South-facing Aspects Research Articles

Effects of forest structure on the interaction between avian hosts, dipteran vectors and haemosporidian parasites

BackgroundForest habitats are important biodiversity refuges for a wide variety of bird species. Parasitism may modulate host species presence and abundance, and parasite effects can change according to forest management practices. Such processes are not well studied in vector-borne avian haemosporidians. We analyzed the effects of forest management on bird-dipteran-haemosporidian interactions, using seven common bird species in managed and unmanaged beech forest habitats in northeastern Germany. We assumed that forest structural heterogeneity affects parasite population parameters in avian hosts (i.e., prevalence and parasitemia), through its effect on the condition of the avian host but also through varying vector abundances.ResultsParasite prevalence was high (about 80%) and homogeneous across different beech forest categories (i.e., young, old, unmanaged) and for all bird species, except Erithacus rubecula (35%). Parasitemia varied across bird species but not across forest categories within each avian species (lowest parasitemia were found in E. rubecula, Turdus merula, and Turdus philomelos). In our study system, we found that vector abundance was not the main driver of parasite dynamics. We found that forest structure affects parasite infection probability directly and potentially host condition via available resources that have to be used either to combat infections (i.e., high parasitemia) or to maintain a good body condition.ConclusionsThe effects of each of the predictors were bird species-specific, and we found that Diptera vectors were not the foremost influence in our host-vector-parasite system. Effects of forest habitat variables indicated that for most bird species in this study, habitat regulation of infection probability was more likely (i.e., E. rubecula, Fringilla coelebs, Sylvia atricapilla), whereas for Parus major habitat characteristics impacted first individuals' body condition and subsequently the probability of infection. Our findings emphasize the need of species-specific analyses and to use continuous forest structural parameters (e.g., the proportion of gap, south facing aspect) to better understand habitat and land use effects on host-vector-parasite dynamics.

Topography influences species-specific patterns of seasonal primary productivity in a semiarid montane forest.

Semiarid forests in the southwestern USA are generally restricted to mountain regions where complex terrain adds to the challenge of characterizing stand productivity. Among the heterogeneous features of these ecosystems, topography represents an important control on system-level processes including snow accumulation and melt. This basic relationship between geology and hydrology affects radiation and water balances within the forests, with implications for canopy structure and function across a range of spatial scales. In this study, we quantify the effect of topographic aspect on primary productivity by observing the response of two codominant native tree species to seasonal changes in the timing and magnitude of energy and water inputs throughout a montane headwater catchment in Arizona, USA. On average, soil moisture on north-facing aspects remained higher during the spring and early summer compared with south-facing aspects. Repeated measurements of net carbon assimilation (Anet) showed that Pinus ponderosa C. Lawson was sensitive to this difference, while Pseudotsuga menziesii (Mirb.) Franco was not. Irrespective of aspect, we observed seasonally divergent patterns at the species level where P. ponderosa maintained significantly greater Anet into the fall despite more efficient water use by P. menziesii individuals during that time. As a result, this study at the southern extent of the geographical P. menziesii distribution suggests that this species could increase water-use efficiency as a response to future warming and/or drying, but at lower rates of production relative to the more drought-adapted P. ponderosa. At the sub-landscape scale, opposing aspects served as a mesocosm of current versus anticipated climate conditions. In this way, these results also constrain the potential for changing carbon sequestration patterns from Pinus-dominated landscapes due to forecasted changes in seasonal moisture availability.

