Arboreal Soil Research Articles

Microclimate buffering by epiphytes reduces climate overlap across elevations

AbstractThermal variation over space and time shapes global patterns of biodiversity and responses of species to climate change. Vertical microclimate gradients from the understory to the canopy mediate biogeographic patterns of arboreal species across larger spatial scales. Yet, the magnitude to which microhabitats in the canopy, such as large epiphytes, alter the exposure of arboreal species to hot and variable canopy conditions across biogeographic gradients is not well known. We first examine the extent to which maximum temperatures and temperature variation in epiphytic bird's nest ferns (BNFs) and the understory are lower than those in the canopy across an elevation gradient in the Philippines and the environmental factors influencing these differences. We find that differences in maximum temperatures (i.e., offset) and temperature variation (i.e., buffering) between the canopy and BNFs are greater than differences between the canopy and understory. Offset and buffering are largest when canopy temperatures are high and are positively impacted by precipitation. Furthermore, we address the theory that exposure to higher thermal variation in the canopy may increase the range sizes of arboreal species. We find that lower thermal variation over time in BNFs reduces the thermal overlap between low and high elevations relative to canopy temperatures. Arboreal species that shelter in BNFs during the day may therefore have narrow physiological tolerances and consequently smaller elevational ranges. By providing thermal regimes more similar to the understory than the canopy, BNFs may therefore effectively function as “arboreal soil”, mediating impacts of arboreality on patterns of biodiversity and trait variation.

Rangewide climatic sensitivities and non-timber values of tall Sequoia sempervirens forests

Heavily exploited for its reddish, decay-resistant heartwood, the tallest conifer, Sequoia sempervirens, is a major component of coastal forests from extreme southwestern Oregon to California’s Santa Lucia Mountains. Primary Sequoia forests are now restricted to < 5 % of their former distribution, and mature secondary forests with trees over 60 m tall are even scarcer due to repeated logging. Leveraging allometric equations recently derived from intensive work in both forest types, we climbed, measured, and core-sampled 235 trees in 45 locations distributed across the species range to examine growth trends and understand how tall Sequoia are responding to recent environmental changes. Paired samples of sapwood and heartwood collected along the height gradient were used to quantify Sequoia investment in decay resistance. During the 20th century, trees in most locations began producing more wood than expected for their size with this growth surge becoming pronounced after 1970 and ending around 2000. Radial increments—ring widths—correlate with climatic variables related to water availability, and these relationships are strengthening as temperatures rise. Sensitivity to drought increased from north to south along a 6° latitudinal gradient of decreasing precipitation and summer fog frequency. Sequoia trees north of 40° were least sensitive to drought, producing similar biomass annually during dry and wet years, whereas trees farther south produced less biomass during individual drought years. Hotter 21st century drought barely affected Sequoia growth efficiency (biomass increment per unit leaf mass) north of 40° until the fourth consecutive year (2015), when growth efficiency dropped precipitously, recovering within two years. South of 40°, Sequoia trees exhibited steadily declining growth efficiency during the multi-year drought followed by recovery, but recovery did not occur south of 37° despite ample precipitation in 2017. Sequoia growth efficiency is currently highest in secondary forests north of 40°, where trees produce relatively small amounts of heartwood with the lowest decay resistance (least fungicide) while receiving the most nocturnal summer fog. Increasing sink limitations, whereby rising temperatures, drier air at night, and extreme tree height collectively lower turgor pressure to inhibit cambial activity, may reduce Sequoia growth efficiency while contributing to more durable biomass production. Heartwood and fungicide increments are higher in primary than secondary forests across the species range. Crown structural complexity promotes development of vascular epiphytes and arboreal soil habitats in Sequoia forests with sufficient moisture availability. These habitats are lacking in secondary forests and rare in primary forests south of 40°. After logging, restoration of tall Sequoia forests can be achieved via silviculture that maximizes height increments during early stand development and then retains some dominant trees in perpetuity, allowing them to gain full stature, produce increasingly decay-resistant heartwood, and support significant arboreal biodiversity.

