Although vines and self-supporting plants differ physiologically, anatomically, and phenologically, the primary differences are biomechanical. Lacking the capacity to hold themselves upright, climbing plants are constrained by their capacity to (i) encounter suitable structure(s) on which to climb; (ii) ascend efficiently; and, (iii) survive the inevitable mechanical demise of their supports. In this chapter, we address some of the biomechanical features of climbing plants within the context of their life history. We emphasize that vines have broken free from the constraints of having to be self-supporting, only to suffer new restrictions associated with mechanical dependence. Most of our comments pertain better to vines that climb by twining or with tendrils than to plants that climb with the aid of adventitious roots or other adhesive structures. Our bias towards woody vines (= lianas) in tropical forests (Figure 3.1) also will be apparent.

Locating suitable supports

Availability of suitable supports is a major constraint on the height growth of forest vines. The vast majority of vine ‘seedlings’ (and vines that have reached the top of their support) produce searcher shoots that grow up, bend over, and are successively replaced as each, in turn, fails to encounter a support (Palm, 1827; Darwin, 1867; Putz, 1984). In lowland forest in Panama, vines experimentally supplied with artificial trellises grew to be much taller than did control individuals (Putz, 1984). Vines can increase their likelihood of encountering a suitable support by: (i) actively searching; (ii) waiting (searching in time); and (iii) being able to ascend a wide range of support sizes.

Synonymy

Litter Godwin & Tansley 1929; Molinietum Godwin 1941, Willis & Jefferies 1959, Ivimey-Cook et al. 1975 p.p.; Molinia-edge Haslam 1965; Cirsio-Molinietum peucedanetosum (Sissingh & De Vries 1942) Wheeler 1978; Cirsio-Molinietum (Sissingh & De Vries 1942) Wheeler 1980c p.p.; Grassy Heath NCC Devon Heathland Report 1980.

Constant species

Carex panicea, Cirsium dissectum, Lotus uliginosus, Molinia caerulea, Potentilla erecta.

Rare species

Hypericum undulatum, Peucedanum palustre, Selinum carvifolia.

Physiognomy

The Cirsio-Molinietum caeruleae includes the bulk of the Molinia caerulea vegetation in the lowland south-east of Britain. Molinia is almost always the dominant plant in the community and it can be very abundant, forming the basis of a rough sward or occurring as a more stronglytussocky cover, a kind of structure well shown in the classic early account of this vegetation from Wicken Fen in Cambridgeshire (Godwin & Tansley 1929). And there are stands in which the abundance of Molinia is so overwhelming that its dense herbage and thick litter reduce the associated flora to scattered individuals of a very few species. Often, however, the number of companions is considerable: although many of the associates are plants of fairly wide distribution among damper meadows and pastures, the most frequent of them comprise a quite distinctive assemblage, and some of the preferentials attain such local prominence as to mask the major contribution which Molinia and the other constants make to the community. Much of this character reflects the origin of this kind of vegetation from rather diverse precursors by the application of particular treatments.

In structural terms, the most important associates of Molinia are other monocotyledons of medium stature, particularly rushes, which can make quite a substantial contribution to the dense layer of herbage characteristic of the community. Typically, this is 20-60 cm tall, though its physiognomy is strongly dependent on the style and incidence of treatment: in grazed stands, for example, the cover can be shorter than this, with stretches of close-cropped sward running among clumps of more resistant plants; where there is no grazing, and where the vegetation has not been mown for some time, the herbage can be taller and ranker. The trophic state of the substrate also influences the structure of the vegetation, with shorter and more open swards developing over more calcareous and impoverished soils.

Synonymy

Limestone heath Hope-Simpson & Willis 1955 p.p.; Agrosto-Ulicetum gallii Shimwell 1968 p.p.; Ulici-Ericetum cinereae Bridgewater 1970; Calluno-S cille turn vernae, Ulex gallii subassociation Malloch 1971 ; Calluna-Ulex gallii heaths Gimingham 1972; Grass-heath Ward et al. 1912a p.p.

Constant species

Calluna vulgaris, Erica cinerea, Ulex gallii.

