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Biology of vines
TREE vol. 4, no. 8, August
1989
Biology ofVines Francis E. Pub, Harold A. Mooney and Stephen H. Bullock THE CLIMBING HABIT IN PLANTS
included phloem, multiple vascular cambia and large bands of xylem parenchyma cause liana stems to react to mechanical stress more like multi-stranded cables than solid cylinders. N.M. Holbrook (Stanford University) reported that the anatomical structure of liana stems is associated with tremendous wood flexibility; the xylem of some lianas continued to conduct water when the stems were twisted by 1800”, but no tree wood tested withstood even a single rotation. Furthermore, research by J.B. Fisher (Fairchild Tropical Garden) and F.W. Ewers (Michigan State University) indicates that when liana stems do suffer mechanical damage, anatomical characteristics such as supernumerary and disjunct cambia promote callus formation and stem repair. Discussions of the functional anatomy of vines led to consideration of their physiological ecology. Particularly revealing were comparisons of water flux and storage in lianas, shrubs and trees in the genus Bauhinia. Compared with other growth forms, liana stems are very narrow relative to the leaf areas that they supply with water. This is hydraulically possible because lianas have long, large-diameter vessels with high rates of water flux. The functions of the numerous short and narrow vessels also characteristic of many liana stems are less clear. S. Carlquist (Ranch0 Santa Ana Botanical Garden) suggested that the smaller vessels and tracheids store water, contribute mechanical support, and serve as an accessory conductive system in the event of largevessel cavitation. Temperate vines also received attention. The physiological ecology of weedy vines like kudzu (Pueraria lobafa) and cultivated vines (e.g. Vitis) was also discussed. A. Teramura, I.N. Forseth and W.G. Gold (University of Maryland) reported on investigations of mesic temperate forest vines, and related patterns of light acclimation, photosynthesis and water use to climbing habit (e.g. twining or tendril climbing). FrancisPutzis at the Dept of Botany, University Their studies are providing the of Florida, Gainesville, FL 32611, USA; Harold physiological background for an exMooney is at the Dept of Biological Sciences, planation of why vines often become Stanford University, Stanford, CA 94305-2433, serious weeds. USA; Stephen Bullock is at the Estacicn de The roles of vines in forest comBiologia Chamela, Universidad National munities was much discussed. The Autcnoma de Msxico, Apartado Postal 21, results of recent research from West 48980San Patricia,Jalisco, MBxico. Africa, Australia and the neotropics has apparently evolved numerous times. Species that climb are well represented from tropical rain forests through temperate forests to semideserts. There are climbing ferns, gymnosperms, palms and peas. Bignoniaceae and Leguminosae are among the most speciose families of climbing plants in the tropics, whereas vines of arid habitats are often cucurbits, and many north temperate forests are draped with grapes and their relatives. Vines are among the world’s most important agricultural crops (e.g. hops and wine grapes) and forest products (e.g. rattan palms), but are also serious weeds both in agriculture (e.g. morning glories) and silviculture (e.g. kudzu). Vines range in size from the diminutive herbaceous species of clearings and forest understories, to the woody species that can attain stem diameters of nearly a meter. At a recent international symposium on vines at the Chamela Biological Station in Jalisco, Mexico, researchers discussed topics ranging from the biomechanics of twining to silvicultural methods for controlling vine infestations. There were detailed accounts of climbing plant evolution, stem anatomy and function, climbing mechanics, carbon and water relations, reproductive ecology, roles in forest communities, and economic importance. Although the study of vines has lagged somewhat behind that of trees and other free-standing plants, sufficient data are now available to warrant synthesis. Woody vines (lianas) differ from trees primarily in stem allometry and anatomy. Whereas tree stems thicken substantially to support the growing crown, liana stems rely on other plants for mechanical support and consequently can remain thin. Reviews of the long history of studies of vine stem anatomy set the stage for discussion of the biomechanical characteristics that allow vines to survive the fall of their host tree. Cambial variants such as
224
were presented on vine effects on trees and tree effects on vines. There is abundant evidence that vines have deleterious effects on trees and that they flourish in disturbed areas. One apparent successional trend after forest disturbance is for tendril climbers to predominate in young regenerating stands, but for twiners and bole climbers to increase in relative abundance through time. New data on vine leaf production and stem growth rates were also presented. Many vines are characterized by rapid stem extension growth rates, short-lived leaves, and extremely slow rates of stem diameter growth. Presence of large diameter vines is thus a good indication that a forest has not been subjected to serious disturbance for many years. In addition to relying on other plants for support, vines display a diverse array of characteristics associated climbing with their habits. Some of the differences between vines and self-supporting plants are related to reproductive biology and phenology. In seasonally dry forests in Costa Rica, for example, P. Opler (US Fish and Wildlife Service) and associates observed flowering patterns that were markedly seasonal in herbaceous vines relatively but aseasonal in lianas. The herbaceous vines that they monitored were also more strictly seasonal than lianas in leaf production. Fruiting phenologies of climbing plants as well as trees and shrubs in the same area seem better related to mode of dispersal than to growth habit. Winddispersed species generally fruited during the dry (windy) season whereas animal-dispersed species tended to fruit during the wet season. Even among climbing plants, however, there are substantial differences in seasonal patterns of leaf production and reproduction. It is still not clear why vines are such successful weeds, but part of the answer may lie in their great phenotypic plasticity in physiology, leaf display patterns and root distribution. Lianas grow where supports are available and thus, in contrast to trees, it makes little sense to try and describe liana ‘crown shapes’. There is also some evidence that vines are as opportunistic in their growth patterns below ground as they are above ground. Progess is being made towards understanding the relationship between form and function of the stems of climbing plants, but below-ground processes in vines (as in so many other plants) for the most part remain to be elucidated.