Not so stressful after all: Epiphytic individuals of accidental epiphytes experience more favourable abiotic conditions than terrestrial conspecifics

Vascular epiphytes are mainly associated with tropical and subtropical forest ecosystems. However, the frequent occurrence of accidental epiphytes in temperate forests proves that epiphytic growth of vascular plants is possible in tree crowns at these latitudes. Comparing the abiotic conditions of epiphytic and terrestrial microhabitats in conjunction with intraspecific differences in functional traits of the inhabiting plants, we identified limitations to vascular epiphytism in the study area in a Central European low mountain range. We determined light availability, winter temperatures, soil moisture, nutrient concentrations, and pH of arboreal soil in crotches of broad-leaved trees and in the immediate vicinity of each tree on the ground. Similarly, we quantified total plant water content, relative foliar chlorophyll content, specific leaf area (SLA), leaf dry matter content (LDMC), root-mass fraction, and aboveground nutrient concentrations of 110 pairs of epiphytic and terrestrial conspecifics. Water and nutrient availability were generally high in crotches filled with arboreal soil, suggesting better growth conditions than on the ground. A trophic advantage of epiphytic individuals over terrestrial conspecifics can be deduced from higher plant nutrient concentrations, higher SLA, and lower LDMC. Advantageous growth conditions might even result in higher growth rates and higher fitness of epiphytic individuals. Our findings highlight that vascular epiphytism in the study area is not necessarily limited by abiotic conditions but at least partly by the availability of old and structurally diverse trees providing suitable microhabitats. Accordingly, management actions in these secondary forest ecosystems should incorporate the preservation of old and large deciduous trees in order to sustain arboreal microhabitats and the associated biota.

Drought resistance does not explain epiphytic abundance of accidental epiphytes

ABSTRACT Background Accidental epiphytism is common among vascular plants in forest ecosystems around the globe. A frequent observation in surveys of accidental epiphytes is the occurrence of few species with high epiphytic abundance, while most co-occurring terrestrial species are rarely found as epiphytes. Aims Based on the general assumption that water is the major limiting factor for epiphytic plants, we hypothesised that differences in drought resistance of accidental epiphytes explain the difference in epiphytic abundances. Methods We exposed 16 species with different epiphytic abundance in central Europe to experimentally induced drought during germination and growth of juvenile plants. Results Drought resistance differed substantially among species but did not correlate with their epiphytic abundance, neither during germination nor during juvenile growth. Conclusions In central Europe, accidental epiphytes are usually found on moss cushions or in accumulated arboreal soil on their host tree. In such water-storing substrates, water availability might be less limiting than it is for obligate epiphytes that typically grow on bare bark, which would explain the lack of a correlation between drought resistance and epiphytic abundance of the studied species. Hence, other factors must explain the consistent differences in epiphytic abundance, e.g. dispersal traits and mass effect.

Accidental epiphytism in the Harz Mountains, Central Europe

AbstractQuestionsVascular epiphytes make up about 9% of all vascular plants globally but are clearly underrepresented in the temperate zones. The accidental epiphytic occurrence of terrestrial species, in contrast, is common at these latitudes and can provide important insights in the evolution of obligate epiphytes. Here, we present the results of the first two annual censuses of a planned long‐term study on accidental epiphytes. We particularly aim to identify: (a) the abundance and species richness of accidental epiphytes; (b) the dynamics of accidental epiphytism; (c) occupied substrates and microsites; and (d) suitable host tree species.LocationHarz Mountains, Germany, Central Europe.MethodsWe surveyed more than 1,200 trees in a low mountain range in two consecutive years for epiphytic individuals of vascular plants, considering host tree species and occupied microsites.ResultsAbout one quarter of the surveyed trees hosted epiphytic plants, totalling 1 450 (2016) and 1 350 (2017) individuals, respectively. These belonged to more than 100 species and 39 different families. The majority of epiphytic individuals newly emerged in 2017, whereas one‐third persisted since 2016 (or earlier) and a smaller proportion even reproduced in the epiphytic habitat. Accidental epiphytes were mostly restricted to host tree species providing water‐storing substrates such as extensive moss pads or arboreal soil accumulated in crotches. Compared to tropical epiphyte communities, accidental epiphytes in the temperate zones show a higher turnover, as they are less consistent in species abundance and composition in time.ConclusionFor the majority of the observed species, epiphytism indeed is an accidental phenomenon. Undoubtedly, abiotic conditions limit the occurrence of obligate epiphytes at higher latitudes, but the presence and persistence of numerous epiphytic individuals illustrate that abiotic conditions do not per se preclude epiphytic occurrence of vascular plants in the north‐temperate zone. Besides water shortage, the availability of suitable host trees is a decisive environmental factor that contributes to limit epiphytism of vascular plants in Central Europe.