Rare species

Agrostis curtisii, Viola lactea.

Physiognomy

The Calluna vulgaris-Ulex gallii heath is a floristically rather diverse community with only three constants overall, but its characteristic mixture of Calluna vulgaris, Ulex gallii and Erica cinerea, typically lacking E. tetralix, Molinia caerulea or Agrostis curtisii, is quite diagnostic. Often, the three sub-shrubs are co-dominant, though their proportions are quite variable and locally each can be poorly represented, E. cinerea in particular tending to become patchy where the community extends on to cooler aspects and to higher altitudes. In the latter situations, too, this kind of heath can have small amounts of Vaccinium myrtillus. On disturbed ground, as along pathways or over abandoned fields and settlements, U. europaeus may occur with some abundance.

Typically, the sub-shrub canopy is of high cover, sometimes excluding all but a very sparse herbaceous component but, quite often, the bushes are separated by systems of grassy runnels and, where the vegetation has been open to grazing, the structural contrast between these two components can be sharply accentuated. Where the bushes themselves are nibbled, a common occurrence, the canopy can be reduced in height: it is generally less than 30 cm, and a frequent picture is of dense ‘hedgehogs’ of gorse with short, but rather more untidy, bushes of heather scattered amongst them. In coastal stands, too, exposure to wind helps limit subshrub growth and, in exceptional cases, cliff-top heaths which are also heavily grazed can have a very tight cover of woody growth no more than a few centimetres high. Burning can also affect the structure and composition of the vegetation: controlled fires are rare but accidental burns can open up the ground, providing an opportunity for local dominance of U. gallii which can sprout vigorously from surviving buried stools, or E. cinerea, which can seed prolifically and out-perform Calluna in the early years of recovery, particularly on warmer aspects. Such temporary perturbations of dominance may also allow Pteridium aquilinum to increase its representation in this kind of heath.

Introduction

The principal advantage of the vine growth form is the potential for rapid growth rate. Carbon that would otherwise go into supporting stem tissue can go into leaves, thus yielding a compounding of the growth increment (Monsi & Murata, 1970). Although the difference in stem allocation between vines and other plants is clear, what has not been well documented is the proportional allocation of carbon and other resources in vines to nonproductive compounds and structures, including roots, compared to other growth forms. Here we examine at least a part of the area by focusing on the pool sizes and utilization patterns of storage reserves in various vine species.

Why should we expect vining plants to have different storage cycles from self-supporting plants in the same habitat? Trees and shrubs often store much of their reserves of water, carbohydrates, and nutrients within the massive stem. As a consequence of the vine growth form, vines have much less stem-to-leaf mass than do self-supporting plants, and so may require specialized sites in which to store reserves, and cycles to deposit and withdraw these reserves. If the vining strategy results in greater risk of physical injury than other growth strategies, as discussed by Fisher & Ewers (Chapter 4), then vines may benefit from having greater energy stores for repair and regrowth than trees. In the case of herbaceous perennials that die back during the unfavorable period, vines may rely upon their stored reserves to regain quickly the canopy position before deterioration of the light climate due to leaf out by over story trees.

Introduction

The classic work on climbers by Schenck (1892, 1893), is focused especially on anatomical features of lianas, but also includes a taxonomic and geographic survey of the occurrence of climbing plants. Such 19th century luminaries as Charles Darwin (1867) were fascinated by the peculiarities of climbing plants. However, despite their obvious importance in the world's flora, especially in tropical forests, climbers have subsequently been generally neglected. As summarized by Jacobs (1976), ‘The ecology of lianas is virtually a blank’. Indeed the significant ecological role played by lianas in tropical forests has only very recently begun to be investigated (e.g. Putz, 1984, 1985; Putz & Chai, 1987). Lianas have been no less neglected by plant collectors: quite probably lianas are the most undercollected of any major habit group of plants.

