Dendrochronological analysis of the growth and growth-climate relationships of conifers in the region of alkaline dust deposition

Relationships between climate and radial growth of Oxalis-Myrtillus-site type Norway spruce and Scots pine stands under different cement dust loads were investigated. Dendrochronological methods were used. Long-term alkaline (pH 13.2-12.7) dust pollution emitted over 40 years from a cement plant was the reason of alkalisation (pH 7.8-8.1) and high concentrations of K, Ca and Mg in soil of affected territories. Two study sites, Kunda and Malla (2.5 and 5.0 km E from the emission source), were influenced by the dust emissions of the cement plant. Two other study sites, Eru (38 km W) and Revoja (34 km W), were situated on a relatively unpolluted area and served as control sites. The relationships between the radial growth and climate were almost similar on the control and dust-polluted sites. The climatic variables that had a significant effect on the radial growth of Norway spruce at both control and polluted sites were the temperature and precipitation of summer months of the current and preceding years. Specific to the Scots pine stands growing under dust pollution was a significant positive impact of the current spring temperature on the radial growth. A positive effect of precipitation during winter months on the radial growth was found at all sites. A significant negative effect of cement dust on the radial growth of Scots pine stands during the period of large amounts of dust emission (1966-1991) was detected. The effect of cement dust emissions on the radial growth of Norway spruce stands was also negative but weak. The decrease in the dust emissions since 1992 improved the growth conditions at pine stand sites.     

Growth responses of three coexisting conifer species to climate across wide geographic and climate ranges in Yukon and British Columbia

This work aimed to compare radial growth–climate relationships among three coexisting coniferous tree species across a wide geographic and climate range from southern British Columbia (BC) to central Yukon, Canada. Tree-ring data were collected from 20 mature stands of white spruce (Picea glauca), lodgepole pine (Pinus contorta var. latifolia), and subalpine fir (Abies lasiocarpa). Linear relationships between annual growth variation and monthly and seasonal climate were quantified with correlation and regression analyses, and variation in climate–growth responses over a climatic gradient were quantified by regressing growth responses against local mean climatic conditions. Temperatures had more consistent and stronger correlations with growth for all three species than precipitation, but growth–climate responses varied among species and among sites. In particular, pine and fir populations showed different responses between BC and Yukon, whereas spruce showed a more consistent response across the study domain. Results indicate that (1) the response and sensitivity of trees to seasonal climate variables vary among species and sites and (2) winter temperatures prior to growth may have significant impacts on pine and fir growth at some sites. The capacity to adapt to climate change will likely vary among the study species and across climatic gradients, which will have implications for the future management of mixed-species forests in Yukon and BC.     

Integrating pine honeydew honey production into forest management optimization

Pine honeydew honey is an economically important non-wood forest product from eastern Mediterranean Pinus brutia forests, which are also important for timber production. Pine honey is produced by bees that feed on the honeydew secretions of Marchalina hellenica, a scale insect that infests pine stands and feeds on pine sap. The aim of this study was to optimize the joint production of pine honeydew honey and timber by maximizing the soil expectation value of pine stands. The simulation of P. brutia stand dynamics and timber production in healthy and infested stands is based on individual-tree growth and yield models that account for the effect of M. hellenica on tree- and stand-level growth and mortality. The optimization procedure uses a direct search method based on nonlinear programming. The results suggest that pine stands growing on good sites should be managed using rather short rotations and mainly aiming at timber production. In contrast, forest management in medium- and poor-quality sites should aim at longer rotations by taking advantage of the joint production of pine honey and timber assortments. Honey-oriented forest management can be much more profitable than timber production in stands growing on medium and poor sites. Pine honey represents an opportunity to increase the value and economic profitability of P. brutia forests.     

