Clonal variation in crown structure, absorbed photosynthetically active radiation and growth of loblolly pine and slash pine

Crown structure, absorbed photosynthetically active radiation (APAR) and growth were analyzed in 300 replicated loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliotti) clones to: (1) quantify genetic variation in crown structural traits, growth and APAR at the species, family and clonal levels; and (2) estimate within-family genetic and environmental influences on measured variables. Species and family-within-species differences were found in some growth traits, crown size, leaf area, APAR and branch angle. Loblolly pine developed larger crowns, exposed more leaf area with an acute angle, and intercepted more radiation than slash pine. Significant differences among clones within-family were found for stem volume and crown architecture. Loblolly pine and slash pine within-family, individual-tree broad-sense heritabilities ranged from 0.00 to 0.41 for growth and crown structural traits and most were between 0.10 and 0.25 when estimated from a combined analysis across families. Genetic correlations of crown size, leaf area and APAR with volume increment generally ranged from 0.60 to 0.75. This knowledge of the genetic interactions among growth and crown structural traits improves our understanding of how crown morphology affects light interception and stand development, and ultimately how these attributes can be incorporated in the selection of families or clones for the development of new crop tree ideotypes.     

Dissolved organic carbon and nitrogen leaching from Scots pine, Norway spruce and silver birch stands in southern Sweden

The effects of three common tree species - Scots pine, Norway spruce and silver birch - on leaching of dissolved organic carbon and dissolved nitrogen were studied in an experimental forest with podzolised soils in southern Sweden. We analyzed soil water collected with lysimeters and modeled water fluxes to estimate dissolved C and N fluxes. Specific UV absorbance (SUVA) was analyzed to get information about the quality of dissolved organic matter leached from the different stands. Under the O horizon, DOC concentrations and fluxes in the birch stands were lower than in the spruce and pine stands; annual fluxes were 21 g m⁻² y⁻¹ for birch and 38 g m⁻² y⁻¹ and 37 g C m⁻² y⁻¹ for spruce and pine, respectively. Under the B horizon, annual fluxes for all tree species ranged between 3 and 5 g C m⁻² y⁻¹, implying greater loss of DOC in the mineral soil in the coniferous stands than in the birch stands. We did not find any effect of tree species on the quality of the dissolved organic matter, as measured by SUVA, indicating that the chemical composition of the organic matter was similar in leachates from all three tree species. Substantial amounts of nitrogen was leached out of the soil profile at the bottom of the B horizon from the pine and birch stands, whereas the spruce stands seemed to retain most of the nitrogen in the soil. These differences in N leaching have implications for soil N budgets.     

Fine root biomass of Scots pine stands differing in age and soil fertility in southern Finland

The biomass of small and large fine roots (相似文献   

Differences in soil properties in adjacent stands of Scots pine, Norway spruce and silver birch in SW Sweden

Soil properties were compared in adjacent 50-year-old Norway spruce, Scots pine and silver birch stands growing on similar soils in south-west Sweden. The effects of tree species were most apparent in the humus layer and decreased with soil depth. At 20-30 cm depth in the mineral soil, species differences in soil properties were small and mostly not significant. Soil C, N, K, Ca, Mg, and Na content, pH, base saturation and fine root biomass all significantly differed between humus layers of different species. Since the climate, parent material, land use history and soil type were similar, the differences can be ascribed to tree species. Spruce stands had the largest amounts of carbon stored down to 30 cm depth in mineral soil (7.3 kg C m⁻²), whereas birch stands, with the lowest production, smallest amount of litterfall and lowest C:N ratio in litter and humus, had the smallest carbon pool (4.1 kg C m⁻²), with pine intermediate (4.9 kg C m⁻²). Similarly, soil nitrogen pools amounted to 349, 269, and 240 g N m⁻² for spruce, pine, and birch stands, respectively. The humus layer in birch stands was thin and mixed with mineral soil, and soil pH was highest in the birch stands. Spruce had the thickest humus layer with the lowest pH.     