Diversity and spatial distribution of epiphytic flora associated with four tree species of partially disturbed ecosystem in tropical rainforest zone

As components of forest communities, epiphytes influence litter and nutrient cycling while providing shelter, nesting materials and food for arboreal animals, thereby promoting diversity. Their preference for certain tree species (phorophytes) influences biodiversity and distribution, but this association is poorly understood in the tropics. We assessed the diversity and spatial distribution of epiphytes associated with four phorophytes ( Alstonia booneii , Peltophorum pterocarpum , Mangifera indica and Terminalia catappa ) in southern Nigeria, with number of trees sampled as 4, 29, 32 and 44, respectively. The epiphytes were delineated, sampled and identified. Soil samples were collected from tree pockets for textural and pH analyses. On the four phorophytes, 265 epiphytes under seven species ( Platycerium elephantotis , Microgamma owariensis , Nephrolepis biserrata , Funaria hygrometrica , Axonopus compressus , Commelina benghalensis and Ficus spp.) and five families ( Polypoidaceae , Funariaceae , Poaceae , Commelinaceae and Moraceae ) were recorded. The three most abundant were Funaria hygrometrica (109), Platycerium elephantotis (102) and Microgamma owariensis (44), being present on all four phorophytes. Funaria hygrometrica and Platycerium elephantotis were the most abundant on M. indica (32 each) and T. catappa (44 and 39, respectively). Nephrolepis biserrata appeared only once on T. catappa ; so too did Axonopus compressus and Commelina benghalensis on P. pterocarpum . Altogether, A. booneii , P. pterocarpum , M. indica and T. catappa had 11, 62, 89 and 103 epiphytes, respectively. Funaria hygrometrica traversed three tree strata, while others were restricted to two or even one stratum. Canopy layer, middle stratum and lower portion hosted four, five and three epiphytic species, respectively out of the seven recorded, pointing to the relative importance of light, spaciousness and moisture, respectively in epiphyte abundance on trees. Epiphytes distribution on phorophytes was not influenced by texture of the arboreal soils, but was inversely related to their pH. This study has provided useful information on epiphyte-phorophyte association in tropical environments and deserves repetition with more tree species in more natural forests. Keywords: forest tree species, tree spatial strata, epiphyte distribution, species abundance, Nigeria

Large, retained trees of Cryptomeria japonica functioned as refugia for canopy woody plants after logging 350 years ago in Yakushima, Japan