Model-based analysis of the spatial variability and long-term trends of soil drought at Scots pine stands in northeastern Germany

Soil water availability determines the vitality of trees and forest stands to a large degree. Over the last decades, an increasing number of drought spells has been observed in several parts of Europe. Our study aims to estimate long-term trends of soil drought at Scots pine (Pinus sylvestris L.) stands along the prevailing climatic gradient in Mecklenburg-Western Pomerania, northeastern Germany. To this end, soil water balance simulations were carried out at 24 sites over the period from 1951 to 2009 with the physically based model LWF-BROOK90. As a threshold for soil water stress, we used 40% of relative extractable water (REW). The results indicated an increased number of drought days further east, together with declining totals of precipitation. However, specific site conditions had a large influence on the occurrence of soil drought, partly overriding the climatic differences across the study area. Soil drought has distinctly increased in the recent past, both in duration and in intensity, affecting the eastern sites more than the western sites. The increased soil dryness could be attributed to higher atmospheric evaporative demand due to higher temperatures, as well as slightly lower precipitation sums during the summer months. To mitigate the negative effects of future climate change, adaptation measures should preferably be conducted in the eastern parts of northeastern Germany.     

Tree-rings reflect the impact of climate change on Quercus ilex L. along a temperature gradient in Spain over the last 100 years

We analyzed tree rings over the past 100 years to understand the response of Quercus ilex L. to climate change at four different sites along a temperature gradient in a highly anthropogenically transformed ecosystem. To test the hypothesis of a climate change related decrease in productivity at warmer sites, we discuss the effect of historical management on the growth of forest stands and the spatio-temporal variability of growth in response to climate, analyzing departures from linearity in that relationship. We reconstructed stand history and investigated past growth trends using tree-rings. Then we used a dendroecological approach to study the regional, local and age-dependent response to climate, analyzing the relationship between precipitation and tree growth using non-linear mixed models. Tree rings reflected the origin of the studied landscape, mainly a simplification of an original closed forest and progressive canopy opening for agrosilvopastoral purposes after the mid 1800s. As expected, trees were principally responding to water availability, and regional growth (as expressed by the first principal component from the matrix of chronologies) was highly responsive to hydrological year precipitation (r = 0.7). In this water limited ecosystem, the response of growth to precipitation was asymptotic and independent of age, but variable in time. Maximum growth was variable at the different sites and the non-linear function of growth saturated (i.e. reached an asymptote) at temperature dependent site specific precipitation levels within the range considered in the region to lead a shift towards deciduous species dominated woodlands (around 600 mm, variable with mean temperature). Only trees at warmer sites showed symptoms of growth decline, most likely explained by water stress increase in the last decades affecting the highly transformed open (i.e. low competition) tree structure. Stands at colder locations did not show any negative growth trend and may benefit from the current increase in winter temperatures. Coinciding with the decrease in productivity, trees at warmer sites responded more to moisture availability, exhibited a slower response to precipitation and reached maximum growth at higher precipitation levels than trees at colder sites. This suggests that warmer stands are threatened by climate change. The non-linear response of growth to precipitation described is meaningful for different ecological applications and provides new insights in the way trees respond to climate.     

The effects of species mixture on the growth and yield of mid-rotation mixed stands of Scots pine and silver birch

The effect of tree species mixture on stand volume yield and on tree-species-specific diameter and height growth rates were analysed in managed mixed stands of Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Ehrn.).Data were obtained from 14 repeatedly measured stands located in Southern Finland on mineral soil sites with varying admixture of Scots pine and silver birch. Statistical analysis was carried out for studying the effect of species mixture on the development of stand characteristics. For the analysis, the plots were categorised into three groups (plot types) according to the species dominance. In order to analyse species-specific growth rates, individual-tree mixed linear growth models for tree diameter and height growth were developed for both tree species.The results clearly show that the yield of the managed mid-rotation, mixed stands was greater for stands dominated by Scots pine than for stands dominated by birch, and the stand volume increment decreased with an increasing proportion of silver birch. Analysis of diameter and height growth by tree species revealed that the main reason for this pattern is the negative impact of birch competition on the growth of pine trees. The increase in diameter of pine was clearly hampered if the proportion of birch was high. An abundance of birch also slightly decreased the growth in height of Scots pine, although the effect was less than on diameter growth. Species mixture did not affect the diameter growth of birch but did have a significant effect on height development. Height growth of birch was considerably greater in pine-dominated stands than in birch-dominated stands. In pine-dominated mixed stands, the height growth of birch was quite close to that of dominant pine trees, and birches can endure in competition with pines for light.The results apply for even-aged and single-storey managed stands, where stocking density and structure are controlled with pre-commercial and commercial thinnings. The results are not applicable to unmanaged mixed stands undergoing self-thinning. This study provides new information on mixed stands from a silvicultural perspective, which can be applied in decisions involving the management of mixed stands.     