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.     

Differences in Agrobacterium infections in silver birch and Scots pine

The aim of this study was to investigate the differences in infections caused by Agrobacterium tumefaciens in a conifer, Scots pine (Pinus sylvestris), and in a non-host deciduous species, silver birch (Betula pendula). All the Agrobacterium tumefaciens strains tested caused crown-gall formation in both tree species, but the infection rates varied remarkably. In Scots pine, the development of galls was rare, and slower than in silver birch. Inoculation into the base of the stem were the most successful in gall induction. Silver-birch galls were large, often surrounding the whole stem, in contrast to Scots pine galls, which were characterized by their small size and neck-like connection with the host plant. In silver birch, no other morphological changes could be seen. In Scots pine, abnormal phenotypes with proliferating short shoots above the galls were observed during the second and third growing season. The results indicate that, of the two non-host tree species, the deciduous one, silver birch, is more susceptible to an A. tumefaciens infection than the conifer, Scots pine. The matrix for A. tumefaciens infection in silver birch differs from that in Scots pine, since the terpene compounds of Scots pine seem either to kill the agrobacteria or to suppress their growth. The differences between the species could be partly caused by their difference in sensitivity to phytohormones. These features reflect evolutionary incompatibility between A. tumefaciens and a gymnosperm.     

Thinning intensity and growth response in SW-European Scots pine stands

The effect of different thinning intensities on growth and yield was studied in Pinus sylvestris L. stands at the south-western limit of its distribution area (Central Spain), using five long-term thinning trials. Data were analysed collectively considering several factors (trial, block, plot and period) as random effects. Total volume and volume increment decreased with thinning intensity, this loss being more significant in the case of moderate and heavy thinning. No difference was found among treatments for total basal area or the increment in basal area. The results revealed an optimum basal area (Assmann’s definition) between 85 and 100% of the basal area in unthinned plots. Volume growth loss associated with heavy thinnings (reduction of 18% in volume increment) was smaller than that reported in Central and Northern European regions (greater than 25%). Height increment was not influenced by thinning, whereas dominant and quadratic mean diameter increments increased with the thinning intensity. The response of diameter growth to thinning was greater at younger ages (less than 50 y) and in medium-sized trees.     

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.     

Oak natural regeneration and conversion processes in mixed Scots pine stands

The main task of the study was to find out if spontaneous oakregeneration can play an important role in conversion processesof mixed Scots pine stands to native broadleaved forests. Thepaper examines the amount and structure of oak natural regenerationunder different gap sizes and defines the optimal gap size forinitiation, growth and development of oak regeneration. Theinvestigation was conducted in managed forests in the GarwolinForest District in the central part of Poland. All gaps, definedas openings in the canopy     

Estimation of nutrient removals in stem-only and whole-tree harvesting of Scots pine, Norway spruce, and birch stands with generalized nutrient equations

Whole-tree harvesting (WTH), where logging residues are removed in addition to stems, is widely practised in Fennoscandian boreal forests. WTH increases the export of nutrients from forest ecosystems. The extent of nutrient removals may depend on tree species, harvesting method, and the intensity of harvesting. We developed generalized nutrient equations for Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karsten), and birch (Betula pendula Roth and Betula pubescens Ehrh.) stands to be able to calculate the amounts of nitrogen, phosphorus, potassium, and calcium in stems and above-ground biomass (stem and crown) as a function of stand volume. The equations were based on Fennoscandian literature data from 34 pine, 26 spruce, and 5 birch stands, and they explained, depending on the tree species and nutrient, 61–99% and 56–87% of the variation in the nutrient amounts of stems and above-ground biomass, respectively. The calculations based on the equations showed that nutrient removals caused by stem-only harvesting (SOH) and WTH per harvested stem m³ were smaller in pine than in spruce and birch stands. If the same volume of stem is harvested, nutrient removals are, in general, nearly equal at thinnings and final cuttings in SOH, but larger in thinnings than final cuttings in WTH. If the principal aim is to minimize the nutrient removals per harvested stem m³, the harvesting should be done at mature pine stands. The effect of biomass removal on overall site nutrient status depends on site-specific factors such as atmospheric deposition, weathering of minerals, and the size of the nutrient pools in the soil.     

