Subalpine Species Research Articles

The Subalpine Members of Pittosporum (Pittosporaceae) from Mt Jaya, New Guinea. Contributions to the Flora of Mt Jaya, II

Summary. The subalpine species of Pittosporum Banks ex Gaertn. from Mt Jaya are investigated. Recent collections of Pittosporum from Mt Jaya exhibit a leaf morphology which suggests they are conspecific with P pullifolium Burkill sensu stricto. However, in several characters, inflorescence position in particular, these do not correspond to P pullifolium sensu stricto, but rather to P nubigenum Ridl. Initially known only from a single rather poor collection, P nubigenum has been synonymised with P pullifolium, but is here recognised as distinct. In addition, a new species is described, P spissescens. A key to the alpine and subalpine members of Pittosporum in New Guinea is provided, together with an

SOIL AMINO ACID UTILIZATION AMONG SPECIES OF THE CYPERACEAE: PLANT AND SOIL PROCESSES

Amino acids are released during the decomposition of soil organic matter and have been shown to be utilized as a nitrogen source by some non-mycorrhizal species in the family Cyperaceae (the sedge family). Twelve out of 13 Cyperaceae species examined in the current study were capable of absorbing soil amino acids in the non-mycorrhizal state. With two exceptions (two species in the genus Kobresia), species from subalpine or alpine habitats exhibited lower rates of total nitrogen uptake compared to species from more temperate habitats, which is possibly explained by lower growth rates in the alpine and subalpine species and a lower overall demand for soil nitrogen. The alpine and subalpine species exhibited higher rates of glycine uptake relative to NH 4 1 and NO3 2 uptake, compared to species from the more temperate habitats. This may reflect specialization toward the uptake of organic N in the alpine and subalpine species. In three ecosystems where sedges commonly occur, amino acids were present in the soil pore water, but in highly variable amounts. Seasonal maximum amino acid concentra- tions in alpine soil pore water ranged from 13 to 158 mmol/L in four dry meadow sites. The most common amino acid in these alpine soils was glycine. In a subalpine fen habitat, aspartate was the most commonly observed amino acid, and total amino acid concentrations were 15-20 mmol/L. In a shortgrass steppe habitat, glutamate was the most abundant amino acid, and total amino acid concentrations were 25-45 mmol/L. Soil protease activities correlated positively with soil protein content when all three ecosystems (alpine, subalpine fen, and shortgrass steppe) were considered together. The addition of protein (as casein) significantly increased soil protease activity, indicating that soil protein content contributes to the capacity to generate soil amino acids. Soil protein contents correlated positively with total soil N content when the alpine and shortgrass steppe sites were considered together. The retention of NH4 1 and amino acids on the alpine soil was high compared to soils of lower organic matter content that have been investigated in past studies. We conclude that (1) the potential to take up amino acids in non-mycorrhizal roots of the family Cyperaceae is widespread among species native to a variety of different habitats, (2) amino acids are available for uptake (though most abundant in the alpine), (3) the potential to generate soil amino acids is proportional to soil protein concentration, and (4) soil amino acids can be retained in the soil at high levels, leading to the conclusion that the soil binding affinity of amino acids may constrain uptake by plant roots and microorganisms.

Soil Amino Acid Utilization among Species of the Cyperaceae: Plant and Soil Processes

