Subalpine Environments Research Articles

NESTLING GROWTH AND THERMOREGULATORY DEVELOPMENT IN SUBALPINE DUSKY FLYCATCHERS

Abstract The Dusky Flycatcher (Empidonax oberholseri), a small, open-nesting Neotropical migrant, is a relatively common summer inhabitant of subalpine environments in the western and southwestern United States. Nestling growth and development of thermoregulation were studied in a population at Tioga Pass (3,000 m) in the eastern Sierra Nevada of California. Despite the selective advantages that might be expected from accelerating rates of growth and thermoregulatory development, in an environment where the season was relatively short and cold temperatures and inclement weather were common, there was little evidence of adaptive modification in either of those parameters; growth rates were comparable to those of other tyrant flycatchers. Feather eruption began around day 5, brushing in dorsal and ventral tracts began two days later, and brushing of the flight feathers around day 9. Asymptotic body masses were attained around day 12, but nestlings did not fledge for another 4 to 5 days. The physiological de...

Impact of snow cover on photoinhibition and winter dessication in evergreen Rhododendron ferrugineum leaves during subalpine winter.

Effects of winter snow cover on photoinhibition and possible interactions with winter desiccation were investigated in situ in an evergreen subalpine woody species, Rhododendron ferrugineum L., at the alpine timberline (1950 m a.s.l.). Timing and duration of complete snow cover markedly influenced potential efficiency of photosystem II (PSII; F(v) /F(m)). Lack of snow cover led to severe but mostly reversible photoinhibition with F(v)/F(m) values as low as 0.05. Complete snow cover immediately stopped further reductions in PSII efficiency. Snow cover promoted recovery from photoinhibition, but only if, in addition to shading by snow, plants were exposed to nonfreezing temperatures close to 0 degrees C. The F(v)/F(m) ratio was closely related to minimum leaf temperatures because both photoinhibition and recovery from photoinhibition were strongly influenced by temperature. The period without major reductions in PSII efficiency lasted for only two months, reflecting the extremely short growing period in the subalpine environment. Compared with complete snow cover, incomplete snow cover led to significantly higher water losses as well as lower dehydration tolerance, because both osmotic adjustment and changes in turgor maintenance capacity were significantly reduced. Interactions between photoinhibition and winter desiccation were masked by the direct effects of freezing temperatures. However, both photoinhibition and winter desiccation are closely linked and occur together under field conditions in this evergreen subalpine woody species.

Readiness to frost harden during the dehardening period measured in situ in leaves of Rhododendron ferrugineum L. at the alpine timberline

Summary The readiness to frost harden during the dehardening period can be crucial to the frost survival of Rhododendron ferrugineum leaves. When already dehardened plants occasionally fall snow free in late winter or spring still heavy night frosts can occur in the subalpine environment. R. ferrugineum shrubs were treated in situ using a newly developed field portable freezing chamber. They were exposed to controlled night frosts of close to the lowest temperature sustained without frost damage (LT 0 ) to determine the potential frost hardening response under otherwise completely natural conditions. There was a lag period of 3 days during which no significant increase of frost resistance was observed. After three days frost resistance increased suddenly by 5.9°C within 24 hours. High daytime leaf temperatures (+19°C) combined with night frosts further retarded the rate of frost hardening. The in situ frost treatment generally yielded frost resistances (LT 10 ) approaching the highest ever measured in that season. In early spring the in situ frost hardening response was three times greater than early reports for detached twigs with a total hardiness gain between 7.8°C and 9.2°C. It is suggested that the limiting step in frost hardening in leaves of Rhododendron ferrugineum in spring is not the extent of frost resistance achieveable but rather the slow rate of frost hardening.

Snow. A Natural History; an uncertain Future

Alpine and subalpine environments are extremely restricted in Australia, with the highest peaks of the Australian Alps occurring well below the theoretical altitudinal range necessary for a permanent snow cover. The alpine environment also suffers from a lack of continuity, emphasized by the break between the mainland and Tasmanian alpine communities. There is a major concern for the snow country of Australia and the organisms which inhabit, and are totally dependent on, the snow. These environments are under threat from predicted global warming from the enhanced greenhouse effect, leading to a loss of snow cover. Australia is facing the loss, not just of snow, but of the alpine ecosystem itself.

