Crown shyness
Crown shyness is a phenomenon observed in some tree species, in which the crowns of fully stocked trees do not touch each other, forming a canopy with channel-like gaps.[1][2] It is also known as canopy disengagement,[3] canopy shyness,[4] or intercrown spacing.[5] The phenomenon is most prevalent among trees of the same species, but also occurs between trees of different species.[6][7]
Causes
The exact cause of crown shyness is not certain.[6] The phenomenon has been discussed in scientific literature since the 1920s.[8]
One theory is that the tall and slender trees in windy areas may suffer physical damage, as they collide with each other during winds. To prevent abrasions and collisions, they respond with crown shyness. Experiments show that if the crowns are artificially prevented from colliding in the winds, they gradually fill the canopy gaps.[9]
Australian forester M.R. Jacobs, who studied the crown shyness patterns in eucalyptus in 1955, believed that the trees' growing tips were sensitive to abrasion, resulting in canopy gaps.[10] Miguel Franco (1986) observed that the branches of Picea sitchensis (Sitka spruce) and Larix kaempferi (Japanese larch) suffered physical damage due to abrasion, which killed the leading shoots.[11][12]
However, Malaysian scholar Francis S.P. Ng, who studied Dryobalanops aromatica in 1977, found no evidence of abrasions due to contact in that tree. He suggested that the growing tips were sensitive to light levels and stopped growing when nearing the adjacent foliage.[13][6] In Betula pendula (silver birch), fewer buds develop in parts of the crown that are already dense or where the crowns of different trees start meeting, possibly because of less light.[14]
Another explanation is that the crown shyness inhibits spread of leaf-eating insect larvae.[15]
Species
Trees that display crown shyness patterns include:
- Species of Dryobalanops, including Dryobalanops lanceolata[16] and Dryobalanops aromatica (kapur)
- Some species of eucalypt[17]
- Pinus contorta or lodgepole pine[3]
- Avicennia germinans or black mangrove[5]
- Didymopanax pittieri[18][6]
- Clusia alata[18][6]
- K. Paijmans observed crown shyness in a multi-species group of trees, comprising Celtis spinosa and Pterocymbium beccarii[7]
References
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- ↑ TASS III: Simulating the management, growth and yield of complex stands
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