This overview of climbing plants is based largely on 0.1 ha data sets for plants >2.5 cm in diameter at breast height (dbh). The sampling protocol under which these data were gathered was originally set up specifically to facilitate ecological sampling of lianas, which are notorious for clumped distributions related to rampant vegetative reproduction (Peñalosa, 1984; Putz, 1984; Gentry, 1985). Each sample consists of ten 2 × 50 m narrowly rectangular plots set up end to end or separated by c. (10-)20 m, thus covering a relatively large area of forest that exceeds in scale the frequent ‘patches’ of single liana species that presumably derive from vegetative reproduction.

Introduction

Although the distinction between primary and secondary compounds in plants is imprecise and may on occasions appear arbitrary., the two terms effectively group compounds by both structure and role in plant biochemistry. Primary compounds include sugars, fats, protein amino acids, purines and pyrimidines, which are involved in essential cellular biochemical processes. However, plants also contain many thousand so-called secondary compounds which do not appear to be involved in these processes. The detailed structure and function of many of these is still uncertain, but it is generally accepted that their main roles are the selective deterrence or attraction of various classes of herbivore or pollinator (Bate-Smith, 1972; Rhoades, 1983). Such roles are often suggested, in the absence of other evidence, by a distinctive taste or smell. Other compounds such as the phytoalexins are involved in defenses induced by trauma, still others are precursors for biochemical processes within plants. The development of current theories of secondary metabolism in plants is lucidly reviewed by Haslam (1986). Even when a particular compound is known to be present, there may be large quantitive variations, depending on the part or individual sampled, location, age, season, climate, recent herbivory, and even time of day (McKey, 1974; Swain, 1977; Kingsbury, 1980).

After a brief introduction to the role of secondary compounds in plant defence, we will give examples of the more abundant and well-documented classes of secondary compounds found in vines, particularly those which are known to deter herbivores, comparing where possible their distribution in vines and other life forms.

Introduction

Where species diversity of vines is high, usually relative abundance is also high. However, because of their thin stems vines seldom form more than a minor proportion of the biomass of any forest, even in the tropics. Exceptions to this rule are often found during regeneration of very disturbed sites, where one or two species of vine become dominant. This chapter reviews the results of various quantitative studies of vines, mostly from mature tropical and subtropical forests.

As used in this chapter, ‘vines’ include all non-epiphytic climbers and, unless otherwise noted, those which commence life in the soil but may later become epiphytic, i.e. secondary hemiepiphytes. The vines therefore include the predominantly herbaceous, leafy smaller climbers and the mostly woody, bare-stemmed larger lianas (or lianes), between which there are loosely defined distinctions depending on regional usage.

The contribution of vines to forest structure in various regions

Abundance

Comparisons of the abundance of the thicker-stemmed vines (i.e. those greater than 2.5 cm in diameter) in forests of various regions have been made by Gentry (Chapter 1). However, as shown in studies such as those of Rollet (1969a, b), Proctor et al. (1983), Putz (1984) and Hegarty (1988), high proportions of stems of vines are found in the smaller size diameter-classes. Thin vines make an appreciable contribution to species richness (Gentry & Dodson, 1987).

The sampling of mire vegetation

In our survey of mires, the primary purpose has been to provide a classification of their vegetation according to its floristic composition, and not to categorise mires on the basis of their ecological development or hydrology, their situation in the landscape, or their gross morphology or fine surface patterning. Each of these other approaches to describing mires can yield benefits of its own, and we have tried to bring their various perspectives to bear in the interpretation of our results. Indeed, it was our hope that we might achieve some greater measure of understanding as to how the vegetation of mires relates to their form and function as perceived from these different standpoints. In the task of data collection, however, we were not concerned to dispose our samples according to any prior judgements about what did or did not constitute a particular kind of mire environment; rather, to ensure an adequate representation somewhere in our scheme of all vegetation types found in and around mires.

Most of that vegetation is described in this section of the work. Essentially, we are dealing here with communities made up of bryophytes, herbaceous plants and sub-shrubs sampled from a wide variety of bogs and wet heaths, fens, flushes, springs and soakways, where the ground is kept permanently or periodically waterlogged by high atmospheric humidity, a high ground watertable or lateral water flow. Many of the vegetation types occur on soils that are organic in character, but some are characteristic of mineral profiles, and the account presented here is thus not simply a classification of samples from peatlands, a category that is sometimes taken as synonymous with mires. On the other hand, there are certain kinds of vegetation which are often encountered in these different sorts of mires, indeed which frequently form an integral part of their mosaic of communities, but which are not included here. We did sample these, applying the same general principles of data collection throughout, but allowed the floristic distinctions among the vegetation types to emerge in the analyses, and have described certain communities in other sections of the work. Sometimes the reasons for this are more obvious, as with the various kinds of woodland that are associated with mires.