1989
Biology ofVines Francis E. Pub, Harold A. Mooney and Stephen H. Bullock THE CLIMBING HABIT IN PLANTS
included phloem, multiple vascular cambia and large bands of xylem parenchyma cause liana stems to react to mechanical stress more like multi-stranded cables than solid cylinders. N.M. Holbrook (Stanford University) reported that the anatomical structure of liana stems is associated with tremendous wood flexibility; the xylem of some lianas continued to conduct water when the stems were twisted by 1800”, but no tree wood tested withstood even a single rotation. Furthermore, research by J.B. Fisher (Fairchild Tropical Garden) and F.W. Ewers (Michigan State University) indicates that when liana stems do suffer mechanical damage, anatomical characteristics such as supernumerary and disjunct cambia promote callus formation and stem repair. Discussions of the functional anatomy of vines led to consideration of their physiological ecology. Particularly revealing were comparisons of water flux and storage in lianas, shrubs and trees in the genus Bauhinia. Compared with other growth forms, liana stems are very narrow relative to the leaf areas that they supply with water. This is hydraulically possible because lianas have long, large-diameter vessels with high rates of water flux. The functions of the numerous short and narrow vessels also characteristic of many liana stems are less clear. S. Carlquist (Ranch0 Santa Ana Botanical Garden) suggested that the smaller vessels and tracheids store water, contribute mechanical support, and serve as an accessory conductive system in the event of largevessel cavitation. Temperate vines also received attention. The physiological ecology of weedy vines like kudzu (Pueraria lobafa) and cultivated vines (e.g. Vitis) was also discussed. A. Teramura, I.N. Forseth and W.G. Gold (University of Maryland) reported on investigations of mesic temperate forest vines, and related patterns of light acclimation, photosynthesis and water use to climbing habit (e.g. twining or tendril climbing). FrancisPutzis at the Dept of Botany, University Their studies are providing the of Florida, Gainesville, FL 32611, USA; Harold physiological background for an exMooney is at the Dept of Biological Sciences, planation of why vines often become Stanford University, Stanford, CA 94305-2433, serious weeds. USA; Stephen Bullock is at the Estacicn de The roles of vines in forest comBiologia Chamela, Universidad National munities was much discussed. The Autcnoma de Msxico, Apartado Postal 21, results of recent research from West 48980San Patricia,Jalisco, MBxico. Africa, Australia and the neotropics has apparently evolved numerous times. Species that climb are well represented from tropical rain forests through temperate forests to semideserts. There are climbing ferns, gymnosperms, palms and peas. Bignoniaceae and Leguminosae are among the most speciose families of climbing plants in the tropics, whereas vines of arid habitats are often cucurbits, and many north temperate forests are draped with grapes and their relatives. Vines are among the world’s most important agricultural crops (e.g. hops and wine grapes) and forest products (e.g. rattan palms), but are also serious weeds both in agriculture (e.g. morning glories) and silviculture (e.g. kudzu). Vines range in size from the diminutive herbaceous species of clearings and forest understories, to the woody species that can attain stem diameters of nearly a meter. At a recent international symposium on vines at the Chamela Biological Station in Jalisco, Mexico, researchers discussed topics ranging from the biomechanics of twining to silvicultural methods for controlling vine infestations. There were detailed accounts of climbing plant evolution, stem anatomy and function, climbing mechanics, carbon and water relations, reproductive ecology, roles in forest communities, and economic importance. Although the study of vines has lagged somewhat behind that of trees and other free-standing plants, sufficient data are now available to warrant synthesis. Woody vines (lianas) differ from trees primarily in stem allometry and anatomy. Whereas tree stems thicken substantially to support the growing crown, liana stems rely on other plants for mechanical support and consequently can remain thin. Reviews of the long history of studies of vine stem anatomy set the stage for discussion of the biomechanical characteristics that allow vines to survive the fall of their host tree. Cambial variants such as
224
were presented on vine effects on trees and tree effects on vines. There is abundant evidence that vines have deleterious effects on trees and that they flourish in disturbed areas. One apparent successional trend after forest disturbance is for tendril climbers to predominate in young regenerating stands, but for twiners and bole climbers to increase in relative abundance through time. New data on vine leaf production and stem growth rates were also presented. Many vines are characterized by rapid stem extension growth rates, short-lived leaves, and extremely slow rates of stem diameter growth. Presence of large diameter vines is thus a good indication that a forest has not been subjected to serious disturbance for many years. In addition to relying on other plants for support, vines display a diverse array of characteristics associated climbing with their habits. Some of the differences between vines and self-supporting plants are related to reproductive biology and phenology. In seasonally dry forests in Costa Rica, for example, P. Opler (US Fish and Wildlife Service) and associates observed flowering patterns that were markedly seasonal in herbaceous vines relatively but aseasonal in lianas. The herbaceous vines that they monitored were also more strictly seasonal than lianas in leaf production. Fruiting phenologies of climbing plants as well as trees and shrubs in the same area seem better related to mode of dispersal than to growth habit. Winddispersed species generally fruited during the dry (windy) season whereas animal-dispersed species tended to fruit during the wet season. Even among climbing plants, however, there are substantial differences in seasonal patterns of leaf production and reproduction. It is still not clear why vines are such successful weeds, but part of the answer may lie in their great phenotypic plasticity in physiology, leaf display patterns and root distribution. Lianas grow where supports are available and thus, in contrast to trees, it makes little sense to try and describe liana ‘crown shapes’. There is also some evidence that vines are as opportunistic in their growth patterns below ground as they are above ground. Progess is being made towards understanding the relationship between form and function of the stems of climbing plants, but below-ground processes in vines (as in so many other plants) for the most part remain to be elucidated.