Abstract Trees retained during green-tree retention forestry are expected to function as biological legacies that promote biodiversity and enhance ecosystem functions in plantation forests. Investigating how historically retained trees function as biological legacies could help predict the long-term ecological potential of current retention practices. Here, we investigated whether large, retained trees of Cryptomeria japonica D. Don (>1000 years old) functioned as refugia for persistence of canopy woody plants after logging in a 350-year-old secondary forest in Yakushima, southern Japan. We climbed five each of retained and regenerated trees in a 1-ha research plot, measured trunk and crown structures, and tagged and measured every woody plant stem found on each tree. Compared to regenerated trees, retained trees had twice the surface area available for canopy plant colonization. Moreover, retained trees hosted disproportionately greater abundance of canopy woody plants. Together, the five retained trees hosted 22 species of woody plants comprising 1188 individuals, whereas regenerated trees hosted only 8 species (37 individuals). Combined with our ground-based measurement, canopy woody species contributed 16% of all woody plant species in the plot. Among the five retained trees, woody plant abundance increased markedly with increasing age of trunk breaks. This was because numerous epicormic branches had sprouted below trunk breaks creating large surface area upon which arboreal soil accumulated and woody plants established. Canopy woody plants on retained trees showed wide vertical distribution corresponding to complex crown structure, whereas those on regenerated trees occurred almost exclusively on the lower trunk. Maximum stem size of canopy woody plants was constrained by the volume of arboreal soil upon which they grew. Based on their size structures, we inferred that three species endemic to Yakushima (Vaccinium yakushimense Makino., Viburnum urceolatum Sieb. et Zucc., and Rhododendron yakushimanum Nakai), maintain stable populations in the retained trees by sprouting. Several other species scarcely found on the ground were also regenerating in the canopy. Our results demonstrate that retained trees of Cryptomeria functioned as refugia allowing canopy woody plants to persist after logging and give support to the importance of conserving large trees for enhancing biodiversity in forests where canopy plants contribute to species diversity.

Importance of structure for species richness and tree species regeneration niches in old-growth Patagonian swamp forests

Swamp forests have high ecological value and significantly contribute to the productivity of the zones in which they are located because they provide important ecosystem benefits to society. Tepualia stipularis-dominated swamp forests, also called tepuales, are the most common but endangered swamp forests in Patagonia. In these forests, T. stipularis develops very complex structures and accumulates large amounts of biomass due to its horizontal growth habit, which leads to the formation of arboreal soils and nearly impenetrable networks of trunks. Here, we hypothesize that the complex structure of old-growth T. stipularis-dominated forests influences species abundance and the regeneration niches of the different tree species that grow in them. In addition, in these forests with restricted drainage, elevated microsites facilitate the development of regeneration. Using pre-harvesting inventory data from two silvicultural experiments in T. stipularis-dominated forests of Chiloé Island, North Patagonia, we aim to (a) characterize the structure and composition of old-growth, undisturbed stands, (b) evaluate how their structure influences the regeneration niches of the main tree species, and (c) explain the implications of these findings in the context of the traditional silvicultural management of these forests. Our results show for the first time that these forests present low anthropogenic influence (no exotic species) and contain high tree-species richness, which exceeds that of several old-growth swamp forests around the world. Also, their characteristic gap-phase dynamics and complex structures influence the regeneration niches of different coexisting tree species, which mostly germinate and establish on trunks. In this context, silvicultural methods that maintain a continuous cover should be encouraged to increase the ability of different species to reorganize and adapt to new conditions.

Ecosystem engineering by Fascicularia bicolor in the canopy of the South-American temperate rainforest

Ecosystem engineers are organisms that modify habitats and resource flows, they therefore could have a disproportionate impact on the diversity of ecological communities. Evidence suggests that trash basket epiphytes (TBE) can be considered ecosystem engineers of forest canopies, due to their relationship with arboreal soil availability and treetop communities. Here we evaluated whether the TBE Fascicularia bicolor (Bromeliaceae), modulates temperature and humidity in the forest canopy. We also investigated if this bromeliad is related with greater arboreal soil accumulation and is associated to higher diversity of other epiphytic plants and invertebrates in the canopy of the South-American temperate rainforest (SATR), in Chile. We measured temperature and humidity in ten trees within the forest before and after the experimental addition of F. bicolor. We also related the presence of F. bicolor with occurrence of soil macro-fauna and other canopy dwelling plants in a comparative field survey.Temperature variability in the canopy was reduced by F. bicolor. Soil availability was higher in sites with mats of F. bicolor. The richness of vascular epiphytes was unaltered by the presence of F. bicolor, but species composition differed between sites with and without mats on each tree. At the group level, the cover of lichens and bryophytes was greater in sites without F. bicolor, while vascular epiphytes show a larger cover in sites with F. bicolor. The species richness of invertebrates increased in treetop sites colonized by F. bicolor but species composition was not different from soil in branch bifurcations. Our results show that F. bicolor must be considered in forest management practices to determine which trees must be logged, in order to preserve the viability of populations of these key organisms in the treetops of South-American temperate rainforests.