Amino acids are released during the decomposition of soil organic matter and have been shown to be utilized as a nitrogen source by some non-mycorrhizal species in the family Cyperaceae (the sedge family). Twelve out of 13 Cyperaceae species examined in the current study were capable of absorbing soil amino acids in the non-mycorrhizal state. With two exceptions (two species in the genus Kobresia), species from subalpine or alpine habitats exhibited lower rates of total nitrogen uptake compared to species from more temperate habitats, which is possibly explained by lower growth rates in the alpine and subalpine species and a lower overall demand for soil nitrogen. The alpine and subalpine species exhibited higher rates of glycine uptake relative to NH4+ and NO3− uptake, compared to species from the more temperate habitats. This may reflect specialization toward the uptake of organic N in the alpine and subalpine species. In three ecosystems where sedges commonly occur, amino acids were present in the soil pore water, but in highly variable amounts. Seasonal maximum amino acid concentrations in alpine soil pore water ranged from 13 to 158 μmol/L in four dry meadow sites. The most common amino acid in these alpine soils was glycine. In a subalpine fen habitat, aspartate was the most commonly observed amino acid, and total amino acid concentrations were 15–20 μmol/L. In a shortgrass steppe habitat, glutamate was the most abundant amino acid, and total amino acid concentrations were 25–45 μmol/L. Soil protease activities correlated positively with soil protein content when all three ecosystems (alpine, subalpine fen, and shortgrass steppe) were considered together. The addition of protein (as casein) significantly increased soil protease activity, indicating that soil protein content contributes to the capacity to generate soil amino acids. Soil protein contents correlated positively with total soil N content when the alpine and shortgrass steppe sites were considered together. The retention of NH4+ and amino acids on the alpine soil was high compared to soils of lower organic matter content that have been investigated in past studies. We conclude that (1) the potential to take up amino acids in non-mycorrhizal roots of the family Cyperaceae is widespread among species native to a variety of different habitats, (2) amino acids are available for uptake (though most abundant in the alpine), (3) the potential to generate soil amino acids is proportional to soil protein concentration, and (4) soil amino acids can be retained in the soil at high levels, leading to the conclusion that the soil binding affinity of amino acids may constrain uptake by plant roots and microorganisms.

Leaf waxes of slow-growing alpine and fast-growing lowland Poa species: inherent differences and responses to UV-B radiation

We investigated whether alpine and lowland Poa species exhibit inherent differences in leaf cuticular waxes, leaf UV absorbing compounds and/or growth responses to UV-B treatment. All plants were grown hydroponically in a growth cabinet (constant 20°; 14 hr photoperiod; 520 μmol photons m−2 s−1 PAR). Two alpine (P. fawcettiae and P. costiniana), one sub-alpine (P. alpina) and three temperate lowland species (P. pratensis, P. compressa and P. trivialis) were grown under conditions without UV radiation for 36 days. In a subsequent experiment, four Poa species (P. costiniana, P. alpina, P. compressa and P. trivialis) were also exposed for 21 days to UV-B/(UV-A) radiation (`UV-B treatment') that resulted in daily UV-B radiation of 7.5 kJ m−2 day−1, with control plants being grown without UV-B (`UV-A control treatment'). All treatments were carried out in the same growth cabinet. There was no altitudinal trend regarding wax concentrations per unit leaf area, when the six species grown under UV-less conditions, were compared at similar developmental stage (20–30 g shoot fresh mass). However, large differences in cuticular wax chemical composition were observed between the alpine and lowland species grown under UV-less conditions. For example, a single primary alcohol was present in the waxes of the lowland and sub-alpine species (C26H53OH), but was virtually absent in the alpine species. Although alkanes were present in all six species (primarily C29H60 and C31H64), the proportion of total wax present as alkanes was highest in the alpine species. Aldehydes were only present in the waxes of the alpine species. Conversely, substantial amounts of triterpenoids were mainly present in the three lowland species (squalene and lupeol were the dominant forms). The proportion of total wax present as long-chain esters (LCE-s) was similar in all six species grown in the absence of UV radiation. Acetates were observed only in the wax of P. trivialis. Of the four species exposed to UV-B, only P. costiniana and P. compressa showed any differences in wax chemical composition (compared to UV-A control plants). In P. costiniana, the proportion of total waxes present as alkanes was substantially lower in the UV-B grown plants (replaced by an unknown compound with a high retention time value). UV-B grown P. costiniana and P. compressa both exhibited less wax per unit leaf area. In P. compressa, this resulted from a lower absolute amount of alcohol per unit leaf mass in the UV-B treatment. The concentrations of UV absorbing compounds in whole leaf extracts differed between the four investigated species. However, no systematic differences were apparent between the alpine, sub-alpine and lowland species. Exposure to UV-B radiation had no effect on the specific leaf area (ratio of leaf area to leaf dry mass). We conclude that the alpine and lowland Poa species have a cuticular wax composition that is inherently different.

