Willow Thickets Research Articles

The importance of willow thickets for ptarmigan and hares in shrub tundra: the more the better?

In patchy habitats, the relationship between animal abundance and cover of a preferred habitat may change with the availability of that habitat, resulting in a functional response in habitat use. Here, we investigate the relationship of two specialized herbivores, willow ptarmigan (Lagopus lagopus) and mountain hare (Lepus timidus), to willows (Salix spp.) in three regions of the shrub tundra zone-northern Norway, northern European Russia and western Siberia. Shrub tundra is a naturally patchy habitat where willow thickets represent a major structural element and are important for herbivores both as food and shelter. Habitat use was quantified using feces counts in a hierarchical spatial design and related to several measures of willow thicket configuration. We document a functional response in the use of willow thickets by ptarmigan, but not by hares. For hares, whose range extends into forested regions, occurrence increased overall with willow cover. The occurrence of willow ptarmigan showed a strong positive relationship to willow cover and a negative relationship to thicket fragmentation in the region with lowest willow cover at landscape scale, where willow growth may be limited by reindeer browsing. In regions with higher cover, in contrast, such relationships were not observed. Differences in predator communities among the regions may contribute to the observed pattern, enhancing the need for cover where willow thickets are scarce. Such region-specific relationships reflecting regional characteristics of the ecosystem highlight the importance of large-scale investigations to understand the relationships of habitat availability and use, which is a critical issue considering that habitat availability changes quickly with climate change and human impact.

Declining willow ptarmigan populations: The role of habitat structure and community dynamics

The recent range contractions and population declines of many grouse species worldwide have been attributed to loss and fragmentation of their habitats, although the empirical evidence for the actual drivers is often weak. In case of the willow ptarmigan Lagopus lagopus in Fennoscandia, ungulate overbrowsing of willows has been hypothesized to exert such negative habitat-related impacts. Moreover, a steep population decline of willow ptarmigan in southern Fennoscandia has recently been attributed to community interactions linking the fate of the willow ptarmigan to a change in keystone tundra rodent populations. Community and habitat factors may also interact in their impact on willow ptarmigan abundance. Here we assess whether willow thicket structural characteristics sensitive to ungulate browsing impacted willow ptarmigan habitat occupancy and whether such impacts depended on small rodent population dynamics. We employed an extensive survey approach spatially encompassing three riparian tundra regions and covering the phases of increase, peak and crash of the small rodent cycle. Willow ptarmigan habitat occupancy increased with the areal extent of willow thickets, whereas it decreased with increasing degree of thicket fragmentation (i.e. habitat shredding). Both of these effects were consistent with ungulate over-browsing impacting willow ptarmigan abundance negatively. Over the 4-year study period, willow ptarmigan habitat occupancy declined steeply independently of spatial variation in willow thicket areal extent and fragmentation. Moreover, the expected increase in ptarmigan populations during the increase/peak phase of the rodent cycle was not observed. Thus although our study provides support for the hypothesis that intense ungulate browsing negatively impacts willow ptarmigan, our study also suggests that causes of the current steep decline of ptarmigan populations in northern Fennoscandia should be sought in factors other than habitat fragmentation and changed rodent population dynamics.

Population dynamics of tundra voles in relation to configuration of willow thickets in southern arctic tundra

The areal extent and configuration of thickets of willow shrubs are currently changing in the Arctic both as an effect of global warming and changed browsing pressure of reindeer. These changes have been predicted to impact the distribution and abundance of wildlife species relying on willow thickets as habitat. We assessed the relation between variables quantifying willow thicket configuration and population dynamics of tundra voles (Microtus oeconomus) in three riparian regions in Finnmark, northern Norway, which were subject to intense browsing by semi-domesticated reindeer. The tundra vole, which exhibits 5-year population cycles in Finnmark, is the dominant small rodent species in riparian landscape elements in southern arctic tundra. In the course of a 4-year trapping study, tundra vole populations went through the cyclic phases of increase, peak and crash, however, with distinct differences between the three regions in the population dynamics. Within regions, the occupancy pattern during the increase phase was positively related to willow thicket configuration (in particular edge density and willow height) only in the region attaining the highest abundance and occupancy. However, local abundance was not clearly related to habitat features within any regions. The lack of consistency in the response of tundra vole populations to willow thicket configuration, as well as the positive relation between the degree of thicket shredding and tundra vole habitat occupancy in one of the regions, indicates that tundra voles will not be much affected by climate or browsing induced changes in the shrubbiness of the tundra in the future.