Distribution pattern and associated flora of Jurinea dolomiaea in the western Himalayan highlands of Kashmir: An indicator endemic plant of alpine phytodiversity

Jurinea dolomiaea is a prime indicator plant of the alpine regions endemic to the Himalayas which performs important ecosystem services critical to the existence of the associated endemic plants and habitat stability. Current study was designed with the specific objectives to investigate the distribution pattern and community structure of Jurinea dolomiaea and associated flora and analyze the species-environment relationship in the Western Himalayas region of Kashmir, Pakistan. It is hypothesized that distribution pattern of J. dolomiaea and associated community structure is strongly influenced by environment prevalent variables. The present study revealed a total of 60 plant species belonging to 50 genera and 25 families recorded in association with J. dolomiaea with Asteraceae, Poaceae and Rosaceae as the dominant plant families. J. dolomiaea was recorded with highest average IVI value of 31.01 accompanied by Co-dominant taxa including Sibbaldia cunneata, Carex nubigena, Poa alpina and Poa pratensis. Jurinea dolomiaea exhibited a distinct distribution pattern in open sunny slopes confined to the south facing aspect receiving maximum solar insolation enabling the plant to survive in extremely cold alpine habitat. The average values of Simpson’s and Shannon’s diversity for the recorded plant communities were 0.90 and 2.67 respectively, whereas Species evenness averaged as 0.68. Vegetation exhibited relatively higher (>50) value of maturity averaging as 62.57. Analysis of the endemism in the local flora revealed a total of 27 species endemic to the Western Himalayas in an altitude range of 3200–4400 m, making 45.00% of the total recorded species. J. dolomiaea was found to be an important part of plant based local ethnomedicinal healthcare system in the mountain communities. Principal Component Analysis and Cluster Analysis identified the dominant taxa specific species assemblages in the local flora correlated with environmental variables. About 19 species having low (>2) IVI values associated were classified as rare. Current study validated the role of Jurinea dolomiaea as a strong ecological indicator of alpine habitats critically important for the associated valuable endemic alpine flora. An integrated approach is recommended for conservation management of Jurinea dolomiaea communities in the Western Himalayan alpines.

Evaluating Economic Impacts of Prescribed Fire in the Central Hardwood Region

AbstractSurface fires are often prescribed to favor oak (Quercus) regeneration in eastern forests, but there is potential for fire to damage residual overstory timber. This study evaluated the potential economic effects of prescribed fire on sawtimber volume and value across 139 stands, each with a known history of one to six prescribed fires, on the Hoosier, Mark Twain, Wayne, and Daniel Boone National Forests. Sawtimber volume and value losses were highly variable, ranging from 0 to 2,269 bd ft ac–1 and from US$0 to US$272.95 ac–1, respectively, for stands that had received at least one prescribed fire. Volume and value losses increased linearly by +0.9 percent and +1.5 percent per burn, respectively, that a stand received over the past 25 years. Stands with south-facing aspects had greater relative volume and value losses (+1.4 to +1.5 percent, respectively), but this influence was statistically less important than the number of burns in predictive models. The eastern national forests had much lower average relative volume and value losses, <3.0 percent, than the more western Mark Twain National Forest (10–15 percent loss). Species composition affected value loss associated with prescribed fire; red oaks experienced significantly higher value loss than all other species groups.

Management of ecosystems alters vector dynamics and haemosporidian infections

The presence of insect vectors is a key prerequisite for transmission of vector-borne disease such as avian haemosporidians. In general, the effects of land use change on Diptera vectors are not well studied; the response of vectors to forest management depends on vector species, as has been shown previously for the birds. We tested if abundance of insects from different Diptera families and haemosporidian infection are affected through alteration of habitat structural variables (measured by LiDAR) and forest management intensities. We identified higher large-scale variation of female insect abundance in northeastern than in southwestern Germany. Unmanaged forest stands had higher Diptera insect abundances. We found that abundance of female Diptera increased with the amount of forest gaps but decreased in forest plots with more south facing aspect, higher habitat structural heterogeneity, temperature and humidity. We found that haemosporidian infections in Diptera insects increased with increased management intensity and more canopy structural diversity (e.g., amount of edge habitat), but decreased with a denser shrub layer, deeper leaf litter and higher humidity (characteristics for unmanaged forest stands). Although higher forest management intensity decreased vector abundance, the haemosporidian infections in the vectors increased, indicating a significant effect of forest management on disease dynamics.

