Dwarf Forest Research Articles

Climate and seasonal rainfall anomalies along an elevational gradient in the El Sira Mountains, Peru, and their impacts on tree radial growth

The explicit purpose of this study was to characterize climate and vegetation along the western slope of the El Sira Mountains (Peru) and evaluate radial tree growth in response to seasonal rainfall anomalies. From May 2011 until September 2015, we monitored radial stem growth of 67 trees using point dendrometers and measured climate within five sites along an altitudinal gradient. The transect extends from lowland terra firme forests, over submontane forests, late and mid successional montane cloud forests up to exposed elfin forests. Monthly rainfall estimates by the TRMM PR satellite (product 3B42) were highly correlated with our rain gauge observations but underestimate rainfall at high altitudes. Different intra-annual tree growth patterns could be identified within each elevational forest type, showing species with strictly seasonal growth, continuous growth or alternating growth patterns independent of the seasons. Stem growth at each site was generally larger during rainy seasons, except for the elfin forest. The rainy season from October 2013 to March 2014 was extraordinarily dry, with only 73% of long-term mean precipitation received, which resulted in reduced radial growth, again with the exception of the elfin forest. This indicates that montane tropical rain forests may suffer from prolonged droughts, while exposed ridges with elfin forests still receive plenty of precipitation and benefit from receiving more solar radiation for photosynthesis.

The spatial configuration of taxonomic biodiversity along a tropical elevational gradient: α‐, β‐, and γ‐partitions

AbstractBiodiversity at larger spatial scales (γ) can be driven by within‐site partitions (α), with little variation in composition among locations, or can be driven by among‐site partitions (β) that signal the importance of spatial heterogeneity. For tropical elevational gradients, we determined the (a) extent to which variation in γ is driven by α‐ or β‐partitions; (b) elevational form of the relationship for each partition; and (c) extent to which elevational gradients are molded by zonation in vegetation or by gradual variation in climatic or abiotic characteristics. We sampled terrestrial gastropods along two transects in the Luquillo Mountains. One passed through multiple vegetation zones (tabonuco, palo colorado, and elfin forests), and one passed through only palm forest. We quantified variation in hierarchical partitions (α, β, and γ) of species richness, evenness, diversity, and dominance, as well as in the content and quality of litter. Total gastropod abundance linearly decreased with increasing elevation along both transects, but was consistently higher in palm than in other forest types. The gradual linear decline in γ‐richness was a consequence of opposing patterns with regard to α‐richness (monotonic decrease) and β‐richness (monotonic increase). For evenness, diversity, and dominance, α‐partitions and γ‐partitions evinced mid‐elevational peaks. The spatial organization of gastropod biodiversity did not mirror the zonation of vegetation. Rather, it was molded by: (a) elevational variation in productivity or nutrient characteristics, (b) the interspersion of palm forest within other forest types, and (c) the cloud condensation point acting as a transition between low and high elevation faunas.Abstract in Spanish is available with online material.

湖南省阳明山山顶苔藓矮林优势种空间分布格局

湖南省阳明山山顶苔藓矮林优势种空间分布格局

Plant-soil feedbacks on free-living nitrogen fixation over geological time.

Free-living heterotrophic nitrogen fixation (FNF) is a widespread nitrogen input pathway in terrestrial ecosystems. However, questions remain over the relative influence of co-occurring controls on patterns of heterotrophic FNF activity, especially across generalized stages of primary succession, from biomass accumulation to retrogressive phases. Here, we experimentally test two alternative hypotheses regarding FNF rates during ecosystem development: (H1) site (i.e., changes in soil fertility during succession) is the primary driver of leaf-litter FNF rates, vs. (H2) leaf-litter chemistry is the primary determinant of FNF activity across a broad range of ecosystem conditions. We evaluated these hypotheses across a well-studied soil chronosequence in California (i.e., the Ecological Staircase), which spans ~1million years of ecosystem development and displays extreme ranges in plant-soil nutrient conditions, culminating in the nutrient depleted and stunted Pygmy forest. Across this successional gradient, we implemented a reciprocal leaf-litter transplant and a common garden litter bag decomposition experiment with senesced needles of Pinus muricata. Our results support H1: rates of FNF were similar for all leaf-litter types decomposed at the same site regardless of initial leaf-litter C and nutrient contents. FNF rates sharply declined from the maximal to retrogressive stage of succession. Trends in P dynamics during decomposition suggest an important role of P in regulating FNF. For example, P.muricata litter collected from the infertile Pygmy site displayed substantially higher FNF rates when decomposed at the fertile site, in part by immobilizing significant quantities of P from the soil at the fertile site. Conversely, P.muricata litter collected from the fertile site decomposed more slowly at the Pygmy site, with concomitant declines in FNF rates that matched those of Pygmy site litter decomposed insitu. These results are consistent with the idea that, over millennia, long-term declines in P availability feedback to constrain FNF rates, in part explaining the emergence of extremely nutrient-poor and retrograded ecosystems.