The functional roles of epiphytes and arboreal soils in tropical montane cloud forests

Abstract:Epiphytes and their associated decomposing litter and arboreal soils (herein, epiphytic material, EM) are ubiquitous features of tropical montane cloud forests (TMCF) and play important roles in ecosystem function. EM intercepts water and nutrients from the atmosphere and from intercepted host tree sources, and may contribute significant inputs of these resources to the forest floor. Despite the importance of EM in the TMCF, a systematic review of the ecosystem roles of EM has not been compiled before. We have synthesized the literature that documents functions of EM in undisturbed TMCFs and discuss how these roles may be affected by disturbances, including changes in climate and land use. The range of EM biomass and water storage in the TMCF varies greatly across sites, with different amounts associated with stand age and microclimate. EM is important as habitat and food for birds and mammals, with over 200 species of birds documented as using EM in the Neotropics. Given its sensitivity to moisture, projected shifts in cloud base heights or precipitation due to changes in climate will likely have a large impact on this community and changes in EM diversity or abundance may have cascading impacts on the ecosystem function of the TMCF.

Canopy Soils of Sitka Spruce and Bigleaf Maple in the Queets River Watershed, Washington

Canopy or arboreal soils develop from the accumulation and decomposition of epiphytes on branches and in bifurcations of trees in tropical and temperate rainforests. Canopy soils are important because they provide habitat and water, and accumulate allochthonous nutrients for epiphytes and their associated biota. This study characterized the chemical and physical characteristics of canopy soils developed on Sitka spruce [Picea sitchensis (Bong.) Carrière] and bigleaf maple (Acer macrophyllum Pursh) in an old‐growth forest at the Queets River watershed, Washington. Bigleaf maple canopy soils were dominated by hemic horizons, had higher pH, N content, cation exchange capacity, and extractable N levels relative to Sitka spruce canopy soils, which had higher bulk density and C/N ratios. Compared with the forest floor, canopy soils had lower total C, total N, and C/N ratio. The bigleaf maple canopy soil was classified as a Typic Haplohemist, whereas the Sitka spruce canopy soil was classified as a Typic Haplosaprist. The main differences between these canopy soils are due to different inputs of host tree litter and decomposition states of the two species. Canopy soils in this ecosystem are enhancing the pool of C and N by 20 and 25%, respectively, relative to the C and N pools of the forest floor.

A field experiment links forest structure and biodiversity: epiphytes enhance canopy invertebrates in Chilean forests

Epiphytes represent a conspicuous component of the canopy of old‐growth forests, reaching biomass values of up to 44 t/ha. Forest epiphytes host a rich invertebrate community; however, the contribution of epiphytes to the richness and abundance of canopy invertebrates is still quite unknown, and has not been experimentally assessed in old‐growth forests. We studied the contribution of epiphyte loads to invertebrate species composition and abundance in the crown of large old individual trees of Eucryphia cordifolia (Cunoniaceae) in old‐growth forests from southern Chile. We accessed the canopy using arborist techniques and contrasted the invertebrate species richness and biomass inhabiting four large canopy trees (25–30 m high, 1.2 m DBH), two of them with intact epiphytes and two trees from which epiphytes were manually removed. For over a year (April, 2006 to May, 2007) we made monthly collections of invertebrates from each tree's crown using flight‐interception and eclector traps (the latter designed to capture walking invertebrates from trunks and limbs). Once every season we collected samples of epiphytes and their soil to quantify invertebrates using Berlese funnels. We found significantly greater invertebrate species richness and abundance in the control trees' crowns (with epiphytes) compared to the trees from which epiphytes were removed. Predators (such as spiders and centipedes) were disproportionately more abundant on trees with epiphytes, and an entire functional group (detritivores), associated with arboreal soils under the epiphytes, was absent in the trees from which epiphytes were removed. Invertebrate abundances were lower in winter and higher in summer for trees with epiphytes, while for trees without epiphytes invertebrate numbers fluctuated markedly, but with no seasonal pattern. We show that large old trees are an important structural component in forests, supporting additional structure represented by the epiphyte load, which, in turn, sustains a rich community of invertebrates with functional groups not otherwise present in the forest canopy. Our findings strongly recommend that forest managers retain large old trees with their epiphytes in order to sustain biodiversity and important ecosystem processes.