Biogeography of Great Basin Mammals: Paradigm Lost?

Biogeographic relationships of mammals occurring on mountaintops of the Great Basin of western North America are re-examined on the basis of newly acquired information. Contrary to previous indications, a relatively weak pattern is revealed between species richness and island size. The range of species numbers per mountain range varies only by a factor of two, with most islands having between 9 and 13 species, so that a species found on any one island is likely to be found on many, if not all, others. Analyses of species occurrences (nestedness, presence-absence patterns) also do not reveal strong effects of area. Consistent with prior studies, there is no discernible effect of isolation of mountaintops from one another or from putative mainlands; this is explicable from the disproportionate number of mobile woodland species and few sedentary subalpine forms among montane faunas. Although species and populations have disappeared from mountaintops since the late Pleistocene, they involve mostly cold-adapted subalpine species. Biogeographic processes shaping characteristics of modern mountaintop faunas in the Great Basin evidently involve a dynamic interplay between extensive intermountain dispersal and extinction resistance of remaining species. Brown's (1971, 1978) hypothesis, which posits that montane mammals in the Great Basin comprise remnant faunas formed exclusively by extinctions and no colonizations, is not supported.

Latitudinal gradients of coniferous tree species, vegetation, and climate in the Sierran-Cascade axis of Northern California

Latitudinal gradients of tree species composition along the Sierran/Cascade axis in northern California were explored by comparing forests of Lassen Volcanic and Yosemite National Parks, USA. A calibration procedure based on canonical correspondence analysis predicted a mean rate of elevational displacement of 172.1 m/° latitude for Lassen sites in Yosemite. This is a steep latitudinal gradient compared with other temperate uplands (which average around 100 m/0 latitude), but it corresponds with the magnitude of the July mean temperature gradient (143 m/0 latitude) and the annual precipitation gradient (230 m/0 latitude). Elevational displacement of basal-area weighted species means showed considerable variation. The range for montane species was 20–153 m/0 latitude; for subalpine species the range was 142–305 m/0 latitude. This disparity is related to differential temperature lapse rates between regions and is reinforced by contrasting biogeographic affinities of montane vs. subalpine species. Whereas it is uniformly hot and dry during the growing season at lower elevations in both regions, growing seasons in the subalpine zone are significantly warmer and drier (at comparable elevations) in Yosemite, the more southerly locale. Furthermore, montane species are principally of Sierran affinity, whereas subalpine are primarily of Pacific Northwestern affinity.

Factors Controlling Throughfall Characteristics at a High Elevation Sierra Nevada Site, California

AbstractThe composition of throughfall (TF) is influenced by wet and dry deposition on foliar surfaces and by chemical and biological interactions between rain and the foliage. The relative importance of these processes was investigated for TF collected in the summer months of 1985, 1986, and 1987 under three subalpine species, chinquapin (Chrysolepis sempervirens Hjelmqvist), western white pine (Pinus monticola Dougl.), and willow (Salix orestera Schneider), in the Emerald Lake Watershed, Sequoia National Park, California. The depth of rain and days since the last storm were used to predict net‐TF deposition in a multiple linear regression model. Dry deposition to needle surfaces had the greatest influence on western white pine TF composition. Net‐TF data for this species were used to estimate mean dry deposition rates for the summer. These data show that NH+4, NO−3, and SO2−4 dry deposition rates exceed median summer wet deposition rates by 1.5, 1.9, and 1.0 times, respectively. Willow foliage had the greatest influence on TF composition and western white pine the least. Estimated foliar release of cations and organic anions by willow during summer rain is a substantial fraction of annual wet deposition of those ions. Weak organic acid anions derived from foliar release are a significant component of net‐TF in all three species, particularly willow, where summer fluxes of organic acids were at least 51% of the total estimated annual wet deposition of organic anions.

