Canopy Crane Access System


1) Forest epiphytes

Courtesy Gerhard Zotz

The study of vascular epiphytes or air-plants, which root in the crowns of host trees and not in the soil, are still in their infancy due to the difficulty posed by access to the canopy of tall forests. An inventory of the epiphyte flora of the San Lorenzo crane site was recently completed (Zotz & Büche, 2000; Zotz & Vollrath, 2003). While identifying all species within the crane perimeter, we conducted a comprehensive, quantitative census within an area of approximately 0.4 ha. There, we observed more than 12,000 individual epiphytes belonging to more than 100 species. For each individual epiphyte we noted host tree species, plant size, attachment height, and other variables such as substrate (branch) diameter or inclination. Besides being one of the most complete censuses ever conducted with vascular epiphytes of a tropical forest, this data set is now used as the basis for the long-term monitoring of epiphyte community dynamics. Going beyond this descriptive approach, we have also undertaken transplantation experiments to conduct controlled physiological studies and to understand the mechanisms underlying differences in the vertical distribution of epiphyte species.

More info: G. Zotz web page

See also: Zotz, G. & Hietz, P. 2001.
The physiological ecology of vascular epiphytes: current knowledge, open questions. Journal of Experimental Botany, 52, 2067-2078.

Laube, S. and Zotz, G. 2006.
Neither Host-specific nor Random: Vascular Epiphytes on Three Tree Species in a Panamanian Lowland Forest. Annals of Botany 97: 1103–1114.

Epiphytes in the canopy

2) Canopy fungi

Courtesy Don R. Reynolds, Gregory S. Gilbert & Ariadna Bethancourt

The canopy is a distinctive habitat for a large number of algae, bryophytes, fungi, and bacteria. Our work focuses on a guild of ascomycete fungi found only on the surface of living leaves. These epifoliar, or leaf-surface, fungi complete their life cycles on the leaf surface without causing apparent damage to the plant host. They obtain their nutrition either as saprobes that consume detritus on the leaf surface, as honeydew specialists that depend on the waste products of piercing-and-sucking insects, or as apparently innocuous symbionts that use specialized hyphae adapted to absorb nutrients directly from the plant. In turn, they can be important nutritional sources for other microbes and for a wide diversity of arthropods.

All the leaf-surface fungi share common attributes suited to growth in the harsh conditions of the leaf surface in the forest canopy. These include dark pigmentation that protects against UV irradiation, growth and development patterns intimately linked with leaf surface features, and spore dispersal strategies that permit dispersal through flow of water through the canopy. Temperature, moisture, and irradiation extremes in the canopy are likely to be important factors limiting their distribution. In particular, the abundance of epifoliar fungi in the dark understorey increases with increasing light availability, but declines sharply in parts of the canopy exposed to full sun.

Our research aims to evaluate how host specificity and microclimatic preferences drive the abundance, distribution, and diversity of leaf-surface fungi in tropical forests. Using systematic three-dimensional sampling strategies, careful taxonomic work, and detailed measurement of variation in moisture, light, and temperature in the canopy and understorey environments, we are disentangling the effects of host distribution and environmental constraints on the growth of leaf-surface fungi. A rigorous comparison of diversity and distribution patterns across canopy sites in Panama and Australia is providing new insights into the biogeography of these fascinating fungi and the factors that lead to habitat specialization.

While the fungal guild studied above may be harmless for their hosts, other fungi as well as protists, bacteria, viruses and nematodes may cause plant diseases. Adult trees may serve as reservoir for pathogens and may spread disease to undestorey juveniles. Gilbert (1995) investigated the incidence of foliar diseases of sun leaves and shade leaves of five tree species at PNM. He found that foliar plant diseases were common (more than 75% of leaves in Luehea) and that diseases present in the canopy also affect leaves in the shade below. This indeed suggests a potentially important link between diseases of adult trees in the canopy and juveniles in the understorey. Thus, long-term studies to evaluate the role of disease in the canopy and the extent of the canopy-understorey connection appear to be crucial for understanding basic forest dynamics.

More info: G. Gilbert web page

See also: Arnold, A.E. , Maynard, Z. & Gilbert, G.S. 2001.
Fungal endophytes in dicotyledonous neotropical trees: patterns of abundance and diversity. Mycological Research, 105, 1502-1507.

