Appendix B.   Light-level readings from Sandilands Selective Cutting Project site

Plot 9904a 9904h 9904p 9906a 9906h 9906p 9908a 9908h 9908p 0204a 0204h 0204p 0206a 0206h 0206p 0208a 0208h 0208p
1 263 1090 1570 1000 2370 1213 197 480 107 290 410 600 0330 510 250 0143 0260 0390
2 490 1480 1430 400 1670 503 510 1038 247 1750 2250 1260 3050 1440 10000 0355 1640 0750
3 780 2410 840 346 725 503 860 1624 352 127 100 840 4000 3100 510 0224 1640 0750
4 820 2190 1675 992 1000 503 919 1430 365 610 190 8680 1050 14720 5250 0315 0840 0500
5 1560 2360 3520 1675 1820 1256 1967 3470 1784 170 440 2890 68300 2900 3000 0915 19590 1240
6 1800 6270 6380 1470 1389 921 3390 3500 1202 7070 2880 3590 30200 32500 3840 10200 71400 2560
7 9500 14310 1890 1695 1820 1256 2240 12150 766 1400 570 13320 60200 5400 1180 9500 1274 9650
8 578 1770 836 400 5870 611 755 1500 588 340 240 860 690 11150 1430 0346 0560 0529
9 3700 3380 2130 789 8701 5840 2200 2320 1960 1630 400 1950 5300 16000 1140 7350 4490 1125
10 3100 58300 9210 1552 12800 5209 5250 12740 5410 2930 8990 9010 71100 16000 1140 37100 66000 16130
11 3410 78600 6900 591 2600 6110 6730 5606 9800 270 8640 11560 75300 8700 4610 1980 81800 44900
12 5270 5520 1400 6460 3180 7110 2900 6580 1154 6000 180 2110 72800 32600 1040 54000 2890 41900
13 1175 48600 34600 2950 2900 8050 1780 14000 2580 110 7920 14460 2030 80100 19320 19800 9000 1940
14 2390 12700 5490 1222 3200 2550 4730 9250 7280 108 8300 14040 17720 25900 5130 2960 2680 4450
15 2630 12606 16400 26400 4950 16210 3600 7620 5000 620 1130 3310 2110 51800 3050 49100 5960 3450
16 2030 15600 2360 2410 1970 1395 3150 6020 4040 1100 500 7840 1330 1500 34300 0770 8480 7630
17 2070 4950 23402 1875 4100 3260 3500 7400 5350 220 8420 3540 11250 9170 3900 2080 73000 3200
18 2910 82000 2670 2700 27000 1990 2890 64500 4250 2770 1070 4820 102400 80800 4300 2540 65000 1640
19 2040 1880 1690 1549 4690 1290 2720 3020 4340 230 760 9410 2400 5440 2170 1330 71300 0380
20 1166 5530 21960 7989 6600 12960 7989 6600 12960 600 6080 7000 9360 88300 5690 9570 14800 6590
T1 595 1950 6630 697 1317 1560 520 860 1990 490 110 920 400 10540 9450 0163 0810 0387
T2 384 3600 1000 486 2870 820 498 1058 234 204 490 790 4310 4060 2040 0226 0469 0300
T3 4020 14600 3270 3500 2010 2480 1260 2140 989 1500 200 11480 930 1610 4050 0468 1089 1440
T4 4020 14600 347 1260 5800 2590 3500 15860 8050 330 380 410 4440 42300 2590 2100 5770 2690

Note: all readings are in lux units, taken with an Optikon Hagner model EC1 luxmeter.

Note: We had intended to take readings on or about April20, June20, August20, in each of 1999, 2001 and 2003; but the first April readings were taken in 2000 instead of 1999; and we took a complete set of readings in 2002, but not 2001 or 2003. We attempted to take readings on a sunny low-wind day. Each day consists of readings (a) at 3 hours before high-noon, (h) at high-noon, and (p) at 3 hours after high-noon. (High-noon occurs at approximately 1:20pm central-daylight-time at this location.)

Weather notes on the readings days:

1999 June 19 (9906) -- Bud reading, Doris recording. Clear and sunny.
1999 Aug. 15 (9908) -- Bud reading, Doris recording. Intermittent cloud.
2000 April 24 (9904) -- Doris reading, Bud recording. Sunny, some cloud around 1600hrs. A large tree has fallen from the west across plot#17.
2002 April 22 (0204) -- Bud reading, Doris recording. Sunny, very windy. Luxmeter not working so we did the 1600hr readings on Apr26/02.
2002 June 20 (0206) -- Bud reading, Eugene recording. No notes on weather.
2002 Aug. 19 (0208) -- Bud reading, Doris recording. Clear and sunny. Bog wet, standing water in some plots, most overgrown with grass.

