[Forest Fertilization Guidebook Table of Contents]

Appendix 2.

Foliar sampling guidelines

Foliar analysis is used to indicate whether fertilizer may result in a growth response on a particular site. Foliar analysis is not necessary for all stands. It should only be necessary where analysis of other location, site, and stand factors suggest that nutrients other than N may limit fertilizer response (see Table 1 in the section on biological factors). The analysis must be scheduled so that there is sufficient time to order nutrient supplements if indicated by the foliar analysis. Check with the lab well in advance to ensure samples can be analyzed within your time frame.

This appendix provides guidelines for foliar sampling and a brief description of sampling methods. For more extensive coverage, refer to Land Management Report No. 20, Evaluating Forest Stand Nutrient Status (Ballard and Carter, 1985).

Foliar sampling guidelines

For a relatively homogeneous stand type, set up two or more well separated transect lines that cross the stand and any major topographic features. Exclude portions of the lines which may be contaminated by dust (guideline 4 below). Establish equally spaced reference points on these lines, corresponding to the number of trees to be sampled. From each reference point, select the nearest tree that meets guidelines 2 and 3 (below).

For non-homogeneous blocks, use stratified sampling. Where a stratum occurs as numerous small “islands” within the stand, use the above transect approach within the island, to identify individual trees for sampling. This amounts to sampling each stratum as if it were an individual stand. If a stratum occurs as two or more large islands, it is appropriate to use one transect line in each of two (or more) of the largest islands.

Use the following guidelines:

  1. Sample conifer foliage during the dormant season, preferably between September 15 and December 15.

  2. Confine sampling to dominant and co-dominant trees.

  3. Avoid trees likely to yield poor samples because of heavy cone production, insect, or disease damage.

  4. Avoid sampling foliage near unpaved roads or in other situations that may lead to foliage contamination from dust.

  5. Estimate the distance from the top to bottom of the live crown. Collect samples from the top 1/4 to 1/2 of the live crown excluding the top 3 whorls. Sample the current year’s foliage from two branches per tree by collecting a 2 g (fresh mass) subsample (terminals and/or laterals) from each branch.

  6. Usually it is best to put samples into labeled plastic bags, although samples collected under dry conditions can be put into labeled paper bags. Dirty samples should be discarded and replaced.

  7. Drying of samples should begin as soon as possible, preferably on the day of sampling. However, if samples are kept cool (1–5°C), drying may be deferred as much as a week and perhaps longer. It may be easiest to ship samples directly to the analytical laboratory if prompt transport and handling can be arranged. If samples must be dried before shipment, oven drying is best. If no oven drying facilities are available, thorough air drying should be done.

Use color and size of needles to differentiate between current and previous year foliage. The color of foliage is often different for different foliage ages, and can vary from stand to stand. Foliage from the current year is often paler or more yellow-green. Twigs are invariably darker on shoots from the previous year than on shoots from the current year, as are fascicle sheaths in pines. Twig diameter is usually larger in terminal shoots that developed during the previous year and the terminal buds of such shoots, if they have failed to flush, are often larger in diameter and somewhat longer than current-year buds. Care should also be taken to avoid sampling lammas growth.

Dry the samples by transfering them to short, fully opened paper bags (e.g., lunch bags, with the top half rolled down or cut off) on which the sample number has been written. Before drying, remove and discard twigs, bud scales, and other non-foliage material (fascicle sheaths are not normally removed from pine needles). When air drying, leave the bags at ordinary room temperature and humidity for several days. It is preferable to use an electric fan for constant circulation when air drying. When oven drying, use a temperature of 70°C for 8–12 hours, or until needles snap cleanly in two when bent. After drying, fold the top of the bag over and staple shut.

Microwave ovens can also be used to dry foliage samples. Samples should be in paper lunch bags that have the tops cut off sufficiently to allow the bags to stand up inside the microwave. Turn the oven on to maximum power for 2–3 minutes, open the door and check the samples. Then use 2-minute bursts of heat, opening the door to let the steam escape, and 1-minute shots as the samples dry. Check the needles between bursts of heat and mix them up in the bag a little to even out the drying process. The total drying process will take about 8–12 minutes. Needles will burn if over-dried, so be careful as they dry out. The foliage is ready for shipping if it snaps when bent.

Wet foliage can pick up sulphur and boron from paper bags, but slightly damp foliage won’t be at much risk. Samples may be collected in the field in paper bags and, after drying, moved to labelled Ziploc bags for shipment to the lab. Samples collected in heavy rain, or those covered in ice or snow, should be collected in plastic bags, allowed to air dry inside, and then put in paper bags for drying.

If foliage samples are to be used for the evaluation of treatment impacts associated with fertilizer screening trials or other silvicultural treatments it is important to determine needle weight prior to grinding. Ensure that the laboratory is made aware of this requirement where necessary.

Foliage sampling methods

Foliage samples may be collected from the ground by climbing or shooting, or by helicopter. The method chosen depends on tree height and form and the extent of the sampling program. Foliar sampling can efficiently employ two persons: one collecting while the other separates the growth of the current year, bags the samples, indicates when a sufficient sample has been collected from a tree, labels bags, and records field notes.

Ground sampling

If trees are less than 10 m tall, samples may be collected with a hand pruner, long handled orchard pruner, or telescopic pruning pole.

Climbing

Climbing is most feasible in stands less than 30 m in height. See Land Management Report No. 20 for a complete description.

Shooting

Shooting down samples is often the only practical alternative in forest stands greater than 20 m in height. If properly conducted, it can be less hazardous than climbing for samples. See Land Management Report No. 20 for a complete description of the procedure including selection of guns, ammunition and licensing requirements.

Helicopters

If foliar samples are to be collected from several stands in close proximity to each other it may be most efficient to sample from helicopter with a certified helicopter operator.

Table 1. Interpretation of macronutrient concentrations in current year’s foliage of five commercial conifer species of the Pacific Northwest. (From: Diagnosis and Interpretation of Forest Stand Nutrient Status, Carter, R. In Forest Fertilization Sustaining and Improving Nutrition and Growth of Western Forests. H.N. Chappell, G.F. Weetman, R.E. Miller (eds.). 1992.)

Table 2. Interpretation of micronutrient concentrations in current year’s foliage.1 (From: Diagnosis and Interpretation of Forest Stand Nutrient Status, Carter In Forest Fertilization Sustaining and Improving Nutrition and Growth of Western Forests. H.N. Chappell, G.F. Weetman, R.E. Miller (eds). 1992.)

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