Daily and Seasonal Activity Patterns in Two Species of High Altitude Skink, Niveoscincus microlepidotus and N. metallicus, from Tasmania

Daily and Seasonal Activity Patterns in Two Species of High Altitude Skink, Niveoscincus microlepidotus and N. metallicus, from Tasmania

Microclimate factors influencing the frequency and duration of growth season frost for subalpine plants

The subalpine environment of the Medicine Bow Mountains, Wyoming (USA) is characterized by frost events throughout the summer. As a result, growing season length is difficult to define in terms of frost-free days. For example, such a definition would have limited the 1993 growing season for many plants to only 5 days. The frequency of summertime frost events appeared particularly dependent on net losses of infrared energy to a cold night sky (radiation frost). These radiative losses to the night sky were strongly dependent on microsite sky exposure and leaf characteristics as well as meteorological conditions. During the summer of 1993, air temperatures at a height of 8 cm at the center of a subalpine meadow were below 0°C on 26 of 67 nights, while leaves of a broadleaf species ( Erigeron peregrinus) frosted on 41 nights compared to 25 nights for a coniferous sapling ( Abies lasiocarpa). In E. peregrinus, a strong association occurred between the frequency and duration of freezing episodes and the amount of sky exposure, with plants sheltered by forest canopy experiencing frost only 10% to 40% as often as those in the center of the meadow. At exposed locations, longwave radiation minima from the night sky were strongly correlated with the occurrence of leaf temperature minima. Thus, microsite sky exposure as well as the variation in longwave radiation from the atmosphere may have important implications for estimating growing season length and plant distribution patterns at higher elevations. Growth habit also influenced the occurrence of frost because plant height spanned a substantial vertical gradient in air temperature above the soil surface. This was particularly true on nights with low sky infrared radiation and low wind. On calm, clear nights, the coldest leaf temperatures ( T leaf ≈ −11°C with T air ≈ −6°C) occurred because of the combined effects of low sky infrared radiation and low air temperature at plant heights. However, even on relatively windy nights with air temperature above freezing, net radiative losses to clear skies resulted in leaf frost. Flower temperatures of both E. peregrinus and Polygonum bistortoides tended to be significantly warmer (≈ 2°C) than leaf temperatures due to their greater height above the ground. Thus, leaf size, plant height, microsite exposure, and daily variation in sky infrared radiation all have important influences on the determination of frost frequency, duration, and intensity, as well as the length of the growing season.

Energy balance analysis of nighttime leaf temperatures and frost formation in a subalpine environment

Nocturnal leaf temperatures depend primarily on convective heat exchange with the air and longwave radiation exchange with the surroundings. Consequently, the leaf boundary layer and upper hemisphere infrared radiation dominate the energy balance of a leaf. Longwave radiation from the night sky may be particularly low in the subalpine environment because of the decreased atmospheric density, as well as the low moisture content of the atmosphere. The sky infrared radiation input during the growing season was often as low as 230 W m −2 in the subalpine, equating to a blackbody equivalent sky temperature of less than −20°C. Leaf temperatures predicted from energy balance equations were compared with field measurements of leaf temperatures for Erigeron peregrinus, a perennial herb common to subalpine meadows with a characteristic leaf dimension of approximately 2 cm. Differences between predicted and measured temperatures generated a root-mean-square error of 0.9°C, while the root-mean-square deviation between the air and leaf temperature observations was 3.9°C ( n = 461). Leaf temperatures were modelled in simulations addressing the effects of ambient air temperature, wind speed, sky infrared radiation, and sky exposure characteristic of this high elevation environment. Leaf temperature responses to air temperature and sky infrared radiation were linear, while the sensitivity of the leaf temperature response to wind speed increased substantially under calm conditions (less than 0.4 m s −1). Low wind in combination with clear, cold nights generated simulated leaf temperature depressions of over 6°C below air temperature, frequently resulting in frost episodes during the entire growing season.

Studies on the Potential Impact of Recreational Horseriding on some Alpine Environments of the Central Plateau, Tasmania

Horseriding is one of the more controversial recreational uses of the alpine and sub-alpine environments of the Central Plateau in the Tasmanian Wilderness World Heritage Area. Experiments were designed to help determine the impact of horse trampling and horse manure on the soils and vegetation of this area. The passage of 20-30 horses had substantial immediate and delayed effects on the soils of shrubland, herbfield and bolster heath, but little affect on dry grassland soils. Damage to vegetation was most pronounced in the shrubland, where a prostrate shrub, Grevillea australis, lost a large proportion of its biomass. Field experiments showed that weed establishment was limited to manured plots and was favoured by the exclusion of grazing animals and ground disturbance. Several weed species set seed during the 12 months of observation. Trails may be necessary to limit damage in the eroded shrubland, while herbfield and bolster heath are best avoided by horseriders.

