High-elevation Forests Research Articles

The Influence of Western Spruce Budworm on Fire in Spruce-Fir Forests

Western spruce budworm (Choristoneura freemani Razowski; WSBW) is the most significant defoliator of coniferous trees in the western United States. Despite its important influence on Western forests, there are still gaps in our knowledge of WSBW’s impact on fire, and little research has been done on this relationship in high-elevation spruce-fir forests. Although this species is native to western North America, current outbreaks have persisted for many years in some areas, leading to high mortality rates among host tree species. Using the Fire and Fuels Extension of the Forest Vegetation Simulator (FFE-FVS), we examined the current and future impact of an ongoing WSBW outbreak on potential fire behavior in spruce-fir forests in northern New Mexico, USA. We found that this ongoing WSBW outbreak resulted in little to no difference in fire behavior under moderate fire weather conditions. Under high-severity fire weather conditions, stands enduring WSBW outbreaks experienced less severe fire behavior. We also found that WSBW outbreaks resulted in a decrease in fire behavior under severe fire weather conditions for 40 years following the outbreak.

Woody-plant ecosystems under climate change and air pollution-response consistencies across zonobiomes?

Forests store the largest terrestrial pools of carbon (C), helping to stabilize the global climate system, yet are threatened by climate change (CC) and associated air pollution (AP, highlighting ozone (O3) and nitrogen oxides (NOx)). We adopt the perspective that CC-AP drivers and physiological impacts are universal, resulting in consistent stress responses of forest ecosystems across zonobiomes. Evidence supporting this viewpoint is presented from the literature on ecosystem gross/net primary productivity and water cycling. Responses to CC-AP are compared across evergreen/deciduous foliage types, discussing implications of nutrition and resource turnover at tree and ecosystem scales. The availability of data is extremely uneven across zonobiomes, yet unifying patterns of ecosystem response are discernable. Ecosystem warming results in trade-offs between respiration and biomass production, affecting high elevation forests more than in the lowland tropics and low-elevation temperate zone. Resilience to drought is modulated by tree size and species richness. Elevated O3 tends to counteract stimulation by elevated carbon dioxide (CO2). Biotic stress and genomic structure ultimately determine ecosystem responsiveness. Aggrading early- rather than mature late-successional communities respond to CO2 enhancement, whereas O3 affects North American and Eurasian tree species consistently under free-air fumigation. Insect herbivory is exacerbated by CC-AP in biome-specific ways. Rhizosphere responses reflect similar stand-level nutritional dynamics across zonobiomes, but are modulated by differences in tree-soil nutrient cycling between deciduous and evergreen systems, and natural versus anthropogenic nitrogen (N) oversupply. The hypothesis of consistency of forest responses to interacting CC-AP is supported by currently available data, establishing the precedent for a global network of long-term coordinated research sites across zonobiomes to simultaneously advance both bottom-up (e.g., mechanistic) and top-down (systems-level) understanding. This global, synthetic approach is needed because high biological plasticity and physiographic variation across individual ecosystems currently limit development of predictive models of forest responses to CC-AP. Integrated research on C and nutrient cycling, O3-vegetation interactions and water relations must target mechanisms' ecosystem responsiveness. Worldwide case studies must be subject to biostatistical exploration to elucidate overarching response patterns and synthesize the resulting empirical data through advanced modelling, in order to provide regionally coherent, yet globally integrated information in support of internationally coordinated decision-making and policy development.

Acer binzayedii (Sapindaceae), a new maple species from Mexico

Acer binzayedii, a new species of Sapindaceae from cloud and high elevation forests in Jalisco State, Mexico, is described and illustrated. Acer binzayedii is characterized by deeply sagittate anther bases bearing scattered trichomes, the wing sulcus covering more than half of the nutlet, sparsely distributed coalescent and anastomose veins of the wings with reticulate veinlets sometimes present, trichomes on the abaxial leaf surfaces with short nodulations of reduced prominence, conical buds, and grey bark with long vertical ridges. The new species is compared to putative relatives A. skutchii, A. floridanum, A. saccharum, A. grandidentatum, and A. nigrum.