Synonymy

Mixed fen Holdgate 1955b p.p.; Carex nigra-Sanguisorba officinalis nodum Proctor 1974 p.p.; Carex nigra-Sanguisorba officinalis community Wheeler 1980c; Crepido-Juncetum Jones 1984.

Constant species Carex nigra, C. panicea, Crépis paludosa, Equisetum palustre, Filipendula ulmaria, Molinia caerulea, Potentilla erecta, Ranunculus acris, Succisa pratensis, Valeriana dioica, Calliergon cuspidatum.

Rare species

Primula farinosa.

Physiognomy

The Molinia caerulea-Crepis paludosa mire is a striking vegetation type, well-defined by a substantial block of constants and frequent companions, but showing quite considerable variation in its associated flora and embracing stands which, at one extreme, resemble swamp and, towards the other, are of a rank grassy character. Molinia caerulea is almost always present and it is often abundant, being the commonest dominant overall and frequently growing in a strongly-tussocky form, creating an irregular canopy up to 50 cm or so tall, and exerting a marked influence on the character and distribution of the associates. Among these are some other plants which can make a substantial contribution to the herbage. Carex nigra, for example, is a constant and it quite frequently occurs as prominent tufts or tussocks (var. subcaespitosa), sometimes rivalling or exceeding Molinia in its cover, particularly in the Sanguisorba sub-community (Proctor 1974). C. panicea can also be fairly abundant and C. pulicaris occurs commonly, too, though not usually as dense tufts. Then, in stands which are transitional to swamp, there can be some C. appropinquata, as at Malham Tarn in North Yorkshire (Proctor 1974), or C. rostrata, as at Sunbiggin Tarn in Cumbria (Holdgate 19556). In the Festuca subcommunity, by contrast, it is taller rushes and grasses which, together with Molinia, provide the bulk of the cover, Juncus acutiflorus forming locally dense patches, J. conglomeratus occurring as scattered tussocks. J. articulatus is also occasional throughout, though it often grows as a semi-decumbent plant and is rarely abundant.

The other important structural element typical of the community as a whole comprises hemicryptophyte dicotyledons which are capable of moderate to tall growth among the Molinia, sedges and rushes, but many of which can also subsist as rosettes in grazed stands. Most frequent among this group are Succisapratensis, Filipendula ulmaria, Valeriana dioica, Cirsium palustre, Caltha palustris and, adding a particularly distinct regional look, the Continental Northern Crépis paludosa and Northern Montane Trollius europaeus.

Synonymy

Oxyphilous fen vegetation Pallis 1911, Godwin & Turner 1933, Tansley 1939p.p.; Carex rostrata-Acrocladium cor difolium I cuspidatum sociation Spence 1964 p.p.; Carex lasiocarpa-Myrica & Myrica-Carex lasiocarpa sociations Spence 1964 p.p.; Carex nigra-Acrocladium sociation Spence 1964 p.p.; Carex rostrata-Aulacomnium palustre Association Birks 1973; Poor fen communities Proctor 1974 p.p.; General fen Adam et al. 1975 p.p.; Carex curta-Carex rostrata community Wheeler 1978; Caricetum lasiocarpae Koch 1926 sensu Birse 1980 p.p.

Constant species

Carex nigra, C. rostrata, Eriophorum angustifolium, Potentilla palustris, Succisa pratensis, Aulacomnium palustre, Sphagnum squarrosum.

