Drought responses of conifers in ecotone forests of northern Arizona: tree ring growth and leaf δ<Superscript>13</Superscript>C

We sought to understand differences in tree response to meteorological drought among species and soil types at two ecotone forests in northern Arizona, the pinyon-juniper woodland/ponderosa pine ecotone, and the higher elevation, wetter, ponderosa pine/mixed conifer ecotone. We used two approaches that provide different information about drought response: the ratio of standardized radial growth in wet years to dry years (W:D) for the period between years 1950 and 2000 as a measure of growth response to drought, and ¹³C in leaves formed in non-drought (2001) and drought (2002) years as a measure of change in water use efficiency (WUE) in response to drought. W:D and leaf ¹³C response to drought for Pinus edulis and P. ponderosa did not differ for trees growing on coarse-texture soils derived from cinders compared with finer textured soils derived from flow basalts or sedimentary rocks. P. ponderosa growing near its low elevation range limit at the pinyon-juniper woodland/ponderosa pine ecotone had a greater growth response to drought (higher W:D) and a larger increase in WUE in response to drought than co-occurring P. edulis growing near its high elevation range limit. P. flexilis and Pseudotsuga menziesii growing near their low elevation range limit at the ponderosa pine/mixed conifer ecotone had a larger growth response to drought than co-occurring P. ponderosa growing near its high elevation range limit. Increases in WUE in response to drought were similar for all species at the ponderosa pine/mixed conifer ecotone. Low elevation populations of P. ponderosa had greater growth response to drought than high-elevation populations, whereas populations had a similar increase in WUE in response to drought. Our findings of different responses to drought among co-occurring tree species and between low- and high-elevation populations are interpreted in the context of drought impacts on montane coniferous forests of the southwestern USA.     

Patterns of habitat utilization of small rodents in an area of Araucaria forest in Southern Brazil

Abstract We investigated patterns of spatial distribution and microhabitat selection of rodents in a patch (26 ha) of mixed ombrophilous forest (or Araucaria forest), dominated by the Araucaria ‘pine’Araucaria angustifolia, in the National Park of Aparados da Serra, RS, in southern Brazil. We conducted monthly trapping sessions lasting 6 days (from June 2000 to June 2001) using a square grid of 121 trap stations, separated by 15 m (2.25 ha). We measured 10 microhabitat variables that could influence species distribution. These variables were related to the occurrence of mammals by using canonical correspondence analysis (CCA) and stepwise multiple regression. The distribution patterns of the three most common rodents differed significantly (χ² = 38.6; P < 0.002), with Delomys dorsalis being more clumped than the other two species. Both CCA and multiple regression analysis showed a significant effect of microhabitat variables on species occurrence. The multiple regression parameters for Oligoryzomys nigripes were R² = 0.142, P < 0.05, for Akodon montensis were R² = 0.222, P < 0.01, and for D. dorsalis R² = 0.323, P < 0.001. Variables that significantly influenced species distribution were vegetation density at 1 m height and length of fallen logs for O. nigripes, canopy cover for A. montensis, and vegetation density at 2 m height, quantity of leaves of Araucaria trees (negative relationship), tree density (except Araucaria trees), and number of potential shelters, for D. dorsalis. The results indicated that D. dorsalis is the most habitat specialist among the rodent species and that there are no apparent competitive interactions.     

Patterns of bryophyte diversity and rarity at a regional scale

Information on bryophyte diversity and rarity were combined withinformation on soil conditions and land use for Walloon Brabant (centralBelgium, 1091 km²) in order to investigate whichlandscape features sustain the most rare and diverse species assemblages.Presence–absence of 325 bryophyte species was recorded in 87 grid-squaresof 4 × 4 km. Species diversity was significantly correlatedwith forest cover (r = 0.71, P <0.001), sandy soils (r = 0.61, P <0.001), loamy soils, (r = –0.68,P < 0.001), and agricultural fields(r = –0.49, P < 0.001). Themost diverse grid-squares possessed up to 182 species and were characterized byat least 10% forest cover and the presence of unique micro-habitats.Grid-squares with forest cover reaching at least 10% but lacking uniquemicro-habitats contained between 90 and 130 species. Below 10% forest cover,diversity ranged between 55 and 110 species per grid-square. However, even theleast diverse cultivated areas included a significant amount of the regionallyrare species. A number of the latter are characteristic in other areas forspecific primary habitats lacking in Walloon Brabant but display an unexpectedability to disperse throughout hostile areas and colonize secondary habitats.The tendency of such species to occur in man-made habitats decreased our abilityto predict species richness and rarity from landscape features and soilconditions.     

