Paper · 2026 · Biotropica

Variation and Determinants of the Shape of Trees With Irregular Trunks in Central Africa

Melain Merland Nguila Bakala; Grace Jopaul Loubota Panzou; Pierre Ploton; et al.

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Open access · cc-by

Abstract

ABSTRACT Trees developing irregularities on their trunks have an influence on the estimation of above‐ground biomass and carbon stocks in the tropics. This study aims to examine the variation and determinants of the shape of trees with irregular trunks in Central Africa. The study used close‐range photogrammetric data and conventional data to analyze 275 trees belonging to 11 species. For each tree, the isoperimetric quotient (Q) at 1.30 m has been estimated from a cross‐sectional disc. Between sites, we observed a significant variation in Q between two forest types, with trees tending to have lower Q values in the semi‐deciduous forest (Semi‐F) than in the evergreen forest (Ever‐F), indicating trees in Semi‐F had more irregular trunk shapes. Similar trends were reported for the three species shared by both forest types, suggesting an environmental control of the shape of trees with irregular trunks. Within sites, the lowest Q value was observed for Triplochiton scleroxylon in Semi‐F and for Pterocarpus soyauxii in Ever‐F, suggesting that these species had more irregular trunks than other species. The determinants of variations in Q were related to tree characteristics and species traits. At the tree level, Q was positively correlated with wood density and negatively correlated with crown volume, suggesting that trees with larger crowns and lower wood density are more likely to develop irregular trunks. At the species level, wind‐dispersed species and deciduous species tended to have more irregular trunks. These results provide insight into the life cycle strategies of tropical tree species.

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Claims 7

Associationobservedoriginal resultmeasured

Claim · model-written summary

Trunk shape quotient was lower in semi-deciduous than evergreen forest.

Taxon
treest0
Outcome
Q valuese0
Direction
lowere0
Comparator
evergreen forest (Ever‐F)e0
Setting
semi‐deciduous forest (Semi‐F)e0

Verbatim

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“trees tending to have lower Q values in the semi‐deciduous forest (Semi‐F) than in the evergreen forest (Ever‐F)”

✓ located verbatim in the source · abstract, characters 579–691 · show in text ↑
t0

“Trees”

✓ located verbatim in the source · title, characters 43–48 · show in text ↑
Observationobservedoriginal resultmeasured

Claim · model-written summary

Triplochiton scleroxylon had the lowest quotient in semi-deciduous forest.

Taxon
Triplochiton scleroxylonTriplochiton scleroxylone0
Outcome
Q valuee0
Direction
loweste0
Setting
Semi‐Fe0

Organisms pictured · Representative pictures of the matched species, not figures from the paper.

Triplochiton scleroxylon
Triplochiton scleroxylon · TaxonAkouete · CC BY-SA 4.0 · Wikimedia Commons ↗

Verbatim

e0

“the lowest Q value was observed for Triplochiton scleroxylon in Semi‐F”

✓ located verbatim in the source · abstract, characters 928–998 · show in text ↑
Observationobservedoriginal resultmeasured

Claim · model-written summary

Pterocarpus soyauxii had the lowest quotient in evergreen forest.

Taxon
Pterocarpus soyauxiiPterocarpus soyauxiie0
Setting
Ever‐Fe0

Not reportedOutcome

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e0

“for Pterocarpus soyauxii in Ever‐F”

✓ located verbatim in the source · abstract, characters 1003–1037 · show in text ↑
Associationobservedoriginal resultmeasured

Claim · model-written summary

Quotient correlated positively with wood density.

Taxon
treest0
Organ / stage
woode0
Outcome
Qe0
Direction
positively correlatede0
Qualifier
wood densitye0

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e0

“Q was positively correlated with wood density”

✓ located verbatim in the source · abstract, characters 1227–1272 · show in text ↑
t0

“Trees”

✓ located verbatim in the source · title, characters 43–48 · show in text ↑
Associationobservedoriginal resultmeasured

Claim · model-written summary

Quotient correlated negatively with crown volume.

Taxon
treest0
Organ / stage
crowne0
Outcome
Qe1
Direction
negatively correlatede0
Qualifier
crown volumee0

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“negatively correlated with crown volume”

✓ located verbatim in the source · abstract, characters 1277–1316 · show in text ↑
e1

“At the tree level, Q was positively correlated with wood density and negatively correlated with crown volume”

✓ located verbatim in the source · abstract, characters 1208–1316 · show in text ↑
t0

“Trees”

✓ located verbatim in the source · title, characters 43–48 · show in text ↑
Associationobservedoriginal resultmeasured

Claim · model-written summary

Wind dispersed species tended to have more irregular trunks.

Taxon
treest0
Material
wind‐dispersed speciese0
Outcome
irregular trunkse0
Direction
moree0

Verbatim

e0

“wind‐dispersed species and deciduous species tended to have more irregular trunks”

✓ located verbatim in the source · abstract, characters 1449–1530 · show in text ↑
t0

“Trees”

✓ located verbatim in the source · title, characters 43–48 · show in text ↑
Associationobservedoriginal resultmeasured

Claim · model-written summary

Deciduous species tended to have more irregular trunks.

Taxon
treest0
Material
deciduous speciese0
Outcome
irregular trunkse0
Direction
moree0

Verbatim

e0

“wind‐dispersed species and deciduous species tended to have more irregular trunks”

✓ located verbatim in the source · abstract, characters 1449–1530 · show in text ↑
t0

“Trees”

✓ located verbatim in the source · title, characters 43–48 · show in text ↑