Wildfire and topography impacts on snow accumulation and retention in montane forests

Wildfires are increasing in frequency, severity, and size in many parts of the world. Forest fires can fundamentally affect snowpack and watershed hydrology by restructuring forest composition and structure. Topography is an important factor in snowpack accumulation and ablation as it influences exposure to solar radiation and atmospheric conditions. Few direct measurements of post-fire snowpack have been taken and none to this date that evaluate how topographical aspect influences the effect of forest fire on snowpack accumulation and ablation. We set up a two-year experiment on the Twitchell Canyon fire in south-central Utah on both north and south facing aspects and burned and unburned forest conditions across three replicated blocks. There was a significant interaction between burn condition and aspect for snow depth in which there was a reduction in snow depth in burned areas on south facing aspects but not on northern facing aspects. Snowpack disappeared earlier in burned areas than unburned areas, particularly on south facing slopes. Snow water equivalence (SWE) did not vary between burned and unburned forest. Year and topographical aspect were primary drivers of both snow depth and SWE. A review of five similar studies suggests that sites at southern latitudes and lower elevations could be more susceptible to reduction in snowpack after wildfire.

Mountain pine beetle attack faster growing lodgepole pine at low elevations in western Montana, USA

Global change has impacted forests through altered disturbance regimes. In the western US, climate change has resulted in extensive and severe mountain pine beetle outbreaks. These outbreaks have the potential to impact forest function through the selection of certain phenotypes. We investigated the potential for bark beetle-induced selection by way of measuring growth and climate response in mountain pine beetle-killed and surviving lodgepole pine in the Northern Rockies. We had three objectives: (1) investigate differences in growth between beetle-killed and surviving lodgepole pine prior to a recent outbreak, (2) compare the climate-growth relationships for beetle-killed and surviving lodgepole pine and how those relationships explain observed growth differences and predict mortality risk, and (3) investigate growth differences and growth-climate relationships across north- and south-facing aspects and over an elevation range representing local climate gradients. Significantly higher growth rates were observed in beetle-killed trees at low-elevation sites, but not at mid or high elevations. While aspect influenced overall growth, it did not have a significant influence on the difference in growth between beetle-killed and surviving trees. Growth showed significant relationships with several climate variables (i.e., previous-year August temperatures, October temperatures, annual precipitation, and summertime climatic water deficit), with slight differences in those relationships between beetle-killed and surviving trees. Mixed effects models demonstrated that higher growth rates and age increased the probability of mortality during the outbreak at all elevations, and also that climatic water deficit and previous-year August maximum temperatures were related to the magnitude of growth differences between beetle-killed and surviving trees. Overall, mountain pine beetles tended to attack large, fast-growing, lodgepole trees, especially at lower elevations where trees may be more susceptible to seasonal water stress.

Historical Climate Warming in the White Mountains of New Hampshire (USA): Implications for Snowmaking Water Needs at Ski Areas

The objectives of this study were to examine changing snowmaking conditions in the New Hampshire White Mountains and how changes in snowmaking operations have compared with winter warming. We analyzed three 50-year high-quality daily temperature records representing different elevations and aspects to assess changes in snowmaking conditions during important snowmaking periods. The analysis provides context for discussing the historical relationships between temperatures, water, and snowmaking infrastructure. There was significant warming of winter temperatures over the 50-year record, notably strongest at the early portion of the snowmaking season, especially in the weeks between 1 December and 25 December. While the rates of warming were comparable on both north- and south-facing aspects, the implied reduction in days suitable for snowmaking in each period was always lowest on the north-facing aspect as the mean temperatures on this aspect were farther below the snowmaking threshold. Daily average temperatures of –2°C and –5°C were both explored as thresholds for snowmaking. The implied reduction in snowmaking opportunity during the 1 November to 25 December period using a –2°C snowmaking threshold at the north-facing site was 20%, while the implied reduction for the entire season for that site was 8.5%.This decrease in opportunity for snowmaking, especially in the economically important early season, suggests an increasing need for large volumes of water to make snow in less time, given that holiday vacations are fixed in time. Analysis of snowmaking operations at Loon Mountain Resort suggest that modern snowmaking investments there have outpaced the pressure from climate warming to date, but this has concentrated demand for water into smaller time frames.