Carbohydrate dynamics and mortality in a piñon‐juniper woodland under three future precipitation scenarios

Drought‐induced forest mortality is an increasing global problem with wide‐ranging consequences, yet mortality mechanisms remain poorly understood. Depletion of non‐structural carbohydrate (NSC) stores has been implicated as an important mechanism in drought‐induced mortality, but experimental field tests are rare. We used an ecosystem‐scale precipitation manipulation experiment to evaluate leaf and twig NSC dynamics of two co‐occurring conifers that differ in patterns of stomatal regulation of water loss and recent mortality: the relatively desiccation‐avoiding piñon pine (Pinus edulis) and the relatively desiccation‐tolerant one‐seed juniper (Juniperus monosperma). Piñon pine experienced 72% mortality after 13–25 months of experimental drought and juniper experienced 20% mortality after 32–47 months. Juniper maintained three times more NSC in the foliage than twigs, and converted NSC to glucose and fructose under drought, consistent with osmoregulation requirements to maintain higher stomatal conductance during drought than piñon. Despite these species differences, experimental drought caused decreased leaf starch content in dying trees of both species (P < 0.001). Average dry‐season leaf starch content was also a good predictor of drought‐survival time for both species (R² = 0.93). These results, along with observations of drought‐induced reductions to photosynthesis and growth, support carbon limitation as an important process during mortality of these two conifer species.     

Sexual reproduction, clonal diversity and genetic differentiation in patchily distributed populations of the temperate forest herb Paris quadrifolia (Trilliaceae)

Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m²) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio = 0.43 and Simpson’s D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (Φ _ST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species.     

北京地区同域分布的普通和黑头种群密度比较

2007年4月至7月,2007年12月至2008年1月,分别在北京市门头沟区小龙门森林公园、百花山自然保护区以及延庆县松山自然保护区,对同域分布的普通(Sitta europaea)和黑头(Sitta villosa)两种同域分布的类种群密度进行了调查。普通在小龙门森林公园、百花山自然保护区和松山自然保护区的种群密度分别是40.92、96.67只/km2和16.67只/km2。而黑头在上述3个调查区域的种群密度分别是2.03、16.67只/km2和23.33只/km2。普通的总体平均密度(51.4只/km2)高于黑头(20.68只/km2)。两种类分布的海拔和林型存在着差异。普通在海拔高度1070—1350 m的分布比较多。在海拔段1070—1250 m区间,普通的数量随海拔高度的增加呈递增的趋势。而黑头在海拔600—800 m分布较多,随着海拔高度的增加,种群数量呈递减趋势。普通主要分布在阔叶林和针阔混交林中,而黑头主要分布在针叶林中。     

Habitat Conditions Associated With Lynx Hunting Behavior During Winter in Northern Washington

Abstract Effectively managing habitat for threatened populations of Canada lynx (Lynx canadensis) requires knowledge of habitat conditions that provide for the ecological needs of lynx. We snow-tracked lynx to identify habitat conditions associated with hunting behavior and predation during winters of 2002–2003 and 2003–2004 in the northern Cascade Range in Washington state, USA. We recorded number and success of predation attempts, prey species killed, and trail sinuosity on 149 km of lynx trails. Lynx killed snowshoe hares (Lepus americanus), red squirrels (Tamiasciurus hudsonicus), and cricetids more than expected in Englemann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) forests, where snowshoe hare densities were highest. Lynx killed prey less than expected in Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) forests and forest openings. We used the sinuosity of lynx trails as an index of quality of habitat hunted. Lynx trails that included predation attempts were more sinuous than trail segments without predation attempts. Lynx trails had greater sinuosity in forest stands with high hare densities dominated by Engelmann spruce and subalpine fir than in stands with low hare densities dominated by Douglas-fir and ponderosa pine or in forest openings. We encourage forest managers to maintain or create sufficient understory cover to support high densities of snowshoe hares as foraging habitat for lynx.     

