The world's southernmost tree and the climate and windscapes of the southernmost forests

The world's southernmost tree has been documented along with the condition and growth pattern of the world's southernmost forest on Isla Hornos, Chile. The distribution of trees at broad scales is strongly influenced by the abiotic environment and determining the position and condition of tree limits around the world is an important way to monitor global change. This offers an ideal way to test the relationship between the biogeography of individual species and the effects of climate/climate change. The limits of trees, as all ecotones, are also useful communication points – easily understood signposts of ecosystems and their change through time. The southernmost trees in the world exist at soil temperatures that correspond to the low range of global treeline temperatures, with a climate analogous to equatorial treeline despite the high latitude (56° S). However, their fine‐scale distribution is strongly influenced by wind exposure rather than simply aspect and/or elevation, as one would expect if temperature were limiting the range. Recent establishment further south was found from core forest areas, however significant dieback along wind‐exposed edges of the contiguous forest was also noted. In contrast to the wide extension of land where boreal or subarctic forests grow in the Northern Hemisphere, in the Southern Hemisphere Isla Hornos represents a single point embedded in the ocean under much milder climatic conditions. Documented shifts in wind intensity and direction as result of larger‐scale climate change will likely continue to strongly shape the condition of these unique forests.     

Vegetation patterns,plant distribution and life forms across the alpine zone in southern Tierra del Fuego,Argentina

The alpine zone is examined at meso‐ and microscales in southern Tierra del Fuego (54°49′S), where the full zone is expressed. Mesoscale patterns were studied on opposing aspects, and microscale patterns were studied on a series of solifluction terraces, in a hanging valley overlooking the Beagle Channel. Plant cover and life form data were collected within 50‐m altitudinal bands on north and south aspects and comprehensive plant lists were compiled for each band. Topography and associated surface cover were recorded on the terraces. Six alpine plant communities, in lower and upper floristic zones, were differentiated with multivariate analyses and significantly related to five ecological factors. Equivalent communities were separated by approximately 185 m altitude on opposing aspects, which related to a soil temperature difference of approximately 3.0°C. The richness (and range) of 80 local vascular taxa (18.6% of the regional flora), decreased with increasing altitude (6.6 per 100 m); however, richness differed significantly with aspect (north: 5.6, south: 7.5). Upper altitudinal limits (approximately 1250 m a.s.l.), were associated with a midsummer isotherm of approximately 1.7°C. Chamaephytes and hemicryptophytes dominated throughout but the tall tussock form was conspicuously absent. Reasons for this are discussed in the context of the Nothofagus treeline, which conformed to a midsummer isotherm of only approximately 6.0°C. Such patterns are at variance with those found in the oceanic subantarctic islands, other oceanic perhumid temperate mountain regions and tropical high mountains. However, the microscale pattern of fines, pebbles, stones and rock across the active solifluction terraces, with dense vegetation on their steep risers, had a clear affinity with that of other subantarctic regions. Inferences that alpine systems of the Southern Hemisphere are necessarily equivalent to those at similar northern latitudes are cautioned against. Likewise, such comparisons within the Southern Hemisphere may also be invalid.     

Ecosystem engineering by invasive exotic beavers reduces in-stream diversity and enhances ecosystem function in Cape Horn,Chile

Species invasions are of global significance, but predicting their impacts can be difficult. Introduced ecosystem engineers, however, provide an opportunity to test the underlying mechanisms that may be common to all invasive engineers and link relationships between changes in diversity and ecosystem function, thereby providing explanatory power for observed ecological patterns. Here we test specific predictions for an invasive ecosystem engineer by quantifying the impacts of habitat and resource modifications caused by North American beavers (Castor canadensis) on aquatic macroinvertebrate community structure and stream ecosystem function in the Cape Horn Biosphere Reserve, Chile. We compared responses to beavers in three habitat types: (1) forested (unimpacted) stream reaches, (2) beaver ponds, and (3) sites immediately downstream of beaver dams in four streams. We found that beaver engineering in ponds created taxonomically simplified, but more productive, benthic macroinvertebrate assemblages. Specifically, macroinvertebrate richness, diversity and number of functional feeding groups were reduced by half, while abundance, biomass and secondary production increased three- to fivefold in beaver ponds compared to forested sites. Reaches downstream of beaver ponds were very similar to natural forested sections. Beaver invasion effects on both community and ecosystem parameters occurred predominantly via increased retention of fine particulate organic matter, which was associated with reduced macroinvertebrate richness and diversity (via homogenization of benthic microhabitat) and increased macroinvertebrate biomass and production (via greater food availability). Beaver modifications to macroinvertebrate community structure were largely confined to ponds, but increased benthic production in beaver-modified habitats adds to energy retention and flow for the entire stream ecosystem. Furthermore, the effects of beavers on taxa richness (negative) and measures of macroinvertebrate biomass (positive) were inversely related. Thus, while a generally positive relationship between diversity and ecosystem function has been found in a variety of systems, this work shows how they can be decoupled by responding to alterative mechanisms. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The application of environmental ethics in biological conservation: a case study from the southernmost tip of the Americas

