Crown asymmetry in high latitude forests: disentangling the directional effects of tree competition and solar radiation

Tuomas Aakala, Kenichiro Shimatani, Toshihiro Abe, Yasuhiro Kubota, Timo Kuuluvainen

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Light foraging by trees is a fundamental process shaping forest communities. In heterogeneous light environments this behavior is expressed as plasticity of tree growth and the development of structural asymmetries. We studied the relative influence of neighborhood structure and directional solar radiation on horizontal asymmetry of tree crowns in late-successional high latitude (67-68 degrees N) forests in northern Fennoscandia. We described crown asymmetries as crown vectors (i.e. horizontal vectors from stem center to crown center), which we obtained from canopy maps based on crown perimeter measurements in the field. To disentangle the influence of the two main determinants, inter-tree competition and directionality of above-canopy solar radiation at high latitudes, we applied circular statistical models, utilizing cylindrical distributions, to these data consisting of orientations and intensities of crown asymmetry. At the individual tree level, our model predicted crown asymmetry vectors from the current stand structure, and the predictions became better when the intensity of asymmetry (i.e. crown vector length) was higher. Competition was the main determinant of crown asymmetry for 2/3 of trees, and the model predictions improved when we incorporated the directionality of solar radiation. At the stand-level, these asymmetries had resulted in a small increment of the projected canopy area and an increased regularity of spatial structure. Our circular statistical modelling approach provided a quantitative evaluation of the relative importance of directionality of solar radiation and neighborhood stand structure, showing how both of these factors play a role in formation of crown asymmetries in high latitude forests. This approach further demonstrated the applicability of circular statistical modeling in ecological studies where the response variable has both orientation and intensity.
Original languageEnglish
JournalOikos
Volume125
Issue number7
Pages (from-to)1035-1043
Number of pages9
ISSN0030-1299
DOIs
Publication statusPublished - Jul 2016
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 1172 Environmental sciences
  • PINE FOREST
  • CANOPY
  • PLASTICITY
  • PATTERNS
  • MODEL
  • DISTRIBUTIONS
  • DISTURBANCE
  • TREEFALLS
  • SWEDEN
  • GROWTH
  • 4112 Forestry

Cite this

Aakala, Tuomas ; Shimatani, Kenichiro ; Abe, Toshihiro ; Kubota, Yasuhiro ; Kuuluvainen, Timo. / Crown asymmetry in high latitude forests: disentangling the directional effects of tree competition and solar radiation. In: Oikos. 2016 ; Vol. 125, No. 7. pp. 1035-1043.
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abstract = "Light foraging by trees is a fundamental process shaping forest communities. In heterogeneous light environments this behavior is expressed as plasticity of tree growth and the development of structural asymmetries. We studied the relative influence of neighborhood structure and directional solar radiation on horizontal asymmetry of tree crowns in late-successional high latitude (67-68 degrees N) forests in northern Fennoscandia. We described crown asymmetries as crown vectors (i.e. horizontal vectors from stem center to crown center), which we obtained from canopy maps based on crown perimeter measurements in the field. To disentangle the influence of the two main determinants, inter-tree competition and directionality of above-canopy solar radiation at high latitudes, we applied circular statistical models, utilizing cylindrical distributions, to these data consisting of orientations and intensities of crown asymmetry. At the individual tree level, our model predicted crown asymmetry vectors from the current stand structure, and the predictions became better when the intensity of asymmetry (i.e. crown vector length) was higher. Competition was the main determinant of crown asymmetry for 2/3 of trees, and the model predictions improved when we incorporated the directionality of solar radiation. At the stand-level, these asymmetries had resulted in a small increment of the projected canopy area and an increased regularity of spatial structure. Our circular statistical modelling approach provided a quantitative evaluation of the relative importance of directionality of solar radiation and neighborhood stand structure, showing how both of these factors play a role in formation of crown asymmetries in high latitude forests. This approach further demonstrated the applicability of circular statistical modeling in ecological studies where the response variable has both orientation and intensity.",
keywords = "1172 Environmental sciences, PINE FOREST , CANOPY , PLASTICITY , PATTERNS , MODEL , DISTRIBUTIONS , DISTURBANCE , TREEFALLS , SWEDEN , GROWTH, 4112 Forestry",
author = "Tuomas Aakala and Kenichiro Shimatani and Toshihiro Abe and Yasuhiro Kubota and Timo Kuuluvainen",
year = "2016",
month = "7",
doi = "10.1111/oik.02858",
language = "English",
volume = "125",
pages = "1035--1043",
journal = "Oikos",
issn = "0030-1299",
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Crown asymmetry in high latitude forests: disentangling the directional effects of tree competition and solar radiation. / Aakala, Tuomas; Shimatani, Kenichiro; Abe, Toshihiro; Kubota, Yasuhiro; Kuuluvainen, Timo.