Stability of height positions in young naturally regenerated stands of Scots pine

The stability of height positions of saplings in young stands of Scots pine (Pinus sylvestris L.) was examined by comparing the height order of trees at successive measurements. The data consisted of six naturally regenerated stands and one planted stand for comparison. The length of the examination period was approximately 20 years, covering the mean height development of stands from 0.5 to 5.5 m. For each stand, a structural equation model was fitted by which the covariance structure occurring in the data could be described. In terms of the stability coefficients between the variables produced by the model, the height position of the saplings was very stable. The height positions had mainly been established during the first 5–10 years of age and at a mean height of less than 0.5–1 m. In the naturally regenerated stands, stability was virtually complete from the stage of 15–20 years and 1.5–2 m onwards. In the planted stand, stability became complete slightly later than in the naturally regenerated stands. According to the results, the height of the sapling can be emphasized as a selection criterion in precommercial thinning.     

Profitability of alternative management regimes in Scots pine stands on drained peatlands

In drained, forested peatlands, ditch network maintenance (DNM) is often considered necessary for tree growth, but it also constitutes additional management costs. Commercial thinnings, in turn, in addition to their silvicultural benefits, are generally applied to enhance the financial performance of stand management but results from peatland stands are scarce. In this study, our aim was to find financially feasible management practices for Scots pine-dominated stands on drained peatland sites in Finland. Using mainly inventory data sets, we compiled altogether 29 typical model-stands for four climatic areas, four site types, and two stand conditions according to need for silvicultural care. We used MOTTI stand simulator to predict the development of the model-stands according to different management regimes consisting of various combinations of 0–2 DNM and 0–2 thinnings with different timings and thinning intensities. We then calculated and compared the financial feasibility of the regimes using net present value (NPV; discount rate 3%) analysis. The separate effect of DNM on the profitability was marginal, but the positive effect of thinnings was clear. The harvesting removals varied within a wide range, depending on the timing and intensity of thinnings, but on average, the NPV doubled due to the thinnings. In the stands of initially good silvicultural condition, regimes including only one thinning and a DNM operation generally displayed a good financial result. In the stands of initially poor silvicultural condition due to neglected early care, regimes with two thinnings produced the best NPV regardless of the often low-yielding first thinning.     

Browsing and damage inflicted by moose in young Scots pine stands subjected to high-stump precommercial thinning

In Fennoscandia, young stands of Scots pine (Pinus sylvestris L.) are intensively used by moose (Alces alces L.) during winter. We studied whether forage amounts on high-cut pines in high-stump commercial thinning influenced browsing intensity and damage incidence on retained (i.e. uncut) pine stems. High-cut pines were browsed, but to a lesser extent than retained pines. At a scale corresponding to individual feeding sites (≈40 m²), browsing intensity on retained pines was not influenced by the amount of forage on high-cut pines but was positively related to moose pellet group counts. The incidence of lower-height damage (stem breakage and bark stripping) was positively related to the amount of forage on high-cut pines, whereas higher damage (leader shoot browsing) was not. Overall browsing damage incidence on retained pines was positively related to the density of deciduous trees and negatively related to the amount of forage on retained pines. Our results suggest that although high-stump thinning supplies additional food resources for moose, larger amounts of forage on high-cut pines may increase the risk for bark stripping and stem breakage on retained trees. Further research is needed at larger spatial scales to assess the feasibility of high-stump thinning as a damage mitigation measure.     