Reliability of this data:

Many of these readings are inconsistent with being outdoors on a sunny day. So either there was cloud, or the meter was malfunctioning, or it was misread. The easiest mistakes to make when reading the type of meter being used, are (1) to be out by a factor of 100, and (2) to be out by a factor of 10. On one occasion we had a borrowed meter which behaved more like a random-number generator, than a light-measuring device -- several readings at the same location would differ by more than a factor of 10.

One thing that most human observers agree on, is that Plot#20 is the least shaded of all these plots; and yet one observes at best a weak tendency for Plot#20 to have the brightest readings; it is among the top-3 only 6 times out of 18 (one-third of the time it falls into the top one-eighth). Plot#18 has the most first-places; plots 11, 13, 15, 20 also have multiple firsts; and plots 6, 10, 12, 16 have a first; in all 18 cases the plot with the brightest reading is among those that human observers had placed into the top half.

One expects June readings to be brighter than either April or August readings; one also expects high-noon readings to be brighter than either the morning or afternoon readings. On 4 of the 6 days, the brightest reading was among the high-noon ones. In both years, the brightest of the morning readings came in June; in 1 of 2 years, the brightest noon reading came in June; in neither year did the brightest afternoon reading come in June; the all-time brightest reading came in June, but in the morning.

The low readings are the dubious ones, for 2 reasons: (1) the most likely reading-errors involve the omission of the "times-10" and "times-100" portions of the lux-meter, and (2) on a partly-cloudy day, the light-conditions are highly variable over the time it takes to visit all 24 plots. Useful readings could be taken on clear days and on thoroughly overcast days, though we have no readings from an overcast day. For readings on a partly-cloudy day, the data is likely made more useful by discarding suspiciously low readings.

The original design called for light-level readings in years 1, 3 and 5 of the 5-year study-period, in order to show how canopy-closure changed over that period; however the frequency of dubious readings has caused us to abandon such use of the data. However once we think of canopy-closure as being constant over the 5-year period, then we think our data becomes a reasonably good estimator of that canopy-closure.

In order to use this data as an estimator of canopy-closure, a reasonable approach seems to be one of:
(A) for each plot, use the brightest reading ever recorded there, or
(B) for each plot, take the average of brightest morning, brightest noon, brightest afternoon readings, or
(C) for each plot, take the average of brightest April, brightest June, brightest August readings, or
(D) for each plot, take average of 9 values, the brightest from each time-of-day from each month.
Method-A uses one-eighteenth of the readings, both B and C use one-sixth, and D uses one-half. Method-D would seem best if most of the readings were reliable; however the high number of dubious readings, casts doubt on method-D.

The following table summarizes the results for both methods A and B.

Plot max-am max-hinoon max-pm method-A method-B rank-A rank-B
1 1000 2370 1570 2370 1647 24 24
2 3050 2250 10000 10000 5100 21 20
3 4000 3100 840 4000 2647 23 23
4 1050 14720 8680 14720 8150 17 18
5 68300 19590 3520 68300 30470 10 10
6 30200 71400 6380 71400 35993 07 08
7 60200 14310 13320 60200 29277 11 11
8 755 11150 1430 11150 4445 19 21
9 7350 16000 5840 16000 9730 16 17
10 71100 66000 16130 71100 51077 09 03
11 75300 81800 44900 81800 67333 03 01
12 72800 32600 41900 72800 49100 06 04
13 19800 80100 34600 80100 44833 04 05
14 17720 25900 14040 25900 19220 15 13
15 49100 51800 16400 51800 39100 12 07
16 3150 15600 34300 34300 17683 14 15
17 11250 73000 23400 73000 35883 05 09
18 102400 82000 4820 102400 63073 01 02
19 3020 71300 9410 71300 27910 08 12
20 9570 88300 21960 88300 39943 02 06
T1 697 10540 9450 10540 6896 20 19
T2 4310 4060 2040 4310 3470 22 22
T3 4020 14600 11480 14600 10033 18 16
T4 4440 42300 8050 42300 18263 13 14

The rankings are very similar for the 2 methods; we will use the method-B rankings as an estimator of canopy-closure.