3) Insect diversity and host specificity

Courtesy Frode Ødegaard

A study of host specificity of two beetle families, the leaf beetles and weevils, associated with 24 tree species and 26 liana species was carried out in the canopy at the dry forest crane site. After 700 hours spent in the crane gondola during one year, a total of 35,479 beetle individuals belonging to 1,167 species were collected (Ødegaard, 2003). Out of this material 2,561 host observations of 697 beetle species were recorded as feeding observations and probability-based methods. Lianas appear to be very important growth forms of plants for the maintenance of species richness at this site (Ødegaard, 2000a). Lianas and trees were hosts for a similar number of phytophagous beetle species, but the beetles associated with lianas were more host-specific than those associated with trees. For instance, a large group of virtually unknown weevils survive by scraping the tendrils of lianas that weave through the canopy. These are important findings in the context of estimating global species richness of arthropods, because previously trees have been regarded as the only hosts of importance in tropical forests.

The average host specificity for the phytophagous beetles in this forest in Panama is estimated to range from 7-10% if the forest consists of between 300 and 550 species of trees and lianas, i.e. fewer than one out of ten species are on average monophagous in the beetle community. The species richness of phytophagous beetles in the same forest is estimated to contain 1,600-2,000 species (Ødegaard et al., 2000). These results were used to revise host specificity-based estimates of global arthropod species richness. It is concluded that the higher estimates of 30-100 million species of tropical arthropods are not tenable. By way of comparison, the revised estimate gives approximately 5 million species, which resembles the results of other independent estimation methods. However, uncertainty is still too high for promoting a confident conclusion on the number of species existing on the planet (Ødegaard, 2000b).

A comparative study of 52 plant species from the San Lorenzo crane site yielded about 40% more beetle species than in the dry forest. The beetle fauna at this site was even more host specific than in PNM. Lianas did not dominate in the wet forest but their beetle faunas were more specific than on trees, confirming the results from the dry forest. The species composition in PNM and SL was rather distinct as only 12% of the total number of species was common to both sites (Ødegaard, 2006).

Milton García (University Santa Maria La Antigua and STRI, Panama) has also studied the beetle fauna of the tree Luehea seemannii (Tilliaceae) with the crane at PNM. This tree species is famous for being the primary focus of Terry Erwin’s canopy fogging in Panama, which led to a controversial estimate of 30 million insect species on Earth (Erwin & Scott, 1980; Erwin, 1983). García’s study, which could be performed in situ in the canopy with the crane as opposed to Erwin’s foggings carried out from ground level, highlighted that only a fraction of beetle species collected on this tree was effectively able to feed on its foliage. Most beetle species had no specific relationships with Luehea seemannii and could be considered as transient (García, 1999).

More info: Research fact sheet

More info: F. Ødegaard web page

See also: Ødegaard, F., Diserud, O. H., Engen, S. & Aagaard, K. (2000)
The magnitude of local host specificity for phytophagous insects and its implications for estimates of global species richness. Conservation Biology, 14, 1182-1186.

Ødegaard, F. (2004) Species richness of phytophagous beetles in the tropical tree Brosimum utile (Moraceae): the effects of sampling strategy and the problem of tourists. Ecological Entomology, 29, 76-88.

Ødegaard F., Diserud, O.H. & Østbye, K. (2005)
The importance of plant relatedness for host utilization among phytophagous insects. Ecology Letters, 8, 612-617.

Baridine weevils feeding on liana tendrils in the canopy

4) Vertical stratification of arthropods

Courtesy Yves Basset & Héctor Barrios

David Roubik studied the vertical stratification of euglossine bees by placing baited traps at different heights with the PNM crane. Few faunal differences were observed between the upper canopy and the understorey. However, two nocturnal bee species consistently foraged within the upper canopy and larger euglossine bees showed a tendency to forage high. These observations were directly related to their capacity to reduce heat loss during flight as compared to smaller bees (Roubik, 1993). Roubik also showed that many bee species learn which layer of the forest is most rewarding with respect to flowers and keep returning to this layer. For some bee species this stratum fidelity changes seasonally. Thus these bees forage in the canopy during the dry season when trees and lianas flower profusely and in the understorey during the rainy season when shrubs and treelets reproduce.

