Montane Settings Research Articles

A tree-ring record of historical fire activity in a piedmont longleaf pine (Pinus palustris Mill.) woodland in North Carolina, USA

BackgroundLongleaf pine (Pinus palustris Mill.) ecosystems were historically widespread in the North American Coastal Plain and in some southeastern piedmont and montane settings. The naval stores industry, deforestation, and other human activities resulted in an extensive loss (c. 97% loss) of the original woodlands and savannas. Longleaf pine ecosystems are maintained by frequent surface fire which promotes successful regeneration and maintains open canopy conditions and a largely herbaceous understory. Fire regimes (including the frequency and seasonality of fire) likely varied across the entire range of longleaf pine and through time; further research is needed to elucidate this variability.ResultsWe used fire scars in stumps and snags to reconstruct fire history in a piedmont longleaf pine ecosystem in North Carolina. For each tree sampled, we examined multiple cross sections to avoid omission of fire events recorded by smaller fire scars. Our samples revealed evidence of frequent fire (c. 3–4-year fire interval) beginning in the early eighteenth century and extending to the mid-nineteenth century. Fires occurred in the dormant and early earlywood positions of annual rings and were likely human ignited.ConclusionsTo our knowledge, this is the first tree-ring-based fire history in longleaf pine of the piedmont. As such, it offers a rare glimpse into historical fire activity in a now scarce but important ecological setting. More research is needed to develop additional fire chronologies in the piedmont region, including for longer periods of time and for larger spatial areas.

Towards a unified framework to study causality in Earth-life systems.

There is considerable interest in better understanding how earth processes shape the generation and distribution of life on Earth. This question, at its heart, is one of causation. In this article I propose that at a regional level, earth processes can be thought of as behaving somewhat deterministically and may have an organized effect on the diversification and distribution of species. However, the study of how landscape features shape biology is challenged by pseudocongruent or collinear variables. I demonstrate that causal structures can be used to depict the cause–effect relationships between earth processes and biological patterns using recent examples from the literature about speciation and species richness in montane settings. This application shows that causal diagrams can be used to better decipher the details of causal relationships by motivating new hypotheses. Additionally, the abstraction of this knowledge into structural equation metamodels can be used to formulate theory about relationships within Earth–life systems more broadly. Causal structures are a natural point of collaboration between biologists and Earth scientists, and their use can mitigate against the risk of misassigning causality within studies. My goal is that by applying causal theory through application of causal structures, we can build a systems‐level understanding of what landscape features or earth processes most shape the distribution and diversification of species, what types of organisms are most affected, and why.

Stable or seral? Fire-driven alternative states in aspen forests of western North America

As important centres for biological diversity, aspen forests are essential to the function and aesthetics of montane ecosystems in western North America. Aspen stands are maintained by a nuanced relationship with wildfire, although in recent decades aspen mortality has increased. The need to understand the baseline environmental conditions that favour aspen is clear; however, long-term fire history reconstructions are rare due to the scarcity of natural archives in dry montane settings. Here, we analyse a high-resolution lake sediment record from southwestern, Utah, USA to quantify the compositional and burning conditions that promote stable (or seral) aspen forests. Our results show that aspen presence is negatively correlated with subalpine fir and that severe fires tend to promote persistent and diverse aspen ecosystems over centennial timescales. This information improves our understanding of aspen disturbance ecology and identifies the circumstances where critical transitions in montane forests may occur.

Four new East Asian species of Aleurodiscus with echinulate basidiospores.

Four new species of Aleurodiscus sensu lato with echinulate basidiospores are described from East Asia: A.alpinus, A.pinicola, A.senticosus, and A.sichuanensis. Aleurodiscusalpinus is from northwest Yunnan of China where it occurs on Rhododendron in montane habitats. Aleurodiscuspinicola occurs on Pinus in montane settings in Taiwan and northwest Yunnan. Aleurodiscussenticosus is from subtropical Taiwan, where it occurs on angiosperms. Aleurodiscussichuanensis is reported from southwest China on angiosperms in montane environments. Phylogenetic relationships of these four new species were inferred from analyses of a combined dataset consisting of three genetic markers, viz. 28S, nuc rDNA ITS1-5.8S-ITS2 (ITS), and a portion of the translation elongation factor 1-alpha gene, TEF1.

