1

Fig. 1. Locations of the Liperi training site and the Kiihtelysvaara and Koli test sites. In Liperi, the field plots were located max. 20 km away from the presented point, whereas in Kiihtelysvaara and Koli sites, all plots were located <3 km away from the presented points.

Table 1. Attributes of Scots pines used for training (Liperi site) and testing (Kiihtelysvaara and Koli sites) the mixed effect models. N = number, DBH = diameter at breast height, H = height, CBH = Crown base height. The range of values is given in parentheses.
Site Coordinates Nplot Ntree Mean DBH, cm Mean H, m Mean CBH, m
Liperi 62°28´N, 29°02´E 47 1051 24.8 (17.0–48.1) 21.2 (12.4–35.6) 13.3 (5.1–27.3)
Kiihtelysvaara 62°31´N, 30°11´E 66 414 23.1 (16.0–42.8) 19.5 (12.3–34.3) 11.0 (3.7–24.3)
Koli 63°03´N, 29°53´E 14 317 24.6 (16.1–44.4) 19.9 (11.2–28.8) 11.2 (2.8–21.8)
Table 2. Details of the laser scanning data obtained from the training (Liperi) and test (Kiihtelysvaara and Koli) sites.
Site Liperi Kiihtelysvaara Koli
Scanning time (month/year) 7/2016 6/2009 7/2005
Sensor type Optech Titan Optech ALTM Gemini Optech ALTM 3100
Flying altitude (m) 850 600 900
Scanning angle (°) 40 26 22
Pulse frequency (kHz) 250 100 100
Overlap (%) 55 55 35
Strip width on ground (m) 650 320 350
Mean pulse density (m–2) 13.2 14.7 5.2
Echoes/crown (First) 243 276 147
Echoes/crown (Last) 74 90 75
Table 3. A list of the predictor variables extracted from airborne laser scanning data. In the height percentiles, i = 5, 10, 15…80, 90, 95 and 99.
ALS metric Definition Computed for
TotalReturns Total number of returns Trees
TotalFirst Total number of first returns Plots
EWIDTH/NWIDTH Tree crown width and depth Trees
HMAX Maximum height Trees & plots
HMIN Minimum height Plots
HMEDIAN Median height Trees & plots
HMEAN Mean height Trees & plots
HSD Standard deviation of heights Trees & plots
HCV Coefficient of variation of heights Trees & plots
ICV Coefficient of variation of intensities Trees & plots
HMOD Mode of heights Trees & plots
H01TH 1st percentile of heights Plots
HiTH ith percentile of heights Trees & plots
HVAR Variance of heights Trees & plots
HKUR Kurtosis of heights Trees & plots
IKUR Kurtosis of intensities Trees & plots
HSKE Skewness of heights Trees & plots
ISKE Skewness of intensities Trees & plots
CRR Canopy relief ratio Plots
Table 4. Parameter estimates of the mixed effects models for diameter at breast height (DBH), height (H), and crown base height (CBH). For the fixed parameters, the standard error is given in parentheses. Subscripts t and p denote tree and plot level metrics, respectively. Variances and covariances of random parameters (unk) and residual errors (enki) are given (correlation shown in parenthesis). The abbreviations of the predictors are explained in Table 3.
Predictor DBH, cm H, m CBH, m
Intercept 28.284 (10.071) 1.756 (0.178) –0.466 (0.593)
H50t 0.660 (0.032)
H90t 0.523 (0.041)
H95t 2.154 (0.265)
ln(H95t) –18.664 (5.057)
HMAXt 0.460 (0.039)
HMEANp 0.237 (0.062)
ln(NWIDTH) 2.313 (0.330)
EWIDTH 2.121 (0.378)
EWIDTH2 –0.128 (0.035)
H70p –0.009 (0.002)
ISKEt –4.425 (0.420) 1.309 (0.207)
IKURt 1.113 (0.206) –0.367 (0.101)
HMEANt/EWIDTH 0.151 (0.047)
Random effects
var(unk) 0.818 0.071 0.976
cov(unk,un+1k) u1k u2k u3k
u2k 0.066 (0.273)
u3k –0.159 (–0.178) 0.083 (0.315)
var(enki) 6.644 0.310 1.556
cov(enki,en+1ki) e1ki e2ki e3ki
e2ki 0.069 (0.048)
e3ki –0.809 (–0.252) 0.048 (0.069)
2

Fig. 2. Observed (DBHobs) versus predicted (DBHpred) Scots pine diameters in the Kiihtelysvaara and Koli test sites. The predicted values were obtained with the fixed part of the mixed model trained at the Liperi site.

3

Fig. 3. Observed (Hobs) versus predicted (Hpred) Scots pine heights at the Kiihtelysvaara and Koli test sites. The predicted values were obtained with the fixed part of the mixed model trained at the Liperi site.

4

Fig. 4. Observed (CBHobs) versus predicted (CBHpred) Scots pine crown base heights at the Kiihtelysvaara and Koli test sites. The predicted values were obtained with the fixed part of the mixed model trained at the Liperi site.

Table 5. Root mean square errors (RMSE) and mean differences (MD) between the observed diameter at breast height (DBH), height (H), and crown base height (CBH) and the estimates obtained from the mixed effects models. The results are shown for the training site (Liperi) and for the two test sites (Kiihtelysvaara and Koli). Calibrations were made at the test sites using the pines with minimum and median diameters.
    Liperi Kiihtelysvaara Koli
DBH   RMSE, cm 2.7 3.1 3.91
RMSE% 10.9 13.4 15.9
RMSE calibrated, cm 2.87 3.58
RMSE% calibrated 12.4 14.6
MD, cm 0 –1.3 –1.3
MD% 0 –5.7 –5.4
MD calibrated, cm –0.77 –0.7
MD% calibrated   –3.3 –2.8
H   RMSE, m 0.6 1.09 1.28
RMSE%, m 2.8 5.6 6.4
RMSE calibrated, m 0.99 1.16
RMSE% calibrated 5.1 5.8
MD, m 0 0.61 –0.48
MD% 0 3.1 –2.4
MD calibrated, m 0.51 –0.22
MD% calibrated   2.6 –1.1
CBH   RMSE, m 1.6 1.46 2.07
RMSE% 12.0 13.3 18.5
RMSE calibrated, m 1.26 1.9
RMSE% calibrated 11.5 17.0
MD fixed, m 0 0.68 –0.65
MD% fixed 0 6.2 –5.8
MD calibrated, m 0.24 –0.33
MD% calibrated   2.2 –2.9