Physiognomy

The Carex rostrata-Sphagnum squarrosum mire is a fairly heterogenous vegetation type characterised overall by the dominance of sedges with scattered poor-fen herbs over a patchy carpet of moderately base-tolerant Sphagna. The sedge cover is usually a few decimetres tall but quite variable in its abundance. The commonest species throughout are Carex rostrata and C. nigra, the former generally the more extensive and sometimes with a dense cover, the latter typically less abundant, though locally dominant, as in some stands of the Carex nigra-Acrocladium sociation described from Scottish lochs by Spence (1964) and in some of the Malham Tarn fens in North Yorkshire (Proctor 1974). C. lasiocarpa extends its occurrence among British mires into this kind of vegetation and it too can attain local prominence, so much so that stands which, on general grounds, clearly belong here have sometimes been included in distinct communities characterised by this sedge: e.g. the Carex lasiocarpa sociations of Spence (1964) and the Caricetum lasiocarpae (Koch 1926) of Birse (1980). C. curta, though generally more characteristic of oligotrophic and base-poor Rhynchosporion pools, is occasionally found (Spence 1964, Birks 1973, Wheeler 1978 who diagnosed a Carex curta-Carex rostrata community from the Ant valley in Norfolk) but C. limosa is typically absent. Likewise, towards the other extreme, C. diandra does not penetrate into this community: it is a good diagnostic species for the closely-related Carex rostrata-Calliergon mire. Finally, there may be a little C. echinata, especially where the Car ex-Sphagnum squarrosum mire extends on to firmer flushed peats.

Synonymy

Dune heath auct. angl., Calluna-Erica cinerea heath Gimingham 19646, 1972 p.p.; Calluna-Empetrum nigrum heath Gimingham 19646, 1972 p.p.

Constant species

Calluna vulgaris, Carex arenaria.

Rare species

Euphorbia portlandica, Trifolium suffocatum, Usnea flammea.

Physiognomy

Calluna vulgaris is the only constant sub-shrub throughout the Calluna-Carex arenaria heath, and it is often present in abundance, sometimes as an overwhelming dominant in rather impoverished vegetation. Generally, though, the cover of heather is discontinuous, decidedly patchy in younger or grazed stands, and there is frequently some other sub-shrub present, either intimately mixed with the Calluna or with the bushes of the codominants forming a more distinct mosaic. The most characteristic of these associaties is Erica cinerea, with Empetrum nigrum ssp. nigrum figuring in some places, and each of these can be abundant, locally to the exclusion of Calluna itself. Very occasionally, Ulex gallii can be found and in some stands Rosa pimpinellifolia is plentiful, with Erica tetralix and Salix repens occurring in transitions to wetter heath. Vaccinium myrtillus is typically very rare.

Even when some of these other sub-shrubs are present, the community can be distinguished from similar assemblages by the constancy of Carex arenaria, though this is hardly ever more than moderately abundant and often distinctly senile, except where the sand substrate becomes locally mobile, when renewed vigour and cover in the plant usually presage a transition to patches of Carex dune vegetation. Ammophila arenaria is also frequent through the community, though it is characteristically sparse and usually decidedly moribund, with just scattered shoots.

In more species-poor stands, little else than these plants may be represented, but other tracts of this kind of heath show considerable enrichment. First, among grasses, there is often some Festuca rubra or F. ovina (inadequately distinguished in the available data), with Agrostis capillaris and Anthoxanthum odoratum also occurring frequently in some situations and, less commonly, Poa pratensis (probably P. subcaerulea). The annuals Air a praecox and, more sparsely, A. caryophyllea can sometimes be found too. Apart from C. arenaria, sedges are absent though Luzula campestris occurs quite often.

Synonymy

Festuca ovina-Calluna ‘Rock Heath’ Coombe & Frost 1956ap.p.; Erica vagans-Ulex europaeus ‘Mixed Heath’, Genista pilosa variant Coombe & Frost 1956tz; Calluno-Scilletum vernae Malloch 1971 p.p.; Maritime heath Urquhart & Gimingham 1979p.p.; Genisto maritimae-Ericetum einereae Bridgewater 1970; Anthyllio corbierei-Ericetum cinereae Bridgewater 1970; Festuca ovina-Calluna vulgaris heath Hopkins 1983; Erica vagans-Ulex europaeus heath, Genista pilosa variant Hopkins 1983.