Evaluation of community and ecosystem monitoring parameters at a high-elevation, rocky mountain study site

A multimedia systems approach was used to field test wilderness monitoring guidelines (U.S. Forest Service) at a high elevation site in western Wyoming. Five evaluation criteria having a primary emphasis on an ecosystem conceptual framework were applied to selected ecological parameters (terrestrial and aquatic) that were ranked on a relative scoring basis. The ecosystem conceptual criterion was based on the general attributes of the subalpine system, the nature of the potential environmental problem (acidic deposition), and ecological resources at risk. The other criteria were data variability, uncertainty, usability of methods, and cost-effectiveness. Data on sulfate deposition and buffering capacity of soils and surface waters relative to an elevational gradient supported the notion of greater risk to ecological resources in the subalpine environment. Within this ecosystem perspective, litter decay and taxonomic richness of lotic macroinvertebrates had the highest rating, followed by lotic functional feeding groups and lignin-to-nitrogen ratios. A biotic index for stream macroinvertebrates received the lowest rating on an ecosystem conceptual basis and also scored low on the uncertainty and cost-effectiveness criteria; however, suggestions were made for future improvement. Most parameters were similar in regard to variability and usability, except for functional groups, which exhibited greater data variability.

Conservation Genetics of Corroboree Frogs, Pseudophryne-Corroboree Moore (Anura, Myobatrachidae) - Population Subdivision and Genetic-Divergence

Reproductive compatibility and population genetic structure were examined in the corroboree frog, Pseudophryne corroboree, a species restricted to montane and subalpine environments in south-eastern Australia. The species comprises three geographic populations, represented by two morphological forms. Hybridisation experiments showed that the allopatric populations are interfertile, although crosses between the Snowy Mountains population (southern form) and each of the two northern populations (northern form) resulted in a significantly higher number of tadpoles with growth abnormalities. An electrophoretic examination of metamorphlings indicated that there was considerable genetic divergence between the two forms, with several loci approaching fixation of alternate alleles. The Snowy Mountains population also had substantially reduced levels of genetic variation compared to the two northern populations. Although genetic distances generally correlate with geographic distance, the genetic differences between the northern and southern populations form a pronounced step, not explicable by geographic distance alone. These findings have taxonomic implications which should be taken into account when considering the conservation management of this uncommon species.

Age and origin of subalpine forest zone

Genera of montane conifers first appeared in the fossil record in large numbers in the Middle Eocene (47-45 Ma) as widespread volcanism in the Cordilleran region provided scattered, cold upland tracts suited for them. Higher subalpine environments, generally above 2,000 m, probably were confined then to upper slopes of scattered strato-volcanos and basement highs covered with thick pyroclastic deposits. As relief increased in the middle Tertiary, and especially during the Pliocene-Quaternary, the area suited for a subalpine forest zone increased significantly, enabling montane conifers to spread into that higher, colder environment and form a new major forest zone. During glaciations the subalpine zone was much larger and probably from 900-1,000 m lower than at present. Spreading post-glacial warmth and drought account for its retreat to higher levels and for the discontinuous distribution of the forest and its species today. Recency of the subalpine adaptive zone is implied also by the close relations of its varieties and subspecies of herbaceous perennials, a few annuals, and pines to those in vegetation zones below it.

Soil–plant water relations of two subalpine herbs from Mount St. Helens

The subalpine environment of Mount St. Helens and other southern Cascade volcanoes is characterized by porous, pyroclastic soils and summer droughts. To evaluate plant drought stress in this environment, we examined plant water relations of Eriogonum pyrolifolium, a wintergreen, shallow-rooted, rosette perennial, and Polygonum newberryi, a deciduous, deep-rooted semierect perennial (both in Polygonaceae), at a subalpine site (elevation 1575 m) on Mount St. Helens. In a very dry summer, soil moisture below 20 cm remained above −0.1 MPa, but surface tephra deposits developed soil water potentials below −4.0 MPa. Surface tephra deposits had a mulching effect on underlying pre-eruption soils. Predawn xylem pressure potentials for adults of each species were never below −0.8 MPa, but midday xylem pressure potentials were often measured near or below the estimated turgor-loss point when vapor pressure deficits were high (maximum 3.1 kPa). Compared with Polygonum, Eriogonum had lower xylem pressure potentials, a lower turgor-loss point (mean −1.00 and −1.42 MPa, respectively), and higher conductance. In both species there was no midday depression in leaf conductance and little photosynthetic response to high evaporative demand. Thus, these species are not particularly conservative in water use and appear to rely on abundant soil moisture throughout the short growing season.

