Introduction
Chainsaw and cable skidder are two main logging machines for wood harvesting in the Caspian forests. Selection cutting is the main silvicultural method in these forests. Harvesting in the Caspian forests has the potential to damage the trees that are left standing. Damages to residual trees during the selection cutting operation may decrease the quality of residual trees and increase stand mortality through insect and disease infestation. The wounds can cause stem deformity and significant losses of the final crop volume and value. The wound characteristics such as size, location, and intensity are the main factors that influence on the future quality of damaged trees. Logging damages to the residual trees increase as the time passes. The literature review shows that minor damage to the stem of residual trees during logging operation can have a major impact on the final stand volume as future saw logs. In the Caspian forests, many studies focused on the primary logging damage (immediately after logging operation) and a few studies were done on the secondary logging damage (after years). The objective of this research was to study the condition of logging wounds on residual trees after 12 years elapsed in the Caspian forests.
 
Materials and methods
The study was carried out in two adjacent compartments (35 and 42) of the district No., one of Nav watershed in Guilan province in the Caspian forest of Iran. The Nav watershed is located between 37° 38' 34" to 37° 42' 21" N and 48° 48' 44" to 48° 52' 30" E. The elevation of the study area is ranged from 1350 to 1600 m and the mean of annual precipitation and temperature are approximately 950 mm and 9.1°C, respectively. The original vegetation of this area is an uneven-aged mixed forestand is dominantly covered by Fagus orientalis and Carpinus betulus stands. These compartments selectively logged by ground-based logging operation during December and January of 2000. The characteristics of wounds (size, intensity, and location) on the residual trees were measured immediately after logging operation. The condition of wounds was restudied after 12 years from logging operation in the year of 2012.  
Results and discussion
The results of this study showed that 67.1% of wounds were closed and 32.8% of the damaged trees were not able to improve their wounds. About 4.2 percent of wounds caused to tree mortality as shown in Table 1.
 
Table 1. The condition of wounds after 12 years from logging damage in the study area




Frequency


Condition of wounds




Closed


Open


Decayed


Tree destroyed




Number


194


52


31


12




Percentage


67.1


18.0


10.7


4.2




Table 2 shows the condition of wounds on the trees with different diameters at breast height (dbh). The trees of dbh < 40 cm are more sensitive to logging wounds so that 58.4% of damaged trees of dbh < 20 cm and 10.5% of damaged trees with a dbh of 21-40 cm caused to tree mortality.
 
Table 2. The condition of wounds on the trees with different diameter at breast height (dbh)




Tree
dbh (cm)


 


Wound condition




 


Closed


 


Open


 


Decayed


 


Tree destroyed




 


N


%


 


N


%


 


N


%


 


N


%




< 20


 


1


8.3


 


1


8.3


 


3


25.0


 


7


58.4




21 - 40


 


34


89.5


 


0


0


 


0


0


 


4


10.5




41 - 60


 


89


92.7


 


4


4.1


 


2


2.1


 


1


1.0




61 - 80


 


49


70.0


 


13


18.6


 


8


11.4


 


0


0




>81


 


21


28.7


 


34


46.6


 


18


24.7


 


0


0




 
The effect of wound characteristics (size, intensity and location) on its future condition was studied and the results were shown in Table 3. Our study indicated that the wounds near the ground have a greater incidence of decay compared to the higher wounds. The wound size is one of the most important characteristics related to decay. The results showed the wounds in sizes <25 cm² had the most ability of healing. The bark squeezed intensity of bole wounds didn’t caused to tree mortality; while about 8.3% of wood-damaged intensity of bole wounds caused to tree mortality and 19.8 % of them caused to wood decayed (Table 3). Overall, results of this study indicated any major wound located in the lower section of the tree have the potential to greatly reduce the quantity and quality of the future wood product by causing stain or decay in the high-value butt log.
 
Table 3. The condition of wounds in the different wound characteristics




Wound characteristics


 


Wound condition




 


Closed


 


Open


 


Decayed


 


Tree destroyed




 


N


%


 


N


%


 


N


%


 


N


%




Size


 


 


 


 


 


 


 


 


 


 


 


 




< 25


 


116


90.6


 


9


7.0


 


3


2.4


 


0


0




26-100


 


74


70.5


 


29


27.6


 


2


1.9


 


0


0




101-1000


 


4


11.8


 


12


35.3


 


15


44.1


 


3


8.8




>1001


 


0


0


 


2


9.1


 


11


50.0


 


9


40.9




Intensity


 


 


 


 


 


 


 


 


 


 


 


 




Bark squeezed


 


60


88.2


 


8


11.8


 


0


0


 


0


0




Bark removed


 


79


79.0


 


12


12.0


 


7


7.0


 


2


2.0




Wood damaged


 


55


45.5


 


32


24.6


 


24


19.8


 


10


8.3




Location


 


 


 


 


 


 


 


 


 


 


 


 




Root


 


4


19.1


 


10


47.6


 


5


23.8


 


2


9.5




<1 m


 


73


60.4


 


20


16.5


 


20


16.5


 


8


6.6




1 – 2 m


 


53


69.8


 


19


25.0


 


3


3.9


 


1


1.3




>2 m


 


64


90.2


 


2


2.8


 


4


5.6


 


1


1.4




 
Table 4 presents the results of Chi square test for the effect of tree dbh and wound characteristics on the wounds condition. These results showed that the dbh of trees and wound characteristics (size, intensity, and location) have significant effect on wounds condition (Table 4).
 
Table 4. The results of Chi square test for the effect of tree dbh and wound characteristics on the wounds condition




Factor


Df


Chi Square Value


P-Value




Tree dbh


12


208.3


0.00**




Wound size


9


227.6


0.00**




Wound intensity


6


52.9


0.00**




Wound location


9


50.2


0.00**




** Significant at α = 0.05.
 
Conclusion
The results of this study showed that logging damage to stand can be reduced substantially.To achieve sustainable forest management, the main requirements are minimization of the logging damages.In the context of selection cutting management, minimizing logging damage to residual trees must therefore remain a major objective.In order to minimize felling damage, directional felling must be applied considering the skid trails.Pre-harvest planning and identifying the winching area before logging operation can reduce damage to the stand in the Caspian forests.