5 Results
5.1 Forest Inventory of Yakpugang Community Forest
5.1.7 Harvesting Intensity and Diameter Distribution
The relationship between harvesting intensity and diameter distribution was studied by comparing the diameter distributions of three categories of harvesting intensity:
• No harvesting for at least 30 years (twelve plots),
• Moderate harvesting during past 30 years, but limited during past ten years (14 plots), and
• Intense harvesting during past ten years (ten plots).
This analysis was carried out for the use categories and for individual species. The
distributions of seedlings and seedlings/saplings were included in separate figures from the larger size classes, as the high numbers of seedlings/saplings made combined figures difficult to interpret.
5.1.7.1 1st Class Timber
The category of 1st Class Timber Species exhibited a strong “inverted J” (i-J) diameter distribution with steeper negative exponential curves in the plots with more logging, as can be seen in Figure 17. Diameter distribution of 1st class timber trees by harvesting intensity and Figure 18. Diameter distribution of 1st class timber seedlings and saplings by harvesting intensity.
The diameter distribution of trees (all size classes except seedlings and saplings) in plots with high harvest during the past ten years was significantly different from the plots with no harvesting during the past 30 years, Z = 2.26, p < .001, and plots with moderate harvesting during the past 30 years, Z = 1.13, p < .05. The diameter distribution of trees in plots with no harvesting was also significantly different from the plots with moderate harvesting, Z = 1.56, p < .001.
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Figure 17. Diameter distribution of 1st class timber trees by harvesting intensity
0 10 20 30 40 50 60 70
10-1 9
20-29 30-39
40-49 50-5
9 60-69
70-79 80-89
90-9 9
100-1 09
110-1 19
120-1 29
130-1 39
140-1 49
DBH Class (cm) Stem
Density (trees/ha)
no harvest 30 yrs mod harvest 30 yrs high harvest 10 yrs
Note: Trees with dbh > 9 cm were included.
Figure 18. Diameter distribution of 1st class timber seedlings and saplings by harvesting intensity
0 100 200 300 400 500 600 700 800 900 1000
Seedlings Saplings (0-4 cm) Saplings (5-9 cm)
Stem Density (per ha)
No harvest 30 yrs Mod. harvest 30 yrs High harvest 10 yrs
62 5.1.7.2 2nd Class Timber
The diameter distribution of the 2nd class timber species was similar to the 1st class timber species, but with a less distinct i-J pattern, as can be seen in Figure 19. Diameter distribution of 2nd class timber trees by harvesting intensity and Figure 20. Diameter distribution of 2nd class timber seedlings and saplings by harvesting intensity. The diameter distribution of trees in plots with high harvest during the past ten years was significantly different from the plots with no harvesting during the past 30 years, Z = 1.60, p < .005, but not with the plots with moderate harvesting during the past 30 years. The diameter distribution of trees in plots with no harvesting was significantly different from the plots with moderate harvesting, Z = 2.27, p
< .001.
Figure 19. Diameter distribution of 2nd class timber trees by harvesting intensity
0 5 10 15 20 25 30 35 40 45
10-19 20-
29 30
-39
40-49 50 -59
60-69 70-
79 80
-89 90
-99 100
-109 110-119
120-1 29
130-139 140-149
150-1 59
160-169
DBH Class (cm)
Stem Density (trees/ha)
no harvest 30 yrs mod harvest 30 yrs high harvest 10 yrs Note: Trees with dbh > 9 cm were included.
Figure 20. Diameter distribution of 2nd class timber seedlings and saplings by harvesting intensity
0 1000 2000 3000 4000 5000 6000 7000
Seedlings Saplings (0-4 cm) Saplings (5-9 cm)
Stem Density (per ha)
No harvest 30 yrs Mod. harvest 30 yrs High harvest 10 yrs
63 5.1.7.3 Other Use Trees
The “other use” category of trees, which had the highest number of trees, exhibited a strong i-J diameter distribution, as can be seen in Figure 21. Diameter distribution of "other use"
trees by harvesting intensity and Figure 22. Diameter distribution of "other use" seedlings and saplings by harvesting intensity. The diameter distribution of trees in plots with high harvest during the past ten years was significantly different from the plots with no harvesting during the past 30 years, Z = 1.11, p < .05, and with the plots with moderate harvesting during the past 30 years, Z = 2.04, p < .001.
Figure 21. Diameter distribution of "other use" trees by harvesting intensity
0 50 100 150 200 250 300
10-19 20-
29 30-
39 40-
49 50-
59 60-
69 70-
79
DBH Class (cm)
Stem Density (trees/ha)
no harvest 30 yrs mod harvest 30 yrs high harvest 10 yrs
Note: Trees with dbh > 9 cm were included.