Soil CO<sub>2</sub> efflux from two mountain forests in the eastern Himalayas, Bhutan: components and controls

Abstract. The biogeochemistry of mountain forests in the Hindu Kush Himalaya range is poorly studied, although climate change is expected to disproportionally affect the region. We measured the soil CO2 efflux (Rs) at a high-elevation (3260 m) mixed forest and a lower-elevation (2460 m) broadleaf forest in Bhutan, eastern Himalayas, during 2015. Trenching was applied to estimate the contribution of autotrophic (Ra) and heterotrophic (Rh) soil respiration. The temperature (Q10) and the moisture sensitivities of Rh were determined under controlled laboratory conditions and were used to model Rh in the field. The higher-elevation mixed forest had a higher standing tree stock, reflected in higher soil C stocks and basal soil respiration. Annual Rs was similar between the two forest sites (14.5 ± 1.2 t C ha−1 for broadleaf; 12.8 ± 1.0 t C ha−1 for mixed). Modelled annual contribution of Rh was ∼ 65 % of Rs at both sites with a higher heterotrophic contribution during winter and lower contribution during the monsoon season. Rh, estimated from trenching, was in the range of modelled Rh but showed higher temporal variability. The measured temperature sensitivity of Rh was similar at the mixed and broadleaf forest sites (Q10 2.2–2.3) under intermediate soil moisture but decreased (Q10 1.5 at both sites) in dry soil. Rs closely followed the annual course of field soil temperature at both sites. Covariation between soil temperature and moisture (cold dry winters and warm wet summers) was likely the main cause for this close relationship. Under the prevailing weather conditions, a simple temperature-driven model was able to explain more than 90 % of the temporal variation in Rs. A longer time series and/or experimental climate manipulations are required to understand the effects of eventually occurring climate extremes such as monsoon failures.

Mitigating Future Avian Malaria Threats to Hawaiian Forest Birds from Climate Change.

Avian malaria, transmitted by Culex quinquefasciatus mosquitoes in the Hawaiian Islands, has been a primary contributor to population range limitations, declines, and extinctions for many endemic Hawaiian honeycreepers. Avian malaria is strongly influenced by climate; therefore, predicted future changes are expected to expand transmission into higher elevations and intensify and lengthen existing transmission periods at lower elevations, leading to further population declines and potential extinction of highly susceptible honeycreepers in mid- and high-elevation forests. Based on future climate changes and resulting malaria risk, we evaluated the viability of alternative conservation strategies to preserve endemic Hawaiian birds at mid and high elevations through the 21st century. We linked an epidemiological model with three alternative climatic projections from the Coupled Model Intercomparison Project to predict future malaria risk and bird population dynamics for the coming century. Based on climate change predictions, proposed strategies included mosquito population suppression using modified males, release of genetically modified refractory mosquitoes, competition from other introduced mosquitoes that are not competent vectors, evolved malaria-tolerance in native honeycreepers, feral pig control to reduce mosquito larval habitats, and predator control to improve bird demographics. Transmission rates of malaria are predicted to be higher than currently observed and are likely to have larger impacts in high-elevation forests where current low rates of transmission create a refuge for highly-susceptible birds. As a result, several current and proposed conservation strategies will be insufficient to maintain existing forest bird populations. We concluded that mitigating malaria transmission at high elevations should be a primary conservation goal. Conservation strategies that maintain highly susceptible species like Iiwi (Drepanis coccinea) will likely benefit other threatened and endangered Hawai’i species, especially in high-elevation forests. Our results showed that mosquito control strategies offer potential long-term benefits to high elevation Hawaiian honeycreepers. However, combined strategies will likely be needed to preserve endemic birds at mid elevations. Given the delay required to research, develop, evaluate, and improve several of these currently untested conservation strategies we suggest that planning should begin expeditiously.