Ascogrammitis lehnertii (Polypodiaceae): A New and Dominant Understory-Species from a Diverse Community of Grammitid Ferns in the Andes of Ecuador

In the scope of pantropical studies aimed at understanding how the diversity of grammitid ferns (Polypodiaceae) has evolved and is maintained, we studied a diverse grammitid community in treeline elfin forests in eight study plots of 400 m2 each at 3200 m on Cerro Toledo, Loja, southern Ecuador. We recorded a total of 7986 individuals of 16 grammitid species. Ascogrammitis lehnertii is here described as a new species.We also recorded Mycopteris leucosticta, a species previously believed to be restricted to the Choco region of Ecuador. We found that the grammitid species were segregated by habitat into trunk-base and trunk specialists, which suggests that species coexistence in these diverse epiphytic communities is at least partly linked to habitat segregation. Ascogrammitis lehnertii and M. leucosticta were the second and third most abundant species, respectively, and both were mostly trunk-base species. The new species A. lehnertii differs from its congeners by the combination of its relatively broad lamina, (2-)3–4 cmwide, fertile leaves bearing 2mmlong reddish setae in and near the sori, and by bearing proliferous roots from which new plants emerge. Phylogenetic analyses of atps, rbcL, rps4, trnG-trnR, andtrnL-trnF DNA molecular sequences, using maximum likelihood, place A. lehnertii as sister to A. cuencana with strong support. Despite previous intensive collection efforts in Loja for the past 30 yr, all but one of the collections of this new species were made in the last three years. The discovery of A. lehnertii and the new record of M. leucosticta highlight the patchy distribution of some species in the Andes and the value of surveying habitats that potentially host unrecognized plant diversity. In order to facilitate further discovery, we provide a key to all species of Ascogrammitis.

Decade dynamics of species composition and diversity of mountaintop mossy dwarf forest on the Yangming Mountains, Hunan Province, China.

Three monitoring plots were established in the Yangming Mountains mossy dwarf forest concentration zone in the Yangmingshan National Nature Reserve in Hunan Province in 2005. The changes of species composition and diversity during 2005-2016 were analyzed from species numerical characteristics, species importance value, diameter class structure, height structure, and species diversity. The results showed that from 2005 to 2016, the individual number for ≥1.0 cm diameter at ground height (DGH) in tree layer decreased by 30.9%. Viburnum dilatatum decreased greatest with 98.6%, and Rhododendron fortunei decreased least with 1.8%. Species richness was increased, and evenness was decreased. Except for R. fortunei, the importance values of all the species decreased significantly after ten years, indicating that R. fortunei was the dominant species in the dwarf forest. The diameter-class distribution of species in the dwarf forest was arranged at 1 cm level. The density of small-diameter (1 cm≤DGH＜6 cm) species was higher, but that of medium-diameter (6 cm≤DGH＜15 cm) and large-diameter (15 cm≤DGH) was lower. The diameter-class distribution of R. fortunei exhibited a reversed 'J' shape, and the height of community increased from 2005 to 2016, indicating the population had a stable and well-developing trend. The other species were poorly renewed and their diameter-class structure was irregular. Generally, the Patrick and Menhinick richness indices and the Simpson index were increased, and the Shannon and Pielou indices were decreased during the ten years.