Associations between Pityogenes bidentatus and fungi in young managed Scots pine stands in Poland

The association between Pityogenes bidentatus and fungi was studied in young, managed Pinus sylvestris stands in Poland. Fungi were isolated from emerged adults and their galleries collected from four populations. In total, 2089 fungal isolates including 42 species, were obtained. Penicillium sp. 1 and Geosmithia sp. 1 were the most commonly isolated fungi from beetles (49% and 41% of beetles respectively). Geosmithia sp. 1 species was the dominant species in P. bidentatus galleries with a frequency of occurrence of 57.9%. Hormonema dematioides was the second most abundant fungus in gallery systems (17.1% of wood samples). Two of the isolated Geosmithia species were previously undescribed. Pityogenes bidentatus also vectored three ophiostomatoid species: Ophiostoma minus, O. piceae and Graphium sp. ‘W’. These species were occasionally isolated from beetles and their galleries, suggesting a non-specific relationship.     

Modelling probability of snow and wind damage in Scots pine stands using tree characteristics

Predictions of damage risk from snow and wind at sites using tree characteristics of Scots pine (Pinus sylvestris L.), were made using a subset of data from permanent sample plots within the Swedish National Forest Inventory (NFI). The plots were sampled twice at five-year intervals between 1983 and 1992. A logistic risk assessment model was developed using data originating from 286 plots, dominated by Scots pine (> 65% of basal area), within one county situated in the boreal zone in northern Sweden (Västerbotten). The model was evaluated with NFI-data from two other counties, one adjacent to Västerbotten (Västermorrland, 99 plots), which is also in the boreal zone, and one (Kalmar, 138 plots) in the hemi-boreal zone in southern Sweden. In each plot, measurements at first inventory of tree characteristics for the largest undamaged sample tree, and measurements at second inventory of damage from snow and wind on all sample trees were used to develop a logistic model that predicts the damage probability for each site. The best predictors were upper diameter (ud, diameter at 3 or 5 m) and the ratio of height/diameter at breast height (rhd). According to the model calculations, the overall damage probability never exceeded 0.26 for any of the sample plots used for model development. At a given ud the probability of damage is higher for a site with trees of low rhd. The fit of the model was better for the adjacent Västernorrland county than for the southern county, Kalmar. This inferior predictability was explained by differences in tree characteristics between Kalmar and the other counties. The results show that it is possible to predict damage from snow and wind at a site by using only single tree characteristics.     

Fine root biomass and production in Scots pine stands in relation to stand age

We determined fine root biomass and production of 15-, 35- and 100-year-old Scots pine (Pinus sylvestris L.) stands during three growing seasons. Fine roots were sampled by the soil core method. Mean (+/- SE) annual fine root biomass of Scots pine in the 15-, 35- and 100-year-old stands was 220 +/- 25, 357 +/- 21 and 259 +/- 26 g m(-2), respectively. Fine root biomass of the understory vegetation was 159 +/- 54 g m(-2), 244 +/- 30 and 408 +/- 81 g m(-2), and fine root necromass was 500 +/- 112, 1,047 +/- 452 and 1,895 +/- 607 g m(-2) in the sapling, pole stage and mature stands, respectively. Both understory and Scots pine fine root production increased with stand age. Mean annual Scots pine fine root production was 165 +/- 131, 775 +/- 339 and 860 +/- 348 g m(-2) year(-1) in the sapling, pole stage and mature stand, respectively. The respective mean annual production of all fine roots (Scots pine and understory) was 181 +/- 129, 1,039 +/- 497 and 1,360 +/- 869 g m(-2) year(-1). The Scots pine and understory fine root biomass, necromass and production varied in relation to stand age, although the variation was not statistically significant.     

