Birch Populations Research Articles

The influence of hybridization on epidermal properties of birch species and the consequences for palaeoclimatic interpretations

The Fennoscandian birch population primarily consists of Betula nana, B. pendula and B. pubescens ssp. czerepanovii, the Mountain birch. Frequent hybridization between the Mountain birch and B. nana generates a wide range of genotypic and phenotypic plasticity in the subarctic birch zone of Fennoscandia. Phases of subarctic conditions prevailed during the Late Glacial in large parts of NW Europe, and palynological as well as macrofossil analysis provide some evidence for the occurrence of birch hybrids during these intervals. Leaves from genetically controlled specimens of Betula pendula, B. pubescensssp. czerepanovii, B. nanaand the hybrids B. pubescensssp. czerepanovii nana and B. nana pubescens ssp. czerepanovii are investigated for their specific characteristics of the epidermis morphology. Frequency and size of epidermal cells and stomata reveal a close affinity of both hybrids to B. nana and allow a differentiation of the intermediate forms between B. nana and the Mountain birch. With respect to palaeoatmospheric CO2 reconstructions based on stomatal index, epidermal analysis shows that a possible occurrence of hybrids in fossil leaf assemblages has no profound consequences for combined species records. However, the significant differences observed in B. nana demand the separation of this species. A comparison of the cuticle properties of B. pendula and B. pubescensfrom Finnish Lapland and leaf material from The Netherlands reveals a divergence of the stomatal index that may be due to differences in day light length.

DYNAMICS IN LATE-SUCCESSIONAL HEMLOCK–HARDWOOD FORESTS OVER THREE DECADES

Permanent plots in old-growth hemlock-northern hardwood forests of Mich- igan's upper peninsula have been remeasured over periods of 16-32 yr. A gradient from hemlock (Tsuga canadensis) to sugar maple (Acer saccharum) dominance is associated with increasing soil pH and calcium. Secondary species include yellow birch (Betula al- leghaniensis) and basswood (Tilia americana). From 1962 to 1994 hemlock increased in basal area and dominance in most plots. Sugar maple showed little overall change, while basswood and especially yellow birch showed sporadic but often large declines in basal area. Birch populations declined due to lack of recruitment, and sugar maple and basswood may be subject to similar decline; only hemlock showed a fairly stable size structure. Mortality rates were lowest for hemlock (0.3%/yr) and highest for yellow birch (1.6%/yr), corresponding to canopy residence times of 357 and 61 yr, respectively. Stem maps allowed assessment of neighborhood influences on growth and mortality. Growth and mortality rates were negatively correlated for all species. Growth rate was influenced by tree size and site conditions for all species, but hemlock and sugar maple growth rates were also affected by size- and distance-weighted indices of neighbor influence. Old-growth stands several centuries old continue to undergo compositional change related to both stand history and current population interactions. Yellow birch and basswood are probably maintained by significant disturbances and will decline under a disturbance regime of small gaps. Hemlock may be the ultimate competitive dominant in most sites but may require well over a mil- lennium without major disturbance to displace sugar maple.

The spread of gray birch (Betula populifolia) in eastern Quebec: landscape and historical considerations

The understanding of recent changes of the spatial distribution of tree species occurring in agricultural landscapes is essential to realistically predict future positions of the range limit of tree species. In Quebec (Canada), it has recently been suggested that gray birch (Betula populifolia Marsh.) is spreading rapidly eastward. We tested the hypothesis that this tree migration is strongly facilitated by human activities. Herbarium specimens, historical landscape reconstructions, botanical surveys in mined peatlands and old fields, and dendrochronological data were used to reconstruct past and recent distribution limits of gray birch in the study area (Bas-Saint-Laurent region). Gray birch has been present in the Bas-Saint-Laurent region since at least 1945. However, herbarium specimens and botanical surveys indicate that gray birch individuals were scarce before 1970. The introduction of gray birch in the Bas-Saint-Laurent region seems to be associated with peat mining activities. All mined peatlands located between Rivière-Ouelle and Isle-Verte were colonized by gray birch, but only 11% of old fields surveyed contained at least one gray birch individual. This suggests that the spread of an early successional tree species in an agricultural landscape is facilitated more by the presence of a few large patches favorable to the growth of the species (mined peatlands) than by numerous small patches (old fields). The recent expansion of gray birch populations in the Bas-Saint-Laurent region could be a major concern for peat mining companies because massive invasions of gray birch in abandoned mined bogs may impede successful restoration of these ecosystems.Key words: Betula populifolia, gray birch, Quebec, peatland, old field, landscape ecology.