Constant species

Calluna vulgaris, Erica cinerea, Festuca ovina, Holcus lanatus, Hypochoeris radicata, Lotus corniculatus, Plantago lanceolata, P. maritima, Potentilla erecta, Scilla verna, Thymus praecox.

Rare species

Allium schoenoprasum, Astragalus danicus, Erica vagans, Euphorbia portlandica, Genista pilosa, Herniaria ciliolata, Isoetes histrix, Minuartia verna, Primula scotica, Scilla autumnalis, S. verna, Spiranthes spiralis, Trifolium bocconei, T. occidentale.

Physiognomy

In the Calluna vulgaris-Scilla verna heath, sub-shrubs are a consistent feature of the vegetation, though they are not always very obvious at first sight. For one thing, the canopy is typically of very short stature, rarely over 20 cm and usually less than 10 cm, with the bushes often wind-shaped over the unconformities of the ground. Then, the cover of the woody plants is rarely continuous and quite often rather open, particularly in unsheltered or rocky situations where it can be reduced to scattered bushes with stretches of grassy sward or exposures between. Even where the sub-shrubs are more extensive, their branches are commonly inter-penetrated by the herbs and, in grazed sites, which occur throughout the range of the community but which are especially preva Lent to the north, the whole vegetation can be trimmed to a neat, tight mat, just 2 or 3 cm high.

Of the sub-shrubs, Calluna vulgaris is the most frequent throughout and the commonest dominant though, on drier soils, it is characteristically accompanied by Erica cinerea and this, too, can be abundant. Where the community extends on to wetter ground, as it often does in the rainier north of the country, the latter is much reduced in frequency and E. tetralix and/or Empetrum nigrum ssp. nigrum (generally one or the other) are the more usual associates of Calluna and sometimes codominant with it.

Synonymy

Scottish Calluna heath Smith 1911b p.p.; Calluna-Arctostaphylos heath Muir & Fraser 1940, Gimingham 1964a, 1972; Arctostaphyleto-Callunetum McVean & Ratcliffe 1962, Ward 1971; Vaccinio-Ericetum cinereae (Birse & Robertson 1976) Birse 1980 p.p.; Arctostaphylos heath Urquhart 1986.

Constant species

Arctostaphylos uva-ursi, Calluna vulgaris, Deschampsia flexuosa, Erica cinerea, Vaccinium vitis-idaea, Dicranum scoparium, Hylocomium splendens, Hypnum jutlandicum, Pleurozium schreberi, Cladonia impexa.

Rare species

Arctostaphylos uva-ursi, Lycopodium annotinum, Pyrola media.

Physiognomy

Arctostaphylos uva-ursi can be found in a variety of heath types as an occasional, locally prominent associate but, in the heart of its range, it is most often found in this community which, though it has much in common with other sub-shrub vegetation of the region, frequently has a distinct boreal character. The Calluna vulgaris-A. uva-ursi heath, like its closest relative, the Calluna-Vaccinium heath, can have a variegated woody cover. Calluna is always present and overall it is the most frequent dominant, usually abundant and often overwhelmingly so, in a canopy that usually attains 2-4 dm in height and which can have a substantial total cover. Where, as is often the case, the vegetation is recovering from fairly recent burning, the heather can grow in dense building-phase stands from which many associates are all but excluded, and in such cases the diagnosis of the community is clearly very difficult. Frequently, however, other sub-shrubs make at least a minor contribution to the canopy and are able in various ways to exploit temporal and spatial gaps in the Calluna cover, attaining some measure of local abundance early in the heather regeneration cycle and sometimes again where the bushes have been allowed to proceed to the degenerate phase. But more precise studies of the effects of fire have been made here than on any other kind of heath (see below) and they show that the patterns of recovery are very varied and often quite persistent (e.g. Hobbs & Gimingham 1984Z?) so, within the general definition, even the proportions of the most frequent contributors to the vegetation can be diverse.

A. uva-ursi, though, is likewise a constant of the community and it can become modestly abundant in gaps within the heather cover but, even there, it typically has a prostrate habit, the branches of the creeping stems forming low mats, often only 5 cm or so thick.