Elsevier

Biological Conservation

Volume 101, Issue 1, September 2001, Pages 23-31
Biological Conservation

Toward the sustainable harvesting of epiphytic bromeliads: a pilot study from the highlands of Chiapas, Mexico

https://doi.org/10.1016/S0006-3207(01)00053-2Get rights and content

Abstract

For the immediately threatened forests and bromeliads in the highlands of Chiapas, Mexico, we suggest an empirical approach to attain sustainability in the gathering of bromeliads for home decoration. On the basis of theoretical considerations and the results from a pilot study in three forest stands along a disturbance gradient at La Florecilla, we propose that harvesting should be limited to populations (1) that have a density no less than 9000 large rosettes/ha, (2) that are evenly distributed in space, and (3) that grow in the lower stratum of the forest, thus having little effect on their reproductive capacity. In a second study at La Florecilla we used a plotless point-centred quarter method to estimate the population density and homogeneity in spatial distribution of all species of bromeliads in the structurally heterogeneous forest. We found one species, Tillandsia vicentina, that met the prerequisites, having both a satisfactory average population density of ca. 24,000 large (>20 cm) rosettes/ha on oaks and a spatially even distribution. We estimate that an annual harvest of 112,000 rosettes of T. vicentina from the lower stratum of the 160 ha forest at La Florecilla can be maintained, in a 4-year rotation cycle. The implementation of a monitoring program should be included in any management plan.

Introduction

The most conspicuous epiphytes in the pine–oak forests of the highlands of Chiapas in the south-west of Mexico are bromeliads (Bromeliaceae), because of their characteristic growth form and large number of individuals. Nearly all of these belong to the genus Tillandsia, of which in total 57 species have been reported from the state, comprising many regional endemics (Utley, 1994). Several of the Tillandsia species are of ceremonial and ornamental value to the indigenous highland people of Maya origin. As a consequence, there is a local market for bromeliads, which are collected in large numbers from natural populations without control of the extraction rate (Breedlove and Laughlin, 1993).

While local harvesting contributes to the decrease of plant populations, the most severe threat to epiphytes is probably the loss and degradation of forest. In the central highlands of Chiapas, annual deforestation rates for 1974–1984 and 1984–1990 were 1.58 and 2.13%, respectively (Ochoa-Gaona and González-Espinosa, 2000). Furthermore, the selective logging of large trees and the destruction of the undergrowth has led to increasingly open and dryer forests, which favour more drought-resilient epiphytic species (Hietz and Hietz-Seifert, 1995a).

One of the reasons forests are degrading and disappearing world-wide is that over exploitation and agricultural use in general have a clear short-term benefit, while the natural habitats are generally under-valued economically, especially for local stake holders (W.R.I., I.U.C.N., U.N.E.P., 1992, Gullison et al., 2000). One option in Chiapas is to allow sustainable production of bromeliads for home decoration, a concept known as canopy farming (Neugebauer et al., 1996, Verhoeven and Beckers, 1999).

Bromeliads from Mexico may provide a commercially viable canopy product as in neighbouring countries (Jenkins and Oldfield, 1992, Rauh, 1992). Between 1993 and 1995, Guatemala exported 14.5 million Tillandsia plants annually (Véliz-Pérez, 1997). According to Rauh (1992), information from the World Wildlife Fund in Germany suggests that in the first three months of 1988 alone, 150,000 kg of these epiphytes, c. six million plants, were exported from Guatemala. Rauh (1992) estimates that at least 75% of the Tillandsia plants in farms are collected from the wild, and holds such activities responsible for a decline of bromeliads in Guatemala, casting doubts upon the sustainability of this harvesting practice (Holbrook, 1991).

When we aim to obtain criteria for sustainable harvesting, two approaches may be followed. By means of demographic and/or genetic studies and modelling we may attempt to establish the minimum viable population size (MVP) and propose management interventions based on population viability analysis (PVA; Menges, 1990, Menges, 2000). The MVP has no universal value (Soulé, 1987) and for epiphytes is likely to vary between trees of different architecture, between forests of different structure, and between ramets and genets of the same population (Damman and Cain, 1998). A reliable PVA, moreover, requires observations over a long period of time. For the immediately threatened bromeliads we advocate a more empirical approach to guarantee sustainability of yield in which we considered three prerequisites that should be met: (1) a high population density; (2) a population which is evenly distributed in space; and (3) a reproductive potential of the population that should not be affected by the removal.

The present study was made in the pine-oak forest of the indigenous Maya community at La Florecilla. First, we carried out a pilot study in three categories of forest disturbance to establish a threshold for the even-distribution prerequisite. Next, we conducted a transect study to identify populations of bromeliads that may be exploited with sustainability of yield and with minimal effort. We recognise that, if the harvesting of bromeliads is used as a means of conserving biodiversity, it must also be compatible with both socio-economic and ecological sustainability (Freese, 1996).

Section snippets

Study site: La Florecilla

La Florecilla is situated within the municipality of San Cristóbal de Las Casas in the central part of the highlands of Chiapas, Mexico (16°42′15′′ N, 92°35′38′′ W). The regional climate is temperate sub-humid (Garcı&#x0301;a, 1988). Climatic records (1978–1995) from a local weather station show an annual average temperature of 14.8°C and precipitation of 1042 mm. There is a pronounced dry period between December and April when monthly precipitation is <30 mm, and night frosts may occur. The

Methods

In 1998, we selected three stands within the continuous forest at La Florecilla, LF-1, LF-2 and LF-3. They were chosen to differ in the relative number of large oaks and the number of resprouted oak trees to reflect differences in disturbance regime. We also considered tree species composition since in the pine–oak forests in Chiapas human intervention may lead to a dominance of pine trees (González-Espinosa, et al., 1991). The distance between the stands was 1–3 km.

At each stand we determined

Methods

We selected a random sample of 35 points on nine parallel transects, evenly distributed over the 160 ha forest at La Florecilla, and selected four host trees at each point, applying the plotless point-centred quarter method (Cottam and Curtis, 1956). Oaks comprised 96 of the 140 trees sampled, but since we treated separate trunks from resprouted oaks as individual trees the number of ‘individuals’ was raised to 110. Tillandsia rosettes only were counted on each tree and only those >20 cm tall,

Discussion

Along the disturbance gradient in the pilot study, both the number of epiphytic species and their total biomass decreased (Table 2). We used the biomass as an estimate of abundance since individual plants may often not be discerned due to the clumped growth habit of many species (Gradstein et al., 1996, Hietz-Seifert et al., 1996). The differences in branch occupation may be attributed to differences in habitat resources such as light or water availability. Studies on the density of orchids

General conclusions

  • 1.

    In a 160 ha pine–oak forest, we identified one species of bromeliad, Tillandsia vicentina, which may be harvested to give an annual sustainable yield of 112,000 rosettes.

  • 2.

    We recommend that monitoring of the population should be part of a management plan for sustainable use.

  • 3.

    Whether the harvesting of bromeliads is also sustainable in the broad sense, depends in part on socio-economic circumstances, not addressed in this paper. We hope that the exploitation of bromeliads as an alternative

Acknowledgments

We are grateful to the community of La Florecilla and the Hermanas Misioneras Clarisas de La Florecilla for their co-operation and for granting us access to their forest. H.E. Castañeda-Ocaña and F. Bolom-Ton assisted with the fieldwork. H.J.F. van Dunné, J.G.B. Oostermeijer, P.F. Quintana-Ascencio and anonymous reviewers provided valuable comments on the manuscript. We thank R.A.A. Oldeman for permitting free use of the term Canopy Farming©. Funds were provided by SIBEJ (Sistema de

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