Environmental and Biotic Determinants of Growth and Height of Arctic Willow Shrubs along a Latitudinal Gradient

Ecological factors determining the growth of arctic shrubs remain poorly understood, thereby obscuring the current predictions about climate change effects. I conducted a study on the Yamal Peninsula, West Siberia, to find out which factors determine the growth and height of upright willows (Salix glauca and S. lanata). I sampled willow thickets at different slope positions at 13 sites along a 300-km-long north-south transect. The measurements included the height of willow shrubs and the length and diameter of shoots.The length and diameter of willow shoots increased southwards and with increasing distance from the sea. At the top of the slope and in areas with shallow thaw, the height and growth of willow were low compared to other slope positions and to areas with deep thaw. An increasing level of reindeer (Rangifer tarandus) grazing intensity was associated with decreased height and growth of willow and also associated with reduced foraging activity of willow grouse (Lagopus lagopus).The results show that even though increasing summer warmth is likely to enhance willow growth, there are other factors such as distance from the sea that also affect the growth and height of willow. The results suggest that reindeer grazing may locally counteract the effects of climate change.

Plant Communities and Floristic Diversity of the Emerald Lake Basin, Sequoia National Park, California

The Emerald Lake Basin forms a subalpine watershed in the upper drainage of the Marble Fork of the Kaweah River in Sequoia National Park. The basin is 120 ha in area and covers an elevational range from 2804 m at Emerald Lake to 3416 m at the summit of Alta Peak. The flora of the basin includes 202 vascular plant species, distributed into 132 genera and 41 families, with the Asteraceae (25 species) and Poaceae (23 species) as the largest families. Herbaceous perennials make up about three-fourths of the flora, but unlike alpine habitats many of these are relatively tall upright species, particularly in wet habitats. The woody plant flora includes five tree species, all conifers, with Pinus monticola as the dominant. There are 19 species of woody shrubs present, including six evergreen and 13 winter deciduous species. Eight plant habitat types were delineated on the basis of geomorphic position related to soil conditions and water availability that influence species composition (Billings 1974). These were subalpine conifer forest, willow thicket, wet meadows, moist rock crevices, dry meadows, dry rock crevices, colluvium, and fellfields.

Biogeography of the Byrranga Mountains, Taymyr Peninsula, Russian Arctic

The Byrranga Mountains (Gory Byrranga) are the most northern mountainous massif of the Taymyr Peninsula (Poluostrov Taymyr) in the Russian Arctic. Although studies of them began in 1736, they are one of the least studied areas of the Arctic. The region has no population, is remote, and has difficult access. As a result, the mountainous tundra ecosystems are preserved practically in a pristine state. The mountains are composed of siltstones and intrusive rocks of neutral composition; vast areas along all the mountain chain are occupied by exposed limestone. Rivers flow in deep intermontane depressions while lakes are found mainly in faults. The climate is an extremely severe continental type. Microclimatic areas provide some relief and support a rich and diverse flora. There have been 391 species and subspecies of vascular plants recorded, but no reliable data on the number of species of mosses and lichens are available. Relict thickets of tall willows are found in protected valleys of piedmont brooks, whereas relict alder-tree thickets occur on warm slopes. The mountain fauna includes nine mammal and 56 bird species. Intermontane depressions serve as corridors for seasonal migrations of wild reindeer that usually spend summers in the southern piedmont areas. Northern piedmonts and wide intermontane depressions are places where herds of musk-ox, introduced in the 1970s, concentrate. The bird fauna of relict willow thickets is highly specific and the fish fauna is quite diverse (16 species), but some species in Taymyr Lake (Ozero Taymyr) have been overexploited. This paper provides the first detailed biogeographical description of the Byrranga Mountains in English.

