Jan H. D. Wolf

Factors controlling the distribution of vascular and non-vascular epiphytes in the northern Andes

The epiphytic vegetation on host trees along an altitudinal transect on the west slope of the Central Cordillera in Colombia was sampled. Bark-type restricted sampling comprised four full-grown forest trees, not necessarily four species, at altitudinal intervals of c. 200 meters from 1000 to 4130 m a.s.l. and included the canopy. Both vascular and non-vascular epiphytes, the latter often more abundant in the montane rain forest, were included in the analyses. Using a method of direct gradient analysis, canonical correspondence analysis, the variation explained by various environmental variables could be discriminated from a great amount of variation that seemed not related to any ecological factor. To a large extent, the randomness in propagule supply appears to determine the floristic composition on branch/trunk segments. The grouping of relevés in a phytosociological analysis concurred with a clustering of samples in an ordination diagram of the first two extracted constrained axes. The sample scores on these two axes were strongly correlated with the complex variables ‘altitude’ and ‘height within the host tree’. Specialists and generalists with respect to the two variables were defined based on tolerances provided by the canonical correspondence analysis as was the position of species on the gradients involved. Independently from any of the other variables entered, a relation between the epiphytic vegetation and host species was detected, particularly in the case of Brunellia occidentalis, a fast growing tree species of higher altitude. No relation between chemical characteristics of suspended soil in the Upper Montane Rain forest and its supporting species could be demonstrated.

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

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.

Dispersal limitation in epiphytic bromeliad communities in a Costa Rican fragmented montane landscape

Transformation of tropical forests is likely to affect seed-dispersal patterns and influence the composition of epiphytic plant communities in human-altered habitats. We tested this hypothesis by carrying out a comparative study of seed influx, survival and growth of transplanted seedlings of epiphytic bromeliads among isolated trees in six pasture areas, six forest edges and six forest sites in a montane area in Costa Rica. In total, 72 traps trapped 1285 seeds over a 2-mo period in the dry season of 2003. For all four investigated bromeliad genera, Catopsis, Guzmania, Tillandsia and Werauhia, the number of trapped seeds in each habitat followed a pattern similar to the numberoffruitingindividualsinthevicinityofthetraps.Trapsinforestedges(30)were1.9timesmorelikelytocollect seeds than traps at forest interiors (30) and pasture trees (12), the latter showing similar probabilities of catching seeds. After 1 y, survival and growth of 3660 transplanted seedlings from three bromeliad species was significantly higher in forest interiors, providing no explanation for the lower abundance of fruiting adults in that habitat. These resultssuggestthatthesuccessfulestablishmentofepiphyticbromeliadsinforestinteriorsismainlydispersal-limited.If corroborated,differencesinabundanceamongspeciesateachhabitatarelikelyrelatedtodifferencesingrowthratesand reproductive success. Further studies on the growth and mortality of seedlings up to theflowering stage, however, are needed.

Recovery and succession of epiphytes in upper Amazonian fallows

The species richness, number of plants, biomass, and species composition of holo- and hemi-epiphytes were recorded in fifty-six 0.04-ha plots, distributed over forest fallows of 2-30 y old and mature forests in lowland Amazonia (Amacayacu National Park, Colombia). A total of 9190 epiphytic plants representing 162 species were recorded on 4277 phorophytes. Seventy species were classified as holo-epiphyte and 85 as hemi-epiphyte. Aroids were most diverse (58 species) and represented 76% of the total recorded biomass. Anemochory was more dominant among holo-epiphytes and zoochory among hemi-epiphytes. The species richness, density and biomass of both holo and hemi-epiphytes increased significantly from young fallows to old fallows and mature forests. Hemi-epiphytes had greater density and biomass than holo-epiphytes. In canonical ordination, forest age did not relate to the species composition of holo-epiphytes. However, for hemi-epiphytes, the age effect was significant, suggesting that species turnover takes place in the ageing fallows.

A protocol for sampling vascular epiphyte richness and abundance.

The sampling of epiphytes is fraught with methodological difficulties. We present a protocol to sample and analyse vascular epiphyte richness and abundance in forests of different structure (SVERA). Epiphyte abundance is estimatedasbiomassbyrecordingthenumberofplantcomponentsinarangeofsizecohorts.Epiphytespeciesbiomass is estimated on 35 sample-trees, evenly distributed over six trunk diameter-size cohorts (10 trees with dbh >30 cm). Tree height, dbh and number of forks (diameter >5 cm) yield a dimensionless estimate of the size of the tree. Epiphyte dry weight and species richness between forests is compared with ANCOVA that controls for tree size. SChao1 is used as an estimate of the total number of species at the sites. The relative dependence of the distribution of the epiphyte communities on environmental and spatial variables may be assessed using multivariate analysis and Mantel test. In a case study, we compared epiphyte vegetation of six Mexican oak forests and one Colombian oak forest at similar elevation.Wefoundastronglysignificantpositivecorrelationbetweentreesizeandepiphyterichnessorbiomassatall sites. In forests with a higher diversity of host trees, more trees must be sampled. Epiphyte biomass at the Colombian site was lower than in any of the Mexican sites; without correction for tree size no significant differences in terms of epiphyte biomass could be detected. The occurrence of spatial dependence, at both the landscape level and at the tree level, shows that the inclusion of spatial descriptors in SVERA is justified.

