Dynamic soil processes on heathland due to changes in vegetation to oak and Sitka spruce

Soil and soil water chemistry under three different vegetation-types on a former heath area were investigated in Jutland, Denmark. An unmanaged heathland left undisturbed since the start of this century is now invaded by the oaks. Together with a small Sitka plantation (age 60 years), soil development due to vegetation changes was investigated. The typical heathland podzol soil had changed within decades under the oak trees towards an acid brown soil. The soil under the Sitka spruce had changed towards a more strongly podzolized soil compared to the former heath soil. Present processes occurring within the soil were investigated by analysis of soil solution chemistry. The leaching of inorganic ions and soluble organic matter had increased manifold under Sitka spruce. Nitrification increased markedly with soil depth probably due to effects of higher pH. The increase of nitrate with soil depth was followed by a similar increase in dissolved aluminium. The equivalence of the dissolved organic carbon varies under oak and heath between 6 and 10 m eqv g⁻¹ TOC and under Sitka the equivalence of the dissolved carbon was between 10 and 15 m eqv g⁻¹. No nitrate and only traces of ammonium were found in soil water from the upper 30 cm of the soil under heath. Soil nitrogen was almost exclusively (more than 90%) connected to the carbon cycle. Under Sitka spruce generally less than 20% of soil water nitrogen was coupled to the carbon cycle, i.e. most of the nitrogen in the soil water leaving the rooting zone under Sitka spruce was nitrate. In the oak forest, nitrate only appeared as traces in the soil water in the winter period and in the summer period in relatively higher amounts. Generally, between 80% and 90% of the nitrogen was coupled to the carbon cycle in the winter and in the summer only 50%.     

Nitrogen budgets for Scots pine and Norway spruce ecosystems 12 and 7 years after the end of long-term fertilisation

The magnitude of nitrogen storage and its temporal change in forest ecosystems are important when analysing global change. For example, the accelerated growth of European forests has been linked to increased nitrogen deposition, but the changes in the N inputs that cause long-term changes in ecosystems have not yet been identified. We used two Swedish forest optimum nutrition experiments with Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) to study the long-term fate of N applied to these forest ecosystems. In the pine experiment, in addition to fertiliser (NPK) application, soil acidity was manipulated by application of lime and dilute sulphuric acid. From the spruce experiment, we selected treatments with similar fertiliser doses as in the pine experiment and with and without lime addition.We quantified various terms in the N budget 12 years (pine) and 7 years (spruce) after the last N addition. In the pine stand the NPK-treatment was the only treatment to produce a significant increase in N in the tree biomass (97% above control), whereas in the spruce stand the N additions increased tree N in all treatment combinations (207% above control). In the pine stand the relative distribution of nitrogen between trees and soil did not vary across treatments, with trees containing around 12% of ecosystem N and humus containing around 44% of soil N. The increases in N stocks in the pine stands were mainly in the soil. In contrast, in the spruce ecosystem trees accumulated most of the added N and the increase in the soil was restricted to the humus layer.In the pine ecosystem, large losses of added N (between 254 and 738 kg ha⁻¹ out of 1040 kg ha⁻¹ added as fertiliser) occurred, whereas in the spruce ecosystem we recovered more N than could be accounted for by inputs (between 250 and 591 kg ha⁻¹). There was no clear pattern in the interaction between acidification/liming and N additions.     

Variability in net primary production and carbon storage in biomass across Oregon forests—an assessment integrating data from forest inventories,intensive sites,and remote sensing

We used a combination of data from USDA Forest Service inventories, intensive chronosequences, extensive sites, and satellite remote sensing, to estimate biomass and net primary production (NPP) for the forested region of western Oregon. The study area was divided into four ecoregions differing widely in climatic conditions and management regime. The forest age distributions (as derived from inventory data) differed by ecozone with fewer old stands in the Coast Range and the East Cascades, and a relatively uniform distribution of ages from 0 to 815 in the Cascade Mountains. Age distributions also differed by land ownership, with fewer old stands on non-federal lands than on national forest lands. Estimated biomass increased rapidly in early stand development and tended to stabilize after about 200 years. Peak biomass in the semi-arid East Cascades was about one-third that of the other ecoregions (median biomass at asymptote ∼9 and ∼25 kg C m⁻², respectively). The timing and magnitude of maximum net primary production also varied by ecoregion, with the high productivity Coast Range forests reaching a maximum NPP before 30 years of age (median ∼1 kg C m⁻² y⁻¹), and the low productivity East Cascades reaching a maximum NPP between 80 and 100 years (median ∼0.3 kg C m⁻² y⁻¹). Productivity was generally lower in older stands with the exception of the East Cascades ecoregion where, contrary to the paradigm of age-related decline in forest growth, the oldest stands had the highest NPP. The East Cascades also differed from the other ecoregions in that the proportion of NPP allocated belowground decreased rather than increased with stand age. This study demonstrates the value of combining data from intensive and extensive measurement sites for improved estimates of carbon stocks and fluxes as well as improved parameterization of process models used in scaling carbon flux over broad regions.     

