Birch Betula Pubescens Research Articles

Afforestation of low-productivity peatlands in Sweden — the potential of natural seeding

In 1971, a series of five afforestation trials were established along a north-south gradient on open peatlands in Sweden. All areas were drained, fertilized and planted with Scots pine (Pinus sylvestris). Survival and height of the planted trees as well as the amount of natural establishment, i.e. downy birch (Betula pubescens), silver birch (Betula pendula), Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and other deciduous species: (e.g. Salix sp., Sorbus aucuparia), by seeding from nearby forests were measured 18–22 years later. The amount of naturally established trees exceeded the number of living planted trees in all five areas. Next to downy birch, Scots pine was the most common naturally established species. Large variations in both amount and height of natural establishment were found along the climatic gradient. Planted trees were taller than naturally established trees, except for the northernmost area. Number and height of naturally established trees correlated positively to closeness to nearest forest and to nearest ditch. These trees also responded positively to PK fertilization in the three southernmost areas. In the two northernmost areas no such response was found. It was concluded that natural seeding from neighbouring forests can be counted on and recommended in afforestation of low-productive peatlands in Sweden, provided that downy birch is accepted as a dominant tree species.

Erratum: Growth and nitrogen utilization in seedlings of mountain birch (Betula pubescens ssp. tortuosa) as affected by ultraviolet radiation (UV-A and UV-B) under laboratory and outdoor conditions. In: Trees (1998) 12:201–207 by Martin Weih, Ulf Johanson, Dylan Gwynn-Jones

Erratum: Growth and nitrogen utilization in seedlings of mountain birch (Betula pubescens ssp. tortuosa) as affected by ultraviolet radiation (UV-A and UV-B) under laboratory and outdoor conditions. In: Trees (1998) 12:201–207 by Martin Weih, Ulf Johanson, Dylan Gwynn-Jones

Cyclic Population Fluctuations of Herbivores as an Effect of Cyclic Seed Cropping of Plants: The Mast Depression Hypothesis

Three sets of time series on plant seed production and herbivore number were analysed in order to test the proposed mast depression hypothesis, which states that cyclic population fluctuations of herbivores is a result of cyclic seed cropping of plants, because high seed crops, termed masts, are produced at the expense of chemical defence against herbivores. From 1880 to 1916, the annual export of small game, mainly willow grouse Lagopus lagopus, from Oslo was positively correlated with the quantity of berries, mainly bilberry Vaccinium myrtillus and cowberry V. ritis-Idaea, exported in the previous year. In vegarshei, South Norway, the intervals between years of high access of bilberry and cow-berry varied from 3 to 5 yr during 1952 95. All mast years were followed by a year of high microtine population. In South Norway, mast years of Norway spruce Picea abies, which usually shows high flowering intensity in the same years as mountain birch Betula pubescens, occurred with a mean interval of 9.8 yr (range 7 13 yr) during 1930-85. Almost all attacks of autumnal moth Epirrita autumnata on mountain birch were reported after a mast year of forest trees. The synchronised flowering cycles of plants indicate that high seed crops are induced by some climatic conditions. Allocating a large proportion of available resources, including chemical defence compounds, to seed production in some years of advantageous conditions may improve a plant's total life-time reproduction, despite the subsequent risk of serious damage by herbivores.

Growth and nitrogen utilization in seedlings of mountain birch (Betula pubescens ssp. tortuosa) as related to plant nitrogen status and temperature: A two-year study

:Patterns of growth and nitrogen utilization in seedlings of mountain birch (Betula pubescens ssp. tortuosa) were monitored by growth analysis over two growing seasons in Abisko, northern Sweden. The seedlings were grown in pots with peat, which were placed outdoors under a clear roof (natural light and temperature) or in a greenhouse (natural light and increased temperature). The plants were exposed to two nutrient (1 and 10 g nitrogen m-2 season-1) and two temperature regimes (ambient and ca 2.5°C above ambient) in a factorial design. The climatic conditions were rather different during the two years of the study, which clearly affected the growth and nitrogen economy of the birch seedlings. Nutrient supply was the main growth-limiting factor during 1992, which resulted in high root growth and a high leaf area per unit plant biomass (leaf area ratio). In contrast, during 1993 temperature was the main growth-limiting factor, which resulted in high leaf growth and a high biomass production per unit leaf area (leaf area productivity). Relative growth rate was affected by temperature early in the season (early to late June), and by plant nitrogen concentration during mid-season (late June to mid August). There were indications of substantial nutrient uptake by the birch seedlings during the winter season (September to May). The inter-annual variations in growth and nitrogen economy are interpreted as consequences of physiological adjustments to the different climatic conditions during the two growing seasons studied. The role of phenotypic plasticity in determining plant performance in a fluctuating environment is discussed, particularly in relation to the variable environmental conditions typical of the natural range of the mountain birch in subarctic Fennoscandia.