Evolutionary history of campo rupestre: an approach for conservation of woody plant communities

The campo rupestre sensu lato is among the most species-rich vegetation in the world, harbouring a high proportion of endemic species. We aimed to identify the processes that could generate a high level of phylogenetic diversity (PD) in campo rupestre for woody species and point out biodiversity hotspot areas which may provide additional information for conservation planning. We compiled a database of 2049 woody species from 185 community inventories. We calculated the evolutionary history using species richness (SR), PD, mean pairwise phylogenetic distance between species (MPD), the mean nearest taxon distance (MNTD) and their equivalents standardised (ses.PDss, ses.MPD, ses.MNTD), evolutionary distinctiveness (ED), and biogeographically weighted evolutionary distinctiveness (BED). Cloud dwarf-forests had the highest SR, PD, MPD and ses.MPD and lowest MNTD, while rupestrian cerrado presented the highest ses.PD and ses.MNTD. All areas are important for conservation, but the intersections between the hotspots should receive special attention in future conservation actions. The grids identified as hotspots by three or more metrics were localized mainly in Espinhaco Range in Minas Gerais State and a further expansion of protected areas is required. Moreover, the intersections between the hotspots obtained by mean ED and ses.PD are concentrated in the rocky dwarf forest and rupestrian cerrado, with considerable conservation gaps. The degree of protection of campo rupestre was low with unprotected areas comprising 56% of the species. Our results show an urgent need for increasing protected areas of campo rupestre in order to avoid the loss of valuable, endemic species with unique evolutionary history.

Checklist of ferns and lycophytes from the highlands of Pico Paraná State Park, Paraná, Brazil

Abstract We present a checklist for the ferns and lycophytes from Pico Paraná State Park, in Southern Brazil. The Park is entirely located at the Serra do Mar mountains, and represents an important remnant of the Atlantic Rain Forest with altitude achieving 1,887 m. In this locality is the Pico Paraná, the highest mountain in Southern Brazil. This study was focused on the altitudes above 1,000 m, which are mainly represented by dwarf forests and altitudinal fields. A total of 142 species were recorded, three of them (Ceradenia maackii, Diplazium tamandarei, and Stenogrammitis wittigiana) are only found in the park in Southern Brazil. Besides of the checklist of the species, we highlight some important aspects related to endangered species, geographic distribution, and life forms. The high level of endemism, the presence of endangered species, and the phylogenetic diversity as represented by distinct families of ferns and lycophytes show the biogeographic importance of this area for the conservation of these groups of plants.

Fog Water Is Important in Maintaining the Water Budgets of Vascular Epiphytes in an Asian Tropical Karst Forests during the Dry Season

Fog may be an important source of water for forest vascular epiphytes on trees, because they lack direct access to sources of soil water, but little is known about the water use proportions from various sources and potential water uptake pathways in epiphytes. Here, we analyzed leaf carbon isotope ratios as a measure of water use efficiency (WUE), proportions of fog, rain, and soil water use, and foliar water uptake (FWU) in species of epiphyte and their host trees in a tropical karst dwarf forest in China during the dry season. We found that the WUE, as represented by leaf δ13C, was generally enriched in the epiphyte species compared to their host trees. Epiphytes used substantial proportions of fog water, whereas water use in the host trees was dominated by soil water. The leaves of epiphytes and host trees absorbed water following immersion in water for 3 h and FWU possibly related to foliar epicuticular structures, such as fungal endophytes. Our results show a divergence of water use strategies between epiphytes and their hosts and highlight the importance of fog water for epiphytes during the dry season and under a climate change scenario with a reduced occurrence of fog events.