Airborne laser scanning for vegetation structure quantification in a south east Australian scrubby forest‐woodland

Airborne laser scanning (ALS) has the potential to capture a range vegetation structural metrics, but most studies have focussed on conifer or mixed conifer‐deciduous cool‐temperate or boreal forests. This study focuses on a warm‐temperate eucalypt forest, where two epochs of ALS data, captured approximately 2 years apart, were compared with plot and transect field data collected after the second ALS epoch. Linear regression was used to compare metrics from field and ALS data, and Student's t‐tests were used to compare metrics from the two ALS epochs. Statistically significant relationships were found for tree height (R² = 0.915; SE = 2.08 m; P < 0.01) and canopy cover (R² = 0.508; SE = 16.4%; P < 0.01). Foliage projective cover was also significantly correlated (R² = 0.916; SE = 4.5%; P < 0.01) at a 10‐m stratification, but not at the typically computed 2‐m stratification, because of the presence of a tall scrubby understorey. Statistically significant values were also obtained from ALS data captured 2 years earlier, although correlation was not as strong, most likely because of the greater interval between fieldwork and ALS capture. Importantly, significant agreement was found for all metrics when the two ALS epochs were compared, suggesting that the metrics are robust.     

Up-scaling to stand transpiration of an Asian temperate mixed-deciduous forest from single tree sapflow measurements

Species diversity in mixed forest stands is one of the factors that complicate up-scaling of transpiration from individual trees to stand level, since tree species are architecturally and functionally different. In this study, thermal dissipation probes were used to measure sap flow in five different tree species in a mixed-deciduous mountain forest in South Korea. Easily measurable tree characteristics that could serve to define individual tree water use among the different species were employed to scale up transpiration from single trees to stand level. Tree water use (TWU) was derived from sap flux density (SFD) and sapwood area (SA). Canopy transpiration E was scaled from TWU while canopy conductance (g _c) was computed from E and VPD. SFD, TWU and g _c were correlated with tree diameter at breast height (DBH) for all the five measured species (SFD: R ² = 0.21, P = 0.036; TWU: R ² = 0.83, P < 0.001; g _c: R ² = 0.63, P < 0.001). Maximum stand transpiration (E) during June, before the onset of the Asian monsoon rains, was estimated at 0.97 ± 0.12 mm per day. There was a good (R ² = 0.94, P < 0.0001) agreement between measured and estimated E using the relationship between TWU and DBH. Our study shows that using functional models that employ converging traits among species could help in estimating water use in mixed forest stands. Compared to SA, DBH is a better scalar for water use of mixed forest stands since it is non-destructive and easily obtainable.     

Tree growth response to drought and temperature in a mountain landscape in northern Arizona, USA

Aim To understand how tree growth response to regional drought and temperature varies between tree species, elevations and forest types in a mountain landscape. Location Twenty‐one sites on an elevation gradient of 1500 m on the San Francisco Peaks, northern Arizona, USA. Methods Tree‐ring data for the years 1950–2000 for eight tree species (Abies lasiocarpa var. arizonica (Merriam) Lemm., Picea engelmannii Parry ex Engelm., Pinus aristata Engelm., Pinus edulis Engelm., Pinus flexilis James, Pinus ponderosa Dougl. ex Laws., Pseudotsuga menziesii var. glauca (Beissn.) Franco and Quercus gambelii Nutt.) were used to compare sensitivity of radial growth to regional drought and temperature among co‐occurring species at the same site, and between sites that differed in elevation and species composition. Results For Picea engelmannii, Pinus flexilis, Pinus ponderosa and Pseudotsuga menziesii, trees in drier, low‐elevation stands generally had greater sensitivity of radial growth to regional drought than trees of the same species in wetter, high‐elevation stands. Species low in their elevational range had greater drought sensitivity than co‐occurring species high in their elevational range at the pinyon‐juniper/ponderosa pine forest ecotone, ponderosa pine/mixed conifer forest ecotone and high‐elevation invaded meadows, but not at the mixed conifer/subalpine forest ecotone. Sensitivity of radial growth to regional drought was greater at drier, low‐elevation compared with wetter, high‐elevation forests. Yearly growth was positively correlated with measures of regional water availability at all sites, except high‐elevation invaded meadows where growth was weakly correlated with all climatic factors. Yearly growth in high‐elevation forests up to 3300 m a.s.l. was more strongly correlated with water availability than temperature. Main conclusions Severe regional drought reduced growth of all dominant tree species over a gradient of precipitation and temperature represented by a 1500‐m change in elevation, but response to drought varied between species and stands. Growth was reduced the most in drier, low‐elevation forests and in species growing low in their elevational range in ecotones, and the least for trees that had recently invaded high‐elevation meadows. Constraints on tree growth from drought and high temperature are important for high‐elevation subalpine forests located near the southern‐most range of the dominant species.     

