Establishing suitable bio-indicators for cloud forest management

Cloud forest

Cloud forest has high levels of biodiversity, serves as an essential source of freshwater, and is a globally endangered habitat type

Cloud forests are particularly vulnerable to disturbances such as anthropogenic encroachment, invasive species and climate change. Effective management therefore requires efficient early warning systems that detect changes in forest condition before it is too late to intervene. Until now monitoring schemes have been expensive, requiring high tech equipment and trained personnel, but using ecological indicators is a low cost alternative. A study into epiphytic ferns inNorthern Venezuela suggests that, with low levels of effort, time and cost, these species can be monitored and used as indicators of disturbance.

Cloud forest has high levels of biodiversity, serves as an essential source of freshwater, and is a globally endangered habitat type. In this context successful environmental management requires monitoring tools that provide reliable information about fluctuations in ecosystem conditions. We applied this indicator species idea by linking variation in abundance, diversity and dispersal of epiphytic pteridophytes to variation in structure of a Venezuelan coastal montane cloud forest.

Figure 1

Fig 1. Numbers of individuals in the primary forest plots, ecotone plots and disturbed forest plots in comparison

Ecological indicators measure the extent of stress or the ecological response to stressors, providing a simple and efficient method to track the ecological health of an ecosystem. The choice of effective indicators is crucial for a successful monitoring programme. Our intention was to find highly abundant, easily assessed plant species that are sensitive to stresses on cloud forest ecosystems. They need to respond to stress in a predictable manner and to signify changes that can be prevented by appropriate interventions. Since cloud forests are abundant in epiphytes, which rely on the delicate equilibrium of hydrological and ecological conditions found in these environments, vascular epiphytes seemed a priori excellent candidates. Ferns are, moreover, easy to spot, count, identify and distinguish.

Disturbed vs undisturbed sites

We established six 20 by 20 m plots (400 m2), of which in each case three followed a perturbation gradient from primary forest to an ecotone and disturbed forest. To ease counting and identification in future monitoring schemes, we focused on the easily accessible under storey (first 2 m above the ground). Every counted individual was classified with regard to its species, position, host plant and compass-orientation [360°] on the host plant. Voucher specimens were deposited in the herbaria VEN, TUB and STU.

Data is easy to collect, meaning that it can be acquired cheaply and easily

We found decreased diversity and abundance of all epiphytic pteridophytes in disturbed sites, compared to pristine sites; also, the epiphytic fern community tended to more clustered and different orientations on their host plants or phorophytes at disturbed sites versus pristine sites.

Against expectations alpha diversity, the number of species that co-occur in the different habitat types, of epiphytic pteridophytes did not decrease significantly from the primary forest via the transition zone to disturbed forest (see Fig 1). The number of species declined from 32 species in the primary forest plots to 28 species in the transition zone and 26 species in the disturbed forest (Fig 1).

In contrast to diversity, epiphyte abundance considerably decreased by 75% from the primary forest to the disturbed forest (see Fig 2). Therefore the number of individuals may be a more sensitive indicator of environmental and microclimatic changes than species numbers, and is in addition easier to observe than clustering and orientation.

Figure 2

Fig 2. Abundance of the most frequent species in the different habitat types, H. trichomanoides, E. apiculata, E. bellermannianum, S. fraxinifolium and other species, showing a steep decline from the primary to the secondary forest

Suitable indicator species

Our results suggest that disturbance strongly affects diversity and distribution of epiphytic pteridophytes. In particular, we suggest the species Elaphoglossum apiculata, Hymenophyllum trichomanoides, Serpocaulon fraxinifolium and Elaphoglossum bellermannianum suitable as indicators for disturbance in the cloud forest of the Cordillera de la Costa, because they are common and their distributions seem to be strongly affected by disturbance.

Four fern species (particularly Hymenophyllum trichophyllum), which were restricted to the ecotone and disturbed forest, can be seen as indicators for disturbance. However, they do not alter the overall decreasing trend in abundance along the gradient. Vice versa nine species (especially Hymenophyllum undulatum), restricted to the primary forest, may indicate pristine conditions.

Long-term monitoring

For future applications of this method for long-term monitoring projects and as an early warning system, we recommend some improvements on our original study design. The limited plot number of this study should be increased to better represent overall habitat conditions. Indicator sites could be permanently established and marked, and checked every six months or yearly.

The advantages of this approach are clear. Data is easy to collect, meaning that it can be acquired cheaply and easily, if necessary by people without prior scientific education.

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