Feeding by vertebrate herbivores in a chemically heterogeneous environment

:We have studied the constraints that food quality imposes on feeding decisions in three free-ranging herbivores feeding on winter twigs of the mountain birch (Betula pubescens ssp. tortuosa) in the Abisko Mountains (Sweden). Comparison was made between two sites, one at the treeline (600 m above sea level) and the other in a birch wood (380 m above sea level). The concentrations of secondary compounds (phenols) and N varied with respect to twig diameter, among individual trees and between sites, higher phenol and N concentrations recorded at the treeline site and in thinner twigs. Faeces and urine of the mountain hare (Lepus timidus) and faeces of the willow grouse (Lagopus lagopus) showed the same site difference in phenol and N concentrations as found in the birch, with higher concentrations at the treeline. Faeces of the moose (Alces alces) did not show such a pattern. We discuss these differences in relation to size of eaten twigs, digestive strategies, and mobility of the species studied. According to our data, spatial variation in quality might be of greater importance than variation in quantity for small herbivores such as the willow grouse and mountain hare, whereas larger animals such as the moose may be less responsive to variation in quality.

Within-tree variability of mountain birch leaves causes variation in performance for Epirrita autumnata larvae

Within-tree variability in leaf characteristics of the mountain birch (Betula pubescens ssp. tortuosa) was bioassayed for the autumnal moth (Epirrita autumnata) by rearing larvae on birch leaves in a laboratory and measuring their growth, consumption rate, approximate digestibility, efficiency of conversion of ingested food and efficiency of conversion of digested food. Only short shoot leaves, i.e. leaves of the same age, were used. The highest hierarchical level, which included trees and ramets within trees, accounted for most of the total variance in almost all the measured traits. Short shoots (within branches) accounted for more of the variance than branches (within trees/ramets) in most of the traits. The results suggest that differences in leaf quality were reflected in larval growth mainly by differences in food utilization efficiencies (postingestive effects) and less by differences in consumption rate (preingestive effects). The observed within-tree variation is probably a consequence of the modular structure, sectoriality and partial functional independence of tree parts.

Spectral Quality and Absorption of Solar Radiation in a Mountain Birch Forest, Abisko, Sweden

Field measurements of the spectral (300-1100 nm) distribution of the incoming and reflected solar radiant energy above and below the canopy of mountain birch (Betula pubescens ssp. tortuosa) carrie ...

Do avian and mammalian nest predators select for different nest dispersion patterns of Fieldfares Turdus pilaris? A 15‐year study

The Fieldfare Turdus pilaris is an open‐nesting passerine that breeds either solitarily or in colonies. The nest‐spacing pattern of this species in a subalpine homogeneous Birch Betula pubescens forest in central Norway (c. 63°N) was studied during the period 1980–1994. Nest‐spacing patterns varied annually, and the number of Fieldfare colonies present (0–6) within a 3.5‐km2 study area was positively correlated with the annual density of small rodents and the birds' fat index and mean clutch size. After the rodent population crashes, prey switching seems to occur among mustelids. The nest‐spacing pattern of Fieldfares in the Birch forest therefore provides indirect support for the alternative prey hypothesis. Since the nest predation rate in Fieldfares is density dependent, and since their use of ejected faeces in communal defence may be detrimental, even lethal, to avian but not mammalian predators, it is suggested that a high density of mustelids results in selection for solitary breeding, whilst a predominance of avian predation risk selects for colonial breeding by the Fieldfare. The physical condition (fat index) of the Fieldfares is apparently a contributing factor in determining their nest dispersion pattern. The proportion of colonial nesting pairs was negatively correlated with the Fieldfare density and indicated a distributional pattern in a patchy habitat in agreement with the ideal free distribution theory.