Estimation of Free‐Living Energy Expenditure Using a Novel Activity Monitor Designed to Minimize Obtrusiveness

The aim of this study was to investigate the ability of a novel activity monitor designed to be minimally obtrusive in predicting free‐living energy expenditure. Subjects were 18 men and 12 women (age: 41 ± 11 years, BMI: 24.4 ± 3 kg/m²). The habitual physical activity was monitored for 14 days using a DirectLife triaxial accelerometer for movement registration (Tracmor_D) (Philips New Wellness Solutions, Lifestyle Incubator, the Netherlands). Tracmor_D output was expressed as activity counts per day (Cnts/d). Simultaneously, total energy expenditure (TEE) was measured in free living conditions using doubly labeled water (DLW). Activity energy expenditure (AEE) and the physical activity level (PAL) were determined from TEE and sleeping metabolic rate (SMR). A multiple‐linear regression model predicted 76% of the variance in TEE, using as independent variables SMR (partial‐r² = 0.55, P < 0.001), and Cnts/d (partial r² = 0.21, P < 0.001). The s.e. of TEE estimates was 0.9 MJ/day or 7.4% of the average TEE. A model based on body mass (partial‐r² = 0.31, P < 0.001) and Cnts/d (partial‐r² = 0.23, P < 0.001) predicted 54% of the variance in TEE. Cnts/d were significantly and positively associated with AEE (r = 0.54, P < 0.01), PAL (r = 0.68, P < 0.001), and AEE corrected by body mass (r = 0.71, P < 0.001). This study showed that the Tracmor_D is a highly accurate instrument for predicting free‐living energy expenditure. The miniaturized design did not harm the ability of the instrument in measuring physical activity and in determining outcome parameters of physical activity such as TEE, AEE, and PAL.     

Coupling in goshawk and grouse population dynamics in Finland

Different prey species can vary in their significance to a particular predator. In the simplest case, the total available density or biomass of a guild of several prey species might be most relevant to the predator, but behavioural and ecological traits of different prey species can alter the picture. We studied the population dynamics of a predator–prey setting in Finland by fitting first-order log-linear vector autoregressive models to long-term count data from active breeding sites of the northern goshawk (Accipiter gentilis; 1986–2009), and to three of its main prey species (1983–2010): hazel grouse (Bonasa bonasia), black grouse (Tetrao tetrix) and capercaillie (T. urogallus), which belong to the same forest grouse guild and show synchronous fluctuations. Our focus was on modelling the relative significance of prey species and estimating the tightness of predator–prey coupling in order to explain the observed population dynamics, simultaneously accounting for effects of density dependence, winter severity and spatial correlation. We established nine competing candidate models, where different combinations of grouse species affect goshawk dynamics with lags of 1–3 years. Effects of goshawk on grouse were investigated using one model for each grouse species. The most parsimonious model for goshawk indicated separate density effects of hazel grouse and black grouse, and different effects with lags of 1 and 3 years. Capercaillie showed no effects on goshawk populations, while the effect of goshawk on grouse was clearly negative only in capercaillie. Winter severity had significant adverse effects on goshawk and hazel grouse populations. In combination, large-scale goshawk–grouse population dynamics are coupled, but there are no clear mutual effects for any of the individual guild members. In a broader context, our study suggests that pooling data on closely related, synchronously fluctuating prey species can result in the loss of relevant information, rather than increased model parsimony.     