Reproductive strategies and colonizing ability of two sympatric epiphytic bromeliads in a tropical premontane area

Predispersal characteristics that affect the reproductive success in plants may influence their colonizing ability. We evaluated this hypothesis in two sympatric epiphytic bromeliads in Costa Rica, Guzmania monostachia and Tillandsia fasciculata, that show contrasting levels of local seedling recruitment. Genets of G. monostachia, the species with higher recruitment, may reach the reproductive stage faster because of a higher growth rate (6 vs. 13 yr). In addition, in established genets, new asexual ramets develop and reproduce annually, whereas in T. fasciculata, the slower offshoot development implies at least 3 yr to disperse a new batch of seeds. A higher and more continuous seed production in G. monostachia is possible because of a shorter time from flowering to seed dispersal (8–9 vs. 16–20 mo), along with the production of more flowers (29 vs. 22) and naturally pollinated fruits per inflorescence (89% vs. 79% fruit set) and more seeds per fruit (321 vs. 240). Both species showed a high occurrence of spontaneous autogamy that matched the highly selfing condition estimated using microsatellite markers. In all, G. monostachia displayed the reproductive traits of a pioneer species. Here, we emphasize the importance of seed availability in determining the population and community structure of epiphytic bromeliads in secondary and mature forests, along with factors affecting dispersal and plant survival.

Vascular Epiphytes and Their Potential as a Conservation Tool in Pine-Oak Forests of Chiapas, Mexico

The pine-oak forests of Chiapas are rich in epiphytes, harbouring 720 confirmed species. The epiphyte vegetation is uunique and adapted to the marked seasonal climate. Anthropogenic disturbance of the pine-oak forest reduces the richness and abundance of epiphytes, not only in terms of surface area but also on the remaining or re-growing trees, and causes a shift towards more drought-resilient species. Epiphytes show resilience to disturbance when trees are selectively logged, rather than being periodically clear-cut. Notably, the epiphyte community is less affected when some of the larger trees are spared which may serve as nearby epiphyte seed source in the successional forest. Nearby sites are more similar in epiphytes than are sites further apart. Hence, epiphyte protective reserves should be well distributed over a physiographically uniform region. Finally, we conclude that in some areas it may well be possible to harvest up to 700 solitary high-quality rosettes per hectare in a sustainable way. This prognosis raises hope for a successful employment of epiphytic bromeliad populations as a tool to help conserve pine-oak forests.

Commercial harvesting and regeneration of epiphytic macrolichen communities in the Western Ghats, India

SUMMARY Non-timber forest products form a substantial contribution to the livelihood of many rural communities worldwide. In the Western Ghats, India, epiphyticmacrolichensareharvestedbyPaliyantribes to generate supplementary income. Paliyan tribes employ two harvesting methods: shallow harvesting, with a minimum of attached bark substratum, and deep harvesting, which exposes the sapwood. To evaluate the regeneration of the lichen community in termsofspeciesdiversity,abundanceandcomposition, 320 bark samples of up to 50 cm 2 were collected from bark patches where lichens had been harvested previously, as shown by bark scars. Samples selected represented four host tree species, both harvesting methods and seven one-year intervals of time since harvesting. In each case, the field guide estimated sample age, and peer-testing proved these estimates to be reliable up to an age of seven years. Seven years after harvesting, the lichen community showed noteworthy regeneration capacity in terms of total lichencoverageandspeciesrichness.However,toassess the risk of local species loss in the long-term, any harvesting should include continuous monitoring of lichen species composition. Since shallow harvesting resulted in a swifter recovery of species abundance and richness compared with deep harvesting, harvesters should preferentially employ the shallow harvesting method.

Colonization of forest clearings and tree-fall gaps in lowland rain forests of Colombia by hemiepiphytic aroids: experimental and transect studies

The contribution of vegetative recruitment by non-tree species to the regeneration of tropical forests in man-made clearings or tree-fall gaps tends to be ignored. In a series of field studies near Amacayacu, Colombian Amazonia, we tested if hemiepiphytic aroids quickly colonize such open habitats through seed dispersal, sprouting plant fragments, or lateral invasion of flagellar aroids from the closed forest nearby. A seed germination experiment applyingtwosoilsubstratesandthreeshadelevelsshowedthatabundantlightreducedthegerminationsuccessofthree Philodendron species. A total of 400 cuttings from five Philodendron species were placed in forest clearings and almost 12%ofthesesproutedwithin14wk.Monitoringmorethan2000aroidplantsover14moindifferenthabitatsshowed thatrecruitmentwaslow(0.3plantsper10m 2 )comparedwithinitialdensities(3.1plantsper10m 2 ).Flagellararoids grew about 2.5 times faster than non-flagellar aroids. In forest edges they reached a mean apical growth of 98 cm in 14 mo. However, non-flagellar aroids were five to six times more abundant than flagellar individuals everywhere. It was concluded that hemiepiphytic aroids colonize open habitats mostly through a post-disturbance survival of plants or plant fragments.

A novel approach to simulate climate change impacts on vascular epiphytes: case study in Taiwan

In the wet tropics, epiphytes form a conspicuous layer in the forest canopy, support abundant coexisting biota, and are known to have a critical influence on forest hydrology and nutrient cycling. Since canopy-dwelling plants have no vascular connection to the ground or their host plants, they are likely more sensitive to environmental changes than their soil-rooted counterparts, subsequently regarded as one of the groups most vulnerable to global climate change. Epiphytes have adapted to life in highly dynamic forest canopies by producing many, mostly wind-dispersed, seeds or spores. Consequently, epiphytes should colonize trees rapidly, which, in addition to atmospheric sensitivity and short life cycles, make epiphytes suitable climate change indicators. In this study, we assess the impact of climate change on Taiwanese epiphytes using a modeling approach.