HPLC isolation and identification of flavonoids from white birch Betula pubescens leaves

Nine flavonoid glycosides were isolated from birch leaves by preparative HPLC and their structures identified by chromatographic (analytical HPLC), chemical (hydrolysis) and spectroscopic (UV, NMR, MS) techniques. Two acylated compounds: myricetin-3-O-α- l -( acetyl)- rhamnopyranoside and quercetin-3-O-α- l -(4″-O- acetyl)- rhamnopyranoside were found in birch leaves for the first time. Flavonoid concentrations were quantified by HPLC.

Bud Demography of the Mountain Birch Betula Pubescens Ssp. Tortuosa Near Tree Line

The aim of this study was (1) to evaluate the importance of dormant buds for the bud demography of the mountain birch Betula pubesecens ssp. tortuosa near the tree line and (2) to study whether sexual reproduction leads to costs for bud production rates. A bud population census was taken in two consecutive years for six branches of each of 90 mountain birch trees. The trees were growing in a common garden and belonged to 10 different progenies originating from different parts of Finnish Lapland. The data were analyzed with matrix population models. The most important transformations of the bud populations were between vegetative short and long shoots. However, if most apparently dead buds are actually latent dormants, they make an even more important contribution to the bud population growth rate than vegetative long and short shoots. Dormant buds may have considerable importance especially after events such as herbivore outbreaks, in which short and long shoots are damaged. Generative long shoots (with male catkins) and short shoots (with female catkins) had approximately the same bud production rate as the corresponding vegetative shoots, i.e., bud populations did not show any major costs due to sexual reproduction. Meristem costs, i.e., a decrease in the number of buds due to sexual reproduction, may be relatively low in mountain birch, because new axillary buds develop and compensate for lost shoot apices. This compensation capacity may be especially well developed under suboptimal conditions, where canopy expansion is limited by the harsh environment rather than by the availability of meristems. The resource cost of reproduction (e.g., in terms of carbon or mineral nutrients) may also be partly compensated especially when flowering intensity is sufficiently low.

Performance of Insect Herbivores on Hybridizing Trees: The Case of the Subarctic Birches

The consequences of hybridization between two related birch species, the mountain and the dwarf birch (Betula pubescens ssp. tortuosa and B. nana), on the performance of insect herbivores were studied in Finnish Lapland. Leaf quality of both arboretum-grown birches and birches of a natural stand was bioassayed with 14 insect species (one geometrid lepidopteran, one argid, one cimbicid, and 11 tenthredinid sawflies). All the herbivore species belonged to the local birch leaf-chewer guild. There were considerable differences among the herbivore species in the relative suitability of the two parent birch species. Larvae of different species grew equally well on the pure mountain birches and on the hybrids, irrespective of the mother tree

Factors affecting severity of deer browsing damage within coppiced woodlands in the south of England

The damaging impact, by browsing, of roe deer Capreolus capreolus and fallow deer Dama dama in coppice regrowth within 53 cut-over blocks in 28 woodlands in East Anglia, Hampshire, and West Sussex is investigated. The major factors shown to be related to the amount of damage inflicted by roe deer were tree species present, size of the coppice block and the quantity of surrounding cover. Hornbeam Carpinus betulus, willow Salix caprea, sweet chestnut Castanea sativa and birch Betula pubescens were the most susceptible to browsing from roe. On sites browsed by fallow deer, levels of damage were highest on sweet chestnut, ash Fraxinus excelsior and lime Tilia cordata. Higher damage levels were associated with a greater density/activity of roe deer as evinced by dung counts; there was no clear relationship within woodlands frequented by fallow. On freshly cut coppice (<1 year), level of damage decreased as overall size of the block increased (p < 0·05); a higher level of damage was sustained in blocks adjacent to cover habitats. Damage by fallow deer, but not by roe, was also affected by the degree of protection offered to individual stools. Only three coppice blocks studied were fenced; this protection proved the single most effective measure in reducing damage. The practical options for reducing damage by manipulating the habitat and coppice management practice are discussed.

Sources of variation in rapidly inducible responses to leaf damage in the mountain birch-insect herbivore system.

