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Why Be a Shrub? A Basic Model and Hypotheses for the Adaptive Values of a Common Growth Form

Frank Götmark ; Elin Götmark (Institutionen för matematiska vetenskaper) ; A. Jensen
Frontiers in Plant Science (1664-462X). Vol. 7 (2016), p. artikel nr 1095.
[Artikel, refereegranskad vetenskaplig]

Shrubs are multi-stemmed short woody plants, more widespread than trees, important in many ecosystems, neglected in ecology compared to herbs and trees, but currently in focus due to their global expansion. We present a novel model based on scaling relationships and four hypotheses to explain the adaptive significance of shrubs, including a review of the literature with a test of one hypothesis. Our model describes advantages for a small shrub compared to a small tree with the same above-ground woody volume, based on larger cross-sectional stem area, larger area of photosynthetic tissue in bark and stem, larger vascular cambium area, larger epidermis (bark) area, and larger area for sprouting, and faster production of twigs and canopy. These components form our Hypothesis 1 that predicts higher growth rate for a small shrub than a small tree. This prediction was supported by available relevant empirical studies (14 publications). Further, a shrub will produce seeds faster than a tree (Hypothesis 2), multiple stems in shrubs insure future survival and growth if one or more stems die (Hypothesis 3), and three structural traits of short shrub stems improve survival compared to tall tree stems (Hypothesis 4)all hypotheses have some empirical support. Multi-stemmed trees may be distinguished from shrubs by more upright stems, reducing bending moment. Improved understanding of shrubs can clarify their recent expansion on savannas, grasslands, and alpine heaths. More experiments and other empirical studies, followed by more elaborate models, are needed to understand why the shrub growth form is successful in many habitats.

Nyckelord: woody plants, stem, multi-stemmed, shrubland, scrub, tree, growth, canopy



Denna post skapades 2016-08-26. Senast ändrad 2016-10-05.
CPL Pubid: 240825

 

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Institutioner (Chalmers)

Institutionen för biologi och miljövetenskap (GU)
Institutionen för matematiska vetenskaperInstitutionen för matematiska vetenskaper (GU)

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Matematik

Chalmers infrastruktur