Gas Exchange Responses to Variable Sunlight in Two Sonoran Desert Herbs: Comparison with Subalpine Species

Responses in net photosynthesis (A) and stomatal conductance to water vapor (g) in two Sonoran desert herbaceous perennials exposed to atypical conditions of variable sunlight were compared to previously documented responses in subalpine herbs that grow in an environment of extreme sunlight variability. In the desert herb Penstemon parryi, little variation in g (< 80 mmol m-2 s-1) or xylem pressure potential (ψ) was observed during periods of sunlight variability, although A varied substantially. This response was consistent with those subalpine plants that also maintained relatively constant ψ during sun/shade periods. ψ differed significantly between sun and shade periods in the desert herb Ambrosia ambrosioides (-1.65 vs. -1.36 MPa, respectively), and reductions in g during shade were as rapid (24.5 mmol m-2 s-1min-1) as observed in subalpine species with similarly variable ψ. However, recovery in g during sun periods occurred at a rate well below that measured in subalpine herbs. Thus, alterations in g did not closely correspond to variations in A and sunlight in this desert herb. This response pattern was unlike any measured in 22 subalpine species previously studied. Rapid recovery in g during sun periods that follow shade has likely been selected for in subalpine herbs that are exposed daily to sunlight variability. Such a response can substantially increase carbon gain. We suggest that the benefits of a strong tracking response in g to variations in A and sunlight are not realized in desert environments with relatively constant solar regimes. However, rapid stomatal closure during shade periods does insure higher water use efficiency and the potential for recovery in ψ in this desert herb.

The floristic composition of a natural montane forest in Southeast Ethiopia

AbstractA floristic survey was made in a characteristic montane forest in SE‐Ethiopia. Dominant species are the conifers Juniperus procera and Podocarpus gracilior associated with numerous broadleaved trees. The species composition of the different strata of trees, bushes and ground vegetation is described. In openings afroalpine and subalpine species like Helichrysum spp., Lobelia gibberoa, Senecio spp. and others dominate.

Freezing mechanisms, acclimation processes and cold injury in Eucalyptus species planted in the Mediterranean region

Eucalyptus plantations of the Mediterranean countries are frequently jeopardized by the occurrence of relatively severe frosts every 5–10 years. In order to examine the mechanisms of frost injury in the species generally utilized in the region, whole seedlings and samples of tree tissues of different species ( Eucalyptus occidentalis Endl., E. × trabutii Vilm., E. globulus Labill., E. gunnii Hook. f.) were tested by artificial frost regimes. Non-hardened vs. cold-hardened plants, woody vs. leaf tissues and stem pieces of different sizes were compared for their supercooling ability, exotherm characteristics and frost tolerance. The species most often utilized for planting in the Mediterranean region, E. × trabutii, E. occidentalis and E. globulus did not show any capability to respond to artificial or natural hardening regimes; however, the first two species were irreversibly damaged as soon as ice formed in the tissues, probably because of ‘non-equilibrium freezing’. Eucalyptus globulus showed a modest capability to withstand extracellular ice and, therefore, ‘equilibrium freezing’. Eucalyptus gunnii, a subalpine species utilized for interspecific crosses, was able to respond to hardening pretreatments and to withstand, in the hardened state, extracellular ice formation and temperatures as low as −14°C.