Studies on rapidly inducible resistance in trees against insect herbivores show substantial variation in the strength of responses. Here we report the results of a study which examined causes of this variation. We bioassayed the quality of leaves of two developmental phases (young vs. mature) of the mountain birch Betula pubescens ssp. tortuosa by measuring the growth of two instars of Epirrita autumnata larvae. We used only short shoot leaves from trees of a natural stand, uniform in size and age. Damage was caused by larvae and artificial tearing of leaf lamina, varying the scale and time. We separated seasonal changes in plants from instar-dependent effects of the animals by testing experimental larvae in two subsequent growth trials. We found that only larval-made damage induced responses in leaves that made the leaves significantly poorer quality for the test larvae. Artificial damage induced only weak responses, and artificial canopy-wide damage even caused slight improvement of leaf quality. Cumulative leaf damage did not strengthen birch responses. Leaves that were in the expansion phase responded to damage while fully-expanded, mature leaves showed no response. The pattern of responses indicated that there might be physiological constraints: small-scale damage induced resistance against the larvae but largescale damage did not. Prevalent weather conditions might have modified these responses. Larvae of two instars and sexes, of low- and high-density populations responded to leaf damage similarly. However, prior experience of larvae with the host plant may have affected subsequent larval performance. Variation in rapidly inducible responses in birches was caused by plant characters rather than by test animals.

Orbital Forcing and Tree-Limit History: Hypothesis and Preliminary Interpretation of Evidence from Swedish Lappland

The Holocene tree-limit history for an area in Swedish Lappland is analysed from a new set of 67 14C-dated subfossil wood remains. The species involved are Scots pine ( Pinus sylvestris), mountain birch ( Betula pubescens ssp. tortuosa) and grey alder ( Alnus incana). The highest tree-limit was established about 8000 BP by pine. Up to the present it has retreated c. 200 m in altitude at a constant rate of c. 25 m per millennium. A subalpine belt of birch above the pine forest, initially with admixture of alder, developed rapidly after 6000 BP, when birch started to invade the former pine areas and even extended higher. Birch grew at these high elevations until c. 4000 BP, although not necessarily without interruption. After 4000 BP birch also seems to have declined in elevation, although the magnitude is unknown. The steady pine tree-limit recession and the replacement of pine by birch may reflect continuous cooling and change of thermal seasonality. The present results corroborate the general hypothesis that predictable changes in the earth-sun geometry basically force climatic development, and indirectly vegetation history, during an interglacial.

Intraspecific Variation in Photosynthetic Light Response and Photosynthetic Nitrogen Utilization in the Mountain Birch, Betula pubescens ssp. tortuosa

Variation among individuals and sites in photosynthetic light-response characteristics and nitrogen use efficiency in the mountain birch (Betula pubescens ssp. tortuosa) is described and related to leaf nitrogen status. Significant differences among both individuals and sites were found for light-saturated photosynthetic rate (P max ) and leaf nitrogen concentration. P max was correlated with leaf nitrogen concentration. No such relationship was found for quantum yield efficiency or the convexity of the light response curve. The maximum photosynthetic rate and the daily amount of CO 2 assimilated increase with increasing leaf nitrogen content. Both instantaneous and daily photosynthetic production per unit leaf nitrogen decrease with increasing leaf nitrogen content. The daily assimilation per unit leaf nitrogen lost through leaf abscission was inversely related to the proportion leaf nitrogen lost at leaf abscission

Establishment of ectomycorrhizas in aseptic culture: effects of glucose, nitrogen and phosphorus in relation to successions

Birch ( Betula pubescens ) seedlings were grown aseptically on agar slants with variations in available glucose, nitrogen or phosphorus and inoculated with Lactarius pubescens, Tricholoma fulvum and Amanita muscaria (late-stage fungi in mycorrhizal successions) or Laccaria proxima and Hebeloma crustuliniforme (early stage fungi). Hyphal extension rates were assessed on plates of the same media. Mycorrhiza formation by late stage fungi was suppressed more than by early stage fungi at low P levels, but all were markedly suppressed by low nitrogen. With adequate mineral nutrients, early stage fungi formed mycorrhizas at low (0 or 0·01%) and moderate (0·1%) glucose levels, whereas four out of five late stage isolates required moderate (0·1%) or high (1·0%) glucose for mycorrhizal development. Sustained colony extension by early stage fungi occurred in the absence of glucose, whereas all late stage fungi required high glucose levels for continued extension. The differences in glucose- and P-dependence between early and late-stage fungi are discussed in relation to mycorrhizal successions.