Assessing a Multi-Platform Data Fusion Technique in Capturing Spatiotemporal Dynamics of Heterogeneous Dryland Ecosystems in Topographically Complex Terrain

Water-limited ecosystems encompass approximately 40% of terrestrial land mass and play a critical role in modulating Earth’s climate and provisioning ecosystem services to humanity. Spaceborne remote sensing is a critical tool for characterizing ecohydrologic patterns and advancing the understanding of the interactions between atmospheric forcings and ecohydrologic responses. Fine to medium scale spatial and temporal resolutions are needed to capture the spatial heterogeneity and the temporally intermittent response of these ecosystems to environmental forcings. Techniques combining complementary remote sensing datasets have been developed, but the heterogeneous nature of these regions present significant challenges. Here we investigate the capacity of one such approach, the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM) algorithm, to map Normalized Difference Vegetation Index (NDVI) at 30 m spatial resolution and at a daily temporal resolution in an experimental watershed in southwest Idaho, USA. The Dry Creek Experimental Watershed captures an ecotone from a sagebrush steppe ecosystem to evergreen needle-leaf forests along an approximately 1000 m elevation gradient. We used STARFM to fuse NDVI retrievals from the MODerate-resolution Imaging Spectroradiometer (MODIS) and Landsat during the course of a growing season (April to September). Specifically we input to STARFM a pair of Landsat NDVI retrievals bracketing a sequence of daily MODIS NDVI retrievals to yield daily estimates of NDVI at resolutions of 30 m. In a suite of data denial experiments we compared these STARFM predictions against corresponding Landsat NDVI retrievals and characterized errors in predicted NDVI. We investigated how errors vary as a function of vegetation functional type and topographic aspect. We find that errors in predicting NDVI were highest during green-up and senescence and lowest during the middle of the growing season. Absolute errors were generally greatest in tree-covered portions of the watershed and lowest in locations characterized by grasses/bare ground. On average, relative errors in predicted average NDVI were greatest in grass/bare ground regions, on south-facing aspects, and at the height of the growing season. We present several ramifications revealed in this study for the use of multi-sensor remote sensing data for the study of spatiotemporal ecohydrologic patterns in dryland ecosystems.

Species, Climate and Landscape Physiography Drive Variable Growth Trends in Subalpine Forests

Forests around the world are undergoing rapid changes due to changing climate and increasing physiological stress, but forest response to climate at the ecosystem scale can be highly variable due to the mixed responses of different trees across heterogeneous landscapes. To determine the response of ecosystems in the Rocky Mountains to climate stress, we investigated the response of subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii), two widely distributed subalpine forest species of Rocky Mountains, to climate warming across a region characterized by gradients of elevation, aspect and soil type. We investigated the growth trend of individual trees through time, determined the climate variables most important for driving growth and quantified the interactions between climate and topography that influence long-term growth trends and potential ecological changes across the study region. Growth trends of these two species are similar through the first part of the century, but diverge during the last several decades. Since 1975, subalpine fir growth decreased through time, while Engelmann spruce growth increased. We find that aspect and warm summer temperatures are the most important factors determining growth in subalpine fir, and subalpine fir growth declines are greatest on east- and south-facing aspects. In contrast, Engelmann spruce growth is uniformly unresponsive to climate. In addition to highlighting the importance of species-level differences in growth response to climate, our results also identify interactions between climate and local physiography as controls on long-term growth trends and suggest that the local landscape physiography can mediate climate-related stress in forested ecosystems. This work advances our understanding of how forest stress is mitigated by landscape factors at the ecosystem scale, and how interactions of species, landscape and climate will control future ecosystem composition and forest growth dynamics.