Relationships between long-term trends of air temperature,precipitation, nitrogen nutrition and growth of coniferous stands in Central Europe and Finland

Height growth of 19 Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) stands in Germany, Austria and Finland, for which long-term records of foliar nutrient levels were available, was assessed retrospectively by stem analyses and compared with data from regionally applied yield tables as references. Gridded historical time series of monthly temperature and precipitation were used to characterise the meteorologic conditions at the sampling sites. Climate parameters were tested against height growth in period 1950–2000, and needle N content was tested against height growth for the periods where N measurements were available by means of graphical comparison, as well as simple and multiple regression analyses with the aim to get evidence for causes of possible growth acceleration. Trends of referenced height increment of six out of nine Scots pine stands in Germany were positive during the observation period, and improved N nutrition appeared to be the most important driving factor for this growth acceleration. The variation of precipitation—exhibiting no consistent and uniform long-term temporal trend during the observation period—in contrast seems to be mainly responsible for the interannual fluctuation of height growth. We were not able to detect any general statistical influence of temperature parameters on height growth, although they generally increased. The referenced height growth of three Finnish pine stands slightly decreased during the observation period and there was no indication of a significant improvement of their N supply. Among four Norway spruce stands investigated in Germany and Austria, referenced height increment also increased in three cases; there was again some evidence that improved N nutrition was the stimulating factor. At three study sites in Finland, however, referenced height growth of this species decreased at least from 1985 onwards, whereas mostly no significant trends in N nutrition or precipitation were identified. These differences observed between species and regions are discussed in detail.     

Growth responses of West-Mediterranean Pinus nigra to climate change are modulated by competition and productivity: Past trends and future perspectives

Positive and negative effects of climate change on forest growth have been observed in different parts of the world. However, much is still unknown about how forest structure and productivity might affect climate-growth relationships in the future. We examined the effects of climate, site quality, and competition on tree basal area growth of black pine (Pinus nigra Arn.) between 1964 and 2005 in 21 sites in the Iberian Peninsula. We used a new approach to simultaneously account for climate-growth relationships, inter-annual growth variability, and stand structural changes, by fitting a linear mixed effects model (LMEM) for basal area increments (BAI) using climate data, tree-ring chronologies, and repeated forest inventory data. This approach showed the potential to improve our understanding of climate effects on tree growth and to include climate in empirical forest growth models. We used the LMEM to make projections of BAI growth under two CO₂ emission scenarios and two global circulation models (GCM). The main climate drivers for growth were precipitation from previous autumn to summer and winter temperature with a positive effect, and temperature in spring-summer which had a negative effect. Tree response to climate was modulated by stand conditions, tree competition, and productivity. The more productive stands showed greater ability to either maintain or increase growth at warmer spring-summer temperatures under different levels of autumn-summer precipitation. Growth projections showed important regional differences. In general, growth under future climate is predicted to decrease although moderate growth increases might be expected in the northern region for highly and moderately productive stands.     