In contrast, patterns of vertical stratification for insect herbivores (leaf-chewers and sap-suckers) appear to be more evident. Three studies compared the herbivore fauna feeding on seedlings/saplings in the understorey and conspecific mature trees in the canopy. Two studies were performed at PNM and one at SL, and they all converge to the same conclusions. The study in SL targeted herbivores associated with 25 saplings and 3 conspecific mature trees of Pourouma bicolor (Cecropiaceae). A similar area of foliage (ca 370 m2) was surveyed from both saplings and trees but samples obtained from the latter included three times as much young foliage than the former. Arthropods, including herbivores and leaf-chewing insects with a proven ability to feed on the foliage of P. bicolor were 1.6, 2.5 and 2.9 times more abundant on the foliage of trees than on that of saplings, respectively. The species richness of herbivores and proven chewers were 1.5 (n = 145 species) and 3.5 (n = 21) times as high on trees than on saplings, respectively. Many herbivore species preferred or were restricted to one or other of the host stages. Host stage and young foliage area in the samples explained 52 % of the variance in the spatial distribution of herbivore species (Basset, 2001).

Two similar studies were performed at PNM on Luehea seemannii and Castilla elastica (Moraceae). For the latter, 2,000 understorey saplings and 12 canopy trees were surveyed. Sample sizes in the canopy and understorey were equal; amounting, in both cases, to 364 m2 of leaf area surveyed. Arthropod abundance was significantly higher in the canopy than in the understorey. A total of 120 morphospecies of insect herbivores were collected from both matures trees and saplings. For a similar leaf area sampled, insect herbivores were 19 times more abundant and 1.6 times more species-rich on the foliage of mature trees than on that of saplings. Herbivore species found on both saplings and trees comprised only one leaf-chewing species (Chrysomelidae) and 16 sap-sucking species (mostly Tingidae, Cicadellidae and Membracidae; Barrios, 2003).

Insect herbivory in rain forests is usually restricted to young, more palatable leaves, production and palatability of which can be drastically affected by light regime, thus affecting insect foraging patterns. This limitation may be particularly important for leaf-mining and gall-making insects. Hence, it is expected that both insect abundance and diversity differ between forest layers. Abundance and diversity of leaf- mining and gall-making insects was compared at the PNM and SL crane sites. Every 15 days during two consecutive years, 258 host plants were sampled at both the understorey and canopy levels at both sites. At both sites, the canopy fauna is more diverse (145 out of 258 species) than the understorey fauna. Only two out of 137 species of leaf-miners (1.5%) and one out of 109 gall makers (0.9%) are common to both levels, which confirms the high specificity of insect populations to specific vertical strata within the forest (Medianero et al., 2003).

Adult chrysomelids (leaf beetles) were surveyed with similar sampling effort by beating and flight-interception traps (FIT) in the canopy and understorey of the PNM and SL sites. Beating and FIT data yielded similar results and included 5412 individuals representing 269 species. At both sites, chrysomelids were significantly more species-rich in the canopy than in the understorey. The proportion of species shared between the two study sites was 20%, whereas 11% and 27% of species were shared between the canopy and understorey of the wet and dry sites, respectively. Thus, stratification was more marked at the wet site than at the dry site. This result may relate to differences in forest physiognomy (a tall and closed canopy at the wet site) and to the high interconnectivity via lianas between the understorey and canopy at the dry site (Charles & Basset, 2005).

Another project contrasted the vertical distribution and the plant use at San Lorenzo of two different guilds of herbivores: leaf-chewing Curculionoidea (weevils) and sap-sucking Membracoidea (treehoppers). The data are largely congruent with the other studies mentioned above but point out that taxa with different life-histories may be distributed differently along the vertical profile of the rainforest. In this study sun-loving treehoppers were principally collected in forest gaps in the understorey and the proportion of the fauna shared with the canopy was higher than that for weevils (Y. Basset & H. Barrios, unpublished data). Eventually, a large on-going project, IBISCA, is comparing the beta-diversity and vertical stratification of ca. 60 arthropod groups in the San Lorenzo forest

These various studies suggest that the higher availability of food resources, such as young foliage, in the canopy than in the understorey, perhaps combined with other factors such as resource quality and enemy-free space, may generate complex gradients of abundance and species richness of insect herbivores in wet closed tropical forests.

More info: Y. Basset web page

See also: Basset, Y., Novotny, V., Miller, S. E. & Kitching, R. L., Eds. (2003). Arthropods of Tropical Forests. Spatio-temporal Dynamics and Resource Use in the Canopy. Cambridge, Cambridge University Press.

