Introduction: International conference on forest ecosystems: Ecology,conservation and sustainable management

Abstract

A pollen diagram from a small lake, Kutulahdenlampi, in northern Finland is interpreted in terms of the development of forest vegetation during the Holocene. The abundance of each of the forest taxa is considered independently by means of pollen accumulation rates (PARs), using as the reference material, long term average pollen deposition values monitored by a network of pollen traps. Particular attention is paid to the arrival of spruce and to the species in the original forests that this newcomer replaces. A model of pollen dispersal and deposition developed by Sugita is used to estimate the area around the lake that the pollen assemblage is most clearly reflecting. This relevant source area of pollen (RSAP), for the present day situations is c. 1,500 m. Pollen loadings calculated for a simulated landscape that mimics (i) that of the present day and (ii) for the situation at 8,000 BP (as deduced from the PARs) are compared with the pollen assemblages from the diagram at those points in time, and are seen to be compatible. The advantages of combining PAR and modelling to look at the spatial scale of vegetation reconstructions are discussed.     

Effects of plant leachates from four boreal understorey species on soil N mineralization, and white spruce (Picea glauca) germination and seedling growth

BACKGROUND AND AIMS: Natural regeneration of white spruce (Picea glauca) after disturbance has been reported to be very poor. Here a study was made to determine whether C compounds released from understorey species growing together with white spruce could be involved in this regeneration failure, either by (1) changing soil nutrient dynamics, (2) inhibiting germination, and/or (3) delaying seedling growth. METHODS: Foliage leachates were obtained from two shrubs (Ledum palustre and Empetrum hermaphroditum) and one bryophyte (Sphagnum sp.) with high phenolic compound concentrations that have been reported to depress growth of conifers in boreal forests, and, as a comparison, one bryophyte (Hylocomium splendens) with negligible phenolic compounds. Mineral soil from a white spruce forest was amended with plant leachates to examine the effect of each species on net N mineralization. Additionally, white spruce seeds and seedlings were watered with plant leachates to determine their effects on germination and growth. KEY RESULTS: Leachates from the shrubs L. palustre and E. hermaphroditum contained high phenolic compound concentrations and dissolved organic carbon (DOC), while no detectable levels of C compounds were released from the bryophytes Sphagnum sp. or H. splendens. A decrease in net N mineralization was determined in soils amended with L. palustre or E. hermaphroditum leachates, and this effect was inversely proportional to the phenolic concentrations, DOC and leachate C/N ratio. The total percentage of white spruce germination and the growth of white spruce seedlings were similar among treatments. CONCLUSIONS: These results suggest that the shrubs L. palustre and E. hermaphroditum could negatively affect the performance of white spruce due to a decrease in soil N availability, but not by direct effects on plant physiology.     

Disentangling the roles of history and local selection in shaping clinal variation of allele frequencies and gene expression in Norway spruce (Picea abies)

Understanding the genetic basis of local adaptation is challenging due to the subtle balance among conflicting evolutionary forces that are involved in its establishment and maintenance. One system with which to tease apart these difficulties is clines in adaptive characters. Here we analyzed genetic and phenotypic variation in bud set, a highly heritable and adaptive trait, among 18 populations of Norway spruce (Picea abies), arrayed along a latitudinal gradient ranging from 47°N to 68°N. We confirmed that variation in bud set is strongly clinal, using a subset of five populations. Genotypes for 137 single-nucleotide polymorphisms (SNPs) chosen from 18 candidate genes putatively affecting bud set and 308 control SNPs chosen from 264 random genes were analyzed for patterns of genetic structure and correlation to environment. Population genetic structure was low (F(ST) = 0.05), but latitudinal patterns were apparent among Scandinavian populations. Hence, part of the observed clinal variation should be attributable to population demography. Conditional on patterns of genetic structure, there was enrichment of SNPs within candidate genes for correlations with latitude. Twenty-nine SNPs were also outliers with respect to F(ST). The enrichment for clinal variation at SNPs within candidate genes (i.e., SNPs in PaGI, PaPhyP, PaPhyN, PaPRR7, and PaFTL2) indicated that local selection in the 18 populations, and/or selection in the ancestral populations from which they were recently derived, shaped the observed cline. Validation of these genes using expression studies also revealed that PaFTL2 expression is significantly associated with latitude, thereby confirming the central role played by this gene in the control of phenology in plants.     

Changes in the microbial community in a forest soil amended with aluminium in situ

Considerable knowledge exists about the effect of aluminium (Al) on root vitality, but whether elevated levels of Al affect soil microorganisms is largely unknown. We thus compared soils from Al-treated and control plots of a field experiment with respect to microbial and chemical parameters, as well as root growth and vitality. The field experiment was established in a 50-year-old Norway spruce (Picea abies L.) stand where no Al or low concentrations of Al had been added every 7–10 days during the growth season for 7 years. Analysis of soil solutions collected using zero tension lysimeters and porous suction cups showed that Al treatment lead to increased concentrations of Al, Ca and Mg and lower pH and [Ca + Mg + K/Al] molar ratio. Corresponding soil analyses showed that soil pH remained unaffected (pH 3.8), that exchangeable Al increased, while exchangeable Ca and Mg decreased due to the Al treatment. Root in-growth into cores placed in the upper 20 cm of the soil during three growth seasons was not affected by Al additions, neither was nutrient concentration or mortality of these roots. The biomass of some taxonomic groups of soil microorganisms, analyzed using specific membrane components (phospholipid fatty acids; PLFAs), was clearly affected by the imposed Al treatment, both in the organic soil horizon and in the underlying mineral soil. Microbial community structure in both horizons was also clearly modified by the Al treatment. Shifts in PLFA trans/cis ratios indicative of short term physiological stress were not observed. Yet, aluminium stress was indicated both by changes in community structure and in ratios of single PLFAs for treated/untreated plots. Thus, soil microorganisms were more sensitive indicators of subtle chemical changes in soil than chemical composition and vitality of roots.     

