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close this bookCloud Forests in the Humid Tropics: A Bibliographic Review (UNU, 1987, 81 pages)
View the documentPreface
View the document1. Introduction
Open this folder and view contents2. Cloud forest distribution in the humid tropics
View the document3. Cloud forest terminology
Open this folder and view contents4. Cloud forest ecology
View the document5. Structure, composition and silvicultural aspects
View the document6. Conversion and conservation of cloud forests
View the document7. Conclusions and recommendations
View the documentList of references

5. Structure, composition and silvicultural aspects

Various different studies of the structure and floral composition of cloud forests exist. Given the great variety and heterogenous nature of different ones described in literature, it is difficult to generalize. However, this present chapter will limit itself by briefly describing studies of structure, followed by mentioning those of the composition and floristics of cloud forests, and ultimately there will be a discussion of the possibilities of forest management.

Leigh (1975) emphasized that in mountain forests affected by the presence of clouds, the "storey structure" is much more obvious than in lowland forests.

In the case of dwarf cloud forests, where a single tree-stratum exists above epiphyte-covered peat, a microclimatic explanation of this phenomenon is given by Leigh (1975) (see chapter 4, Climatic Elements and Factors).

The majority of studies of the structure of specific cloud forests have been undertaken in Andean cloud forests in Venezuela (Lamprecht, 1954, 1958, 1976, 1977; Roth and Merida de Bifano, 1971, 1979; Hoheisel, 1976; Huber, 1976; Bockor, 1979; Vareschi, 1980). Practically all these, which contain a large number of vegetation profiles, confirm the fact that structure displays distinct strata. However, Vareschi (1980) emphasizes that in different locations of the same cloud forest, the number and distribution of the strata can vary considerably (see figure 12).



Figure 12: Tree storey diagrams in different cloud forest sites of Roncho Grande, Venezuela, according to Vareschi (1980)

According to Beard (1955), the structure of a typical cloud forest (montane rain forest) has two tree strata that reach 10 m and 20 m, respectively. The upper stratum can be higher under favourable conditions. The four principal cloud forest formations, according to Beard (1944,1955), are shown in figure 13.



Figure 13 Profiles of the tour principal cloud forest types according to Beord
(1944, 1955)

Concerning the floristic composition of cloud forests, this present work has to limit itself to mentioning the principle studies undertaken in specific areas. The ecological, phytogeographical and climatic conditions of the different cloud forests studied are quite distinct, resulting in equally differentiated floristic compositions. Table 3 lists the authors of key studies and their study locations.

Table 3. List of authors of key studies of floristic composition in specific cloud forests

Beard (1949) Lesser Antilles
Beebe and Crane (1947) Rancho Grande, Venezuela
Bockor (1979) La Carbonera, Venezuela
Brass (1956, 1959,1964) New Guinea
Burgess (1969) Malaysia
Grubb et al. (1963) Cordillera de Guarca Urcu, Ecuador
Hoheisel (1976) San Eusebio, Venezuela
Howard (1968) Pico del Oeste, Puerto Rico
Huber (1976) Rancho Grande, Venezuela
Lamprecht (1954,1958) Valley de Mucuy, Venezuela
Lawton and Dryer (1980) Monteverde, Costa Rica
Lonard and Ross (1979) Tamaulipas, Mexico
Puig, Bracho and Sosa (1983) Tamaulipas, Mexico
Roth and Merida de Bifano (1971,1979) Rancho Grande, Venezuela
Schweinfurth (1957) Eastern Himalayas
Sobrevila, Ramirez and de Enrech (1983) Sierra de San Luis, Venezuela
Steyermark (1974, 1975) Sierra de San Luis, Venezuela
Sudgen (1982a, b, c, 1983) Serrania de Macuira, Colombia
Tanner (1977) Blue Mountains, Jamaica
Vareschi (1980) Rancho Grande, Venezuela
Veillon (1955, 1974) Andean cloud forests, Venezuela
Whitmore and Burnham (1969) Malaysia


More general publications on important floral aspects in tropical mountain areas, including incidence of clouds, are those of Knapp (1965) for the Central American region; Troll (1959) and Hueck (1978) for the South American subcontinent; Whitmore (1975) for Southeast Asia; and Richards (1952) and Letonzey (1978) for the tropics worldwide.