Photosynthesis, water and nitrogen use efficiencies of four paper birch ( Betula papyrifera) populations grown under different soil moisture and nutrient regimes

A greenhouse experiment was conducted to determine how four populations of paper birch ( Betula papyrifera Marsh.), adapted to particular temperature, water and photoperiod regimes responded physiologically to different soil water and nutrient regimes. Seedlings of each of the four populations (Eaglet, LeeCreek, Porcupine and Skeena) from British Columbia were planted in pots and subjected to high and low water and nitrogen regimes for 4 months. Net photosynthesis ( A), stomatal conductance ( g s), water use efficiency (WUE) and nitrogen use efficiency (NUE) were measured and compared among treatments. Trade-offs between WUE and NUE were examined. Soil moisture was the major factor affecting A for all the populations. All populations showed relatively high A in the high-water and high-nitrogen (HWHN) treatment, ranging from 8.5 to 9.9 μmol CO 2 m −2 s −1. Photosynthesis of trees in the low-water and high-nitrogen (LWHN) treatment was about 45% of that in the HWHN treatment. There was a linear increase in A as g s increased in all populations. A decreased with increasing vapor pressure deficit (VPD). The populations demonstrated significantly different relationships between A and g s, and VPD, with the LeeCreek population being the most conservative. This may provide a physiological basis for provenance selection and seed transfer. Eaglet and LeeCreek populations had lower WUE at the same level of NUE compared with Porcupine and Skeena populations. Porcupine and Skeena populations may be more suitable for moist sites due to their greater capacity to sequester water quickly, while the LeeCreek and Eaglet populations may be more suitable for drier interior sites where long drought periods can occur.

Pathophysiology of birch populations affected by aerial emission

Pathophysiology of birch populations affected by aerial emission

Isolation of Nectria galligena from Cankers on Sweet Birch.

The fungus Nectria galligena infects many species of hardwood trees, causing "perennial canker," "European canker," or "target canker." Cultures from ascospores produced in stromata on the cankers have confirmed the pathogen species, but the fungus has rarely been successfully isolated from inside the cankers. Concern for the sweet birch trees affected by this disease in Connecticut prompted us to try isolations, using a method successful in isolating chestnut tree pathogens. Small pieces of cankered bark were stabbed into Granny Smith apples and, after incubation in boxes in the laboratory, pure cultures of N. galligena were easily removed as the pathogen slowly grew out, unchallenged, into the tissue of the apples. This technique will now be used to sample the N. galligena population in the birch populations being studied.

Productivity of mixed stands of Norway spruce and birch affected by population dynamics: a model analysis

Bolewood volume accumulation patterns and levels of mixed Norway spruce and birch forests in Estonia based on modelled population dynamics are discussed in this paper. Trees were divided into separate populations according to species and canopy class. Diameter growth was estimated from increment cores in ten 0.1 ha-sample plots to provide the growth component of the population model. Multiple regression was used to estimate the effect of tree attributes and stand composition on the individual tree diameter growth. The stand growth in the present model is described by modelling the growth of a mean tree of the population. Since birch has a greater diameter growth than spruce, stand productivity should increase when the birch proportion is greater. However, this conclusion is true only in middle-aged stands because more birch in a stand inhibits the diameter growth of both species. These two components (greater birch increment and growth inhibition by birch) have been quantified and the dependence of growth patterns on these factors is investigated. Trials with a simulation model demonstrate the increase in stand productivity accompanying birch population decline. Decreasing birch percentage occurs naturally in the course of secondary forest succession in Estonia.