Soil Organic Matter Processes in Old‐Growth Redwood Forest Canopies

Organic soils up to 1 m thick cover tree surfaces within the canopies of old‐growth redwood [Sequoia sempervirens (D. Don) Endl.] forests 50 m or more above the ground. Very little is known about litter quality and litter decomposition processes within these canopies. A combination of solid‐state cross‐polarization magic‐angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy, natural 13C and 15N isotopic analyses, and proximate analyses were used to gain insight into soil organic matter accumulation and decay processes within two arboreal soils. Arboreal soil, redwood, and fern (Polypodium scouleri Hook. &amp; Grev.) litter as well as epiphyte roots were analyzed. Proximate analyses showed that the arboreal soil parent materials contained a high concentration of the acid residue fraction (i.e., Klason lignin), from 379 g kg−1 for fern rhizomes up to 652 g kg−1 for redwood bark litter. This high concentration of acid residue fraction in the soil parent materials probably promotes organic matter accumulation within the tree crown. Results from 13C NMR spectroscopy analyses indicated a preferential decomposition of carbohydrates and an accumulation of alkyl structures from the redwood and fern litter to the &lt;2‐mm soil materials and from the Oi to the Oa horizons in both soils. On the other hand, there was no consistent variation in terms of C/N ratios and stable isotope composition along the depth gradient, suggesting that organic matter in these soils has undergone limited microbial processing but instead reflects the selective preservation of recalcitrant litter moieties.

Cover Caption

Cover: Tropical pastures present multiple barriers to tree regeneration, but canopies of relict trees can serve as repositories of viable seeds deposited when the forest was intact. When mats of arboreal soil fall to the pasture floor, their seedbank can contribute to forest regeneration, their seeds serving as “time capsules” from the primary forest. The lush epiphytic ferns (Polypodium spp.) and accompanying arboreal soil on this mature live oak are viewed from above in a subtropical landscape of Florida. Photo by John T. Longino. See pages 1117–1126.

Microbial communities of arboreal and ground soils in the Esquinas rainforest, Costa Rica

We investigated the microbial community structure and population size of arboreal soils—including canopy and bromeliad epiphytic leaf-tank soils—and ground soils in a tropical lowland rainforest in Costa Rica using molecular and cultivation methods. PCR-DGGE analysis of 16S rRNA and 18S rRNA gene fragments and quantitative real-time PCR were applied to survey the bacteria, ammonia-oxidizing bacteria (AOB), and fungi. Bacteria from epiphytic tank soils were isolated and identified. Bacillaceae, Pseudomonadaceae and Micrococcaceae were the most abundant families. According to cluster analysis of DGGE fingerprints a significant difference among the three soil types was evident for bacterial communities. In addition, the microbial communities of canopy and tank soils clustered apart from ground soils. The fungal and AOB communities were diverse but non-specific for the soil types analyzed.

Arboreal Histosols in Old‐Growth Redwood Forest Canopies, Northern California

Within the canopy of old‐growth redwood (Sequoia sempervirens [D. Don] Endl.) forests, accumulations of plant debris in crotches and on massive limbs serve as parent materials for “arboreal soils” up to 1 m thick and over 50 m above the forest floor. These soils are important habitats and water sources for desiccation‐sensitive organisms in the forest canopy ecosystem. We investigated two of these arboreal soils to better understand how they form and function. The primary vascular epiphyte growing in these soils is leather‐leaf fern (Polypodium scouleri). Fern biomass and redwood leaves and bark are the main parent materials of the soils, which are entirely organic. The soils have distinct horizons and soil structure, and have been changed from their initial parent materials as a result of additions, losses, and transformations of organic matter. They are classified as Typic Udifolists. The soils become more decomposed with depth as fibrous components transition to sapric materials. They have low bulk densities (0.07–0.16 g cm−3) and lose most of their water at relatively high matric potentials. Field water contents and potentials of the arboreal soil materials taken near the end of the dry season indicate that water remains available for uptake by ferns. High base saturation values (&gt;55%) suggest that nutrients are available for plant uptake. The soils are extremely acidic, with pH values around 3.0 in 0.01 M CaCl2 Decomposition may be hindered by the low soil pH and by relatively low soil moisture contents in surface horizons during the dry season.