Impact of a 100‐year flood on vegetation, benthic invertebrates, riparian fauna and large woody debris standing stock in an alpine floodplain

AbstractThis paper investigates the impact of a 100‐year flood in May 1999 on community composition and large woody debris standing stock in an alpine floodplain (Isar, Germany). Detailed pre‐flood data sampled from 1993 to 1998 are compared with the situation directly after the flood. In those parts of the Isar floodplain mainly covered with pioneer vegetation prior to flooding, the coverage of unvegetated gravel bars increased by 22% following the flood. However, the flood did not remove larger amounts of older successional vegetation stages (willow thickets, floodplain forest). No significant changes in the benthic invertebrate fauna were recorded. The lowest densities of riparian ground beetles (Carabidae) within the study were recorded one month after the flood. Two months later, the ground beetle densities increased to the highest values ever recorded, indicating the ground beetle's high potential for recolonization. These results highlight the degree of resilience of both the aquatic and the riparian invertebrate fauna. The flood also caused a significant increase in large woody debris standing stock; in one section the number of logs increased tenfold and the volume increased by a factor of 20, leading to the assumption that most woody debris in alluvial flood‐plains is provided by catastrophic events. Copyright © 2004 John Wiley & Sons, Ltd.

Евтрофные сообщества кустарниковых ив в среднем течении реки Паляваам (западная часть Чукотского нагорья, Северо-Восточная Азия)

The paper characterizes a new association, Pedi­cularo lapponicae—Salicetum lanatae ass. nov., distin­guished by the floristic criteria and referred to the alliance Arcto erytrocarpae-Salicion all. nov. which comprises eutrophic willow shrub communities of Chukotka and Alaska. The association is described fr om the middle reaches of the Palyavaam R., the area located in the fringe, rather dissected part of the Chukotka Plateau. The vegetation of this area is more typical of the southern than of the northern hypoarctic tundras in its general outlook and life-form compo­sition. The Pedicularo lapponicae—Salicetum lanatae communities represent the impoverished and more moistened variants of the eutrophic willow thickets from the eastern part of the Chukotka Peninsula wh ere the Paleozoic carbonate outcrops are present. Commu­nities similar in their floristic composition are probable to be met in the other parts of the Arctic, but the center of their distribution ranges is undoubtedly bound to the montane areas of Beringian Chukotka.

The Matrix Matters: Effective Isolation in Fragmented Landscapes

Traditional approaches to the study of fragmented landscapes invoke an island-ocean model and assume that the nonhabitat matrix surrounding remnant patches is uniform. Patch isolation, a crucial parameter to the predictions of island biogeography and metapopulation theories, is measured by distance alone. To test whether the type of interpatch matrix can contribute significantly to patch isolation, I conducted a mark-recapture study on a butterfly community inhabiting meadows in a naturally patchy landscape. I used maximum likelihood to estimate the relative resistances of the two major matrix types (willow thicket and conifer forest) to butterfly movement between meadow patches. For four of the six butterfly taxa (subfamilies or tribes) studied, conifer was 3-12 times more resistant than willow. For the two remaining taxa (the most vagile and least vagile in the community), resistance estimates for willow and conifer were not significantly different, indicating that responses to matrix differ even among closely related species. These results suggest that the surrounding matrix can significantly influence the "effective isolation" of habitat patches, rendering them more or less isolated than simple distance or classic models would indicate. Modification of the matrix may provide opportunities for reducing patch isolation and thus the extinction risk of populations in fragmented landscapes.

Vegetation succession in a newly exposed Danube riverbed

Abstract. This paper describes vegetation development after a severe drop in water level. Diversion of the Danube river in 1992 resulted in a substantial water level reduction and the appearance of new terrestrial habitats in the Szigetköz region, a unique part of the Danube Valley in Hungary. Plant colonization was very rapid in the recently exposed river bed, where the establishment of a new willow thicket zone took only 4 yr. Our results clearly indicate that the elevation/moisture gradient is primarily responsible for the small‐scale vegetation heterogeneity that developed as succession proceeded. Further changes in vegetation patterns will be determined by the position of the water level as a result of water management.