Canopy reduction as a possible measure for adaptation of young Scots pine stand to insufficient precipitation in Central Europe

Climate change towards a warmer and dryer vegetation period may negatively impact growing conditions for Scots pine monocultures situated on dry, sandy soils in Central Europe. The purpose of the study was to evaluate the effect of thinning on precipitation throughfall in young Scots pine stands on typical pine sites. In 1992, observation of precipitation and throughfall started at the Tyniště research site (lowland of Eastern Bohemia) in a 7-year-old pine stand planted in rows at a stocking of ca 10,000 trees ha⁻¹. Throughfall was measured at weekly intervals during the growing season (April-September) by gauges randomly located in two treatments - variant 1C - Control without thinning and variant 2T - Thinned - and compared to precipitation at an open space outside of the canopy. The results demonstrated the positive effects of heavy low thinning (removal of 47% of the total number of trees and 31% of total pre-treatment basal area) on the water supply of young Scots pine stands. On the Thinned treatment, throughfall increased by 2-8% compared to Control plot. This positive effect persisted for six years after the first canopy reduction and the differences were significant for the first four years after thinning. After the second treatment (high thinning), throughfall on the Thinned treatment showed a nominal, but statistically insignificant increase. The likely reason for this result is that the application of a different type of thinning increased the variability of the canopy and, consequently, the effect of released crowns could not be detected.     

Natural mortality in thinning and fertilisation experiments with pine and spruce in Sweden

Natural mortality in a 30-year period was examined in thinning and fertilisation experiments with 48 blocks in Scots pine (Pinus sylvstris L.) and 23 blocks in Norway spruce (Picea abies (L.) Karst.) with up to 12 different treatments. Of about 90,000 living trees at start of the experiments 18.7% were registered as dead by natural mortality in the 30-year observation period. In non-thinned stands about 20% of the volume growth disappeared by natural mortality, in thinned stands about 10%. In normally thinned pine stands (repeated thinning from below with moderate intensity) the annual mortality of the basal area at start of an average 7-year period was 0.34%. In spruce stands, on more fertile sites, the corresponding figure was about 0.6%. In an effort to model the mortality, severe damage not leading to final felling was identified in 1.7% of the observation periods. It was assumed that this part of the mortality, representing 24% of the total volume mortality, could be recovered by active thinning. The probability for severe damage increased sharply with stand top height, as shown in a logistic regression. The more sparse mortality was expressed as a function of site fertility, stand density, disturbance by thinning and form of treatment (thinned from above or below or non-thinned). The naturally dead trees were approximately of mean size in normally thinned stands while the self-thinning in non-thinned stands tended to occur amongst smaller than average trees. Diagrams were presented for basal area development and stem number reduction in the non-thinned stands.     

Detecting forest stress and decline in response to increasing river flow in southwest Florida, USA

Forest stress and decline resulting from increased river levels were investigated in Myakka River State Park (MRSP), FL, USA. Since 1977, land-use changes around the upper Myakka River watershed have resulted in significant increases in water entering the river, which have caused extensive mortality in the upper watershed. The present study assessed whether similar forest stress and mortality was occurring downstream within the park. Our objectives were to (1) determine if tree die-off and/or stress resulting from increased river levels were present in MRSP and (2) determine the relationship between historical and present river levels regimes and growth of actively managed forested stands undergoing restoration located both above and below a dam. We used two methodological approaches. The first was recording indications of tree stress and decline (crown dieback, crown thinning, trunk rot, foliage discoloration, and parasitism) in Fraxinus caroliniana Miller dominated forested wetlands, Pinus elliottii Englem. var. densa Little & Dorman dominated mesic pine flatwoods, and Quercus laurifolia Michaux dominated oak palm hammocks. Our second approach was tree-ring analyses, which allows for more detailed analyses of growth in response to precipitation and river flow (a surrogate variable for water table depth) in the pine flatwoods stands.