Aspects and altitudes modify the requirement of disturbance in oak (Quercus leucotrichophora A. Camus) belt of Garhwal Himalaya

Present study measures the impact of forest disturbance on population structure and regeneration status of a Himalayan banj oak (Qsuercus leucotrichophora A. Camus) forest at different aspects and altitudes. The whole study was carried out by placing 300 systematically selected sample plots in banj oak forest. The study revealed that moderately disturbed forest patches were present in all elevation ranges and both north and south facing aspects whereas most of the highly disturbed patches were situated near middle and lower stretches of forests or close to habitations. Density of primary diameter class (5–15cm) was recorded highest in moderately disturbed zone in upper elevation ranges and north facing aspect and ‘fair’ category of regeneration was most frequent in all elevation ranges and aspects. The paper concludes a positive effect of mid-level disturbance on plant community for better regeneration and study recommends a minimum resource extraction and silvicultural practices in banj-oak belt of Himalaya for a minimum canopy opening which not only be able to provide biomass to local communities for their daily needs but also would be able to maintain and improve forest health.

A general framework to describe the alteration of natural tree species composition as an indicator of forest naturalness

The alteration of natural tree species composition is defined as the deviation of the current tree species composition from that of the natural state. It can be used as a measure of human influence on forest vegetation, and thus as an indicator of the naturalness of forest vegetation. The aim of the study was to develop a standard procedure for estimating the alteration of natural tree species composition, to explain factors driving alteration and to examine its significance for susceptibility of forest stands to natural disturbances. The alteration of natural tree species composition was estimated for the Dinaric region (5556km2, Slovenia) by the Robič Index of Dissimilarity (RID), ranging from 0 (completely natural) to 100 (completely altered). The index was calculated on the compartment level (24ha each on average) with data on current and potential natural forest vegetation. The influence of human activities on tree species alteration was examined by using topographic and accessibility variables. The susceptibility of forest stands to natural disturbances was analysed with data on sanitary felling. In the study area, the natural tree species composition of forest stands is moderately preserved; the average value of RID was 50.05, ranging from 1.76 to 100, and the coefficient of variation was 0.49. The alteration of the natural tree species composition of forest stands is primarily the result of forest management and past land use, conditioned either by topography or accessibility of forests. The degree of alteration of tree species composition decreased along the gradients of rockiness, inclination and elevation. A greater degree of alteration appeared on the slopes of intermediate and south facing aspects than on north facing slopes, and in areas that were closer to the forest edge. A higher level of alteration significantly increases the susceptibility of forest stands to natural disturbances. The procedure represents a novel approach in modelling the alteration (naturalness) of tree species composition of forest vegetation. It is applicable at different spatial scales and fosters an understanding of the patterns of tree species composition under the influence of human activity across forest landscapes.

Replicated landscape genetic and network analyses reveal wide variation in functional connectivity for American pikas.