High-Elevation Observations of Long-Tailed Weasel and Eastern Chipmunk in North Carolina

Abstract Observations of Mustela frenata (Long-tailed Weasel) are rare within the southern Appalachians, while observations of Tamias striatus (Eastern Chipmunk) are uncommon in high-elevation spruce-fir forests. We conducted camera-trap surveys at Roan Mountain Highlands, Mitchell County, NC, during summer 2016 in a Picea rubens (Red Spruce)—Abies fraseri (Fraser Fir) forest. During the survey, we observed a Long-tailed Weasel at 1893 m in elevation and an Eastern Chipmunk at 1703 m in elevation. These are the highest-elevation records for both species in the eastern United States outside of Great Smoky Mountains National Park, and the highest elevation record for Longtailed Weasel in North Carolina.

Home range, den selection and habitat use of Carolina northern flying squirrels (Glaucomys sabrinus coloratus)

Context Understanding habitat selection is important for determining conservation and management strategies for endangered species. The Carolina northern flying squirrel (CNFS; Glaucomys sabrinus coloratus) is an endangered subspecies found in the high-elevation montane forests of the southern Appalachians, USA. The primary use of nest boxes to monitor CNFS has provided biased information on habitat use for this subspecies, as nest boxes are typically placed in suitable denning habitat. Aims We conducted a radio-telemetry study on CNFS to determine home range, den site selection and habitat use at multiple spatial scales. Methods We radio-collared 21 CNFS in 2012 and 2014–15. We tracked squirrels to diurnal den sites and during night-time activity. Key results The MCP (minimum convex polygon) home range at 95% for males was 5.2±1.2ha and for females was 4.0±0.7. The BRB (biased random bridge) home range at 95% for males was 10.8±3.8ha and for females was 8.3±2.1. Den site (n=81) selection occurred more frequently in montane conifer dominate forests (81.4%) vs northern hardwood forests or conifer–northern hardwood forests (9.9% and 8.7%, respectively). We assessed habitat selection using Euclidean distance-based analysis at the 2nd order and 3rd order scale. We found that squirrels were non-randomly selecting for habitat at both 2nd and 3rd order scales. Conclusions At both spatial scales, CNFS preferentially selected for montane conifer forests more than expected based on availability on the landscape. Squirrels selected neither for nor against northern hardwood forests, regardless of availability on the landscape. Additionally, CNFS denned in montane conifer forests more than other habitat types. Implications Our results highlight the importance of montane conifer to CNFS in the southern Appalachians. Management and restoration activities that increase the quality, connectivity and extent of this naturally rare forest type may be important for long-term conservation of this subspecies, especially with the impending threat of anthropogenic climate change.

Regional modeling of climate change impacts on smallholder agriculture and ecosystems in Central America

Climate change will have serious repercussions for agriculture, ecosystems, and farmer livelihoods in Central America. Smallholder farmers are particularly vulnerable due to their reliance on agriculture and ecosystem services for their livelihoods. There is an urgent need to develop national and local adaptation responses to reduce these impacts, yet evidence from historical climate change is fragmentary. Modeling efforts help bridge this gap. Here, we review the past decade of research on agricultural and ecological climate change impact models for Central America. The results of this review provide insights into the expected impacts of climate change and suggest policy actions that can help minimize these impacts. Modeling indicates future climate-driven changes, often declines, in suitability for Central American crops. Declines in suitability for coffee, a central crop in the regional economy, are noteworthy. Ecosystem models suggest that climate-driven changes are likely at low- and high-elevation montane forest transitions. Modeling of vulnerability suggests that smallholders in many parts of the region have one or more vulnerability factors that put them at risk. Initial adaptation policies can be guided by these existing modeling results. At the same time, improved modeling is being developed that will allow policy action specifically targeted to vulnerable groups, crops, and locations. We suggest that more robust modeling of ecological responses to climate change, improved representation of the region in climate models, and simulation of climate influences on crop yields and diseases (especially coffee leaf rust) are key priorities for future research.

Assessing forest vulnerability to climate warming using a process-based model of tree growth: bad prospects for rear-edges.