Estimation of Above Ground Biomass in a Tropical Mountain Forest in Southern Ecuador Using Airborne LiDAR Data

A reliable estimation of Above Ground Biomass (AGB) in Tropical Mountain Forest (TMF) is still complicated, due to fast-changing climate and topographic conditions, which modifies the forest structure within fine scales. The variations in vertical and horizontal forest structure are hardly detectable by small field plots, especially in natural TMF due to the high tree diversity and the inaccessibility of remote areas. Therefore, the present approach used remotely sensed data from a Light Detection and Ranging (LiDAR) sensor in combination with field measurements to estimate AGB accurately for a catchment in the Andes of south-eastern Ecuador. From the LiDAR data, information about horizontal and vertical structure of the TMF could be derived and the vegetation at tree level classified, differentiated between the prevailing forest types (ravine forest, ridge forest and Elfin Forest). Furthermore, topographical variables (Topographic Position Index, TPI; Morphometric Protection Index, MPI) were calculated by means of the high-resolution LiDAR data to analyse the AGB distribution within the catchment. The field measurements included different tree parameters of the species present in the plots, which were used to determine the local mean Wood Density (WD) as well as the specific height-diameter relationship to calculate AGB, applying regional scale modelling at tree level. The results confirmed that field plot measurements alone cannot capture completely the forest structure in TMF but in combination with high resolution LiDAR data, applying a classification at tree level, the AGB amount (Mg ha−1) and its distribution in the entire catchment could be estimated adequately (model accuracy at tree level: R2 > 0.91). It was found that the AGB distribution is strongly related to ridges and depressions (TPI) and to the protection of the site (MPI), because high AGB was also detected at higher elevations (up to 196.6 Mg ha−1, above 2700 m), if the site is situated in depressions (ravine forest) and protected by the surrounding terrain. In general, highest AGB is stored in the protected ravine TMF parts, also at higher elevations, which could only be detected by means of the remote sensed data in high resolution, because most of these areas are inaccessible. Other vegetation units, present in the study catchment (pasture and subpáramo) do not contain large AGB stocks, which underlines the importance of intact natural forest stands.

Phanerogamic flora and phytogeography of the Cloud Dwarf Forests of Ibitipoca State Park, Minas Gerais, Brazil

Abstract: This study was developed in Ibitipoca State Park (ISP), a mountainous massif that stands out in the Serra da Mantiqueira, in the Southeastern Region of Brazil. The vegetation is represented by a phytophysiognomic mosaic where areas of campos rupestres interspersed with cloud dwarf forests predominate, at altitudes of 1100 to 1700 m.s.m. The cloud dwarf forests exist in narrow altitude belts on the mountain peaks, immersed in a layer of clouds. They form a peculiar landscape high in the mountains by the short stature of the arboreal elements and richness of lichens and bryophytes, which develop under constant condensation of humidity, low temperatures, and frequent winds. The objective of the present work was to determine the floristic composition and phytogeography of the cloud dwarf forests of ISP. Twelve monthly campaigns were conducted to collect botanical material during the years 2014 and 2015. The collected material was deposited in the collection of the CESJ Herbarium. A total of 372 species, 209 genera, and 73 families of phanerogams were found. The richest families were Orchidaceae (84 spp.), Asteraceae (39 spp.), and Melastomataceae (21 spp). The genera with the greatest wealth were Leandra (09 spp.), Epidendrum (09 spp.), Pleurothallis (09 spp.), Mikania (07 spp.), and Miconia (07 spp). The arboreal habit was predominant with 103 species (27.7%), followed by 83 shrubs (22.3%), 82 epiphytic herbs (22%), 80 terrestrial herbs (21.5%), and 23 lianas (6.5%). The floristic composition presents elements typical of altitude vegetation, including species of campos rupestres and high epiphytes richness, especially of the families Orchidaceae and Bromeliaceae. The genera with tropical distribution represent 86.5%, whereas the temperate elements represent 13.5% of the total. The cloud dwarf forests presented similarity, at the family and gender levels, with the upper montane forests of the Andes, besides phytogeographic characteristics that allow to associate them to a transition environment between the campos rupestres and the upper montane forests of the Southeast Region of Brazil.

Small trees, big problems: Comparative leaf function under extreme edaphic stress.