Species Richness and Patterns of Invasion in Plants, Birds, and Fishes in the United States*

We quantified broad-scale patterns of species richness and species density (mean # species/km²) for native and non-indigenous plants, birds, and fishes in the continental USA and Hawaii. We hypothesized that the species density of native and non-indigenous taxa would generally decrease in northern latitudes and higher elevations following declines in potential evapotranspiration, mean temperature, and precipitation. County data on plants (n = 3004 counties) and birds (n=3074 counties), and drainage (6 HUC) data on fishes (n = 328 drainages) showed that the densities of native and non-indigenous species were strongly positively correlated for plant species (r = 0.86, P < 0.0001), bird species (r = 0.93, P<0.0001), and fish species (r = 0.41, P<0.0001). Multiple regression models showed that the densities of native plant and bird species could be strongly predicted (adj. R² = 0.66 in both models) at county levels, but fish species densities were less predictable at drainage levels (adj. R² = 0.31, P<0.0001). Similarly, non-indigenous plant and bird species densities were strongly predictable (adj. R² = 0.84 and 0.91 respectively), but non-indigenous fish species density was less predictable (adj. R² = 0.38). County level hotspots of native and non-indigenous plants, birds, and fishes were located in low elevation areas close to the coast with high precipitation and productivity (vegetation carbon). We show that (1) native species richness can be moderately well predicted with abiotic factors; (2) human populations have tended to settle in areas rich in native species; and (3) the richness and density of non-indigenous plant, bird, and fish species can be accurately predicted from biotic and abiotic factors largely because they are positively correlated to native species densities. We conclude that while humans facilitate the initial establishment, invasions of non-indigenous species, the spread and subsequent distributions of non-indigenous species may be controlled largely by environmental factors. The U.S. Government’s right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

Seed germination and seedling physiology of Larix kaempferi and Pinus densiflora in seedbeds with charcoal and elevated CO2

We investigated the effect of ectomycorrhizal colonization, charcoal and CO₂ levels on the germination of seeds of Larix kaempferi and Pinus densiflora, and also their subsequent physiological activity and growth. The seeds were sown in brown forest soil or brown forest soil mixed with charcoal, at ambient CO₂ (360 μmol mol⁻¹) or elevated CO₂ (720 μmol mol⁻¹), with or without ectomycorrhiza. The proportions of both conifer seeds that germinated in forest soil mixed with charcoal were significantly greater than for seeds sown in forest soil grown at each CO₂ level (P < 0.05; t-test). However, the ectomycorrhizal colonization rate of each species grown in brown forest soil mixed with charcoal was significantly lower than in forest soil at each CO₂ treatment [CO₂] (P < 0.01; t-test). The phosphorus concentrations in needles of each seedling colonized with ectomycorrhiza and grown in forest soil were greater than in nonectomycorrhizal seedlings at each CO₂ level, especially for L. kaempferi seedlings (P < 0.05; t-test), but the concentrations in seedlings grown in brown forest soil mixed with charcoal were not increased at any CO₂ level. Moreover, the maximum net photosynthetic rate of each seedling for light and CO₂ saturation (P _max) increased when the seedlings were grown with ectomycorrhiza at 720 μmol mol⁻¹ [CO₂]. Ectomycorrhizal colonization led to an increase in the stem diameter of each species grown in each soil treatment at each CO₂ level. However, charcoal slowed the initial growth of both species of seedling, constraining ectomycorrhizal development. These results indicate that charcoal strongly assists seed germination and physiological activity.     