Anomalies in the distribution of silver birch (Betula pendulaRoth) populations in Scotland

Summary Populations of silver birch are less frequent in western areas of the western and northern Highlands, and in much of southern Scotland, than is recognized in standard ecological texts. Over large areas the species appears to be virtually absent. There appears to have been over-recording of silver birch in botanical surveys, maybe largely as a result of downy birch being mis-identified as silver birch. The lack of silver birch on the west coast of the Highlands raises the question of its native status there. However, its scarcity is considered to be the result of a combination of ecological and landuse factors including: its requirement for freely draining soil; its inability to persist in refuges in heavily farmed landscapes, e.g. on bogs or as a woodland understorey; difficulties in recolonizing many types of grass sward compared with larger seeded tree species; insufficient large scale disturbance in the landscape; its relatively short life span. Until further information becomes available, plan...

Relative growth rate and biomass allocation of paper birch (Betula papyrifera) populations under different soil moisture and nutrient regimes

Seedlings of four geographically diverse paper birch (Betula papyrifera Marsh.) populations native to British Columbia were grown under low and high levels of water and nitrogen in a greenhouse for 3 months to examine the relative sensitivity of each population to water and nutrient availability. Nine sequential measurements on height and basal diameter growth were made, and then the seedlings were harvested for final biomass measurements. Under optimal conditions the highest elevation population ceased height growth, while the low-elevation coastal population continued to increase in height under all treatment conditions. Plants of all populations grown under high N conditions grew faster and had larger total biomass and lower root/shoot ratios than plants grown under low N conditions. Relative growth rate was significantly correlated with shoot and foliage biomass, leaf area, and root weight ratio. All populations generally responded more to low N level than to low moisture level in terms of height growth, relative growth rate, total biomass, and root/shoot ratio. This suggests that the populations observed in this study are better adapted to drought than poor soil nutrient availability. Therefore, consideration of site quality, which includes soil moisture regime and soil nutrient regime, should be a primary concern when allocating birch seed lots in a planting program.

Relative growth rate and biomass allocation of paper birch (<i>Betula papyrifera</i>) populations under different soil moisture and nutrient regimes

Relative growth rate and biomass allocation of paper birch (<i>Betula papyrifera</i>) populations under different soil moisture and nutrient regimes

The Holocene history of Betula at Lake lilompolo, Inari Lapland, northeastern Finland

Betula pollen diameters were systematically measured in a series of Holocene sediment samples from a lake in the northern birch-forest region of eastern Finnish Lapland. The resulting size-frequency distributions were analysed statistically to infer the species identity of the birch populations and to reconstruct the local history of birch. Macrofossil analysis of birch fruits and catkin scales were used as supplementary evidence. The pollen record was also used to reconstruct the forest history. Pinus arrived in the area c. 7500-8000 BP. From 7000 to 4000 BP the surroundings of the lake were probably covered with pine forest where tree birch was also present. Between c. 3700 and 2500 BP the birch pollen size-frequency distribution diagram shows a distinct phase of larger grains with a size range larger than in the other samples. This period coincides with the retreat of pine and is interpreted as reflecting extensive hybridization amongst the birch species and the first appearance of mountain birch (Betula pubecens ssp. tortuosa) in an environment where climatic conditions were becoming more rigorous.