Some data concerning biomass above ground have been published by Brun (1976), Grubb (1977) and Tanner (1977, 1980a). Table 4 summarizes the different data obtained.

Table 4. Soil biomass (t/ha) in different types of cloud forests

Forest type Altitude
masl
Geographical
location
Source Biomass
above
ground
(t/ha)
"Bosque nublado andino" 2300 Venezuelan Andes Brun (1976) 420
Lower montane rain forest 2500 New Guinea Grubb (1977) 310
Lower montane rain forest 500 Puerto Rico Grubb(1977) 148-194
Upper montane rain forest:Morridge forest 1615 Blue Mountains, Tanner (1977 218
    Jamaica 1980a)  
Mull ridge forest 1615 " " 312
Wet slope forest 1570 " " 230
Gap forest 1590 " " 238


Considering the relatively high biomass values in cloud forests of the Venezuelan Andes studied by Brun (1976) it is not surprising that these forests are the only ones to have been subjected to silvicultural studies (Lamprecht, 1954, 1958; Bockor, 1979).

Lamprecht (1954) recommended the selection system ("Plenterbetrieb") for management and exploitation of high production cloud forests, although admitting that this method, which has been successfully applied in many temperate regions, should be modified according to local conditions taking into consideration future new findings. The principal considerations of Lamprecht's recommendations were to improve sustainable production (both in quantify and quality), ensure and promote natural regeneration, and enrich the forest with valuable species.

In another publication Lamprech (1958) concentrates his forest management recommendations on two types of cloud forests within which the valuable Podocarpus spp. dominate.

The most recent research into the possibility of managing Andean cloud forests is the work of Bockor (1979). According to his studies, almost 70% of the trees with dbh > 10 cm are likely to eventually find a place in the upper forest canopy. In addition there is considerable potential for the natural regeneration of wood-producing trees that in their natural environment do not have a great deal of competition from shrubs, ferns or bamboo.

Bockor (1979) emphasizes the importance of the genus Podocarpus and indicates the possibility of enriching the forest with species of this genus. In addition. he mentions the possibility of taking advantage of the high rate of natural regeneration, to transform certain parts of the forest, through careful management procedures, into more uniform and economically valuable stands without reducing its secondary functions.

The silvicultural studies undertaken by Lamprecht (1954, 1958) and Bockor (1979) represent a theoretical base for possible future management of certain Andean Venezuelan cloud forests, but practical experience is lacking. Such forests, due to composition and climate (relatively low rainl:a]l), are not comparable in silvicultural terms, with the majority of other cloud forests.

Generally, most of the tropical cloud forests do not offer reasonable or favourable conditions for forest management and exploitation due to one or a variety of the following reasons:

  1. unfavourable climatic conditions (particularly high rainfall)
  2. unfavourable topographical conditions (cloud forests are usually found on steeply-sloping or highly irregular terrain)
  3. unfavourable edaphic conditions
  4. high erosion risk (combination of 1, 2 and 3)
  5. hydrological function (many cloud forests are found in upper watersheds, being the principal regulators of the water regime, protecting: a) the downstream areas of the watershed and ensuring continuity in the water flow; b) the hydroelectric potential; and c) the useful lifespan of reservoirs)
  6. protection of communities of endemic flora and fauna; conservation of genetic resources
  7. protection of unique landscapes

Any future attempt lo manage cloud forests should take into account the above mentioned points. Only those cloud forests that do not present one or a variety of the above mentioned characteristics can be considered for future management and sustained exploitation, on the condition that there is a certain quantity and uniformity of valuable species (e.g. Podocarpus spp. or Quercus spp.) as for example in certain Costa Rican cloud forests, where Closer (1987) found a relative abundance of Quercus spp. of 76% within the trees with dbh > 25 cm and of 93%, within the trees with dbh > 45 cm