In: Oikos, Vol. 125, No. 7, 07.2016, p. 1035-1043.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Crown asymmetry in high latitude forests: disentangling the directional effects of tree competition and solar radiation

AU - Aakala, Tuomas

AU - Shimatani, Kenichiro

AU - Abe, Toshihiro

AU - Kubota, Yasuhiro

AU - Kuuluvainen, Timo

PY - 2016/7

Y1 - 2016/7

N2 - Light foraging by trees is a fundamental process shaping forest communities. In heterogeneous light environments this behavior is expressed as plasticity of tree growth and the development of structural asymmetries. We studied the relative influence of neighborhood structure and directional solar radiation on horizontal asymmetry of tree crowns in late-successional high latitude (67-68 degrees N) forests in northern Fennoscandia. We described crown asymmetries as crown vectors (i.e. horizontal vectors from stem center to crown center), which we obtained from canopy maps based on crown perimeter measurements in the field. To disentangle the influence of the two main determinants, inter-tree competition and directionality of above-canopy solar radiation at high latitudes, we applied circular statistical models, utilizing cylindrical distributions, to these data consisting of orientations and intensities of crown asymmetry. At the individual tree level, our model predicted crown asymmetry vectors from the current stand structure, and the predictions became better when the intensity of asymmetry (i.e. crown vector length) was higher. Competition was the main determinant of crown asymmetry for 2/3 of trees, and the model predictions improved when we incorporated the directionality of solar radiation. At the stand-level, these asymmetries had resulted in a small increment of the projected canopy area and an increased regularity of spatial structure. Our circular statistical modelling approach provided a quantitative evaluation of the relative importance of directionality of solar radiation and neighborhood stand structure, showing how both of these factors play a role in formation of crown asymmetries in high latitude forests. This approach further demonstrated the applicability of circular statistical modeling in ecological studies where the response variable has both orientation and intensity.

AB - Light foraging by trees is a fundamental process shaping forest communities. In heterogeneous light environments this behavior is expressed as plasticity of tree growth and the development of structural asymmetries. We studied the relative influence of neighborhood structure and directional solar radiation on horizontal asymmetry of tree crowns in late-successional high latitude (67-68 degrees N) forests in northern Fennoscandia. We described crown asymmetries as crown vectors (i.e. horizontal vectors from stem center to crown center), which we obtained from canopy maps based on crown perimeter measurements in the field. To disentangle the influence of the two main determinants, inter-tree competition and directionality of above-canopy solar radiation at high latitudes, we applied circular statistical models, utilizing cylindrical distributions, to these data consisting of orientations and intensities of crown asymmetry. At the individual tree level, our model predicted crown asymmetry vectors from the current stand structure, and the predictions became better when the intensity of asymmetry (i.e. crown vector length) was higher. Competition was the main determinant of crown asymmetry for 2/3 of trees, and the model predictions improved when we incorporated the directionality of solar radiation. At the stand-level, these asymmetries had resulted in a small increment of the projected canopy area and an increased regularity of spatial structure. Our circular statistical modelling approach provided a quantitative evaluation of the relative importance of directionality of solar radiation and neighborhood stand structure, showing how both of these factors play a role in formation of crown asymmetries in high latitude forests. This approach further demonstrated the applicability of circular statistical modeling in ecological studies where the response variable has both orientation and intensity.

KW - 1172 Environmental sciences

KW - PINE FOREST

KW - CANOPY

KW - PLASTICITY

KW - PATTERNS

KW - MODEL

KW - DISTRIBUTIONS

KW - DISTURBANCE

KW - TREEFALLS

KW - SWEDEN

KW - GROWTH

KW - 4112 Forestry

U2 - 10.1111/oik.02858

DO - 10.1111/oik.02858

M3 - Article

VL - 125

SP - 1035

EP - 1043

JO - Oikos

JF - Oikos

SN - 0030-1299

IS - 7

ER -