Basset Y. 2001. Invertebrates in the canopy of tropical rain forests: how much do we really know? Plant Ecology, 153, 87-107.

Lewinsohn, T.M., Novotny, V. & Basset, Y. (2005)
Insects on plants: Diversity of herbivore assemblages revisited. Annual Review in Ecology, Evolution and Systematics, 36, 597-620.

Didham, R.K. & Fagan, L.L. (2003) Project IBISCA – Investigating the Biodiversity of Soil and Canopy Arthropods. The Weta, 26, 1-6.

Castaño-Meneses, G. et al. (2006) Poster: Springtails (Hexapoda: Collembola) from the forest canopy in San Lorenzo, Colon Province, Panama.

Project IBISCA: density activity of arthropods at different heights in the San Lorenzo forest

References cited

Barrios, H. (2003).
Insect herbivores feeding on conspecific seedlings and trees. Arthropods of Tropical Forests. Spatio-temporal Dynamics and Resource Use in the Canopy. Y. Basset, V. Novotny, S. E. Miller and R. L. Kitching. Cambridge, Cambridge University Press: 282-290.

Basset, Y. (2001)
Communities of insect herbivores foraging on saplings versus mature trees of Pourouma bicolor (Cecropiaceae) in Panama. Oecologia, 129, 253-260.

Charles, E. & Basset, Y. 2005.
Stratification of leaf beetle assemblages (Coleoptera: Chrysomelidae) in two forest types in Panama. Journal of Tropical Ecology, 21, 329-336.

Erwin, T. L. (1983)
Tropical forest canopies: the last biotic frontier. Bulletin of the Entomological Society of America, 29, 14-19.

Erwin, T. L. & Scott, J. C. (1980)
Seasonal and size patterns, trophic structure and richness of Coleoptera in the tropical arboreal ecosystem: the fauna of the tree Luehea seemannii Triana and Planch in the Canal Zone of Panama. The Coleopterists' Bulletin, 34, 305-322.

García , M. N. J. 1999.
Estructura y dinámica de los insectos del orden Coleoptera en la copa del arbol Luehea seemannii Triana y Planch 1862 (Tiliaceae), en el dosel del bosque del Parque Metropolitano, Panamá, Universidad Santa Maria La Antigua, Panamá.

Gilbert, G. S. (1995)
Rainforest plant diseases: the canopy - understory connection. Selbyana, 16, 75-77.

Medianero, E., Valderrama, A. & Barrios, H. (2003)
Diversidad de insectos minadores y formadores de agallas en el dosel y sotobosque del bosque tropical. Acta Zoológica Mexicana, 89, 153-168.

Ødegaard, F. (2000a)
The relative importance of trees versus lianas as hosts for phytophagous beetles (Coleoptera) in tropical forests. Journal of Biogeography, 27, 283-296.

Ødegaard, F. (2000b)
How many species of arthropods? Erwin's estimate revised. Biological Journal of the Linnean Society, 71, 583-597.

Ødegaard, F. (2003).
Species richness, taxonomic composition and host specificity of phytophagous beetles in the canopy of a tropical dry forest in Panama. Arthropods of Tropical Forests. Spatio-temporal Dynamics and Resource Use in the Canopy. Y. Basset, V. Novotny, S. E. Miller and R. L. Kitching. Cambridge, UK, Cambridge University Press: 220-236.

Ødegaard, F. (2006).
Host specificity, alpha- and beta-diversity of phytophagous beetles in two tropical forests in Panama. Biodiversity and Conservation, 15, 83-105.

Ødegaard, F., Diserud, O. H., Engen, S. & Aagaard, K. (2000)
The magnitude of local host specificity for phytophagous insects and its implications for estimates of global species richness. Conservation Biology, 14, 1182-1186.

Roubik, D. W. (1993)
Tropical pollinators in the canopy and understorey: field data and theory for stratum "preferences". Journal of Insect Behavior, 6, 659-673.

Zotz, G. & Büche, M. (2000)
The epiphytic filmy ferns of a tropical lowland forest - species occurrence and habitat preferences. Ecotropica, 6, 203-206.

Zotz, G. & Vollrath, B. (2003)
The epiphyte vegetation of the palm, Socratea exorrhiza - correlations with tree size, tree age, and bryophyte cover. Journal of Tropical Ecology, 19, 81-90.

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