The Matrix Matters: Effective Isolation in Fragmented Landscapes

Traditional approaches to the study of fragmented landscapes invoke an island‐ocean model and assume that the nonhabitat matrix surrounding remnant patches is uniform. Patch isolation, a crucial parameter to the predictions of island biogeography and metapopulation theories, is measured by distance alone. To test whether the type of interpatch matrix can contribute significantly to patch isolation, I conducted a mark‐recapture study on a butterfly community inhabiting meadows in a naturally patchy landscape. I used maximum likelihood to estimate the relative resistances of the two major matrix types (willow thicket and conifer forest) to butterfly movement between meadow patches. For four of the six butterfly taxa (subfamilies or tribes) studied, conifer was 3–12 times more resistant than willow. For the two remaining taxa (the most vagile and least vagile in the community), resistance estimates for willow and conifer were not significantly different, indicating that responses to matrix differ even among closely related species. These results suggest that the surrounding matrix can significantly influence the “effective isolation” of habitat patches, rendering them more or less isolated than simple distance or classic models would indicate. Modification of the matrix may provide opportunities for reducing patch isolation and thus the extinction risk of populations in fragmented landscapes.

Pollination Ecology of Pedicularis parryi ssp. purpurea (Parry) Carr (Scrophulariaceae)

Abstract The pollination ecology of Pedicularis parryi purpurea growing in a drier, upland, sagebrush meadow was studied in association with P. bracteosa paysoniana immediately adjacent in a rich, moist willow thicket in the Teton Mountain Region of Wyoming. By insect exclosure, P. parryi purpurea was found to be Bombus pollinator‐dependent. While both plants bloomed synchronously, had nectariferous corollas with similar nectars analyzed by refractometry and thin‐layer chromatography, and shared the same eight Bombus pollinator species, P. parryi purpurea was pollinated primarily by short‐tongued, sternotribic pollen‐foragers and P. bracteosa by long‐tongued, nototribic, nectar gatherers. Microscopic examination of 276 corbicular pollen loads from Pedicularis pollinators to determine pollen‐foraging constancy yielded 49% queens and 82% workers constant on P. parryi purpurea, 83% queens and 78% workers on P. bracteosa paysoniana. No putative hybrids between these species were identified; hybridization in Pedicularis is considered rare or absent.

Grasshoppers (Orthoptera, Saltatoria) on alpine and dealpine riverbanks and their use as indicators for natural floodplain dynamics

AbstractGravel banks with sparse vegetation are typical habitats of braided alpine and dealpine floodplains. They are not only habitats for semiaquatic or hygrophilous organisms, but include also xerophilous elements: 17 species of grasshoppers were recorded in the floodplain of the Upper Isar (Bavaria, FRG). In the alpine region, two species (Bryodema tuberculata, Chorthippus pullus) occur only in floodplains, colonizing young gravel banks with sparse vegetation. Population dynamics and habitat selection of Bryodema tuberculata, studied on the Upper Isar for several years, are characterized by small scale movements of marked individuals between neighbouring gravel banks and fluctuations of the abundance on different sections of the gravel banks. Furthermore, the periodic desiccation of small watercourses is important for the dispersal of the females by walking. Historically widespread, today its distribution corresponds to the few remaining inundation areas. The main causes of decrease and extinction in most localities are man‐made changes in floodplain dynamics. The building of retention reservoirs and the diverting of streams for hydropower influenced succession in the downstream floodplains. Most of the gravel banks with sparse vegetation changed into willow thickets or pine forests. All remaining inundation areas should be protected. Bryodema tuberculata is a good indicator for the balance between progressing succession and the reorganization of gravel banks by floods.

Distribution, activity and range use of male caribou in early summer in Northern Yukon, Canada

Males of the Porcupine Caribou Herd separated from females from the onset of spring migration until they joined them on the calving grounds in late June or early July, 4-6 weeks later. From late May to late June males spent an average of 50% of their time feeding and less than 2% standing and trotting/running. Males spent an average of 29% of their time lying and 19% walking, except in mid-June (40% lying, 6% walking). The average lengths of active and resting periods were 112 minutes and 104 minutes, respectively, from late May to mid-June, but decreased sharply in late June to 78 minutes and 69 minutes, respectively. Tussock meadows were selected in late May and early June, wet sedge meadows were avoided until late June, dwarf shrub heaths were avoided after late May, and alluvial willow thickets were avoided in late May and early June but were selected in mid-June and late June. Caribou fed primarily on lichens and Vaccinium in late May, lichens and Eriophorum in early June, Eriophorum in mid-June and Salix in late June.

