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 MSc Student in Forest Science and Engineering-Forest Management, Faculty of Forest Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, I. R. Iran

2 Professor, Faculty of Forest Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, I. R. Iran

3 Ph.D. in Forestry, Faculty of Forest Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, I. R. Iran

Abstract

Background and Objective: Forest canopy gaps play a crucial role in regulating the structure and dynamics of forest ecosystems. By altering light patterns, moisture levels, and spatial competition, these gaps can directly influence the crown growth of adjacent trees. Since gaps are decisive factors in regulating the spatial and light dynamics of the forest, obtaining precise information regarding their status and analyzing their impact on canopy growth is a key pillar in planning and implementing sustainable forest management strategies. Such data can be utilized in formulating management policies, restoring stand structures, and optimizing harvest intensity. Therefore, this study investigated the impact of canopy gaps on crown expansion, specifically the radial crown growth of trees adjacent to gaps compared to those not adjacent to gaps. The research was conducted in sections of both managed and unmanaged natural stands within the Shast-Kalateh Research and Educational Forest in Gorgan, utilizing UltraCam digital aerial imagery from 2011 and 2016.
Material and Methods: For this purpose, the expansion and growth status of tree crowns surrounding gaps, as well as those of non-adjacent trees, were analyzed for the periods of 2011 and 2016 using UltraCam-D digital aerial imagery. Precise georeferencing and the generation of high-spatial-resolution digital orthophotomosaics were performed for both periods. Subsequently, 20 canopy gaps with appropriate distribution and varying sizes, small (20–150 m²), medium (150–300 m²), and large (greater than 300 m²), were selected from the 2011 and 2016 orthophotomosaics (identifying gaps common to both periods). The crown extent of trees adjacent and non-adjacent to these gaps was then delineated via visual interpretation for both periods, and their areas were calculated. To test data normality and compare the crown area growth (for both adjacent and non-adjacent trees) over the study period, the Kolmogorov-Smirnov normality test and paired t-tests were employed. Furthermore, an independent t-test was used to compare the difference in crown growth rates between trees adjacent to gaps and those not adjacent to them.
Results: Descriptive statistics of the crown extent for trees surrounding the selected gaps revealed that in 2016 compared to 2011, both adjacent and non-adjacent trees exhibited significant increases in minimum, maximum, and mean crown areas. The results of the paired t-test indicated that the radial growth of trees adjacent to gaps (mean = 20.811 m²) and non-adjacent trees (mean = 14.703 m²) over the five-year period was significant at a 99% confidence level. Furthermore, the independent t-test used to compare the radial crown growth between the two groups showed that the difference in mean radial growth for trees adjacent to gaps versus non-adjacent ones was statistically significant at the 99% confidence level. Trees proximal to gaps exhibited higher radial growth rates during the study period (2011–2016). Additionally, the average annual growth was estimated at 4.16 m² for adjacent trees and 2.94 m² for non-adjacent trees.
Conclusion: This research demonstrates that forest canopy gaps, by increasing sunlight penetration to the lower strata, improve photosynthetic conditions and consequently enhance the crown growth of adjacent trees. The comparison between trees adjacent to gaps and those located in dense stands without gaps revealed significant differences in radial crown growth patterns and light productivity. These findings highlight the importance of gaps in regulating spatial competition and promoting the structural dynamics of forests. Moreover, the utilization of high-resolution aerial imagery, such as UltraCam, enables the precise monitoring of tree crown structural changes across broad temporal and spatial scales, serving as an effective tool for analyzing ecological trends and evaluating forest stand responses to management interventions. Such data can play a pivotal role in designing sustainable forest resource management strategies and optimizing managerial decision-making.

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References

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Forest Research and Development
Volume 12, Issue 1
June 2026
Pages 1-19

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