Landscape connectivity is essential for maintaining viable populations, particularly for species restricted to fragmented habitats or naturally arrayed in metapopulations and facing rapid climate change. The importance of assessing both structural connectivity (physical distribution of favorable habitat patches) and functional connectivity (how species move among habitat patches) for managing such species is well understood. However, the degree to which functional connectivity for a species varies among landscapes, and the resulting implications for conservation, have rarely been assessed. We used a landscape genetics approach to evaluate resistance to gene flow and, thus, to determine how landscape and climate-related variables influence gene flow for American pikas (Ochotona princeps) in eight federally managed sites in the western United States. We used empirically derived, individual-based landscape resistance models in conjunction with predictive occupancy models to generate patch-based network models describing functional landscape connectivity. Metareplication across landscapes enabled identification of limiting factors for dispersal that would not otherwise have been apparent. Despite the cool microclimates characteristic of pika habitat, south-facing aspects consistently represented higher resistance to movement, supporting the previous hypothesis that exposure to relatively high temperatures may limit dispersal in American pikas. We found that other barriers to dispersal included areas with a high degree of topographic relief, such as cliffs and ravines, as well as streams and distances greater than 1-4 km depending on the site. Using the empirically derived network models of habitat patch connectivity, we identified habitat patches that were likely disproportionately important for maintaining functional connectivity, areas in which habitat appeared fragmented, and locations that could be targeted for management actions to improve functional connectivity. We concluded that climate change, besides influencing patch occupancy as predicted by other studies, may alter landscape resistance for pikas, thereby influencing functional connectivity through multiple pathways simultaneously. Spatial autocorrelation among genotypes varied across study sites and was largest where habitat was most dispersed, suggesting that dispersal distances increased with habitat fragmentation, up to a point. This study demonstrates how landscape features linked to climate can affect functional connectivity for species with naturally fragmented distributions, and reinforces the importance of replicating studies across landscapes.

Site-specific water-use strategies of mountain pine and larch to cope with recent climate change.

We aim to achieve a mechanistic understanding of the eco-physiological processes in Larix decidua and Pinus mugo var. uncinata growing on north- and south-facing aspects in the Swiss National Park in order to distinguish the short- and long-term effects of a changing climate. To strengthen the interpretation of the δ(18)O signal in tree rings and its coherence with the main factors and processes driving evaporative δ(18)O needle water enrichment, we analyzed the δ(18)O in needle, xylem and soil water over the growing season in 2013 and applied the mechanistic Craig-Gordon model (1965) for the short-term responses. We found that δ(18)O needle water strongly reflected the variability of relative humidity mainly for larch, while only δ(18)O in pine xylem water showed a strong link to δ(18)O in precipitation. Larger differences in offsets between modeled and measured δ(18)O needle water for both species from the south-facing aspects were detected, which could be explained by the high transpiration rates. Different soil water and needle water responses for the two species indicate different water-use strategies, further modulated by the site conditions. To reveal the long-term physiological response of the studied trees to recent and past climate changes, we analyzed δ(13)C and δ(18)O in wood chronologies from 1900 to 2013. Summer temperatures as well as summer and annual amount of precipitations are important factors for growth of both studied species from both aspects. However, mountain pine trees reduced sensitivity to temperature changes, while precipitation changes come to play an important role for the period from 1980 to 2013. Intrinsic water-use efficiency (WUEi) calculated for larch trees since the 1990s reached a saturation point at elevated CO2 Divergent trends between pine WUEi and δ(18)O are most likely indicative of a decline of mountain pine trees and are also reflected in decoupling mechanisms in the isotope signals between needles and tree-rings.

Interactions between macroclimate, microclimate, and anthropogenic disturbance affect the distribution of aspen near its northern edge in Quebec: Implications for climate change related range expansions

Policy to address the shifting tree species distributions anticipated in coming decades requires a sound understanding of how forests respond to environmental change. Using a combination of remote sensing, geographic information systems (GIS) analysis, and ground-based techniques, we explored the environmental factors associated with the distribution and abundance of trembling aspen (Populus tremuloides Michx.) across regional gradients near its northern range limit in northwestern Quebec, Canada. Although not regionally abundant, aspen is the main deciduous tree species in this conifer-dominated landscape. Regionally, the ∼51,200-km2 study area has very few settlements or roads, and little industrial resource extraction. Most of the region is inaccessible to humans except by foot or water travel. We utilized Landsat Thematic Mapper images from 2010 and 2011, and a robust collection of ground reference data developed from aerial photography, supported by field verification (vegetation sampling) where access permitted, to construct a thematic map of 11 land cover classes. The map highlights the spatial distribution of aspen, which represents only 0.3% of the study area. Map validation indicated an overall mapping accuracy of 74%, and the aspen predicted class was determined to be over 77% accurate. The regional-scale distribution of aspen stands ⩾0.5ha within the study area shows two patterns: (1) a shift toward greatest abundance on south-facing aspects with increasing latitude; and (2) a highly clustered pattern with a strong signal of concentration in areas of human activity. These patterns suggest that aspen range expansion due to climate warming will vary with topographic and other microclimatic factors (i.e. be a function of climate change interacting with landscapes) and that anthropogenic activities have the potential to influence future aspen abundance independently of climate. Forest management policies concerned with changing forest composition in these northern landscapes should recognize the potentially important role of human activity in driving the abundance of aspen.