Growth responses and related biochemical and ultrastructural changes of the photosynthetic apparatus in birch (Betula pendula) saplings exposed to low concentrations of ozone

Saplings of ozone-sensitive and ozone-tolerant birch (Betula pendula Roth.), clones B and C, respectively, were exposed to ozone concentrations that were 1.7-fold higher than ambient for one growing season under open-field conditions. Ambient air was used as the control treatment. In the ozone-sensitive clone B, there was an initial stimulation of leaf area growth in response to the ozone treatment, but further ozone exposure caused reductions in leaf and stem biomass growth, Rubisco and chlorophyll a contents, net photosynthesis, water use efficiency and chloroplast size. It also caused an alteration in chloroplast shape and injury to thylakoid membranes. In the ozone-tolerant clone C, ozone fumigation did not affect growth rate, and there were no consistent changes in chlorophyll content, photosynthesis or water use efficiency. There were also fewer ultrastructural abnormalities in the chloroplasts of clone C than of clone B. Based on the observed biochemical, physiological and structural changes in chloroplasts of clone B in response to low concentrations of ozone, we conclude that the increasing concentration of tropospheric ozone represents a risk to natural birch populations.

Late Quaternary Pollen Record from Cheyenne Bottoms, Kansas

A sediment and pollen record from Cheyenne Bottoms, a large (166 km 2) enclosed basin in central Kansas, provides evidence for local and regional vegetation and climate change during the late Quaternary (ca. 30,000 yr.). Although radiocarbon dating of the carbonate-rich lacustrine sediments remains problematic, a basic chronological framework for the section is established. Two major litho- and biostratigraphic units, a Farmdalian zone (ca. 30,000 to 24,000 yr B.P.) and a Holocene zone (ca. 11,000 yr B.P. to present), are separated by a major unconformity spanning the Woodfordian (ca. 24,000 to 11,000 yr B.P.). Pollen and sedimentary data indicate a period of basin-wide drying preceding this unconformity. The sustained absence of sediment accumulation within this playa-like basin suggests that early Woodfordian conditions were increasingly arid with strengthened surface winds. Before this, persistent shallow water marshland dominated the local basin-bottom vegetation. Regional upland vegetation was an open grassland-sage steppe throughout the Farmdalian with limited populations of spruce, juniper, aspen, birch, and boxelder in riparian settings and escarpments. Throughout the Holocene, water levels within the basin fluctuated. Changes in wetland vegetation resulting from water level fluctuation have increased during the last 3,000 yr indicating that periodic episodes of wetland loss and rebound are not unique to postsettlement conditions but are an ongoing phenomenon at Cheyenne Bottoms.

Growth and stomatal responses of birch (Betula pendula Roth.) clones to ozone in open-air and chamber fumigations.

It is evident that even outside the classical high ozone areas some plant species are at risk. In this study seedlings of five birch clones (Betula pendula Roth.) were exposed to a slightly elevated ozone level in an open-field experiment over two growing seasons. The ozone doses were 1.2 × (1991) and 15 × (1992) higher than the ambient. The clones were also fumigated with 150 nl I1 ozone for 24 d (12 h d-1 ) in a chamber experiment. They were found to differ in their susceptibility to ozone: ozone fumigation decreased the height growth and leaf biomass, and increased the amount of advanced visible injury in leaves of the most sensitive clone, but did not affect the height growth or amount of visible injury of the most tolerant clone. The other three clones were intermediate with respect to their sensitivity to ozone. In all clones, elevated O3 concentrations increased diffusive resistance to water vapour but increased the stomatal density in the emerging leaves. The appearance of autumn colouring was accelerated in the field experiments. The results support the conclusion that birch populations in Finland can be negatively affected by ozone. The effect is most likely in sensitive birch individuals during ozone episodes.