Growth models can be used to assess forest vulnerability to climate warming. If global warming amplifies water deficit in drought-prone areas, tree populations located at the driest and southernmost distribution limits (rear-edges) should be particularly threatened. Here, we address these statements by analyzing and projecting growth responses to climate of three major tree species (silver fir, Abies alba; Scots pine, Pinus sylvestris; and mountain pine, Pinus uncinata) in mountainous areas of NE Spain. This region is subjected to Mediterranean continental conditions, it encompasses wide climatic, topographic and environmental gradients, and, more importantly, it includes rear-edges of the continuous distributions of these tree species. We used tree-ring width data from a network of 110 forests in combination with the process-based Vaganov-Shashkin-Lite growth model and climate-growth analyses to forecast changes in tree growth during the 21st century. Climatic projections were based on four ensembles CO2 emission scenarios. Warm and dry conditions during the growing season constrain silver fir and Scots pine growth, particularly at the species rear-edge. By contrast, growth of high-elevation mountain pine forests is enhanced by climate warming. The emission scenario (RCP 8.5) corresponding to the most pronounced warming (+1.4 to 4.8°C) forecasted mean growth reductions of -10.7% and -16.4% in silver fir and Scots pine, respectively, after 2050. This indicates that rising temperatures could amplify drought stress and thus constrain the growth of silver fir and Scots pine rear-edge populations growing at xeric sites. Contrastingly, mountain pine growth is expected to increase by +12.5% due to a longer and warmer growing season. The projections of growth reduction in silver fir and Scots pine portend dieback and a contraction of their species distribution areas through potential local extinctions of the most vulnerable driest rear-edge stands. Our modeling approach provides accessible tools to evaluate forest vulnerability to warmer conditions.

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.

Abundance and habitat use of the lizard Sceloporus utiformis (Squamata: Phrynosomatidae) during the seasonal transition in a tropical environment

Several behavioral and ecological studies have focused on the comparison of different variables among seasons. However, little is known about the transitional period between the end of the rainy season and the start of the dry season. To address this transition, we measured the abundance and habitat use of the lizard Sceloporus utiformis from the end of the rainy season to the beginning of the dry season. Two study sites were employed, both located in western Mexico: Chamela Biological Station and Manantlán Biosphere Reserve. These sites vary in elevation and distance from the coast. We compared the 2 environments with respect to ambient temperature, relative humidity and canopy cover in both the drier areas in the surrounding tropical dry forest and in wetter environment in vegetation along banks. Our results indicated that the abundance and habitat use of S. utiformis change gradually with seasonal transition, less abrupt changes in vegetation, followed by the high elevation forest and finally the low elevation forest. The population abundance of S. utiformis increased during the seasonal transition, and the age structure changed from adult-dominated to juvenile-dominated. During the wet-to-dry transition, the use of herbaceous microhabitat was reduced and the use of leaflitter and trees increased at all sites.

Tree regeneration, understory development, and biomass dynamics following wildfire in a mountain hemlock (Tsuga mertensiana) forest

Processes initiated by wildfire largely determine ecological characteristics of forested landscapes in subsequent decades, including vegetation composition, habitat quality, carbon balance, and probability of fire recurrence. Post-fire biomass dynamics have rarely been observed directly for high-elevation forests of the Pacific Northwest. We examined changes in total biomass and its components (attrition of coarse woody debris (CWD), growth of shrubs and herbaceous plants, and tree recruitment) over the first 15years following wildfire in a mountain hemlock (Tsuga mertensiana) forest in Oregon, using permanent plots representing random samples of four levels of fire-severity, from unburned to >90% tree mortality. Understory vegetation was transformed by fire, inasmuch as only shrubs were detected in unburned plots, while burned plots also had significant amounts of graminoids and forbs. Conifer recruitment was sparse in plots with high fire-severity two years after fire, but was abundant after 15years. Recruitment was predominantly mountain hemlock and most were seedlings <1m tall. The breakage of snags and resulting increase in logs created microsites (north sides of logs) conducive to tree regeneration. Mass of understory vegetation and conifer regeneration was far outweighed by CWD. Toppling, fragmentation, and advancing decay of snags resulted in a decrease in snag mass and an increase in log mass. The loss of snag mass exceeded the increase in log mass, resulting in an overall decline. For some portions of the burned area, particularly areas of high fire-severity, it may be more than a century before the growth of live trees balances the loss of mass of CWD.