Habitat Use and Habitat Overlap of Riparian Birds in Three Elevational Zones

I examined patterns of variance in habitat use and habitat overlap in 20 breeding bird species found along a riparian vegetational gradient in southeastern Wyoming to test whether habitat use in species differed (1) from availability of random habitat resources, (2) among elevation zones, and (3) between species that inhabited only one zone and species that occupied multiple zones. I sampled habitat features in bird territories and at random stations on 10 8.1—ha study grids distributed over an elevational gradient of 940 m. Principal components analysis was performed on both randomly sampled and territory—centered habitat data to examine the habitat use of each bird species in relation to the random centroid in n—dimensional habitat space. Using this transformed data set, I computed habitat size of each species, defined as degree of specialization in habitat use; species—habitat position, defined as use of common or scarce habitat; habitat overlap among species; and sum of variation in structure of the available habitat. Habitat size was significantly smaller for bird species found in subalpine riparian shrublands than for those found in foothill woodlands, but this result was partly a reflection of variation among elevational zones in structural diversity of the available habitat. The null hypothesis that species used habitat as it occurred randomly was rejected for all three subalpine bird species examined, 6 of 10 dominant mid—elevation species, and 1 of 10 lowland species. Habitat overlap among species did not vary among zones, but habitats used by lowland species were closer to the random expectation than habitats used by mid—elevation or subalpine species. In general, species restricted in distribution to one zone had smaller habitat sizes than species occupying multiple zones, but some zone—dependent species were generalists within their zones. Vegetation of lowland riparian habitats was structurally more complex than that of riparian habitats at higher elevations, and bird species richness and bird abundance were greatest in riparian lowlands. Because most lowland species were generalized in habitat use and occupied habitats that were similar among species, I concluded that bird species diversity was greater in lowlands than in mid—elevation and subalpine shrublands merely because woodlands were more heterogeneous. The large proportion of generalists in deciduous woodlands of the central Rocky Mountains may be explained by geographic dispersal patterns. Woodland species may have been historically prevented from dispersal by the ecological barrier of the Great Plains grasslands. Recent establishment of widespread riparian forest permitted colonization of woodland bird species, with generalists colonizing first.

Influence of Growth from on Ecophysiological Responses to Variable Sunlight in Subalpine Plants

Periods of variable sunlight due to intermittent cloudcover are common in the subalpine zone of the central Rocky Mountains. To evaluate the ecophysiological significance of daily variations in sunlight, responses in net photosynthesis, stomatal conductance to water vapor, and water use efficiency (CO2 uptake per unit H2O lost) were measured in 12 subalpine species including trees, shrubs, and herbs. Measurements were made during intervals of alternating full sun and shade throughout a growth season that included daily and seasonal periods of water stress. In general, photosynthesis responded rapidly in all growth forms to changes in sunlight due to clouds, while stomatal conductance responded more slowly or not at all. Large reductions in photosynthesis were measured during clouds periods for all species, while stomatal conductance was considerably less responsive to changes in sunlight in woody species. The greatest and most variable reductions in stomatal conductance during shade (&lt;10 to a 68% reduction of full sun levels) occurred in herbaceous species. Carbon gain in the woody species was enhanced because stomatal conductance remained relatively high during both sun and shade periods. Water use efficiency in most species was generally lower during shade periods compared to full sun periods. However, woody plants maintained higher xylem pressure potentials that were much nearer shade values compared to herbs. The greater decrease in stomatal conductance and photosynthesis in herbs during shade resulted in improved water use efficiency, although carbon gain was reduced during both shade and the subsequent full—sun period. These apparent growth strategies during non—steady—state response periods appear opposite to generalizations made previously for woody vs. herbaceous species under steady—state conditions.