The pygmy forest, a plant community of severely stunted conifers and ericaceous angiosperms, occurs on patches of highly acidic, nutrient-poor soils along the coast of Northern California, USA. This system is an excellent opportunity to study the effect of severe nutrient deficiency on leaf physiology in a naturally-occurring ecosystem. In this study, we seek to understand the physiological mechanisms stunting the plants' growth and their implications for whole plant function. We measured 14 traits pertaining to leaf photosynthetic function or physical structure on seven species. Samples were taken from the pygmy forest community and from conspecifics growing on higher-nutrient soils, where trees may grow over 30 m tall. Pygmy plants of most species maintained similar area-based photosynthetic and stomatal conductance rates to conspecific controls, but had lower specific leaf area (leaf area divided by dry weight), lower percent nitrogen, and less leaf area relative to xylem growth. Sequoia sempervirens, a species rare in the pygmy forest, had a categorically different response from the more common plants and had remarkably low photosynthetic rates. Pygmy plants were not stunted by low photosynthetic rates on a leaf-area basis; instead, several species had restricted whole-plant photosynthesis due to low leaf area production. Pygmy plants of all species showed signs of greater carbon investment in their leaves and higher production of nonphotosynthetic leaf tissue, further contributing to slow growth rates.

Tank bromeliads capture Saharan dust in El Yunque National Forest, Puerto Rico

Dust from Saharan Africa commonly blows across the Atlantic Ocean and into the Caribbean. Most methods for measuring this dust either are expensive if collected directly from the atmosphere, or depend on very small concentrations that may be chemically altered if collected from soil. Tank bromeliads in the dwarf forest of El Yunque National Forest, Puerto Rico, have a structure of overlapping leaves used to capture rainwater and other atmospheric inputs. Therefore, it is likely that these bromeliads are collecting in their tanks Saharan dust along with local inputs. Here we analyze the elemental chemistry, including rare earth elements (REEs), of tank contents in order to match their chemical fingerprint to a provenance of the Earth's crust. We find that the tank contents differ from the local soils and bedrock and are more similar to published values of Saharan dust. Our study confirms the feasibility of using bromeliad tanks to trace Saharan dust in the Caribbean.

The components of biodiversity, with a particular focus on phylogenetic information.

We present a framework for biodiversity metrics that organizes the growing panoply of metrics. Our framework distinguishes metrics based on the type of information–abundance, phylogeny, function–and two common properties–magnitude and variability. Our new metrics of phylogenetic diversity are based on a partition of the total branch lengths of a cladogram into the proportional share of each species, including: a measure of divergence which standardizes the amount of evolutionary divergence by species richness and time depth of the cladogram; a measure of regularity which is maximal when the tree is perfectly symmetrical so that all species have the same proportional branch lengths; a measure that combines information on the magnitude and variability of abundance with phylogenetic variability, and a measure of phylogenetically weighted effective mean abundance; and indicate how those metrics can be decomposed into α and β components. We illustrate the utility of these new metrics using empirical data on the bat fauna of Manu, Peru. Divergence was greatest in lowland rainforest and at the transition between cloud and elfin forests, and least in upper elfin forests and in cloud forests. In contrast, regularity was greatest in lowland rainforest, dipping to its smallest values in mid‐elevation cloud forests, and then increasing in high elevation elfin forests. These patterns indicate that the first species to drop out with increasing elevation are ones that are closely related to other species in the metacommunity. Measures of the effective number of phylogenetically independent or distinct species decreased very rapidly with elevation, and β‐diversity was larger. In contrast, a comparison of feeding guilds shows a different effect of phylogenetic patterning. Along the elevational gradient, each guild generally loses some species from each clade–rather than entire clades–explaining the maintenance of functional diversity as phylogenetic diversity decreases.

New insights on above ground biomass and forest attributes in tropical montane forests