Figure 22. Diameter distribution of "other use" seedlings and saplings by harvesting intensity
0 2000 4000 6000 8000 10000 12000 14000
Seedlings Saplings (0-4 cm) Saplings (5-9 cm)
Stem Density (per ha)
No harvest 30 yrs Mod. harvest 30 yrs High harvest 10 yrs
64 5.1.7.4 Quercus
The stem density for the Quercus category (four species) was much lower than the three other categories, with no more than ten trees*ha-1 for any size class except seedlings. The distributions exhibited sporadic or bimodal patterns in all harvesting classes with very limited regeneration of seedlings and saplings, as can be seen in Figure 23. Diameter distribution of Quercus trees by harvesting intensity and Figure 24. Diameter distribution of Quercus
seedlings and saplings by harvesting intensity. The diameter distribution of trees in plots with high harvest during the past ten years was significantly different from the plots with no harvesting during the past 30 years, Z = 2.51, p < .001, and the plots with moderate
harvesting during the past 30 years, Z = 2.64, p < .001. The diameter distribution of trees in plots with no harvesting was significantly different from the plots with moderate harvesting, Z
= 1.15, p < .05.
Figure 23. Diameter distribution of Quercus trees by harvesting intensity
0 1 2 3 4 5 6 7 8 9 10
10-19 20
-29 30
-39 40
-49 50
-59 60
-69 70
-79 80
-89
90-99 10 0-109
110-1 19
120-12 9
130-13 9
140-1 49 DBH Class (cm)
Stem Density (trees/ha)
no harvest 30 yrs mod harvest 30 yrs high harvest 10 yrs
Note: Trees with dbh > 9 cm were included.
Figure 24. Diameter distribution of Quercus seedlings and saplings by harvesting intensity
0 50 100 150 200 250 300 350 400 450
Seedlings Saplings (0-4 cm ) Saplings (5-9 cm)
Stem Density (per ha)
No harvest 30 yrs Mod. harvest 30 yrs High harvest 10 yrs
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Q. semiserrata was the only species of Quercus with any seedling regeneration. Even though Q. lamellosa had the 2nd highest BA of the 39 recorded tree species, no stems under 10 cm dbh were found in any of the plots.
5.1.7.5 Individual Species
When the diameter distributions of individual species were analyzed, there were no
significant differences between the three classes of harvesting intensity. Eight of the species exhibited i-J distribution patterns in most of the individual plots, while the other species exhibited sporadic distributions.
Schima khasiana, a first class timber species, exhibited an i-J distribution pattern in all 12 plots where it occurred. The i-J distribution pattern was the most distinct in the plots that had received high harvest levels during the past 10 years, but was also exhibited in plots which had not been harvested for 30 years, as can be seen in two representative plot examples in Figure 25. DBH distribution of Schima khasiana in a plot with no harvest for 30 years and Figure 26. DBH distribution of Schima khasiana in a plot with high harvest for 10 years Figure 25. DBH distribution of Schima
khasiana in a plot with no harvest for 30 years
0-9 10-19
Diameter Class
0 100 200 300 400 500
Sum Number Stems/ha
Spp: Schima khasiana, HC: None 30 yrs, Plot: 218
Figure 26. DBH distribution of Schima khasiana in a plot with high harvest for 10 years
0-9 10-19 20-29 30-39 40-49 50-59
Diameter Class
0 200 400 600 800 1,000 1,200 1,400
Sum Number Stems/ha
Spp: Schima khasiana, HC: High 10 yrs, Plot: 214
Several 2nd class timber species followed the same pattern. Cinnamomum bejolghota exhibited an i-J distribution pattern in 20 of 24 plots where it occurred; while Castanopsis hystrix exhibited an i-J distribution pattern in 12 of 23 plots. Cinnamomum bejolghota tended to exhibit more distinct i-J distribution patterns in plots that had been harvested during the past 10 years, whereas Castanopsis hystrix followed the opposite pattern, as can be seen in Figure 27- Figure 30.
66 Figure 27. DBH distribution of
Cinnamomum bejolghota in a plot with no harvest for 30 years
0-9 20-29 30-39 90-99
Diameter Class
0 100 200 300 400 500 600
Sum Number Stems/ha
Spp: Cinnamomum bejolghota, HC: None 30 yrs, Plot: 219
Figure 28. DBH distribution of
Cinnamomum bejolghota in a plot with high harvest for 10 years
0-9 20-29 40-49 50-59
Diameter Class 0
50 100 150 200
Sum Number Stems/ha
Spp: Cinnamomum bejolghota, HC: High 10 yrs, Plot: 213
Figure 29. DBH distribution of Castanopsis hystrix in a plot with no harvest for 30 years
0-9 10-19 160-169
Diameter Class
0 20 40 60 80 100 120
Sum Number Stems/ha
Spp: Castonopsis hystrix, HC: None 30 yrs, Plot: 209
Figure 30. DBH distribution of Castanopsis hystrix in a plot with high harvest for 10 years
0-9 10-19 20-29 30-39 40-49 50-59 110-119
Diameter Class
0 50 100 150 200 250
Sum Number Stems/ha
Spp: Castonopsis hystrix, HC: High 10 yrs, Plot: 202
Five species in the “other use” category also exhibited i-J distribution patterns:
Daphniphyllum chartaceum, Maesa chisia, Neolitsea spp, Symplocos glomerata, and Symplocos ramosissima. The diameter distributions of these species in representative plots can be seen in Appendix 9.
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