EFFECT OF WATER STRESS ON STOMATAL AND PHOTOSYNTHETIC RESPONSES IN SUBALPINE PLANTS TO CLOUD PATTERNS

Daily cloudcover is a frequent and persistent environmental feature of subalpine habitats. Response patterns in net photosynthesis (A), stomatal conductance to water vapor diffusion (g), transpiration (E), and water use efficiency (WUE = A/E) to intermittent cloudcover were evaluated for two subalpine species to determine if their responses supported the hypothesis that species that undergo water stress during sunlit intervals may have more rapid and greater stomatal responses to irradiance fluctuations than species under little apparent water stress. In Helianthella quinquenervis, a herbaceous perennial with midday xylem pressure potential &lt; –2.0 MPa, responses in both A and g to simulated changes in natural irradiance occurred almost simultaneously and were relatively rapid. Although A was reduced by 22% during periods of shade compared with full sunlight periods, E was similarly reduced, and thus, no reduction in WUE occurred. In contrast, the riparian herb Senecio triangularis was under little apparent water stress and g was relatively insensitive to fluctuations in irradiance. As a result, periods of cloudcover led to a smaller reduction in A of only 15% relative to full sunlight with little concurrent reduction in E, leading to a corresponding 12% decrease in WUE compared with steady state values under full sunlight. These data suggest that species that experience apparent water stress during sunlit intervals may maintain higher WUE during intermittent cloudcover through water conservation at the expense of carbon gain. In contrast, species in which water stress does not occur during sunlit intervals can maximize carbon gain at the expense of reduced WUE. The degree of competition for water and sunlight in a habitat may determine the particular physiological response pattern expressed during natural cloudcover regimes.

Mechanisms of Early Primary Succession in Subalpine Habitats on Mount St. Helens

In the 6 yr following the 1980 eruption of Mount St. Helens in Washington state, vascular plant invasion of barren substrates in subalpine habitats has been limited despite the proximity of seed sources from resprouted vegetation. From 1983—1985 we counted 1st—yr seedlings and estimated percent cover of adults in grids of permanent plots located across the ecotone between residual vegetation and barren substrate created in 1980. We found that (1) seedling recruitment declined from 1983 to 1985, apparently in response to drought; (2) most seedlings occurred within 3 m of a conspecific adult; and (3) plots with an intermediate vegetation cover (5—72%) contained a significantly higher fraction of seedlings than did unvegetated plots. Thus, dispersal is limited in many species and nurse plants may play a key role in trapping seeds and promoting seedling establishment. We sowed 16 000 viable seeds from 22 subalpine species into 264 plots in barren substrates at two sites on the volcano. The design was a complete factorial, with species, site, and fertilizer as treatments. Survivorship through 1985 varied from 0 to 12%, with Sitanion jubatum, Stipa occidentalis, Polygonum newberryi, Eriogonum pyrolifolium, and Spraguea umbellata attaining the highest values. Survivorship was correlated with seed mass, and was higher at the site where the pre—eruption surface was exposed. Fertilizer increased the size of most seedlings but had only a marginal effect on survivorship. Species with high environmental tolerance generally dispersed short distances, whereas species that dispersed farther generally had low tolerances and apparently require site amelioration prior to establishment. The path of early succession depends upon the spatial position and dispersal abilities of species in the seed pool, and may not reflect environmental gradients.

Postglacial Development of the Subalpine-Boreal Transition Forest of Western Canada

(1) The subalpine-boreal transition forest of western Canada has long been of interest because of its mixture of boreal and subalpine species. However, an understanding of vegetation dynamics in the region is impeded by a lack of information on long-term patterns of vegetation development, peatland formation and fire activity. (2) Fossil pollen and charcoal from the sediments of small lakes in the northern subalpine-boreal transition region are used to reconstruct the postglacial history of regional vegetation change, peatland development and fire. Interpretation of the fossil pollen spectra is aided by multivariate numerical comparison with modern spectra from western Canada. (3) From 11 000 B.P. until 5000 B.P. there was continuous vegetation change. There are no modern, regional analogues for the early postglacial communities. By approximately 5000 B.P. the extent of peatland and fire activity were similar to the modern conditions. Vegetation has remained relatively constant since then. (4) The pattern of vegetation development in the subalpine-boreal transition forest is completely different from postglacial vegetation development in the subalpine forest, but has clear similarities with the early Holocene development of the southern boreal forest.

