Effect of Canopy Gaps on the Radial Growth of Trees Crown of the Hyrcanian Natural Forest Stands Using Digital Aerial Camera Images

Document Type : Scientific article

Authors

1 Forestry Department Gorgan University of Agricultural Sciences and Natural Resources

2 forest sciences facualty, Gorgan university of agricultural sciences and natural resources

3 Forestry department, Gorgan University of Agricultural Sciences and Natural Resources

Abstract

Abstract
Introduction and Aims:
Forest canopy cover gaps caused by natural or human factors can have a significant impact on the growth and development of the stand structure of the surrounding trees. In this study, the impact of the gaps on the growth rate of the crown in the radial growth of the crown of gap-edge trees was investigated compared to the growth of crowns of nongap-edge trees in some managed and unmanaged natural stands of the ShastKalateh Forest, Gorgan.

Material and methods:
In this study, the status of the crown area and the growth of gap-edge trees and nongap-edge trees were analyzed over the two periods of 2011 and 2016 using Ultracam-D digital aerial images. Accurate georeferencing and producing high spatial accuracy digital orthophotomosaics were performed by digital images of both periods. Then, twenty extracted gaps with proper spatial distribution were selected from the images of 2011 and 2016. Then, the crown extent of the trees located in the gap-edge and non-gap-edge areas was digitized by visual interpretation in both periods, and their area was computed. The normalization analysis of the data was performed by the Kolmogorov-Smirnov normalization test, and the significant difference analysis between the growing rate of the crown area of gap-edge trees compared with non-edge gap trees was done using a paired and independent T-test in the R and R Studio software.

Results:
Descriptive statistics of the crown area of gap-edge trees in the selected gaps showed that in the period 2011 to 2016, both gap-edge and non-gap-edge trees had a significant increase in the minimum, maximum, and average crown area. In addition, the results of the significant analysis of the crown radial growth of trees in 2011 and 2016 indicate a significant difference between these two periods at the confidence level of 99 %. The results also showed that the average growth of the crown area in the studied period was 21.09 and 7.14 square meters, and the annual average crown area growth was 4.21 and 2.94 square meters, respectively, for gap-edge and non-edge gap trees.

Conclusion:
This research made it clear that the canopy cover gaps can cause crown growth in gap-edge trees than the trees in the non-gap-edge trees, caused by the provision of appropriate light conditions and optical growth. Also, the use of high-resolution aerial images, such as Ultracam, enables changes to the crown structure of the trees over large time and scales.

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