Effects of Rabbit Grazing and Fire on a Subalpine Environment. II. Tree Vegetation

The effects of two low-intensity fires andlor grazing by rabbits and wombats upon trees of Eucalyptus pauciflora and E. stellulata. in a subalpine environment were studied between 1977 and 1984. The experimental plot design permitted comparisons to be made between unburnt and burnt areas, each of which was subjected to four grazing regimes. Tall shrubs, mainly Bossiaea foliosa, which were present under the trees during the first fire but not the second increased fire intensity and flame height and hence damage to trees. The first fire in March 1978 did not completely kill any trees, but killed all the stems 2 m or more in height on 34% of trees and stimulated basal regrowth on a further 17% without killing all the stems. The first fire also reduced the basal area of live stems by about 17%. Small saplings less than 2 m high and seedlings were generally top-killed but resprouted from the base. In the second fire only lignotub- erous regrowth and seedlings were affected as they were in the first fire; the older trees showed no sign of damage. Rabbits killed a significant number of trees by first ring-barking the stems and then grazing the regrowth. Both the fires facilitated the establishment of tree seedlings in the frost-hollow by exposing bare soil, but few of these seedlings survived to the end of the 7-year study period. Frost was probably the main cause of tree death, but drought and competition from other species may also have contributed to losses.

Reproductive Response to three Temperature Regimes of four Poa Alpina Populations from The Rocky Mountains of Alberta, Canada

The effects of temperature and population origin on the reproductive response of Poa alpina L. tussocks from the Rocky Mountains of Alberta were investigated. Clones from four tussocks (samples) collected from two alpine and two subalpine environments were tested simultaneously in growth chambers using three temperature regimes (8/1°C, 15/8°C, 22/15°C, light/dark) with a 16-h photoperiod. Eight reproductive traits were observed on each clone. Normal panicles were present in all the clones tested at the 8/1°C temperature, while at the 15/8°C and 22/15°C temperatures the reproductive structures were mainly abnormal, viviparous, or nonexistent. At the low temperature regime the clones from the high alpine environment (elevation 2700 m) had more florets and seeds per panicle than the clones from the low subalpine environment (elevation 1480 m). In the 15/8°C and 22/15°C regimes this relationship was reversed, suggesting temperature-specific adaptation in the tested samples. The effects of sample and sample-te...

Effects of Rabbit Grazing and Fire on a Sub-Alpine Environment .I. Herbaceous and Shrubby Vegetation

The effects upon shrubby and herbaceous vegetation of two low-intensity fires and/or grazing by feral rabbits and wombats were studied in a subalpine environment between 1977 and 1984. Fire reduced shrub cover and biomass to low levels and their recovery was slow. When unburnt, tall shrubs increased, then decreased as a result of extreme frost and drought and subsequently continued to decrease. The recovery of the herb cover and biomass after fire was complete within a year except when delayed by drought andlor disturbance by rabbits. Bare ground was less than 2% in the absence of fire and rabbit grazing but increased to nearly 20% after fire in the presence of rabbits. Rabbits reduced the cover and biomass of 39 species of forb, in some cases to zero. Feral rabbit populations survived and multiplied on burnt areas but decreased on areas left unburnt. The implications of this research for the management of similar environments are discussed.

Density and Seasonal Movements of the Adder (Vipera berus L. 1758) in a Subalpine Environment

AbstractWithin a study area of about 1 km2 in a subalpine dwarf shrub community in the Swiss Alps, 148 adders (Vipera berus) were marked and observed during more than six months in 1981. There was no synchronized prenuptial sloughing of males. They seemed to slough only when they had found a female. After copulation the female was guarded by the male. Adult males sloughed three times, adult females only twice or once a year. Adder density was estimated to be about three adults per hectare. Survival of adults probably surpassed 80% after three years. Displacement rate was higher in foraging adders than in pregnant females. Most neonates stayed near the birth place until hibernation. The median home range was 5.20 ha in adult males and 0.76 ha in reproductive females, when estimated with Jennrich & Turner's (1969) method. The difference was probably due to the increased distances the males travelled during the mating period. After the mating period no difference could be found between adult males and pregnant females, in distances travelled, measured as a straight line. Spacing of home ranges was absent even within sexes. Pregnant females seemed to choose microhabitats more selectively than nonreproductive females. Sites of pregnant females had a more southerly exposure than sites of nonreproductive females.