Nutritional ecology of elk during summer and autumn in the Pacific Northwest

Nutritional ecology of elk during summer and autumn in the Pacific Northwest

Back to the Future: The Responses of Alpine Treelines to Climate Warming are Constrained by the Current Ecotone Structure

Alpine treeline ecotones are considered early-warning monitors of the effects of climate change on terrestrial ecosystems, but it is still unclear how accurately treeline dynamics may track the expected temperature rises. Site-specific abiotic constraints, such as topography and demographic trends may make treelines less responsive to environmental fluctuations. A better understanding on how local processes modulate treelines’ response to warming is thus required. We developed a model of treeline dynamics based on individual data of growth, mortality and reproduction. Specifically, we modeled growth patterns, mortality rates and reproductive size thresholds as a function of temperature and stand structure to evaluate the influence of climate- and stand-related processes on treeline dynamics. In this study, we analyze the dynamics of four Pyrenean mountain pine treeline sites with contrasting stand structures, and subjected to differing rates of climate warming. Our models indicate that Pyrenean treelines could reach basal areas and reproductive potentials similar to those currently observed in high-elevation subalpine forest by the mid twenty-first century. The fastest paces of treeline densification are forecasted by the late twenty-first century and are associated with higher warming rates. We found a common densification response of Pyrenean treelines to climate warming, but contrasting paces arise due to current size structures. Treelines characterized by a multistratified stand structure and subjected to lower mean annual temperatures were the most responsive to climate warming. In monostratified stands, tree growth was less sensitive to temperature than in multistratified stands and trees reached their reproductive size threshold later. Therefore, our simulations highlight that stand structure is paramount in modulating treeline responsiveness to ongoing climate warming. Synthesis. Treeline densification over the twenty-first century is likely to occur at different rates contingent on current stand structure and its effects on individual-level tree growth responses to warming. Accurate projections of future treeline dynamics must thus incorporate site-specific factors other than climate, specifically those related to stand structure and its influence on tree growth.

Carbon Costs of Constitutive and Expressed Resistance to a Non-Native Pathogen in Limber Pine.

Increasing the frequency of resistance to the non-native fungus Cronartium ribicola (causative agent of white pine blister rust, WPBR) in limber pine populations is a primary management objective to sustain high-elevation forest communities. However, it is not known to what extent genetic disease resistance is costly to plant growth or carbon economy. In this study, we measured growth and leaf-level physiology in (1) seedling families from seed trees that have previously been inferred to carry or not carry Cr4, the dominant R gene allele conferring complete, gene-for-gene resistance to WPBR in limber pine, and (2) populations that were and were not infected with C. ribicola. We found that, in the absence of C. ribicola exposure, there was no significant difference in carbon relations between families born from seed trees that harbor the resistance allele compared to those that lack it, either to plant growth and phenology or leaf-level photosynthetic traits. However, post-infection with C. ribicola, growth was significantly reduced in inoculation survivors expressing complete resistance compared to uninoculated seedlings. Furthermore, inoculation survivors exhibited significant increases in a suite of traits including photosynthetic rate, respiration rate, leaf N, and stomatal conductance and a decrease in photosynthetic water-use efficiency. The lack of constitutive carbon costs associated with Cr4 resistance in non-stressed limber pine is consistent with a previous report that the R gene allele is not under selection in the absence of C. ribicola and suggests that host resistance may not bear a constitutive cost in pathosystems that have not coevolved. However, under challenge by C. ribicola, complete resistance to WPBR in limber pine has a significant cost to plant growth, though enhanced carbon acquisition post-infection may offset this somewhat. These costs and effects on performance further complicate predictions of this species’ response in warmer future climates in the presence of WPBR.