Biogeographic links between southern Atlantic Forest and western South America: Rediscovery, re-description, and phylogenetic relationships of two rare montane anole lizards from Brazil

Data on species ranges and phylogenetic relationships are key in historical biogeographical inference. In South America, our understanding of the evolutionary processes that underlie biodiversity patterns varies greatly across regions. Little is known, for instance, about the drivers of high endemism in the southern montane region of the Atlantic Rainforest. In this region, former biogeographic connections with other South American ecosystems have been invoked to explain the phylogenetic affinities of a number of endemic taxa. This may also be the case of the montane anole lizards Anolis nasofrontalis and A. pseudotigrinus, known from few specimens collected more than 40years ago. We combine new genetic data with published sequences of species in the Dactyloa clade of Anolis to investigate the phylogenetic relationships of A. nasofrontalis and A. pseudotigrinus, as well as estimate divergence times from their closest relatives. Based on newly sampled and previously overlooked specimens, we provide a taxonomic re-description of those two taxa. Our phylogenetic analysis recovered six main clades within Dactyloa, five of which were previously referred to as species series (aequatorialis, heterodermus, latifrons, punctatus, roquet). A sixth clade clustered A. nasofrontalis and A. pseudotigrinus with A. dissimilis from western Amazonia, A. calimae from the Andes, A. neblininus from the Guiana Shield, and two undescribed Andean taxa. We therefore define a sixth species series within Dactyloa: the neblininus series. Close phylogenetic relationships between highly disjunct, narrowly-distributed anoles suggest that patches of suitable habitat connected the southern Atlantic Forest to western South America during the Miocene, in agreement with the age of former connections between the central Andes and the Brazilian Shield as a result of Andean orogeny. The data also support the view of recurrent evolution (or loss) of a twig anole-like phenotype in mainland anoles, in apparent association with the occurrence in montane settings. Our findings stress the value of complementary genetic sampling efforts across South American countries to advance studies of mainland anole taxonomy and evolution.

Contemporary human uses of tropical forested watersheds and riparian corridors: Ecosystem services and hazard mitigation, with examples from Panama, Puerto Rico, and Venezuela

Humans have long favored settlement along rivers for access to water for drinking and agriculture, transport corridors, and food sources. Settlement in or near montane tropical (and other) forests include additional benefits such as food and wood supply, and high quality water derived from watersheds where upstream human disturbance and environmental degradation are generally low. However, the advantages afforded by these floodplain and montane settings are offset by episodic risks to communities located there as floods, landslides, wildfires, volcanoes, (and tsunamis for coastal communities), cause loss of life and damage or destroy infrastructure and crops. A basic understanding of rainfall and flood patterns, as well as hillslope stability, by residents in these environments mitigates these risks. Modern global urbanization, particularly in regions of rapid economic growth, has resulted in much of this “organic” knowledge being lost, as megacities encroach on floodplains and mountain fronts. Moreover, the most likely occupants of these hazardous locations are often marginalized economically, which increases their vulnerability. Effective stewardship of river floodplains and upstream montane forests maintains a key ecosystem service, which in addition to the well-described services, (i.e. water, food, hydroelectric energy, wood products, carbon sequestration, maintenance of biodiversity, etc.) is the mitigation of natural hazards and vulnerability.

Calibration of the clumped isotope geothermometer in soil carbonate in Wyoming and Nebraska, USA: Implications for paleoelevation and paleoclimate reconstruction

Recent work has shown that soil carbonates typically form as the soil dries after seasonal rainfall, and therefore record seasonal aspects of climate rather than mean annual conditions. Because soil carbonate formation is closely related to the timing of local rainfall and drying, it is necessary to understand the formation seasonality and temperature, and soil water δO18 values recorded in modern soil carbonate before accurate estimates of stable isotope-based paleoelevation and paleoclimate can be made. Here we study carbonate clumped-isotope (Δ47) and oxygen isotope (δO18) compositions of modern soil carbonates and seasonal variations of soil moisture and temperature of nearby climate stations in Wyoming and western Nebraska, USA, to understand the seasonality of soil carbonate formation in semi-arid to arid temperate montane settings. We find that soil carbonate clumped-isotope temperatures (T(Δ47)) are 3–5 °C higher than mean summer air temperature and are similar to or higher than average summer soil temperature. At depths >40 cm, soil moisture dramatically decreases in early summer following the cessation of spring rains and snowmelt and shows only brief increases after major mid–late summer rain events. Soil water δO18 values calculated using carbonate δO18 and T(Δ47) values are similar to the δO18 values of local mean summer precipitation. These lines of evidence suggest that soil carbonates in our study area formed during times of soil dewatering in early summer and after major summer storm events in mid–late summer, and in or near equilibrium with mean summer precipitation δO18 values.T(Δ47) values of modern soil carbonates are inversely correlated with elevation, with a lapse rate, −4.0 °C/km, similar to the modern air and soil temperature lapse rates. Calculated soil water δO18 values also are inversely correlated with elevation, with a lapse rate of −3.7‰/km. Sample elevations can be reconstructed using both T(Δ47) values and calculated soil water δO18 values between 900 m and 2600 m in our studied area, with an accuracy of ±0.5 km or less. However, δO18 values of precipitation and soil water reflect the complex interaction of climatic, environmental, and topographic conditions prior to carbonate formation, whereas T(Δ47) values may be influenced by site-specific conditions. We suggest that both soil carbonate T(Δ47) values and calculated soil water δO18 values should be used to corroborate paleoelevation reconstruction, and the seasonal nature of soil carbonate formation should be considered when soil carbonate T(Δ47) values and δO18 values are applied for paleoclimate reconstruction.