Gene flow between three eucalypt species at Snug Plains

The extent of hybridisation and gene flow between the three Monocalyptus species, Eucalyptus pulchella, E. coccifera (series Piperitae) and E. delegatensis (series Obliquae) at Snug Plains (600 m) in southeastern Tasmania was examined. The flowering time of E. pulchella was two months later than usual for this normally low-altitude species. It consequently overlapped the flowering period of both sub-alpine species E. coccifera and E. delegatensis and had its peak f10wering period intermediate between the two. The movements of pollinators across the species boundaries indicated the potential for hybridisation between E. pulchella and the other two species. Adult morphology suggested that the Snug Plains E. pulchella tended towards E. coccifera compared to typical, low-altitude E. pulchella and progeny tests reinforced this view. In addition, two out of twelve E. pulchella adults sampled appeared intermediate between this species and E. coccifera and produced progeny overlapping those from E. coccifera. These results suggest that introgression of E. coccifera genes may be occurring into E. pulchella at Snug Plains although adaptive convergence cannot be excluded. Quite a different picture is seen for the results of hybridisation between E. pulchella and E. delegatensis. Six putative Fl hybrids between E. pulchella and E. delegatensis occurred in progeny from two E. pulchella mothers. However, this appears to have had little genetic impact on the species, since no evidence of introgression or convergence was apparent in adult populations of these species.

Additions to the flora of the Queen Charlotte Islands on limestone

The following montane, subalpine, and alpine species not previously reported from the Queen Charlotte Islands are documented: Astragalus robbinsii, Taraxacum ceratophorum, Pyrola asarifolia, Salix stolonifera, Senecio lugens, Selaginella densa, and Cystopteris montana. Many plants disjunctly distributed and endemic in the Queen Charlotte Islands are found more frequently on limestones than on other rocks. Causes for this concentration on limestones are suggested and related to similar phenomena in Europe.

English

English

Diesel oil spill in a subalpine meadow: 9 years of recovery

Two subalpine meadow communities near Mt. Baker, Washington, were inundated by a spill of 26 000 L of diesel oil in 1972. Studies were made of the initial impact of the oil on the vegetation and of community recovery over 9 years. Within two growing seasons following the spill, plant cover had decreased from a prespill cover of nearly 100% to 1% and all species except Phyllodoce empetriformis, Carex lenticularis, and Rhacomitrium sudeticum had died. Seedlings of Carex nigricans began to appear on bare soil after 1 year, followed by seedlings of other common subalpine species 2 to 4 years later. Nine years after the perturbation 5 to 20% of the ground was covered with vegetation and the original disturbance could no longer be discerned by a casual observer.

Freezing Resistance of Trees of the South Temperate Zone, Especially Subalpine Species of Australasia

Maximal resistance to winter freezing of trees of the South Temperate Zone, especially subalpine trees of Australasia, was assessed. Most of the tree species which grow in lower altitudes were marginally hardy to - 10?. Subalpine and alpine shrubby species such as Podocarpus nivalis, P. lawrencei and Dacrydium bidwillii were the hardiest conifers in New Zealand and Australia, resisting freezing to -20? to -23?. This hardiness was comparable to that of conifers native to the warm temperate or temperate parts of Japan. In Nothofagus, the deciduous, subalpine N. antarctica of South America was the hardiest, resisting freezing at -22?. A New Zealand evergreen timberline species, N. solandri var. cliffortioides was marginally hardy to - 15?. Of the Eucalyptus species, E. pauciflora which forms the alpine tree limit on the mainland of Australia was the hardiest, resisting freezing to - 15? in the leaves. Other high-altitude angiosperm species tested mostly survived freezing to only -10? or -15?. Very hardy tree species that withstand freezing below -30? seem not to have evolved in the Southern Hemisphere, because the mild, oceanic winters did not provide the stimulus, and because hardy northern tree genera, with minor exceptions, have been unable to cross the barrier formed by the tropics.