Genetic Variation in the Date of Budburst in Scottish Birch Populations: Implications for Climate Change

To estimate the heritability of budburst, seedlings from up to 10 birch trees at each of 10 sites in Scotland (seven of Betula pubescens Ehrh. and three of B. pendula Roth) were grown together in a randomized field experiment near Penicuik, Scotland (550 51'N, 198m). Using a nine-stage scale, budburst and leaf elongation were assessed in late April 1984 and 1986. Heritability of budburst varied from 0 00 to 0 65. The potential for dates of budburst to evolve within birch populations in response to climatic warming depends on the amount of additive genetic variation and on the rate at which the environment is changing. The selection differentials needed for populations to change in response to climatic warming of 2 0C over a period of 60 years show that, even in the most genetically variable populations, the rate of change in temperature (assuming an increase in mean annual temperature of 0 70C every 20 years) is too rapid for native populations to evolve in the absence of gene flow from birch populations with earlier dates of budburst. Key-words: Betula pubescens, B. pendula, budburst, climate change, heritability

Hybridization, introgression and taxonomy of the Mountain birch in SW Greenland compared with related results from Iceland and Finnish Lapland

Samples from birch populations were collected in Qingua-dalen and Narssarssuaq during the excursion of SBP (the Subarctic Birch Project) to SW Greenland 1984. In Qingua-dalen, where the environmental conditions are more favourable, the stems of the Mountain birch (Betula pubescens ssp. tortuosa) are taller and thicker and the leaf size is larger than in populations at Narssarssuaq. Intermediate forms – probably introgressions - between B. pubescens and B. glandulosa were found in both populations.
 According to cytological investigations of Qingua-dalen populations, the putative hybrids between B. glandulosa (2n = 28) and B. pubescens (2n = 56) were found to be triploids (2n = 42). Seeds collected from hybrids did not germinate but the germination of the Mountain birch was also extremely low in 1984. In the same year, B. glandulosa produced abundantly seeds with high germination percentage. Germination experiments with seeds collected in 1982 and 1985 indicated that under climatically favourable conditions Mountain birch produces viable seeds. Reproduction through vegetative means was found to be strong in all birch taxa.
 Considerable differences have been found between the provenances of birches from SW Greenland and Finland in cultivation experiments carried out since 1976 in South and North Finland. The clones of B. pubescens and B. glandulosa, originating from Kangerdluarssuk , mature very late in autumn and the shoots above snow level were badly frostdamaged during the winter. This was particularly noticeable for B.
 pubescens in test fields in Lapland. The plants have survived, however, by means of re-suckering and started flowering at an early stage producing viable seeds. Probably no reproductive barriers between birches of the two geographically isolated areas, SW Greenland and Finland, have developed.

Disturbance regime of a cold temperate forest as deduced from tree-ring patterns: the Tantaré Ecological Reserve, Quebec

The recent history and disturbance regime of an old-growth sugar maple – yellow birch forest located in the Tantaré Ecological Reserve, Québec, were determined using tree-ring growth patterns of individual trees that had undergone suppression and release. Within a sampling quadrat (0.25 ha) where all living and dead trees were mapped, the age, size, and spatial pattern of gaps formed since the mid-19th century were inferred from tree-ring signatures of standing trees. From 1860 onwards, more than 30 gaps of various form and size occurred, most gaps being < 200 m2 and covering a total area of 3775 m2. During the 1930–1985 period, the tree-fall frequency was 0.45 per year, the tree fall free interval was 3.2 years, and the tree-fall rotation period (turnover rate) was estimated to be 45 years. The rather short life-span of most trees (<125 years) may be attributed to the cool and humid conditions prevailing at the site, which stimulated self-pruning of mature trees. The spatiotemporal development of the sugar maple forest has been active during the past 2 centuries through small-scale disturbances associated with successve, often overlapping, single and multiple tree falls. This situation explains the uneven age distribution of sugar maple and yellow birch populations subjected to differential survival conditions caused by gap dynamics. It is concluded that tree-ring patterns corresponding to periods of suppression and release will likely give a finer resolution record of gap dynamics than other methods of determining natural disturbance regime and reconstruction of recent stand history.