Effects of Slope Aspects on Soil Bacterial and Arbuscular Fungal Communities in a Boreal Forest in China

The effects of slope aspects on soil biogeochemical properties and plant communities in forested environments have been studied extensively; however, slope aspect influence on soil microbial communities remains largely unexamined, despite the central role of soil biota in ecosystem functioning. In this study, the communities of both soil bacteria and arbuscular mycorrhizal fungi (AMF) were investigated using tagged pyrosequencing for three types of slope aspects (south-facing aspect, north-facing aspect and flat area) in a boreal forest of the Greater Khingan Mountains, China. The bacterial and AMF community composition differed with slope aspects. Bacterial diversity was the lowest on the north-facing aspect, and AMF diversity was the lowest on the flat area. Aspects also had a significant impact on soil pH and available phosphorus (P) and shrubby biomass. Soil pH and understory shrub biomass were significantly correlated with bacterial communities, and soil available P and shrub biomass showed significant correlations with AMF communities. Our results suggested that slope aspects affected bacterial and AMF communities, mediated by aspect-induced changes in plant community and soil chemical properties (e.g., pH and available P), which improved the knowledge on the effects of forest slope aspects on aboveground and belowground communities.

Landscape Patterns of Burn Severity in the Soberanes Fire of 2016

The Soberanes Fire started on July 22, 2016 in Monterey County on the California Central Coast from an illegal campfire. This disastrous fire burned for 10 weeks at a record cost of more than $208 million for protection and control. A progressive analysis of the normalized burn ratio from the Landsat satellite showed that the final high burn severity (HBS) area for the Soberanes Fire comprised 22% of the total area burned, whereas final moderate burn severity (MBS) area comprised about 10% of the total area burned of approximately 53,470 ha (132,130 acres). The resulting landscape pattern of burn severity classes from the 2016 Soberanes Fire revealed that the majority of HBS area was located in the elevation zone between 500 and 1000 m, in the slope zone between 15% and 30%, or on south-facing aspects. The total edge length of HBS areas nearly doubled over the course of the event, indicating a gradually increasing landscape complexity pattern for this fire. The perimeter-to-area ratio for HBS patches decreased by just 3% over the course of the fire, while the HBS clumpiness metric remained nearly constant at a relatively high aggregation value. Weather conditions during the Soberanes Fires showed maximum daily temperatures exceeding 30°C on seven different days (including the date of ignition), which puts the HBS to total area burned of this 2016 event near the expected percentage for large wildfires on the California central coast since the 1980s.

Local-scale and regional climate controls on historical fire regimes in the San Juan Mountains, Colorado