Despite the potential of tropical montane forests to store and sequester substantial amounts of carbon, little is known about the above ground biomass (AGB) and the factors affecting it in these ecosystems, especially in Africa. We investigated the height-diameter allometry, AGB, and related differences in AGB to taxonomic and structural forest attributes in three distinct forest types (dry, mixed species and elfin) in three mountains of northern Kenya. We established 24 permanent plots (20m×100m) and sampled all trees ≥10cm diameter following standard Rainfor protocols.We identified that different height-diameter allometric models could be used for different forests types, with the exception of the Michaelis–Menten model. In our study area, model choice had little effects on AGB estimates.In general, mixed forests had greater AGB than other forest types: in Mt Nyiro AGB estimates were 611, 408 and 241Mgha−1 for mixed, elfin and dry forests respectively. Forests in Mt Nyiro, the highest mountain had greater AGB than in the other mountains. In our study area, differences in AGB were related to forest structure attributes, with little influence of taxonomic attributes. The mixed and elfin forests in Mt Nyiro, dominated by Podocarpus latifolius and Faurea saligna contained comparable AGB to lowland rainforests, highlighting the importance of tropical montane forests as large carbon stock, which could be released if converted to another land cover type.

Consistent temperature sensitivity of labile soil organic carbon mineralization along an elevation gradient in the Wuyi Mountains, China

Labile soil organic carbon (LOC) is an essential component in the global carbon (C) cycling due to its fast turnover and sensitivity to environmental changes. However, responses of the mineralization of LOC to current global warming are still not fully understood. In this study, we investigated LOC mineralization at 5, 15, 25 and 35°C incubation temperatures through laboratory incubation of soil samples and estimated the temperature sensitivity of LOC mineralization at various temperature ranges (i.e. 5–15, 15–25, and 25–35°C) in an evergreen broad-leaf forest (EBF), a coniferous forest (CF), a sub-alpine dwarf forest (SDF), and an alpine meadow (AM) along an elevation gradient in the Wuyi Mountains in southeastern China. Our results showed that mineralization of LOC significantly increased along the elevation gradient and with increasing incubation temperatures. The interaction of elevation and incubation temperatures was additive on LOC mineralization. Moreover, the temperature sensitivity (Q10) of LOC mineralization significantly decreased with increasing incubation temperature ranges. However, elevation gradient had no statistically significant impact on Q10 within each incubation temperature range. Our results suggest that soil organic C (SOC) at high elevations is more vulnerable to global warming. Moreover, consistent Q10 of LOC mineralization along the elevation gradient indicates that locally, C quality maybe a minor factor in affecting LOC mineralization and it may be adequate to use a constant Q10 value to represent the response of LOC mineralization to warming in regional climate-C cycling models.

Leaf size indices and structure of the peat swamp forest

Leaf size indices of the tree species in the peatland of Agusan del Sur in Mindanao in Philippines was examined to deduce the variation of forest structure and observed forest zonation. Using raunkiaer and webb’s leaf size classification, the leaf morphometrics of seven tree species consistently found on the established sampling plots were determined. The species includes Ternstroemia philippinensis Merr., Polyscias aherniana Merr. Lowry and G.M. Plunkett, Calophyllum sclerophyllum Vesque, Fagraea racemosa Jack, Ilex cymosa Blume, Syzygium tenuirame (Miq.) Merr. and Tristaniopsis micrantha Merr. Peter G.Wilson and J.T.Waterh.The LSI were correlated against the variables of the peat physico-chemical properties (such as bulk density, acrotelm thickness, peat depth, total organic carbon, nitrogen, phosphorus, and potassium, pH); water (pH, ammonium, nitrate, phosphate); and leaf tissue elements (nitrogen, phosphorus and potassium). Result showed a decreasing leaf size indices and a three leaf size category consisting of mesophyllous, mesophyllous-notophyllous and microphyllous were observed which corresponds to the structure of vegetation i.e., from the tall-pole forest having the biggest average leaf area of 6,142.29 mm2 to the pygmy forest with average leaf area of 1,670.10 mm2. Such decreased leaf size indices were strongly correlated to soil nitrogen, acrotelm thickness, peat depth, phosphate in water, nitrogen and phosphorus in the plant tissue.

What Explains Wildlife Value Orientations? A Study among Central African Forest Dwellers

This study of values placed on wildlife by Bantu and Yaka Pygmy forest dwellers (n = 200) in Northern Congo identified and analyzed two wildlife value orientations - “anthropocentric” and “biocentric.” The former, strongly displayed across all segments of both societies, was likely motivated by heavy reliance on bushmeat and human–wildlife conflicts, and was linked to attitudes approving the killing of animals for human benefit. The “biocentric” orientation was more common among formally educated male respondents who do not hunt and positively linked to attitudes favoring conservation. Wildlife management strategies should consider including 1) sustainable local wildlife exploitation, 2) livelihood projects that provide a real alternative to hunting, and 3) human–wildlife conflict mitigation.

