prescription.”

Procedure – stump top survey

Overview

Due to the inconsistent expression of above-ground tree symptoms, surveying for root diseases, particularly Inonotus tomentosus, in mature stands is difficult and costly. When no above-ground symptoms are evident, root assessment must be done by either drilling or chopping to the core of roots. This is expensive and time consuming since a minimum of three main roots per tree should be assessed on each of perhaps hundreds of trees in a typical block.

An alternative to pre-harvest surveys is a post-harvest stump top survey. Since many infected spruce trees have evidence of Tomentosus infection at stump top, a reliable estimate can be made post-harvest. Reliable detection and assessment involves training observers to distinguish between the honeycomb pattern of heartwood decay caused by Tomentosus and other patterns of decay that are common in spruce. Stumps should be cut clean with a chainsaw or sharp feller buncher saw to a maximum 30 cm height. This assessment is strictly visual with no additional drilling or chopping of roots.

The stump top survey is not intended as a substitute for a pre-harvest assessment. It may be used to accurately delineate treatment strata or confirm disease incidence in the following situations:

Field procedure

  1. Stratify the selected area by former tree cover, using biogeoclimatic and forest cover maps, aerial photos, and available history records. Spruce-leading strata have the highest Tomentosus root disease hazard rating.

  2. Using a hip-chain, establish a base line and place survey transects 100 m apart. Layout 3 m wide transects divided into 25 m long plots (pixels). Record the location of all infected stumps. Tally all stumps by infection class (healthy or infected) and by species for every 3 x 25 m pixel.

  3. Map all infected stumps and all stratum boundaries.

  4. Determine the disease incidence of each stratum using the following formula:

    This calculation may also be modified to calculate the amount of infected trees by species, root disease, and stratum.

  5. Summarize root disease incidence for each stratum.

  6. Determine the appropriate site treatment required, if any, using the results obtained and threshold levels for treatment described in the section on “Evaluation and final prescription.”

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