Growth and phenology variation in progeny of Scots pine seed orchards and commercial seed stands

Tree improvement in Poland has been most advanced for Scots pine, but existing seed orchards have not been progeny-tested yet. We examined variation in growth traits—tree height at ages 4 and 8 years, and diameter at age 13 years—in the common garden experiment testing open-pollinated progenies of 31 seed orchards and 5 commercial seed stands (referred to as populations) at 5 locations. We also examined bud burst phenology at two to five sites at three growing seasons. At one experimental site during the 5th growing season, we measured shoot growth rhythm on all populations. Similar measurements of shoot growth were done on a subset of populations during the 6th growing season together with the analysis of needle growth and foliar chemistry. We found significant variation among populations in growth traits, but also significant population × site (G × E) interactions. We used the regression approach and ecovalence analysis to examine populations’ performance stability. Most populations had average responsiveness to environment, and a set of least-responsive poor-growing populations contributed the most to the G × E interaction. Variation in bud burst phenology was associated with geographical distribution of tested progenies. The early bud-bursting populations originated from the north-eastern to north-central Poland, and a group of late bud-bursting populations originated mainly from the south-eastern region. Correlations between bud burst and growth traits were weak to medium and varied by site, but early bud-bursting populations tended to show stronger growth on height and diameter. We found significant differences among populations in final leader length, shoot elongation time and relative growth rate (RGR). However, RGR and shoot elongation time explained less than 30% of variation in leader length and were weakly correlated with tree height. Populations varied in needle length, specific leaf area and foliar nitrogen concentration, but time trends in these traits did not vary among populations or predefined groups of populations. Therefore, the analysis of growth rhythm or needle traits did not help resolve variation in tree growth to support selection decisions. Contrary to our expectation, progeny of seed orchards did not perform significantly better than that of commercial seed stands. This finding, however, should not be extrapolated beyond our set of populations. Nonetheless, the local seed sources were not always the best. From a selection standpoint, our results help culling the worst populations rather than selecting the best ones. Therefore, testing individual family progeny and genetic roguing of existing seed orchards is highly recommended.     

Identifying the biological effects of pre-commercial thinning on diameter growth in young Scots pine stands

Data from seven Scots pine (Pinus sylvestris L.) stands in central Sweden that had undergone pre-commercial thinning (PCT) were used to investigate the biological effect of PCT on the diameter at breast height (DBH) growth of the remaining trees. Two treatments were considered: a PCT treatment and a control (C) with no PCT. The DBH of the trees in each stand was measured on up to four occasions over 15 years. We examined mean DBH and DBH growth of the largest 300, 600, 900 and 1200 trees ha^?1. Two methods of selecting the trees used to calculate the mean DBH values for each measurement occasion were considered: the actual mean DBH (Dma), which is based on the DBH distribution of the trees on the measurement occasion in question, and the genuine mean DBH (Dmg), which is based on the DBH distribution of the trees on the final measurement occasion of the study and therefore focuses on the same set of trees for all measurement occasions. There was no clear difference between the Dma- and Dmg-based DBH increments, but the Dmg values tended to be somewhat larger both for the C and PCT treatments. Over a 15-year period, the relative mean yearly increments (Dma/Dmg) for different tree size classes ranged from 0.91 to 0.98, with lower values for the C treatment and larger DBH size classes. We found that PCT promotes DBH growth: over a 15-year period, the increased growth amounted to about 2.0 mm year^?1 compared to the trees in unthinned plots.     

Growth patterns from different forest generations of Scots pine in Estonia

There is strong evidence that climate change alters tree growth in boreal forests. In Estonia, the analysis of ring measurements has been a common method to study growth changes. In this study, annual height growth data from dominant or co-dominant Scots pine (Pinus sylvestris L.) trees were used to develop a growth model for three forest generations. Stem analysis was applied and annual height growth was measured as the distance between whorls, as detected by branch knots of whorls on the split stem surface. Retrospective analysis of height growth produced comparative trends for three different age groups. Statistical analyses were used to estimate the impact of different factors on growth. Annual height growth was considered the best indicator for detecting possible trends in the growth potential of trees. Study results indicate that three generations (separated by time periods of 30–40 years) showed significant differences in growth patterns caused by shifts in climatic factors and management regimes (anthropogenic and natural disturbances).