Potential effects of climate change on canopy communities in a tropical cloud forest: an experimental approach.

Global climate change models predict reduced cloud water in tropical montane forests. To test the effects of reduced cloud water on epiphytes, plants that are tightly coupled to atmospheric inputs, we transplanted epiphytes and their arboreal soil from upper cloud forest trees to trees at slightly lower elevations that are naturally exposed to less cloud water. Control plants moved between trees within the upper site showed no transplantation effects, but experimental plants at lower sites had significantly higher leaf mortality, lower leaf production, and reduced longevity. After the epiphytes died, seedlings of terrestrial gap-colonizing tree species grew from the seed banks within the residual mats of arboreal soil. Greenhouse experiments confirmed that the death of epiphytes can result in radical compositional changes of canopy communities. Thus, tropical montane epiphyte communities constitute both a potentially powerful tool for detecting climate changes and a rich arena to study plant/soil/seed interactions under natural and manipulated conditions. This study also provides experimental evidence that the potential effects of global climate change on canopy and terrestrial communities can be significant for cloud forest biota. Results suggest there will be negative effects on the productivity and longevity of particular epiphytes and a subsequent emergence of an emerging terrestrial component into the canopy community from a previously suppressed seed bank.

Vesicular-arbuscular mycorrhizal fungi, particularly Glomus tenue, in Venezuelan bromeliad epiphytes

The mycorrhizal status of water-impounding “tank” bromeliad epiphytes from three locales differing in altitude and moisture regime within Venezuelan cloud forest was examined. Species of vesicular-arbuscular mycorrhizal (VAM) fungi found in arboreal soils were compared to VAM fungi found in terrestrial soils. Sixteen of the 19 epiphytes examined for the presence of VAM fungi had roots with infection stages; 14 of these specimens showed growth of the fine endophyte Glomus tenue. Fine endophyte was the only VAM fungus found associated with epiphytes in the driest locale studied, while coarse VAM fungi (Gigaspora and Scutellospora spp.) were found at sampling locales receiving more moisture. Root infection was usually composed of intercellular hyphae and peletons; few arbuscules were observed. However, abundant extracellular hyphae were often observed tangled about roots in arboreal soil. It is concluded that epiphytic bromeliads probably benefit, at least periodically, from VAM fungi scavenging for sporadically available nutrients in arboreal soils. Glomus tenue may be particularly important as a colonizing VAM fungus in drier sites of Venezuelan cloud forest. The species composition of VAM fungi in arboreal soils was different to that of terrestrial soils sampled directly under epiphytic bromeliad perches, suggesting that VAM fungi species associated with bromeliads are dispersed to their hosts by vagile animal vectors.

Diversity of soil fauna in the canopy and forest floor of a Venezuelan cloud forest

ABSTRACTArboreal and terresterial soil and lilter were sampled for macro-and microinvertebrates at two locations in a Venezuelan cloud forest. Fauna were most abundant in forest floor soil and associated litter. However, media suspended in the canopy and particularly those trapped in bromeliad shoots were most densely populated, while the diversities of the arboreal and terrestrial soil fauna were indistinguishable. Rates of leaf litter decomposition in the arboreal and terrestrial soils were similar, but the arboreal soils contained higher concentrations of mineral nutrients and carbon. Implications of these findings for the definition of soil in humid tropical forests, and related differences between temperate and tropical forests are discussed. The similarities in diversity and differences in species composition between arboreal and terrestrial soil fauna raise questions concerning the evolution of tropical soil fauna, as well as the estimate of global biotic diversity.