Canada lynx occurrence and forest management in the Acadian Forest

We evaluated patterns of occurrence and non-occurrence for Canada lynx (Lynx canadensis) across a 16,530-km² study area in Maine to provide a better understanding of lynx habitat selection and habitat ecology on commercially managed forestlands in the Acadian Forest. Because of the influence of forest structure on lynx habitat selection and abundance of their primary prey, the snowshoe hare (Lepus americanus), and to improve our ability to build robust models, we used habitat information derived from a time series of Landsat satellite imagery spanning the period 1973–2004. We defined and mapped 10 forest types based on forest harvest history, time since harvest, and current forest condition. We compared a suite of models to evaluate relative influences of forest composition, habitat patch configuration, and hare density on habitat selection by lynx at the landscape scale. Occupied areas had greater average hare densities and percentage of mature conifer. Average hare density in occupied areas (0.74 hares/ha) was greater than in unoccupied areas (0.62 hares/ha), but was less than previous research has suggested may be necessary to support lynx populations in the southern portion of the species' range. No occupied areas occurred where average hare density was <0.5 hares/ha. Average hare density at the landscape-scale was strongly influenced by amount of high-quality hare habitat (i.e., conifer or mixedwood regenerating forest, 15–35 yr post-harvest). Edge density between mature conifer and high-quality hare habitat was substantially greater in occupied areas compared to unoccupied areas. Juxtaposition of those 2 forest types may provide edge habitat where lynx experience easier travel and improved access to prey in landscapes with extensive areas of high-quality hare habitat where travel and access may be somewhat limited by high understory stem density. Probability of occurrence declined nonlinearly with changes in hare density and percent mature conifer forest in the landscape; thus, suitability of currently occupied landscapes could change markedly with future changes in landscape-level hare densities and changing habitat associated with forest management. Where lynx conservation is a priority, we recommend that managers focus on creating and maintaining a minimum of 27% high-quality hare habitat within 100-km² areas to promote landscape-scale hare densities >0.5 hares/ha. © The Wildlife Society, 2013     

Multiscale habitat relationships of snowshoe hares (Lepus americanus) in the mixed conifer landscape of the Northern Rockies,USA: Cross‐scale effects of horizontal cover with implications for forest management

Snowshoe hares (Lepus americanus) are an ecologically important herbivore because they modify vegetation through browsing and serve as a prey resource for multiple predators. We implemented a multiscale approach to characterize habitat relationships for snowshoe hares across the mixed conifer landscape of the northern Rocky Mountains, USA. Our objectives were to (1) assess the relationship between horizontal cover and snowshoe hares, (2) estimate how forest metrics vary across the gradient of snowshoe hare use and horizontal cover, and (3) model and map snowshoe hare occupancy and intensity of use. Results indicated that both occupancy and intensity of use by snowshoe hares increased with horizontal cover and that the effect became stronger as intensity of use increased. This underscores the importance of dense horizontal cover to achieve high use, and likely density, of snowshoe hares. Forest structure in areas with high snowshoe hare use and horizontal cover was characterized as multistoried with dense canopy cover and medium‐sized trees (e.g., 12.7–24.4 cm). The abundance of lodgepole pine (Pinus contorta) was associated with snowshoe hare use within a mixed conifer context, and the only species to increase in abundance with horizontal cover was Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa). Our landscape‐level modeling produced similar patterns in that we observed a positive effect of lodgepole pine and horizontal cover on both occupancy and use by snowshoe hares, but we also observed a positive yet parabolic effect of snow depth on snowshoe hare occupancy. This work is among the first to characterize the multiscale habitat relationships of snowshoe hares across a mixed conifer landscape as well as to map their occupancy and intensity of use. Moreover, our results provide stand‐ and landscape‐level insights that directly relate to management agencies, which aids in conservation efforts of snowshoe hares and their associated predators.     

Primers designed to amplify a mitochondrial nad1 intron in ponderosa pine, Pinus ponderosa, limber pine, P. flexilis, and Scots pine, P. sylvestris

The b/c intron of the mitochondrial nad1 gene, was sequenced to characterize the indel region of ponderosa pine, Pinus ponderosa. The sequence in ponderosa pine was aligned with the sequence in Scots pine, Pinus sylvestris, to design seven primers that are useful for sequencing and for revealing size variation in amplified fragments in ponderosa pine, Scots pine, and limber pine, Pinus flexilis. These primers reveal variability in all three species, and the pattern of variability within ponderosa pine is described by a preliminary survey. The indel region of ponderosa pine contains three distinct elements with lengths of 31, 32, and 34 bp. Received: 1 March 2000 / Accepted: 14 April 2000<@head-com-p1a.lf>Communicated by P.M.A. Tigerstedt     