Biological conservation is not only about facts and technical measures concerning ecology, rather it must also consider values. This pertains to both the balancing of various human interests and also to the ethical evaluation of human actions towards nature. Here we discuss how environmental ethics can be incorporated into conservation decisions, and what implications the inclusion of ethical valuation has for the practice of conservation biology. While this is done mostly on a rather abstract level, we illustrate this here by applying ethical theory to a case study: the options for management of the introduced North American beaver (Castor canadensis) in the very south of Chile (Navarino Island). The beaver is an exotic species to the area and has substantially altered the ecological systems of the region. We discuss different options for dealing with the beaver (eradicate, control, tolerate, promote) from the viewpoint of anthropocentric environmental ethics and biocentric ethics. The results of our analysis demonstrate the value of ethical discussions in clarifying and underpinning arguments for and against specific actions. At the same time, they also show that ethical arguments do not decrease the need for sound scientific data but, on the contrary, may even increase this demand. We also highlight that the conclusions regarding adequate actions to be taken vary depending on the specific ethical theory embraced.

Pleistocene refugia and polytopic replacement of diploids by tetraploids in the Patagonian and Subantarctic plant Hypochaeris incana (Asteraceae, Cichorieae)

We report the phylogeographic pattern of the Patagonian and Subantarctic plant Hypochaeris incana endemic to southeastern South America. We applied amplified fragment length polymorphism (AFLP) and chloroplast DNA (cpDNA) analysis to 28 and 32 populations, respectively, throughout its distributional range and assessed ploidy levels using flow cytometry. While cpDNA data suggest repeated or simultaneous parallel colonization of Patagonia and Tierra del Fuego by several haplotypes and/or hybridization, AFLPs reveal three clusters corresponding to geographic regions. The central and northern Patagonian clusters (∼38–51° S), which are closer to the outgroup, contain mainly tetraploid, isolated and highly differentiated populations with low genetic diversity. To the contrary, the southern Patagonian and Fuegian cluster (∼51–55° S) contains mainly diploid populations with high genetic diversity and connected by high levels of gene flow. The data suggest that H. incana originated at the diploid level in central or northern Patagonia, from where it migrated south. All three areas, northern, central and southern, have similar levels of rare and private AFLP bands, suggesting that all three served as refugia for H. incana during glacial times. In southern Patagonia and Tierra del Fuego, the species seems to have expanded its populational system in postglacial times, when the climate became warmer and more humid. In central and northern Patagonia, the populations seem to have become restricted to favourable sites with increasing temperature and decreasing moisture and there was a parallel replacement of diploids by tetraploids in local populations.     

Land use history, hurricane disturbance, and the fate of introduced species in a subtropical wet forest in Puerto Rico

Tropical forests are suffering from increasing intensities and frequency of disturbances. As a result, non-native species accidentally introduced or intentionally planted for farming, plantations, and ornamental purposes may spread and potentially invade undisturbed native forest. It is not known if these introduced species will become invasive, as a result of recurrent natural disturbances such as hurricanes. Using data from three censuses (spanning 15 years) of a 16-ha subtropical wet forest plot, we investigated the impact of two hurricanes on populations of plant species that were planted in farms and plantations that were then abandoned and from the natural spread of species introduced into Puerto Rico in the past. The populations of four species (Citrus paradis, Mangifera indica, Musa sp., and Simarouba glauca) changed little over time. Six species (Artocarpus altilis, Calophyllum calaba, Genipa americana, Hibiscus pernambucensis, Syzygium jambos, and Swietenia macrophylla) declined between the first two censuses after Hurricane Hugo, then increased again in Census 3 after Hurricane Georges. Spathodea campanulata gradually increased from census to census, while Coffea arabica declined. These introduced species represent only a small part of the forest basal area and few show signs of increasing over time. The number of stems per plant, new recruits, and the growth rates of these introduced species were within the ranges of those for native plant species. The mortality rates over both census intervals were significantly lower for introduced species (<5% year⁻¹) than for native ones (15% year⁻¹). Many new recruits established after Hurricane Hugo (prior to this study) had opened the forest canopy and these high mortality rates reflect their death as the canopy recovered. Only Swietenia macrophylla and Syzygium jambos showed an increase in stem numbers in the closed canopy area of forest that had suffered limited human disturbance in the past. A future increase in frequency of disturbance may enable greater stem numbers of introduced species to establish, while lower-mortality rates compared to native species, may allow them to persist during inter-hurricane intervals. An increase in the population of introduced species, especially for those that grow into large trees, may have an impact on this tropical forest in the future.     