Recent Retrogression of the Forest-Alpine Tundra Ecotone (Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) in the Scandes Mountains, Sweden

Demography of mountain birch (Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) was studied in permanent plots (1972/73-85/86), in the forest- alpine tundra ecotone of the Swedish Scandes Mountains. The censused tree population, which to a large extent became established in response to the climatic warming c. 1915-50, declined in certain respects during the study period. A sympathetic cooling trend for the summers, and a few years with relatively severe and protracted snowpack influences were recorded for the study area. The number of tree-sized birches decreased by c. 16%, while sexual regeneration failed and many individuals declined in vigour. The major cause of mortality and vigour decline was mechanical stress, imposed by delayed snowmelt, possibly in combination with age-related mechanical weakening. A measure of tree-line inertia in relation to climatic variability was obtained by extrapolating the demographic trend of the study period indefinitely. Given the same degree of thermal change, extinction of the birch tree-line population needs much more time than establishing it.

Intraspecific variation in nitrogen status and photosynthetic capacity within mountain birch populations

The relative variation in leaf nitrogen concentration and photosynthetic capacity among individuals and sites are compared for mountain birch populations (Betula pubsecens Ehrh. ssp tortuosa (Ledeb.) Nyman).Leaf nitrogen concentration and photosynthetic capacity showed significant differences among individuals; 35 and 26% of the total sum of squares respectively, was attributable to differences among individuals. Two measures of leaf morphology also showed differences among individuals (35–58% of total variation). The variation attributable to site differences ranged from 13% (leaf shape, P = 0.11) to 36% (leaf N concentration and photosynthetic capacity, P≤0.01). Of the variation in photosynthetic capacity, 51% was related to leaf nitrogen concentration. Possible causes for and consequences of the differences found are discussed.

Cherry leaf roll virus in the female gametophyte and seed of birch and its relevance to vertical virus transmission

SUMMARYELISA detected cherry leaf roll virus (CLRV) in infected birch leaf sap diluted 1/320 in buffer, in extracts of one infected leaf with nine healthy leaves and in leaf sap frozen for 2 wk. Similarly, ELISA detected CLRV in mixtures of one infected bud with four virus‐free buds. Intensive bioassays and ELISA showed that in some trees CLRV was restricted to only a few branches whereas in others it occurred throughout the tree. The prevalence of CLRV in unmanaged birch populations in Britain was less (3%) than in Midlands street trees (17%).In CLRV‐free birch trees that received pollen from infected ones, ELISA indicated that antigen was introduced into, and multiplied within, the embryos but not the seed coat or the pericarp/wings. In one instance, antigen was detected in a branch of an experimentally pollinated tree but not in those parts of the crown that had been exposed to open pollination. The proportion of seed germinating after crosses in which both parents were CLRV‐free was greater than when either or both parents were infected but the largest difference occurred with infection in the female parent. Few embryos seemed to escape invasion with CLRV when the maternal tissue was naturally infected. Overall, seed transmission ranged between 0 and 38% (mean 17%) when only females in a cross were infected, and between 11 and 75% (mean 30%) when only the males were infected. Assuming no selective advantage that would help infected plants to achieve reproductive age, we found that CLRV would be lost from a birch population within two generations if transmitted only through seed.Embryos in seeds from CLRV‐infected birch that received CLRV‐free pollen differed from their healthy counterparts in being shrunken and suspended in a loosely fibrillar matrix that contained numerous virus‐like particles in tubular inclusions. In two trees, CLRV‐free pollen tended to fertilise a greater percentage of ovules than did CLRV‐infected pollen. Seedlings derived from infected seed and cuttings from naturally‐infected trees grew less rapidly than their healthy counterparts.In still air, most birch pollen liberated from a height of 3·5 m fell within 3 m of the drop zone and none was detected 10 m from the source. Field observations on the patterns of virus spread as measured by seedling infection were consistent; about 3% of seedlings from a tree 6·9 m away from the nearest source of inoculum were infected but no infected seedlings were detected in more distant trees, even though each was experimentally infectible with CLRV and pollen from the infected tree germinated on their stigmas.