Our results indicate significant stress and decline in some forested wetlands upstream of the dam, significant mortality in wet-mesic pine flatwoods sites close to the river, and significant amounts of stress in wet-mesic pine flatwoods sites upstream of the dam. F. caroliniana sites located upstream of the dam had more individuals with symptoms of stress than those downstream of the dam (67% versus 43%, P=0.031). In Q. laurifolia sites, 70–85% of the trees had evidence of flooding stress and mortality, which is comparable to distributions found in severely disturbed forest in the upper watershed. P. elliottii var. densa sites located <1000 m from the river had higher mortality than sites located >1050 m from the river (P<0.01), and the stressed trees in sites upstream of the dam had significantly lower growth rates in the 1990s versus the 1960s than those downstream. Although, the onset of stress and decline coincided with increasing river levels, we found that river levels were positively correlated with tree growth, both before and after flow increases in the system. Increasing river levels may play an indirect role through increased competition in the stress and decline in wet-mesic pine flatwoods, however, increased river levels seems to be the direct cause for stress and decline found in forested wetland stands.     

Comparison of stand structure and growth between artificial and natural forests of Pinus sylvestiris var, mongolica on sandy land

Mongolian pine (Pinus sylvestiris Linnaeus var. mongolica Litvinov) as a valuable conifer tree species has been broadly introduced to the sandy land areas in “Three North” regions (North, northwest and northeast of China), but many prob-lems occurred in the earliest Mongolian pine plantations in 7hanggutai, 7hangwu County, Liaoning Province (ZZL). In order to clarify the reason, comprehensive investigations were carried out on differences in structure characteristics, growth processes and ecological factors between artificial stands (the first plantation established in ZZL in 1950s) and natural stands (the origin forests of the tree species in Honghuaerji, Inner Mongolia) on sandy land. The results showed that variation of diameter-class distributions in artificial stands and natural stands could be described by Weibull and Normal distribution models, respectively.Chapman-Richards growth model was employed to reconstruct the growth process of Mongolian pine based on the data from field investigation and stem analysis. The ages of maximum of relative growth rate and average growth rate of DBH, height, and volume of planted trees were 11,22 years, 8, 15 years and 35, 59 years earlier than those of natural stand trees, respectively. In respect of the incremental acceleration of volume, the artificial and natural stands reached their maximum values at 14 years and 33 years respectively. The quantitative maturity ages of artificial stands and natural stands were 43 years and 102 years respectively. It was concluded that the life span of the Mongolian pine trees in natural stands was about 60 years longer than those in artificial stands. The differences mentioned above between artificial and natural Mongolian pine forests on sandy land were partially attributed to the drastic variations of ecological conditions such as latitude, temperature, precipitation, evaporation and height above sea level. Human beings‘‘ disturbances and higher density in plantation forest may be ascribed as additional reasons. Those results may be potentially useful for the management and afforestation of Mongolian pine plantations on sandy land in arid and semi-arid areas.     

Impacts of changing climate on the productivity of Norway spruce dominant stands with a mixture of Scots pine and birch in relation to water availability in southern and northern Finland

A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000-99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (P(nc)) and total stem wood growth (V(s)) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (E(T)) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (W(d)) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce.     

Tree regeneration and future stand development after bark beetle infestation and harvesting in Colorado lodgepole pine stands

In the southern Rocky Mountains, current mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreaks and associated harvesting have set millions of hectares of lodgepole pine (Pinus contorta var. latifolia Engelm. ex Wats.) forest onto new stand development trajectories. Information about immediate, post-disturbance tree regeneration will provide insight on dynamics of future stand composition and structure. We compared tree regeneration in eight paired harvested and untreated lodgepole pine stands in the Fraser Experimental Forest that experienced more than 70% overstory mortality due to beetles. New seedlings colonized both harvested and untreated stands in the first years after the beetle outbreak. In harvested areas the density of new seedlings, predominantly lodgepole pine and aspen, was four times higher than in untreated stands. Annual height growth of pine and fir advance regeneration (e.g., trees established prior to the onset of the outbreak) has doubled following overstory mortality in untreated stands. Growth simulations based on our regeneration data suggest that stand basal area and stem density will return to pre-beetle levels in untreated and harvested stands within 80-105 years. Furthermore, lodgepole pine will remain the dominant species in harvested stands over the next century, but subalpine fir will become the most abundant species in untreated areas. Owing to terrain, economic and administrative limitations, active management will treat a small fraction (<15%) of the forests killed by pine beetle. Our findings suggest that the long-term consequences of the outbreak will be most dramatic in untreated forests where the shift in tree species composition will influence timber and water production, wildfire behavior, wildlife habitat and other forest attributes.     