The effects of nitrate loading on the invasive macrophyte Hydrilla verticillata and two common, native macrophytes in Florida

Rising nitrate concentrations in the water column and the spread of invasive, non-native macrophytes are two major threats to Florida's oligotrophic, freshwater ecosystems. We used a replicated mesocosm experiment to test the effects of elevated nitrate concentrations in the water on the growth of the invasive macrophyte Hydrilla verticillata and two common, native submerged macrophytes Vallisneria americana and Sagittaria kurziana. Results from this study indicate that nitrate concentrations of 1.0 mg L⁻¹ NO₃-N in the water increased the final dry-weight biomass of H. verticillata by 2.75 times, while having no statistical effect on the growth of the two native species. Additionally, H. verticillata grew at a faster rate than the two native species in the low nitrate treatments accounting for 82% of the total biomass, indicating that it may have the capacity to invade relatively pristine communities. In waters where nitrate concentrations continue to rise, the cost of control efforts for H. verticillata may substantially increase in the future.     

Southernmost distribution limit for endangered Peladillas (Aplochiton taeniatus) and non-native coho salmon (Oncorhynchus kisutch) coexisting within the Cape Horn biosphere reserve,Chile

The Cape Horn Biosphere Reserve, one of the last wild areas of the planet, is not exempt from the pressures of global change, such as non-native species introductions. During 2018 and 2019 we studied the Róbalo river basin in order to update the diversity and distribution of fishes. Here, we report for the first time the native and endangered “Peladillas” Aplochiton taeniatus and the non-native coho salmon Oncorhynchus kisutch. The coexistence of native and non-native fishes poses a challenge for the management and conservation of aquatic biota from the Cape Horn Biosphere Reserve.     

Potential impacts of future land use and climate change on the Red List status of the Proteaceae in the Cape Floristic Region, South Africa

Using spatial predictions of future threats to biodiversity, we assessed for the first time the relative potential impacts of future land use and climate change on the threat status of plant species. We thus estimated how many taxa could be affected by future threats that are usually not included in current IUCN Red List assessments. Here, we computed the Red List status including future threats of 227 Proteaceae taxa endemic to the Cape Floristic Region, South Africa, and compared this with their Red List status excluding future threats. We developed eight different land use and climate change scenarios for the year 2020, providing a range of best‐ to worst‐case scenarios. Four scenarios include only the effects of future land use change, while the other four also include the impacts of projected anthropogenic climate change (HadCM2 IS92a GGa), using niche‐based models. Up to a third of the 227 Proteaceae taxa are uplisted (become more threatened) by up to three threat categories if future threats as predicted for 2020 are included, and the proportion of threatened Proteaceae taxa rises on average by 9% (range 2–16%), depending on the scenario. With increasing severity of the scenarios, the proportion of Critically Endangered taxa increases from about 1% to 7% and almost 2% of the 227 Proteaceae taxa become Extinct because of climate change. Overall, climate change has the most severe effects on the Proteaceae, but land use change also severely affects some taxa. Most of the threatened taxa occur in low‐lying coastal areas, but the proportion of threatened taxa changes considerably in inland mountain areas if future threats are included. Our approach gives important insights into how, where and when future threats could affect species persistence and can in a sense be seen as a test of the value of planned interventions for conservation.     

Assessing genetic variation and population structure of invasive North American beaver (<Emphasis Type="Italic">Castor Canadensis</Emphasis> Kuhl, 1820) in Tierra Del Fuego (Argentina)

The North American beaver (Castor Canadensis) was introduced into Isla Grande de Tierra del Fuego, Argentina in 1946 as a potential source of wild fur. The species showed high growth potential, reaching close to 100,000 individuals from an original founding stock of 25 females and 25 males. Beavers adapted rapidly to their new environment and became invasive, providing an excellent model of successful adaptation of introduced populations to a new habitat. In this study, we used polymorphic mitochondrial (mt) DNA to evaluate genetic variation in the introduced beaver population from Tierra del Fuego. Nucleotide variation in partial sequences of Cytochrome b (500 bp) and 12S rRNA (421 bp) genes and the main non-coding D-loop region (521 bp) were analyzed. Our study allowed to identify 10 different mtDNA lineages in the invasive population, none of them shared among the source populations. The pattern observed is a consequence of cessation of gene flow following expansion of the founding beaver population since the time of its introduction. This approach contributes to the understanding of effects of genetic changes on survival ability and reproductive success of invasive species. It also has important management implications to invasive species.     

