Tropical Alpine Environments Research Articles

Tropical Alpine Environments: Plant Form and Function

Tropical Alpine Environments: Plant Form and Function

Tropical Alpine Environments: Plant Form and Function.Philip W. Rundel , Alan P. Smith , F. C. Meinzer

<i>Tropical Alpine Environments: Plant Form and Function.</i>Philip W. Rundel , Alan P. Smith , F. C. Meinzer

Reviews

Books reviewed in this article: Light and Photosynthesis in Aquatic Ecosystems. By J. T. O. Kirk. Diversity and Evolutionary Biology of Tropical Flowers. By P. K. Endress. Australian Vegetation. Ed. by R. H. Groves. The Common Ground of Wild and Cultivated Plants: Introduction, Invasion, Control and Conservation. (Botanical Society of the British Isles Conference Report number 22.) (Ed. by A. Roy Perry and R. Gwynn Ellis). Tropical Alpine Environments: Plant Form and Function. (Ed. by P. W. Rundel, A. P. Smith and F. C. Meinzer).

Tropical Alpine Environments: Plant Form and Function.

Tropical Alpine Environments: Plant Form and Function.

Tropical Alpine Environments: Plant Form and Function

Tropical Alpine Environments: Plant Form and Function

Wuchsformuntersuchungen im Páramo Costa Ricas I. Einführung. II. Acaena cylindristachya Ruiz et Pavon, Acaena elongata L. (Rosaceae-Sanguisorbeae) und Chusquea subtessellata Hitchcock (Poaceae)

The results presented here are the first part of a series of studies on growth forms in the tropical alpine environment of the Costa Rican Páramo. After a brief description of climatic and edaphic life conditions in the páramo of the Cordillera de Talamanca the growth forms of three species which are highly characteristic for the páramo-vegetation arc described and discussed in relation tò their environmental conditions. Chusqllea suhtessellata , a perennial monocarpic bamboo shrub prevailing in certain parts of the páramo. shows typical bamboo type of growth with its rhizomatic main ramification system in sheltered position of upper soil layers and production of 2-3 (4) m long erect halms. These branch in a very distinct manner by the development of regular and accessory axillary buds. Whereas the growth of the main-axis is completed within a few months only. the development of its branches and their further ramification can extend over several years. The compact spherical shape which can often be found in the páramo plants results from the mesotonie ramification of the stiff halms. the leafy branches reaching the top of their mother axes, but not overlopping them. Thus a green mantle of several decimeter dcpth is formed. Acaena cylindristachya , a polycarpic perennial rosette plant, is restricted to the páramo vegetation. By contraction of the roots the growing point of the rosette is kept in the sheltered conditions of the upper soil layer. The ramification of the plant is restricted to the production of axillary flowering branches. Since there is no production of vegetative branches the plant has no possibility of vegative propagation and thus is totally depending on success of generative reproduction. Acaena elongata , a small squarrose polycarpic shrub, is not restricted to habitats of the paramo. The depelopment of the main axis shows a certain rhythm resulting in the regular sequence of branched and unbranched zones, of long and short internodes and the production of axillary flowering shoots — in some respect similar to the closely related genus Polylepis . Acaena elongata , however, shows a fundamentally basitonic mode of ramification with monopodially growing branches, while Polylepis has sympodially ramified branches. The erect habit of Acaena elongata can be lost under certain conditions. Appearently the plant grows as a pioneer in many places, but cannot persist strong competition with other shrubs of the páramo as Hypericum irazuense or Vaccinium consanguineum . Success of colonizing disturbed sites (roadsides) may be due to the high degree of generative reproduction, the highly effective zoochorous diaspores and the ability of vegetative spreading.

Function of Dead Leaves in Espeletia schultzii (Compositae), and Andean Caulescent Rosette Species