Tree species composition affects productivity and carbon dynamics of different site types in boreal forests

The objective was to analyse how differences in the initial proportions of tree species and site fertility affect carbon sequestration in living biomass and soil. We used the individual-based simulation model EFIMOD, which is able to simulate spatially explicit competition between trees for light and nutrients. Simulations were carried out for three site types with distinct initial stocks of soil nutrients. For each site, the 100-years undisturbed dynamics of monocultures and mixtures of three tree species (Betula pendula Roth, Pinus sylvestris L. and Picea abies (L.) H. Karst.) was predicted. Changes in the proportions of competing tree species were dependent on the fertility of the site: on poor sites, pine was the most competent species, while on rich sites, spruce increased its proportion during stand succession. Net primary production (NPP) and soil respiration were the highest in stands of two coniferous species and in stands with a high initial proportion of pine. Mixed stands were more productive than monocultures; the highest overyielding was observed with mixtures of two coniferous species. Simulated NPP and carbon stocks in all pools increased from poor to rich sites. The highest carbon stocks in standing biomass were observed for mixtures of conifer species and three-species mixtures; the greatest accumulation of forest floor occurred in stands with high proportions of pine.     

Growth, healthy status and seed production of differently aged allochtonous and autochtonous Pinus mugo stands in the Giant Mts. over 30 years

Plant communities with Dwarf pine (Pinus mugo var. pumilio) form characteristic vegetation in the subalpine belt of the Giant Mountains (Krkono?e, Karkonosze and Riesengebirge, Czech Republic). This “island” of arcto-alpine tundra represents the northernmost edge of Dwarf pine natural range. We asked how concentration of sulphur in needles, growth, healthy status and fructification changed over three decades (1981–2011) with different air pollution in differently aged (45–120 years) autochtonous and allochtonous (introduced from the Alps) Dwarf pine stands. Different Dwarf pine stands above the alpine timberline were able to withstand 1980s, the period of heavy air pollution, without any decrease in growth rate or remarkable decrease in healthy status. Dwarf pine is thus highly tolerant to deposition of sulphur compounds. High concentration of SO₂ in the air positively affected sulphur concentration in needles and eliminated thus sulphur deficiency. Higher germination rate of seeds in 2000s in comparison with 1980s indicate that the air pollution could decrease germination ability of seeds. High insect outbreaks (by Thecodiplosis brachyntera and Neodiprion sertifer) in 1990s and 2000s caused decrease in needle year classes. As there was a gradual increase in mean annual temperature over years 1981–2011, Dwarf pine stands can be more and more endangered by insect outbreaks in the future. There was no remarkable difference between autochtonous and allochtonous stands in all measured growth, healthy status and fructification characteristics. To determine real effects of air pollution and insect outbreaks on Dwarf pine stands from year to year fluctuations, decade-long monitoring is necessary.     