Responses to climate change in radial growth of Picea schrenkiana along elevations of the eastern Tianshan Mountains, northwest China

Tree growth is largely driven by climate conditions in arid and alpine areas. A strong change in climate from warm-dry to warm-wet has already been observed in northwest China. However, little is known about the impacts of regional climate variability on the radial growth of trees along elevations of the eastern Tianshan Mountains. Consequently, we developed three tree-ring width chronologies of Schrenk spruce (Picea schrenkiana Fisch. et Mey.) ranging in elevation from 2159 to 2552m above sea level (a.s.l.), which play an important role in the forestry ecosystem, agriculture, and local economy of Central Asia. In our study, the correlation analyses of growth-drought using the monthly standardized precipitation-evapotranspiration index (SPEI) at different temporal scales demonstrated that drought in growing season was the main factor limiting tree growth, regardless of elevation. The relationships between radial growth of Schrenk spruce and main climate factors were relatively stable by moving correlation function, and the trend of STD chronologies and basal area increment (BAI) also showed a synchronous decline across the three elevations in recent decades. And meanwhile, slight differences in responses to climate change in radial growth along elevations were examined. The drought stress increased as elevations decreased. Radial growth at the higher elevation depended on moisture availability due to high temperature, as indicated by the significant negative correlation with mean temperature in the late growing season of the previous year (August-September, p<0.001). However, radial growth at the lower elevation were restricted by drought stress due to less precipitation and higher temperatures, as demonstrated by the significant negative correlation with mean temperature but positive with total precipitation in the early growing season of the current year (April-May, p<0.05). In addition, the decline of radial growth (BAI) at the higher elevation (3.710cm2yr−1/decade, p<0.001) was faster than that of the middle elevation (2.344cm2yr−1/decade, p<0.001) and the lower elevation (3.005cm2yr−1/decade, p<0.001) since 2000, indicating that the trees at higher elevation of a relatively humid environment were more susceptible to the effects of climate change due to their poor adaptability to water deficit. Therefore, the forest ecosystems would be suppressed as a result of increasing drought stress in the future, especially in the high-elevation forests of arid and semi-arid areas.

Defense traits in the long-lived Great Basin bristlecone pine and resistance to the native herbivore mountain pine beetle.

Summary Mountain pine beetle (MPB, Dendroctonus ponderosae) is a significant mortality agent of Pinus, and climate‐driven range expansion is occurring. Pinus defenses in recently invaded areas, including high elevations, are predicted to be lower than in areas with longer term MPB presence. MPB was recently observed in high‐elevation forests of the Great Basin (GB) region, North America. Defense and susceptibility in two long‐lived species, GB bristlecone pine (Pinus longaeva) and foxtail pine (P. balfouriana), are unclear, although they are sympatric with a common MPB host, limber pine (P. flexilis).We surveyed stands with sympatric GB bristlecone–limber pine and foxtail–limber pine to determine relative MPB attack susceptibility and constitutive defenses. MPB‐caused mortality was extensive in limber, low in foxtail and absent in GB bristlecone pine. Defense traits, including constitutive monoterpenes, resin ducts and wood density, were higher in GB bristlecone and foxtail than in limber pine. GB bristlecone and foxtail pines have relatively high levels of constitutive defenses which make them less vulnerable to climate‐driven MPB range expansion relative to other high‐elevation pines. Long‐term selective herbivore pressure and exaptation of traits for tree longevity are potential explanations, highlighting the complexity of predicting plant–insect interactions under climate change.

Burn me twice, shame on who? Interactions between successive forest fires across a temperate mountain region.