Espeletia schultzii (Compositae) Wedd., a caulescent rosette species common above treeline in the Venezuelan Andes, retains dead leaves on the stem. Plants with bare stems have a higher probability of dying than control plants during the dry season. REGIONS ABOVE THE TREELINE in the tropics are typically characterized by plants with the caulescent rosette growth form. These plants have unbranched or little-branched semiwoody stems supporting rosettes of evergreen leaves; leaves are generally marcescent, remaining on the stem after they senesce. The form has evolved independently in the Andes (Espeletia, Compositae; Puya, Bromeliaceae; Plantago, Plantaginaceae; Paepalanthus, Eriocaulaceae; Draba, Cruciferae; Culcitium, Compositae; Blechnum, Blechnaceae), in Hawaii (Argyroxiphium, Compositae), in New Guinea (Cyatheap, Cyatheaceae; Blechnum, Blechnaceae), and in East Africa (Lobelia, Lobeliaceae; Carduus and Senecio, Compositae). The repeated evolution of the form suggests that it is an adaptive response to the tropical alpine environment. Tropical alpine regions are characterized by strong diurnal fluctuations in temperature and, generally, strong seasonal fluctuations in rainfall; wind speeds are generally low (Smith 1972). Mean monthly temperatures vary little through the year; however, clear weather during low rainfall periods produces lower minimum and higher maximum temperatures than in wet periods. Thus, both temperature stress and moisture stress are greatest during the dry season (fig. 1, table 1). It is probable that the caulescent rosette form provides a buffering effect against these diurnal and seasonal extremes (Hedberg 1964; Coe 1967; Smith 1974, 1975; Mabberley 1974). However, few controlled studies are available to test the hypothesis. Hedberg (1964) and Coe (1967) showed that marcescent leaves in Senecio keniodendron kept stem temperatures above 0?C at night despite subfreezing air temperatures. Coe (1967) observed that S. keniodendron plants which had been stripped of their leaves, applarently by visitors, had died. However, no data are given, and no controlled study was undertaken. The present study was designed to determine the function of marcescent leaves in Espeletia schultzii Wedd (Compositae), a widespread caulescent rosette species in the Venezuelan Andes. Populations of Espeletia schultzii extend from 2700 m to 4200 m on sites ranging from bog edges to xeric ridge tops. The stem is unbranched and can reach 120 cm in height. Marcescent leaves form a densely packed cylinder 10 to 15 cm thick. Even the tallest, oldest plants have the stem completely covered with these leaves. Average height-growth varies from one to two cm per year (Smith 1974), depending on topography and elevation. The tallest plants can therefore be over 100 years old. The lowermost leaves on very tall plants are often partly decomposed. Slow decomposition may result in part from low temperatures and in part from the presence of aromatic resins in the leaves. MATERIALS AND METHODS The study was carried out on NE-facing (windward) slopes at 3000 m and 3600 m in the valley of the Rio Sto. Domingo, 45 to 50 km east of Merida, 8?45' N latitude), Estado Merida, Venezuela. On 8 September 1972, the dead leaves were carefully removed from 50 adult plants at 3600 m. The dead leaves retained little or no mechanical connection with the stem, remaining in place only because they were tightly packed together. Thus, removal did not damage the stem. Near each experimental plant, a control plant of similar size was located. All 100 plants were marked with numbered metal tags. On 16 September 1972, the identical procedure was carried out at 3000 m. An unsuccessful attempt was made to repeat the experiment at 4200 m. At this elevation, dead leaves retained strong mechanical connections with the stem due to lower rates of decomposition, making their removal extremely difficult without damaging the

Arctic and Alpine Plant Life Cycles

Of the world's major biomes, tundras, including Antarctica and Green­ land, occupy about 15% of the land surface. These treeless areas, above treeline (alpine ) or beyond treeline latitudinally (arctic ) , contain relatively few plant species. The plants that are preadapted to tundras have bcen se­ lected by environmental regimes that contain less biologically usable energy than in other biomes. Yet Hare (78 ) has shown that even in the Canadian Archipelago the Arctic is not a heat sink on a yearly basis, for solar radia­ tion amounts to 35-40 kilolangleys/year (0-5 kly /year in net radiation), compared with 1 5-20 kly/year at treeline in Alaska and Keewatin. While altitudinal and latitudinal treeline conforms quite well to the lOoC mean for the warmest month, Bryson (46 ) reports that the northern limit of trees also corresponds with the southern limit of the arctic frontal zone in sum­ mer. This dynamic boundary may be controlled by vegetational differences in albedo and surface roughness. The functioning of plants, as influenced directly and indirectly by tem­ perature, becomes central in determining the various strategies that have evolved to enable them to cope with these heat-deficient ecosystems. The purpose of this review is to bring together recent information and theories on the adaptive mechanisms which enable plants to survive and function in environments with cool, short summers and cold, long winters-save for tropical alpine environments where winter comes nearly every night­ and, where possible, to relate these findings to the pattern of species and communities in different tundras. Much research has been done in recent years on the floristics, plant com­ munities, soils, ecophysiology, and now the ecosystems of different tundras. A few key books and articles that speak to this background of information are those of Schroeter ( 169 ) , S0rensen (176 ) , Polunin ( 1 50, 152 ) , Bliss