White pine (Pinus strobus L.) regeneration dynamics at the species’ northern limit of continuous distribution

The abundance of eastern white pine (Pinus strobus L.) has been significantly reduced across its distribution range over the past few centuries. The species’ regeneration dynamics is well documented in the centre of its range, but is poorly understood at the northern limit of continuous distribution. To address this knowledge gap, we quantified natural white pine regeneration in unmanaged mature stands, identified the most important variables influencing it, and evaluated the impact of damaging agents, namely white pine blister rust (Cronartium ribicola J.C. Fisch.), white pine weevil (Pissodes strobi Peck), and herbivory. We also quantified the influence of remnant stands and residual trees on the spatial distribution of regeneration in logged sites. The results reveal continuous but low recruitment in mature stands. The basal area of balsam fir (Abies balsamea (L.) Miller) had a strong negative effect on white pine regeneration. Regeneration was more abundant than expected on moister substrates, including moss, decaying wood and organic matter. White pine regeneration was noted in recently logged areas, where distance from remnant stands had a significant effect on the abundance of white pine regeneration. The northern limit of continuous distribution holds potential for white pine restoration, for example by preserving remnant white pine stands that can provide seed sources for natural regeneration in a shelterwood cut system, or in adjacent clearcut areas. This study illustrates that different management strategies should be used near northern range limits, where effects of site conditions and disturbance agents are different than in the center of a species’ range.     

Ectomycorrhizal communities associated with silver fir seedlings (Abies alba Mill.) differ largely in mature silver fir stands and in Scots pine forecrops

Context

The requirement for rebuilding forecrop stands besides replacement of meadow vegetation with forest plants and formation of soil humus is the presence of a compatible ectomycorrhizal (ECM) fungal community.

Aims

This study aims to assess ectomycorrhizal fungi diversity associated with silver fir (Abies alba Mill.) seedlings regenerating in silver fir stands and Scots pine forecrops.

Methods

One-year-old seedlings were sampled in six study sites: three mature fir forests and three pine forests. ECM fungi were identified by polymerase chain reaction amplification and sequencing of the internal transcribed spacer of rDNA.

Results

The mean mycorrhizal colonization exceeded 90 %. Thirty-six ectomycorrhizal taxa were identified in fir stands and 23 in pine forecrops; ten out of these species were common to both stands. The fungal communities were different between study sites (R?=?0.1721, p?=?0.0001). Tomentella stuposa was the only species present at all sites.

Conclusion

Silver fir seedlings in Scots pine forecrops supported smaller ECM fungal communities than communities identified in mature silver fir stands. Nevertheless, fungal colonization of seedling roots was similar in both cases. This suggests that pine stands afforested on formerly arable land bear enough ECM species to allow survival and growth of silver fir seedlings.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Selection of diurnal roosts by red bats (Lasiurus borealis) in an intensively managed pine forest in Mississippi

Forest managers are increasingly expected to incorporate biodiversity objectives within forest landscapes devoted to timber production. However, data on which to base management recommendations for bats within these systems are limited. Although the red bat (Lasiurus borealis) is a widespread and common species in temperate forests of North America, little is known of its ecology within intensively managed pine (Pinus spp.) forests of the southeastern United States. Diurnal roost sites of red bats may be limiting on industrial pine forests due to a lack of large hardwoods within managed stands. Therefore, we investigated selection of day roosts by red bats at multiple spatial scales during June–September 2000 and May–August 2001 in an intensively managed pine landscape in east-central Mississippi, USA. We captured bats using 4-tier mist nets placed over water and attached 0.47–0.54 g radiotransmitters to captured red bats (n = 46). We located day roosts of red bats (n = 141 roosts of 27 bats) for the life of the transmitters. Red bats roosted in 16 species of hardwood trees (70% of day roosts) and loblolly pine (Pinus taeda; 30% of day roosts). In contrast to other studies in the southeastern United States, red bats roosted in pine trees and in midstory hardwood trees. Within thinned pine stands, red bats tended to prefer roost trees with a denser subcanopy and higher basal area as compared to random sites. Stand-level characteristics appeared more important than individual tree characteristics in choice of diurnal roosts. Except for adult males, logistic regression models of roost sites of red bats had high (≥79%) correct classification rates. Day roost site requirements of red bats may exhibit greater plasticity than previously thought. On our study area, intensive forest management appears compatible with diurnal roost needs of this species.