In ponderosa pine and mixed conifer ecosystems of the Southwestern US, regional-scale climate tends to synchronize fire years among study sites and increase fire extent or severity within a forest. At landscape scales (1–100km2), fire frequency and severity may also be influenced by local-scale differences in elevation and aspect, including fire barriers in rugged terrain. This study examines local-scale and regional controls of past fire regimes in three tributary watersheds of the San Juan Mountains of southwestern Colorado. In each watershed, we sampled fire-scarred trees and tree age structure and identified fire years and cohorts of post-fire tree recruitment. Fire frequency varied by aspect, and we observed the largest differences between the north- and south-facing aspects in the two largest basins. Fire severity was also different by aspect, with low-severity fire regimes on south-facing slopes and mixed-severity fire on north-facing slopes. The majority of fire years were unique, single-basin fires, indicating a lack of synchrony of fire years among basins, which we attributed to fire barriers and rugged terrain. We conducted Superposed Epoch Analysis (SEA) on two groups of fire years, to show average climate conditions before and during fire years. The first group were unique single-basin fires (n=27) and the second group included all years when synchronous fire burned in two or three basins (n=15). Both groups had significantly dry Palmer Drought Severity Index (PDSI) values during the fire year (p<0.01), while the second group also showed significantly wet conditions for two years prior to the fire year (p<0.01). Steep topography and fire barriers likely reduced the influence of regional climatic on the frequency and timing of fires for individual basins, though fires still burned during years of regional drought. Rugged terrain also contributed to asynchronous fire years among basins and longer fire return intervals compared with other ponderosa pine and mixed conifer forests in the region.

Attributes of a Breeding Population of Peregrine Falcons Associated with Reservoirs on the Colorado River

Abstract We describe results from a comprehensive effort to survey and monitor Peregrine Falcons (Falco peregrinus) breeding in Lake Mead National Recreation Area (LMNRA) from 2006–2010. We identified 37 breeding territories, and the annual occupancy rate averaged 94%. Pooled over time, breeding success was 72%, and average reproductive output was 1.8 young per nesting attempt. The closest distance between eyries from neighboring territories was 1.2 km; the lowest annual mean nearest-neighbor distance (NND) was 6.3 km. No relationship was apparent between NND and breeding success or reproductive output. Nesting attempts occurred twice as often in eyries with a north-facing (68%) aspect than in eyries with a south-facing (32%) aspect. Pairs using south-facing eyries began incubating 5 d earlier than those using north-facing eyries, although the difference was not statistically significant. On a finer scale, pairs most commonly selected northwest-facing eyries (45% of nesting attempts), despite experiencing...

Topographic controls on the depth distribution of soil CO2 in a small temperate watershed

Accurate measurements of soil CO2 concentrations (pCO2) are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon (C) cycle. While there have been many studies of soil pCO2, most sample or model only one, or at most a few, landscape positions and therefore do not account for complex topography. Here, we test the hypothesis that soil pCO2 distribution can predictably vary with topographic position. We measured soil pCO2 at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), Pennsylvania, where controls on soil pCO2 (e.g., depth, texture, porosity, and moisture) vary from ridge tops down to the valley floor, between planar slopes and slopes with convergent flow (i.e., swales), and between north and south-facing aspects. We quantified pCO2 generally at 0.1–0.2 m depth intervals down to bedrock from 2008 to 2010 and in 2013. Of the variables tested, topographic position along catenas was the best predictor of soil pCO2 because it controls soil depth, texture, porosity, and moisture, which govern soil CO2 diffusive fluxes. The highest pCO2 values were observed in the valley floor and swales where soils are deep (≥0.7 m) and wet, resulting in low CO2 diffusion through soil profiles. In contrast, the ridge top and planar slope soils have lower pCO2 because they are shallower (≤0.6 m) and drier, resulting in high CO2 diffusion through soil profiles. Aspect was a minor predictor of soil pCO2: the north (i.e., south-facing) swale generally had lower soil moisture content and pCO2 than its south (i.e., north-facing) counterpart. Seasonally, we observed that while the timing of peak soil pCO2 was similar across the watershed, the amplitude of the pCO2 peak was higher in the deep soils due to more variable moisture content. The high pCO2 observed in the deeper, wetter topographic positions could lower soil porewater pH by up to 1 pH unit compared to porewaters equilibrated with atmospheric CO2 alone. CO2 is generally the dominant acid driving weathering in soils: based on our observations, models of chemical weathering and CO2 dynamics would be improved by including landscape controls on soil pCO2.