On visual assessment

29 May

Some of you wonder what I do with all my time at school and why I am always coming home wet and/or dirty. I’ve vaguely explained that it involves plenty of data collection, but I’ve always thought a serious explanation would be tedious at best. But you’re in luck, dear readers, because today I have lots of photos.

My classmates and I were lucky enough to go on an overnight camping trip to the Gifford Pinchot National Forest for silviculture lab. Lots of things were barbecued, of course, and someone may have even carved initials into a tree (for shame!) but we also spent a considerable amount of time running up and down hills at the Wind River Experimental Forest.

Our first stop was at the spacing trial plots, which were planted in 1925. As we walked along the trail and saw gradually rising numbers on the signs indicating spacing distance, a pattern began to emerge. The effect of spacing on forest health and long-term tree mortality became very clear. The closer together the trees are, the more they compete for light and other resources, so they tend to be thinner and weaker when they are dense, leading to more breakage and mortality. The photos begin with 4′ x 4′ spacing, and progress through 5′ x 5′, 6′ x 6′, 8′ x 8′ and 10′ x 10′ spacing. You can really see the difference in how healthy the stand appears to be:

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We also drove over near the old canopy crane to stomp about and look for the provenance study, which sought to discover differences between different seed sources at varying latitudes and elevations.We spent a near-unreasonable amount of time going in circles — yet another reason I hate to rely on GPS units in the field — and eventually found what we were after.

It was no surprise that trees from much different environments — like the coast — would not be doing well, but I was shocked by how well the trees from other higher elevation areas like Santiam were doing; they were consistently some of tallest and biggest dbh trees (although they also had the highest mortality rates). This is especially surprising when compared with the Carson trees, which were sourced from close by in an area with very similar elevation. I’d expect these to look great, but they did not. Other provenance plots put in at the coast (in Hebo) turned up a bunch of short, stunted trees even though you’d expect a coastal site to be more productive in general. It’s quite possible that results were skewed due to lack of adjustments made for site class. Did they even have site class and site index in 1915?

The fertilizer trial plots in the Wind River Experimental Forest were planted in 1929 at 8’ x 8’ spacing. The site was damaged in the Yacolt Burn in 1902, so did not have a particularly high baseline site class when it was planted.

The test site had several different types of plots, of which we visited three: a strip of Douglas-fir interplanted with red alder (1), an untreated control site (2), and a Douglas-fir dominated stand that had been treated with 280 lbs. of ammonium nitrate fertilizer per acre (3). We did a little measuring at each one for the sake of comparison:

Site 1

Site 2

Site 3

DBH (in.)




Ht. (ft.)




LCR (%)








DBH is the diameter at breast height, while the LCR (live crown ratio) is the proportion of the tree with living crown and SI (site index) gives a relative measure of how “good” a particular site is for growing trees; once you have a number, you look it up on a site index curve chart and it helps you determine the site class, which is a relative measure of the land’s productive capacity and quality. I’ll return to an interpretation of this data in a moment.

First, I’d like to approach it in a way that mirrors what we experienced on the ground. Of course, the size and condition of the trees differ at each of the three sites, as the numbers show. However, each site has inherent differences that can be assessed visually. The overstory was dominated by Douglas-fir in all three areas, while the interplanted strip also had some (mostly) dead or dying red alder, and we observed some western hemlock in the other areas, too. The understory was the most immediate visual indication that much of anything changed from place to place. In the alder strip, dwarf Oregon-grape dominated with some salal, red huckleberry, vine maple and vanilla leaf mixed in. Meanwhile the ericaceous species (red huckleberry and salal) — classic indicators of nitrogen deficient soil — were more prevalent at Sites 2 & 3, where the understory was more dense in general. This density happened because the crowns of the trees at those two sites were smaller, thereby letting more light reach the forest floor.

Additionally, the alder interplanted strip (Site 1) had noticeably better color and crown size than the others. The control site had relatively short, thin, yellow trees with crown closure just beginning to take place. The ammonium nitrate treated site looked remarkably similar to the control, though it had better crown closure and more biomass with moderately better height, DBH, LCR and site class (a low IV compared to V at the control site). The lack of appreciable difference is not surprising, though, particularly considering that the fertilizer was applied only once in the 1960s, and ammonium nitrate leaches far more readily in the soil than other fertilizers like urea, which are more commonly used nowadays. The alder strip turned out to have a site class of III (the best being class I), which is a pretty big jump up from the control. This is even more impressive when you consider that the alder strip was on a ridgetop. These tend generally to have a poorer site class because water flows downhill, taking a lot of prime silt and nutrients with it.

So the major difference between the strip being fertilized by nitrogen-fixing alder and the site that was amended with fertilizer is that the alders provided a consistent source of nitrogen in the soil; trees as far as 20 feet from the boundary of the strip even showed significant benefits from the added macronutrient levels. This also makes the alder strip the most economically valuable site because it not only produced trees with a much greater wood volume, but a constant benefit was provided based upon a one-time planting expense. To achieve similar results at the ammonium nitrate treated site, the fertilizer would need to be applied many times, which would  become cost-prohibitive pretty quickly.

Even wildlife damage to the trees can be interpreted as further evidence of the considerable benefits enjoyed by the alder-fertilized Douglas-firs at Site 1. There was evidence of bear damage on many of the trees because these trees were larger with thicker, more nutritious cambium, while the other sites didn’t have any bear sign at all.

So that gives a good picture of the process I go through when making observations in the field, and how my classmates and I use observations to draw various conclusions about things. This term has included some of the best field experiences of my entire time in this program. I’m graduating in a couple weeks, which is exciting and an enormous relief, but I’m already certain that I will miss it — especially all the time we were able to spend in the field.

I’d certainly recommend this forestry program to anyone!

6 Responses to “On visual assessment”

  1. Dori June 1, 2012 at 11:30 am #

    Great stuff!

    • xylem_up June 8, 2012 at 8:14 am #

      Thanks! More to come once I find a reliable Internet connection around here.

  2. Jamie Peacock June 13, 2012 at 9:11 am #

    Well done! I am glad that the experimental forest can and does yeild interesting field data. I have enjoyed being apart of the forestry program with you and wish you the best of luck in your future endeavors. This program has been a great learning experience and the hands on training that is dished out has been priceless. Other than the homework load, many times I have caught our classmates having way more fun than one would expect from college courses. I feel lucky to have met some great people in this program.

    • xylem_up June 14, 2012 at 4:57 pm #

      I agree, and good luck to you, too! Don’t take any guff from those Blue Lake folks!

  3. Pine Student Easel September 10, 2012 at 11:23 pm #

    Magnificent post, very informative. I ponder why the opposite experts of this sector do not understand this. You must continue your writing. I am confident, you have a huge readers’ base already!|What’s Going down i am new to this, I stumbled upon this I’ve discovered It absolutely useful and it has helped me out loads. I hope to give a contribution & assist other customers like its helped me. Great job.


  1. Pseudotsuga menziesii | Find Me A Cure - June 17, 2012

    […] On visual assessment […]

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