Net aerial primary production of a James Bay, Ontario, salt marsh

Aboveground plant biomass and litter measurements were made at four intervals between mid-June and late August 1977 on a subarctic salt marsh located at North Point on the southwestern shore of James Bay, Ontario. We sampled six salt marsh zones ranging from a lower intertidal flat dominated by the grass Puccinellia phryganodes to the edge of willow thickets characterized by Juncus balticus.Peak aboveground biomass was reached in nearly all zones by early August, and ranged from 119.3 to 240.4 g dry weight∙m−2. Litter accumulated in all zones except the lower two zones which were subjected to tidal flows. The highest zone where Juncus balticus occurred had the highest litter mass, 572.8 g dry weight∙m−2, while the lowest, 24.7 g∙m−2, occurred in the lowest zone. Estimates of net aerial primary productivity using Smalley's method ranged from 119.3 g∙m−2 in the upper salt marsh to 384.0 g∙m−2 in the zone dominated by Juncus balticus. The mean marsh net aerial primary productivity was 227.7 g∙m−2 which was low compared with other salt marsh data. The 1977 aboveground biomass was lower in 1976, probably as a result of a cooler summer.

Habitat Preferences and Competition of Wintering Juncos and Golden‐Crowned Sparrows

Trapping and banding of wintering juncos and golden—crowned sparrows was carried out from 1964 to 1968 along the opposite edges of an old field. The juncos ranged freely along the field borders but the golden—crowns were largely restricted to dense willow thickets in one part of the field. An attempt to assess possible competition between the two species by removing juncos in 1966—67 was unsuccessful because of infiltration of new birds from outside the study area. Removal of golden—crowns in 1967—68 reduced their population markedly and resulted in significant increase in use of the willow thickets by juncos. Although juncos are primarily seed eaters in winter, and seeds are a steadily dwindling resource at that season, competition for food between the two species was alleviated because the sparrows subsisted in large part on sprouting annuals, a resource renewed continuously after sprouting started following the fall rains. Further, the green food eaten by the sparrows undoubtedly satisfied their water requirements to a great extent and reduced competition for water sources. The competition demonstrated by removal experiments resulted not from direct competition for the same set of resources but from the proximity of a water trough, an important junco resource, to the heavy cover preferred by the sparrows. Although outnumbered about 5:2, the larger sparrows were able to exclude the juncos from this cover to an appreciable extent.

The Northern Limits of Moose (Alces alces) in Western Canada

Published and unpublished distributional records are presented for moose ( Alces alces ) near treeline and on the tundra between Hudson Bay and the Alaska-Yukon boundary. Moose appear to occur regularly on much of the northwestern tundra between Horton River and Alaska, and locally in the Coppermine area—probably in response to the food supply provided by extensive willow thickets. They have been seen irregularly in many other places on the tundra. There has been an increase in the number of observations of moose in recent years. This increase may reflect either an upward response by moose populations to succession following fire in coniferous forests near treeline, or increased human mobility and travel (or both), rather than a long term northward expansion of the moose population.

Observations of Birds and Mammals at Bluenose Lake

Reports 4 Aug - 3 Sept 1953 observations at this lake at 1800 ft elevation in a large shallow basin in the Melville Hills of Mackenzie District. This belated note is prompted by the lack of other investigations there and by the fact that most of the breeding-bird records constitute range extensions. Only 35 bird species were recorded. The absence of some species could be correlated to an absence of varied habitat: no extensive willow thickets and no rock outcrops. Eleven mammalian species were seen. A barren-ground grizzly was observed to approach a muskox and turn away. There is no known record of a grizzly killing a muskox.

Lichens of Mt. McKinley National Park, Alaska

Lichens of Mt. McKinley National Park, Alaska

An Arctic Forest in the Tundra of Northern Ungava, Quebec

A willow thicket dominated by Salix planifolia and S. alaxensis, is located in a 1500-ft-deep glaciated valley at the southwest end of Watts Lake, 32 mi south of Deception Bay. This "forest" forms a solid green canopy at 12 ft and contains some trees of almost 16 ft height. It grows in deep, well-drained soils (here named arctic thicket type) developed on poorly sorted sand, gravel, pebbles and cobbles, mainly of schist. A flora of 67 species of vascular plants (here listed) have been found in the area, all but two of which are arctic species. The two exceptions are wide-ranging boreal and subarctic species. For so many arctic species to be capable of growing in the shaded environment is of interest. Factors contributing to the existence of such "forests", temperatures, moisture, deep permafrost, snow cover, wind and topography affording protection, are discussed.