Moisture status during a strong El Niño explains a tropical montane cloud forest’s upper limit

Growing evidence suggests short-duration climate events may drive community structure and composition more directly than long-term climate means, particularly at ecotones where taxa are close to their physiological limits. Here we use an empirical habitat model to evaluate the role of microclimate during a strong El Niño in structuring a tropical montane cloud forest's upper limit and composition in Hawai'i. We interpolate climate surfaces, derived from a high-density network of climate stations, to permanent vegetation plots. Climatic predictor variables include (1) total rainfall, (2) mean relative humidity, and (3) mean temperature representing non-El Niño periods and a strong El Niño drought. Habitat models explained species composition within the cloud forest with non-El Niño rainfall; however, the ecotone at the cloud forest's upper limit was modeled with relative humidity during a strong El Niño drought and secondarily with non-El Niño rainfall. This forest ecotone may be particularly responsive to strong, short-duration climate variability because taxa here, particularly the isohydric dominant Metrosideros polymorpha, are near their physiological limits. Overall, this study demonstrates moisture's overarching influence on a tropical montane ecosystem, and suggests that short-term climate events affecting moisture status are particularly relevant at tropical ecotones. This study further suggests that predicting the consequences of climate change here, and perhaps in other tropical montane settings, will rely on the skill and certainty around future climate models of regional rainfall, relative humidity, and El Niño.

Allopatry as a gordian knot for taxonomists: patterns of DNA barcode divergence in arctic-alpine lepidoptera.

Many cold adapted species occur in both montane settings and in the subarctic. Their disjunct distributions create taxonomic complexity because there is no standardized method to establish whether their allopatric populations represent single or different species. This study employs DNA barcoding to gain new perspectives on the levels and patterns of sequence divergence among populations of 122 arctic-alpine species of Lepidoptera from the Alps, Fennoscandia and North America. It reveals intraspecific variability in the barcode region ranging from 0.00–10.08%. Eleven supposedly different species pairs or groups show close genetic similarity, suggesting possible synonymy in many cases. However, a total of 33 species show evidence of cryptic diversity as evidenced by the presence of lineages with over 2% maximum barcode divergence in Europe, in North America or between the two continents. Our study also reveals cases where taxonomic names have been used inconsistently between regions and exposes misidentifications. Overall, DNA barcodes have great potential to both increase taxonomic resolution and to make decisions concerning the taxonomic status of allopatric populations more objective.

Spatial variations in apparent recharge rate to a montane Paleozoic bedrock aquifer, Appalachian Mountains, United States

Hydrograph separation methods for estimating recharge are not useful in all watersheds, but in this article, the hypothesis is tested that they should be reasonably accurate in montane humid locations where dissipation times for runoff are short. The study area is a montane carbonate/clastic Paleozoic aquifer in the Appalachian Mountains, West Virginia and Virginia. For 1 yr, groundwater discharge was continuously measured at three different stream reaches; each has grossly similar climate, soils, and topography, but differing geology underlying the main stream channels and different stream orientations with respect to structure. One station measured base flow in a strike-parallel stream of moderate length (13.4 km [8.3 mi]); the other two in strike-normal streams of shorter length (2.7 km [1.7 mi]). Pronounced differences were observed in apparent recharge rate between the strike-normal and strike-parallel streams, with the strike-parallel stream similar in apparent recharge to 21 other regional streams, with both large and small catchments, of similar climatic and geologic conditions. Similarly, the strike-normal streams in the study area were significantly lower in recharge compared with these. The precise location of stream losses, if any, could not be pinpointed in detailed streamflow measurements. Although the low apparent recharge rates are primarily ascribed to stream losses, underflow, and/or hyporheic interactions, the evidence for this was nonconclusive. This case underscores that even in humid montane settings of moderate relief, complications in the groundwater budget may arise that make recharge estimates based on surface hydrograph analysis inaccurate.

Late Wisconsin/Early Holocene Vegetation in the Bonneville Basin

Woodrat middens from the northern Bonneville Basin allow a reconstruction of vegetation changes from 14,000 to 9000 yr ago. Cold montane steppe, dominated by sagebrush, covered much of the western Bonneville Basin prior to 13,000 yr ago. From 13,000-10,800 yr ago, the region was vegetated by limber pine woodlands in lower montane settings and a mosaic of limber pine and sagebrush steppe along basin flour margins. These low-elevation limber pine woodlands began to retreat upslope after about 11,000 yr ago due to increasingly drier climatic conditions, and were replaced by relatively more xeric desert scrub dominated by sagebrush and shadscale. The growth of limber pine at low elevations suggests that summer temperatures were as much as 6°C lower than at present. This evidence is in apparent conflict with the currently accepted post-Provo Lake Bonneville chronology, especially the magnitude of the postulated near-dessication of Lake Bonneville from ca. 13,000-12,200 yr ago.