Effects of leaf duration, nutrient supply, and temperature on the seasonal pattern of growth and nitrogen uptake in tree seedlings in a subarctic environment

The seasonal dynamics of growth and nitrogen uptake were measured in pine (Pinus sylvestris) and birch (Betula pubescens ssp. tortuosa) seedlings growing in a subarctic environment. Whole-plant dry matter accumulated at about the same rate in both species. A higher rate of early summer assimilation did occur in Pinus as revealed by the simultaneous increase in fine-root weight per unit length and leaf weight per unit area. Fine-root elongation and nitrogen uptake in Pinus preceded that in Betula. Seasonal variations in unit leaf rate and relative growth rate correlated with the prevailing temperature conditions. Pinus did not differ in phenology of growth with changes in nutrient supply while the growth and duration of foliage for Betula increased with increasing nutrient supply. Foliage growth in Pinus increased during spring but not in autumn. The temperature conditions during the growth period was important for determining the seasonal production of foliage in Betula.

Nutrition and Reproduction of the Willow Grouse Lagopus lagopus in Central Sweden

In a 6 yr study of Willow Grouse diet, Vaccinium species dominated crop contents in autumn, together with Eriophorum species in spring. During winter, a diet dominated by shoots and catkins from mountain birch Betula pubescens var. tortuosa was eaten. In vitro digestibility, protein and ash levels of crop contents were 24-34% lower, while fibre content was 20% higher in winter than in the other seasons. Marked annual variation in the yield of mountain birch shoots and catkins were registered. The yield of shoots showed a gradual 4-yr increase followed by a marked decline in the following year. The percentage of different birch parts in late winter crop contents, and their chemical composition, varied significantly between years. Annual variation in winter diet composition as well as the fat level of grouse were to a large extent related to food abundance. Multiple regression equations showed that 92-96% of the observed variability in grouse fat levels was accounted for by the yield of mountain birch shoots and catkins. In spring, large annual variation in species composition of the food was related to variation in the in vitro digestibility. This food quality parameter was positively correlated with the size of the fat reserves of breeding females, which in turn was related to breeding success, indicating that maternal nutrition affects Willow Grouse reproduction. However, the two worst grouse breeding years were associated with declines in the populations of small mammals, so that predator switching may have contributed to the low grouse reproductive success. On the other hand, nutrition alone may have been responsible for the synchrony.

Winter diet, habitat selection and fluctuation of a mountain hare Lepus timidus population in Finnish Forest Lapland

Composition of the winter diet, habitat selection and population fluctuations in the mountain hare Lepus timidus were studied in the Värriötunturi fell area, Eastern Finnish Forest Lapland, during the winters 1968/69–1984/85. The three population lows recorded during this 17‐year period followed each other at intervals of 4 and 8 years. During the lows the hares occurred only in the most favoured (forest‐covered) habitats and in two of them they behaved according to the concept of the refuge theory. The mountain birch Betula pubescens ssp. tortuosa appeared to be the most important, but not the most favoured winter food item. When the population crashed, the proportion of birch in the diet decreased, and was replaced especially by juniper which is one of the secondary food items (and is for this reason often discarded although cut). It is suggested that the quality and/or quantity of the winter food (i.e. winter pastures) are one of the driving forces in the population fluctuation of the mountain hare in this area.

Interactions Between a Generalist Herbivore, the Moose Alces alces, and its Food Resources: An Experimental Study of Winter Foraging Behaviour in Relation to Browse Availability

SUMMARY (1) The browsing behaviour of free-ranging moose Alces alces in winter was evaluated by experimentally altering the availability of their most important food resource, the birch Betula pubescens. Plots of birch saplings (2-5-3-5 m high and about 15 years old) were artificially made at ten different densities in early winter. The browsing behaviour was studied by following the moose tracks in the snow during mid-winter. Intake, measured as dry weight per sapling, was estimated from the number of bites per sapling and bite diameter. (2) The moose responded to these small-scale variations in the available food supply. At high densities of birch saplings, the moose ate less on each sapling, selected twigs of better quality and browsed on more saplings per plot. However, the high-density plots were not visited more frequently than the low-density plots. Instead the moose moved longer distances in the high-density plots and probably spent more time there. (3) The proportion of the available browse exploited decreased curvilinearly as food availability increased. Thus, the exploitation of browse was strongly determined by its spatial distribution. (4) It is suggested that factors that influence the spatial organization of plants may also affect both their potential as food supply for herbivores and the type of anti-herbivores strategy which the plant is likely to evolve.