Increasing rates of natural disturbances under a warming climate raise important questions about how multiple disturbances interact. Escalating wildfire activity in recent decades has resulted in some forests re-burning in short succession, but how the severity of one wildfire affects that of a subsequent wildfire is not fully understood. We used a field-validated, satellite-derived, burn-severity atlas to assess interactions between successive wildfires across the US Northern Rocky Mountains a 300,000-km2 region dominated by fire-prone forests. In areas that experienced two wildfires between 1984 and 2010, we asked: (1) How do overall frequency distributions of burn-severity classes compare between first and second fires? (2) In a given location, how does burn severity of the second fire relate to that of the first? (3) Do interactions between successive fires vary by forest zone or the interval between fires? (4) What factors increase the probability of burning twice as stand-replacing fire? Within the study area, 138,061ha burned twice between 1984 and 2010. Overall, frequency distributions of burn severity classes (low, moderate, high; quantified using relativized remote sensing indices) were similar between the first and second fires; however burn severity was 5-13% lower in second fires on average. Negative interactions between fires were most pronounced in lower-elevation forests and woodlands, when fire intervals were <10yr, and when burn severity was low in the first fire. When the first fire burned as high severity and fire intervals exceeded 10-12yr, burn-severity interactions switched from negative to positive, with high-severity fire begetting subsequent high-severity fire. Locations most likely to experience successive stand-replacing fires were high-elevation forests, which are adapted to high-severity fire, and areas conducive to abundant post-fire tree regeneration. Broadly similar severities among short-interval "re-burns" and other wildfires indicate that positive severity feedbacks, an oft-posited agent of ecosystem decline or state shift, are not an inevitable outcome of re-burning. Nonetheless, context-dependent shifts in both the magnitude and direction of wildfire interactions (associated with forest zone, initial burn-severity, and disturbance interval) illustrate complexities in disturbance interactions and can inform management and predictions of future system dynamics.

Drivers of atmospheric methane uptake by montane forest soils in the southern Peruvian Andes

Abstract. The soils of tropical montane forests can act as sources or sinks of atmospheric methane (CH4). Understanding this activity is important in regional atmospheric CH4 budgets given that these ecosystems account for substantial portions of the landscape in mountainous areas like the Andes. We investigated the drivers of net CH4 fluxes from premontane, lower and upper montane forests, experiencing a seasonal climate, in south-eastern Peru. Between February 2011 and June 2013, these soils all functioned as net sinks for atmospheric CH4. Mean (standard error) net CH4 fluxes for the dry and wet season were −1.6 (0.1) and −1.1 (0.1) mg CH4-C m−2 d−1 in the upper montane forest, −1.1 (0.1) and −1.0 (0.1) mg CH4-C m−2 d−1 in the lower montane forest, and −0.2 (0.1) and −0.1 (0.1) mg CH4-C m−2 d−1 in the premontane forest. Seasonality in CH4 exchange varied among forest types with increased dry season CH4 uptake only apparent in the upper montane forest. Variation across these forests was best explained by available nitrate and water-filled pore space indicating that nitrate inhibition of oxidation or diffusional constraints imposed by changes in water-filled pore space on methanotrophic communities may represent important controls on soil–atmosphere CH4 exchange. Net CH4 flux was inversely related to elevation; a pattern that differs to that observed in Ecuador, the only other extant study site of soil–atmosphere CH4 exchange in the tropical Andes. This may result from differences in rainfall patterns between the regions, suggesting that attention should be paid to the role of rainfall and soil moisture dynamics in modulating CH4 uptake by the organic-rich soils typical of high-elevation tropical forests.

Genetic Analysis of the Indri Reveals No Evidence of Distinct Subspecies

Subspecies were traditionally defined by identifying gaps between phenotypes across the geographic range of a species, and may represent important units in the development of conservation strategies focused on preserving genetic diversity. Previous taxonomic research proposed that phenotypic variation between scattered Indri indri populations warranted the naming of two distinct subspecies, I. i. indri and I. i. variegatus. We tested these subspecific designations using mitochondrial sequence data generated from the control region or D-loop (569 bp) and a large section (2362 bp) of multiple genes and tRNAs known as Pastorini’s fragment and nuclear microsatellite markers. This study used 114 samples of I. indri from 12 rainforest sites in eastern Madagascar, encompassing the entire range of the species. These genetic samples represent multiple populations from low- and high-elevation forests from both putative subspecies. Molecular analyses of the mitochondrial sequence data did not support the two proposed subspecies. Furthermore, the microsatellite analyses showed no significant differences across the range beyond population level differentiation. This study demonstrates the utility of incorporating multiple lines of evidence in addition to phenotypic traits to define species or subspecies.