Climatic signals in tree ring of Picea schrenkiana along an altitudinal gradient in the central Tianshan Mountains, northwestern China

Tree-ring samples of Picea schrenkiana (Fisch. et Mey) were studied along an altitudinal gradient in the central Tianshan Mountains, and ring-width chronologies were developed for three sites at different altitudes: low-forest border (1600–1700 m a.s.l.), interior forest (2100–2200 m a.s.l.), and upper treeline (2600–2700 m a.s.l.). Annual ring-width variations were similar among the three sites but variability was greatest at the low-forest border site. The statistical characters of the chronologies showed that mean sensitivity (MS) and standard deviation (SD) decreased with increasing elevation. In other words, the response of tree growth to environmental changes decreased with increasing altitude. To understand the differing response of trees at different elevations to the environmental changes, response function analysis was used to study the relationships between tree-ring widths and mean monthly temperature and total monthly precipitation from 1961 to 2000. The results showed that precipitation was the most important factor limiting tree radial growth in the arid central Tianshan Mountains, precipitation in August of the prior growth year played an important role on tree's radial growth across the entire altitudinal gradient even at the cold, high-elevation treeline site. It is expected that with increasing altitude air temperature decreased and precipitation increased, the importance of precipitation on tree growth decreased, and the response of tree growth to environmental changes decreased, too. This conclusion may be helpful to understand and research the relationship between climatic change and tree growth in arid and semiarid area.     

Influence of Aspen on Forest Floor Properties in Black Spruce-dominated Stands

In the absence of fire in black spruce-feathermoss stands, a thick forest floor layer dominated by bryophytes and sphagnum accumulates. This layer is associated with wet, cool and nutrient-poor soil conditions conducive to the paludification process and pushing the ecosystem towards an unproductive open black spruce forest. The presence of Populus tremuloides in theses stands may halt this process because this species has a high nutrient cycling rate and a litter that represses moss cover. The main hypothesis of this study is that, despite similar abiotic conditions (slope and drainage), the presence of Populus tremuloides in a stand dominated by Picea mariana affects surface soil nutrient availability, total N, pH as well as the decomposition process. The abundance of Populus tremuloides trees was associated with higher exchangeable cations, cationic exchangeable capacity and pH of the forest floor layer on all sites. A decrease in organic matter thickness with increasing aspen presence was also found on all sites, suggesting that this species affects the decomposition process by the quality of its litter as well as by a general improvement of soil physical and chemical properties. The decomposition rate of a standard substrate as well as in vitro potential net nitrogen mineralization were positively related to Populus tremuloides on only one of the three sites, and non-significant on the other sites. Strong immobilization of added nitrogen during incubation was observed on all sites and was not related to aspen, which suggested that in these stands, the soil microbial community is uniformly and strongly nitrogen limited. The zone of influence of Populus tremuloides was evaluated in areas around the soil sampling plot ranging from 3 to 7 m. The results revealed that this zone varies with soil properties. The results suggest that the presence of Populus tremuloides accelerate nutrient cycling, which could affect stand productivity to some extent.     

Reproducibility of vegetation cover estimates in south‐central Alaska forests

Abstract. Reproducibility of vegetation measurements is critical for large‐scale or long‐term studies, where numerous observers collect data, but past studies have questioned repro‐ducibility of some techniques. Five methods of evaluating understory composition were appraised for reproducibility among six observers in two forest types in south‐central Alaska: ocular estimates in quadrats, overall community species rank and cover estimates, nested rooted frequency, horizontal‐vertical profiles, and pin drop (systematic points). One forest type was selected to represent structure of coastal communities, another to represent structure of interior Alaska communities. Three general methods of evaluating reproducibility were considered: standard deviations (precision among observers), components of variance (percentage of total variance attributable to observers), and analysis of variance (significance of observer variance). Observer variances were generally similar among techniques and significant in most cases. No technique stood out as being more reproducible than others. Features of techniques other than reproducibility may be more important when selecting a technique. Management decisions based on vegetation cover data should consider the observer errors involved as well as biological significance.     

Montane forest ecotones moved downslope in northeastern USA in spite of warming between 1984 and 2011

Ecotones are transition zones that form, in forests, where distinct forest types meet across a climatic gradient. In mountains, ecotones are compressed and act as potential harbingers of species shifts that accompany climate change. As the climate warms in New England, USA, high‐elevation boreal forests are expected to recede upslope, with northern hardwood species moving up behind. Yet recent empirical studies present conflicting findings on this dynamic, reporting both rapid upward ecotonal shifts and concurrent increases in boreal species within the region. These discrepancies may result from the limited spatial extent of observations. We developed a method to model and map the montane forest ecotone using Landsat imagery to observe change at scales not possible for plot‐based studies, covering mountain peaks over 39 000 km². Our results show that ecotones shifted downward or stayed stable on most mountains between 1991 and 2010, but also shifted upward in some cases (13–15% slopes). On average, upper ecotone boundaries moved down ?1.5 m yr^?1 in the Green Mountains, VT, and ?1.3 m yr^?1 in the White Mountains, NH. These changes agree with remeasured forest inventory data from Hubbard Brook Experimental Forest, NH, and suggest that processes of boreal forest recovery from prior red spruce decline, or human land use and disturbance, may swamp out any signal of climate‐mediated migration in this ecosystem. This approach represents a powerful framework for evaluating similar ecotonal dynamics in other mountainous regions of the globe.