Comparison of the effect of elevated CO2 on an invasive species (Centaurea solstitialis) in monoculture and community settings

The ongoing increase in atmospheric CO₂ concentration ([CO₂]) is likely to change the species composition of plant communities. To investigate whether growth of a highly invasive plant species, Centaurea solstitialis (yellow starthistle), was affected by elevated [CO₂], and whether the success of this species would increase under CO₂ enrichment, I grew the species in serpentine soil microcosms, both as a monoculture and as a component of a grassland community. Centaurea grown in monoculture responded strongly to [CO₂] enrichment of 350 mol mol^–1, increasing aboveground biomass production by 70%, inflorescence production by 74%, and midday photosynthesis by an average of 132%. When grown in competition with common serpentine grassland species, Centaurea responded to CO₂ enrichment with similar but nonsignificant increases (+69% aboveground biomass, +71% inflorescence production), while total aboveground biomass of the polyculture increased by 28%. Centaurea's positive CO₂ response in monoculture and parallel (but non-significant) response in polyculture provoke questions about possible consequences of increasing CO₂ for more typical California grasslands, where the invader already causes major problems.     

Alien vascular plants in Iceland: Diversity,spatial patterns,temporal trends,and the impact of climate change

The present study provides first comprehensive and up-to-date results on alien plant taxa in Iceland since 1967. We evidenced the presence of 336 alien vascular plant taxa, including 277 casuals and 59 naturalised taxa, two being invasive. The distribution of the alien flora exhibits a clear spatial pattern showing hotspots of occurrence and diversity within areas of major settlement centres. Altitude above sea level and temperature-related variables proved to be the most important factors shaping alien plant distribution in Iceland. Predictive modelling evidenced that arctic areas of Iceland and the Central Highlands are under serious risk of alien plant invasion due to climate change. The results provide crucial information for alien and invasive plant management and contribute data for meta-analyses of invasion processes worldwide.     

Ants, altitude and change in the northern Cape Floristic Region

Aim Climate‐modelling exercises have demonstrated that the Cape Floristic Region is highly sensitive to climate change and will apparently lose much of its northern limits over the next few decades. Because there is little monitoring of diversity in this area, ant assemblage structure was investigated within the main vegetation types in the Greater Cederberg Biodiversity Corridor. In particular, we sought to determine how ant assemblage structure differs between the main vegetation types, how restricted ants – and in particular the major myrmecochores – are to the major vegetation types, and which environmental variables might underlie differences in the ant assemblages and in the specificity of species to particular areas. Location Northern Cape Floristic Region, Western Cape, South Africa. Methods Sampling was undertaken during October 2002 and March 2003 across an altitudinal gradient ranging from sea level (Lambert's Bay) to c. 2000 m a.s.l. (Sneeukop, Cederberg) and down again to 500 m a.s.l. (Wupperthal) in the Western Cape, South Africa. Pitfall traps were used to sample ants at 17 altitudinal bands, stretching over three vegetation types (Strandveld, Mountain Fynbos and Succulent Karoo). Biotic and abiotic environmental variables were collected at each sampling site. Generalized linear models were used to determine the relationships between species richness, density, abundance and the abundance of the major myrmecochores, and the environmental variables. Redundancy analysis was used to determine the relationship between ant assemblage structure and the environmental variables. The Indicator Value Method was used to identify characteristic ant species for each vegetation type and altitudinal site. Results Temperature explained significant proportions of the variation in species density and abundance, and, together with area and several vegetation variables, contributed significantly to the separation of the assemblages in the major vegetation types and biomes. Four major myrmecochores were identified [Anoplolepis sp. (cf. custodiens), Anoplolepis sp. (cf. steinergroeveri), Camponotus niveosetosus, Tetramorium quadrispinosum]. The abundances of the two Anoplolepis species were related to vegetation variables, while the abundance of the other two species showed opposite relationships with temperature variables. Fourteen ant species were characteristic of certain vegetation types and altitudes. Several of these species contributed to the differences between the assemblages. Main conclusions There are likely to be substantial and complex changes to ant assemblages as climates change in the northern Cape Floristic Region. Moreover, the importance of ants for ecosystem functioning suggests that these responses are not only likely to be a response solely to vegetation changes, but might also precipitate vegetation changes. The changes that are predicted to take place in the next 50 years in the Cape Floristic Region could be substantially exacerbated by such synergistic effects, which have major implications for long‐term conservation plans. Ongoing monitoring of this transect will reveal the nature and pace of the change as it unfolds.