Species interactions in an Andean bird-flowering plant network: phenology is more important than abundance or morphology.

Biological constraints and neutral processes have been proposed to explain the properties of plant–pollinator networks. Using interactions between nectarivorous birds (hummingbirds and flowerpiercers) and flowering plants in high elevation forests (i.e., “elfin” forests) of the Andes, we explore the importance of biological constraints and neutral processes (random interactions) to explain the observed species interactions and network metrics, such as connectance, specialization, nestedness and asymmetry. In cold environments of elfin forests, which are located at the top of the tropical montane forest zone, many plants are adapted for pollination by birds, making this an ideal system to study plant–pollinator networks. To build the network of interactions between birds and plants, we used direct field observations. We measured abundance of birds using mist-nets and flower abundance using transects, and phenology by scoring presence of birds and flowers over time. We compared the length of birds’ bills to flower length to identify “forbidden interactions”—those interactions that could not result in legitimate floral visits based on mis-match in morphology. Diglossa flowerpiercers, which are characterized as “illegitimate” flower visitors, were relatively abundant. We found that the elfin forest network was nested with phenology being the factor that best explained interaction frequencies and nestedness, providing support for biological constraints hypothesis. We did not find morphological constraints to be important in explaining observed interaction frequencies and network metrics. Other network metrics (connectance, evenness and asymmetry), however, were better predicted by abundance (neutral process) models. Flowerpiercers, which cut holes and access flowers at their base and, consequently, facilitate nectar access for other hummingbirds, explain why morphological mis-matches were relatively unimportant in this system. Future work should focus on how changes in abundance and phenology, likely results of climate change and habitat fragmentation, and the role of nectar robbers impact ecological and evolutionary dynamics of plant–pollinator (or flower-visitor) interactions.

Plant communities as bioclimate indicators on Isla Navarino, one of the southernmost forested areas of the world

Variation in climactic vegetation with altitude is widely used as an ecological indicator to identify bioclimatic belts. Tierra del Fuego is known to undergo structural and functional changes in forests along altitudinal gradients. However there is still little knowledge of the changes in plant-community composition and plant diversity –including both forests and tundra and their area of contact (krummholz)– and their relation to climatic factors along an altitudinal gradient. This study focuses on Isla Navarino (Chile), at the eastern part of Beagle Channel, included in the Cape Horn Biosphere Reserve. Numerical analysis revealed four community types along the cited gradient: a) mixed forest of Nothofagus betuloides and Nothofagus pumilio distributed at lower altitudes (0-300 masl); b) pure forests of Nothofagus pumilio distributed at higher altitudes (350-550 masl); c) krummholz forest of Nothofagus pumilio near the tree line (500-550 masl); and d) pulvinate-cushion vegetation –tundra– of Bolax gummifera and Abrotanella emarginata at altitudes above 600 masl. Species turnover showed that the most abrupt change in plant composition occurs from 550 to 600 masl, producing a drastic landscape change when the high-altitude tree limit formed by dwarf forest of deciduous N. pumilio yields to tundra at a calculated biotemperature of 2.9 oC. Two other minor changes occur in the understory of pure Nothofagus pumilio forests: a transition from a thermophilous element to a more orophilous element at a calculated biotemperature of 4.3 oC, and a drop in the number of species as the erect forest changes to low krummholz forest at a calculated biotemperature of 3.3 oC. The identification of bioclimatic belts based on changes in vegetation and the calculation of biotemperature along the altitudinal gradient suggests that the following plant communities are reliable regional bioclimatic bioindicators: lowermiddle- oroantiboreal mixed forest of Nothofagus betuloides-Nothofagus pumilio; oroantiboreal pure forest of Nothofagus pumilio; hemi oroantarctic krummholz of Nothofagus pumilio; and oroantartic tundra of Bolax gummifera and Abrotanella emarginata.