Comparative Dynamics of Australasian Rabbit-Populations

Shot samples of rabbits were collected over several years at 11 sites in Australia and one in New Zealand. At any one site, pregnancy rates and litter sizes vary both with age of mother and with time of year. Few rabbits become pregnant before the age of 19 weeks; pregnancy rate increases until the full adult rate is achieved about 27 weeks old. Litter size is also affected by age, adult litter size being reached by females at about 43 weeks old. Rates and timing of reproduction vary greatly from site to site in response to local conditions. The annual production of young per fully adult female is highest at Wairarapa, N.Z. (53 young) and lowest in the semiarid (17) and subalpine (15) environments. At six of the sites cohorts of marked rabbits provided estimates of seasonal survival rates; survival improves with age but becomes relatively constant in rabbits aged more than 24 weeks; survival patterns differ between sites. Life tables were constructed combining the information on reproduction and survival. Their possible usefulness is discussed.

Late Quaternary vegetation near Battle Ground Lake, southern Puget Trough, Washington

Pollen and plant-macrofossil records from Battle Ground Lake, along with published data, are used to reconstruct the late-Quaternary vegetation history of the nonglaciated southern Puget Trough. Coinciding with the end of the Evans Creek Stade (circa 20,000-17,000 yr B.P.) of Fraser Glaciation, Gramineae, Artemisia , herbs, and Picea cf. engelmannii grew in a parkland/tundra around Battle Ground. This assemblage, recorded throughout the southern Puget Trough, implies cold, relatively dry conditions similar to subalpine environments east of the Cascade Range. The presence of Pseudotsuga, Picea sitchensis , and Alnus rubra as macrofossils suggests a slight interstadial warming between 17,000 and 15,000 yr B.P. Cool, humid conditions prevailed during the Vashon Stade when, south of the Cordilleran Ice Sheet, open forest or parkland featured mesophytic subalpine taxa. At Battle Ground Lake, temperate conifers were part of forest communities circa 11,200 yr B.P., but elsewhere they were present as early as 12,500 yr B.P. From 10,000 to 4500 yr B.P., Pseudotsuga-Quercus savannah spread into the Battle Ground area, offering evidence for summer drought more severe than today. Pseudotsuga and Thuja forest was established in the late Holocene with the introduction of the modern humid climate. Consideration of all the pollen data from the southern Puget Trough and the available radiometric chronology suggests that postglacial migration of most lowland conifers into the Puget Trough was rapid and not necessarily from southern refugia.

Phenology and Water Relations of Three Plant Life Forms in a Dry Tree‐Line Meadow

The relationship between physiological and phenological adaptations to drought was examined in three species of different life form in a tree—line meadow in the Sierra Nevada. Soil moisture in this meadow is predictably high following snow melt, but decreases through the summer because of infrequent precipitation. There were large differences among the life forms in allocation patterns and in vegetative and reproductive phenologies, but there were no comparable differences in their water relations. The annual Polygonum minimum and the hemicryptophyte Penstemon heterodoxus respond to decreasing soil moisture by reducing conductance; they consequently maintain a longer activity period. The geophyte Saxifraga aprica has little stomatal control of water loss and becomes dormant as soils dry. Penstemon heterodozus is a long—lived perennial with an intermediate root:shoot ratio (1.9), evergreen leaves, and high allocation to vegetative structures. Leaf growth occurs during the first part of the season, while the soil is moist. Flowering beings at the end of shoot growth, and fruits dehisce 3 mo after snow melt. During a dry summer, plants were observed to lose many leaves; 25% of the plants died, and none of the remaining plants flowered the next year. Although Penstemon decreases conductances under a limited range of leaf water potential, it is still not well adapted to long dry periods. Polygonum minimum is a very small annual with a low root:shoot ratio (0.15) and an indeterminate growth pattern. After a period of solely vegetative growth, leaves and floral structures are produced continually until °soil reaches —5 MPa. Seeds dehisce °2 mo after snow melt. Total seed production is a function of the length of the growth period. Regulation of water balance by stomatal control assures adequate time for fruit production. Other annuals in the community had a very similar phenological pattern. Saxifraga aprica has a high root:shoot ratio (5.0) and a small basal rosette of leaves. Leaf growth occurs for only 2 wk and is followed immediately by flowering. Only 5—10% of the plants flower each year. Fruits mature 5 wk after snow melt, and plants become dormant at —0.5 Mpa or within 6 wk of snow melt. This species and the other ephemeral geophytes complete their growth during the period of predictable high soil moisture, and therefore require little ability to regulate water balance. This study provides evidence that high diversity in life forms is maintained in environments with high yearly variability in the lengths of the drought and snow—free periods. No single set of phenological and physiological characteristics is optimally adapted to the variability in the subalpine environment that was studied, and therefore several adaptive strategies co—occur.

Geoecology of the Colorado Front Range: A Study of Alpine and Subalpine Environments

Geoecology of the Colorado Front Range: A Study of Alpine and Subalpine Environments