Plasma concentration of α-tocopherol in different free-ranging birds of prey

In this study, we investigated the α-tocopherol plasma concentrations in healthy free-ranging nestlings of the white-tailed sea eagle (Haliaeetus albicilla) (n = 32), osprey (Pandion haliaetus) (n = 39), northern goshawk (Accipiter gentilis) (n = 25), common buzzard (Buteo buteo) (n = 31), and honey buzzard (Pernis apivorus) (n = 18) as well as of free-ranging adults of the white-tailed sea eagle (n = 10), osprey (n = 31), and northern goshawk (n = 45). α-Tocopherol plasma concentrations were determined by reverse-phase high-performance liquid chromatography. α-Tocopherol plasma concentrations in nestlings of osprey, white-tailed sea eagle, and northern goshawk did not differ significantly amongst the species, but the common buzzard and honey buzzard nestlings had significantly lower α-tocopherol plasma concentrations than nestlings of the other species (both P < 0.001). Adult male ospreys and white-tailed sea eagles had significantly higher α-tocopherol concentrations compared to adult females (both P < 0.005). Adult ospreys and northern goshawks had significantly higher α-tocopherol plasma concentrations compared to their nestlings (both P < 0.001). In adult female northern goshawks, plasma concentrations of α-tocopherol increased significantly before egg laying (P < 0.001). These results demonstrate α-tocopherol plasma concentrations in birds of prey to be species specific and influenced by age and reproductive status.     

Carbon and Nitrogen Dynamics of Boreal Jack Pine Stands With and Without a Green Alder Understory

We compared the species composition, structure and selected components of the carbon (C) and nitrogen (N) budgets of similar-aged, mature boreal jack pine (Pinus banksiana Lamb.) forests with and without green alder [Alnus crispa (Ait.) Pursh.] in two different boreal environments. The C and N content of the overstory biomass components (for example, stem, branch, and foliage), total vegetation, forest floor, and mineral soil were greater (P= 0.05 to P= 0.10) for jack pine with alder (JPA) stands than for jack pine without alder (JP) stands at both study areas. Jack pine foliage N isotopic discrimination (δ¹⁵N) and annual litterfall N content were significantly greater (P < 0.05) in the JPA than the JP stands at both study areas, suggesting that alder was fixing N and that N availability was greater in the JPA than the JP stands. The greater leaf area index (LAI) and overstory C accumulation in the JPA than the JP stands (P < 0.05) is likely because of the greater N availability in the JPA stands, but the effect of soil texture discontinuity on water availability in the JPA stands can not be dismissed. Percent ground cover by feathermoss varied among the jack pine communities and was positively correlated with overstory LAI (r ²= 0.83, P< 0.05). One index of N-use efficiency (NUE), defined as aboveground net primary productivity (ANPP) per litterfall N, was significantly greater (P < 0.05) for the JP than the JPA stands, but a second index of NUE, ANPP/N uptake, did not differ between the two jack pine communities. Jack pine trees growing without alder produced more organic matter per unit of N, but percent N retranslocation from senescing foliage and N mean residence time in the overstory did not differ between the JPA and the JP stands. A conceptual model is presented that illustrates the potential influence of alder on the species composition, structure, and function of boreal jack pine forests. Received 6 January 1998; accepted 15 April 1998.     

Role of species identity in plant invasions: experimental test using Imperata cylindrica

The role of species richness, functional diversity and species identity of native Florida sandhill understory species were tested with Imperata cylindrica, an exotic rhizomatous grass, in mesocosms. I. cylindrica was introduced 1 year after the following treatments were established: a control with no native species, five monocultures, a grass mix treatment, a forb mix treatment, and a 3-species treatment and a 5-species treatment. Monthly cover, final biomass, root length, root length density (RLD) and specific root length (SRL) of all species were determined for one full growing season. There was a significant negative linear relationship between the cover of native species and I. cylindrica (r ² = 0.59, P = 0.01) and a negative logarithmic relationship between the biomass of native species and I. cylindrica (r ² = 0.70, P = 0.003). There was no diversity–invasibility relationship. Grasses proved to be the most resistant functional group providing resistance alone and in mixed functional communities. Repeated measures analysis demonstrated that treatments including Andropogon virginicus were the most resistant to invasion over time (P < 0.001). Significantly greater root length (P = 0.002), RLD (P = 0.011) and SRL (P < 0.001) than all of the native species and I. cylindrica in monocultures and in mixed communities made A. virginicus successful. The root morphology characteristics allowed it to be a great competitor belowground where I. cylindrica was most aggressive. The results suggest that species identity could be more important than species or functional richness in determining community resistance to invasion.