Dead trees and protected polypores in unmanaged north-temperate forest stands of Lithuania

The availability of coarse woody debris (CWD) and distribution of dead trees into categories of mortality (dead standing, broken and uprooted) were investigated in north-temperate forests of central Europe (Lithuania). The studied area comprised 188.7 ha and included 18 different stands 40–130 years of age with a variety of tree species (spruce (Picea abies (L.) Karst.), pine (Pinus sylvestris L.), alder (Alnus glutinosa (L.) Gaertn.), birch (Betula pendula Roth and B. pubescens Ehrh.), aspen (Populus tremula L.), oak (Quercus robur L.), forest types (caricus-sphagnum, vaccinium-myrtillus, oxalis, myrtillus-oxalis, caricus-calamagrostis) and edaphic conditions (peaty, sandy, loamy soils of different moisture). The stands were excluded from wood harvesting for at least 30 years. A total of 11 365 dead trees (over 10 cm in DBH) or 6160.7 m³ of dead wood was found (60.2 trees/ha and 32.6 m³/ha). The volume of CWD per hectare was larger in older stands (r_S=0.78, P<0.01). Tree mortality during the last 2 years consisted of 482 trees and 381 m³, or 1.28 trees/ha×year and 1.01 m³/ha×year. In 25–33% of cases it was wind-related. Uprooted and broken trees were of larger DBH than dead standing. The distribution into the categories of mortality was strongly dependent on tree species (chi-square test, d.f.=10,P=0). Dead standing dominated in CWD of pine and alder. Broken trees comprised almost a half in CWD of aspen, and about one-third in birch, alder and oak. Uprooting most often occurred in spruce, aspen and birch. Edaphic conditions and stand age had a pronounced impact on distribution into mortality categories for spruce (chi-square test, d.f.=20, P<0.00001) and pine (d.f.=8, P≤0.0003). On peat soil, only a minority of trees of both pine and spruce was uprooted, and standing dead prevailed. In CWD of spruce and pine, the proportions of both dead standing and broken decreased and that of uprooted trees increased on mineral soils of higher moisture and bulk density in older stands. By contrast, uprooting in birch and alder occurred less often on more wet sites, where the proportions of standing snags were higher. A total of 41 species of wood-decomposing polypores were found in the study area. Among those, 10 (24%) were of conservation value.     

Water and element fluxes during the regeneration of Norway spruce with European beech: Effects of shelterwood-cut and clear-cut

The regeneration of mature Norway spruce with European beech using the shelterwood silvicultural system is a good example of continuous cover forestry. In contrast, the regeneration may also start with clear-cut plots, which often occur after calamities like wind-throw or bark beetle attack. During regeneration the forest ecosystem becomes a highly dynamic system. Nutrient losses from the soil may occur as the element turnover is affected by the reduced nutrient uptake of forest trees as well as the enhanced mineralisation and nitrification due to higher soil temperature and soil moisture. Continuous cover forestry may help to reduce these nutrient losses. In order to test this, we investigated water and element fluxes of two chronosequences. The first investigated regeneration in the shelterwood system, while the second concerned itself with regeneration on clear-cut plots. In a shelterwood-cut about 30% of the mature spruce trees are removed and young beech trees are planted. Some 10 years later a secondary felling is carried out and at age 20 of the beech regeneration the final harvest of the mature trees occurs. Thus, the studied time steps were (a) the first 5 years after the initial cut and planting, (b) 10-year-old beech regeneration after the second shelterwood cut and (c) 20-year-old beech regeneration after the final harvest.Our results indicate that nutrient losses with seepage water – especially nitrogen, calcium and magnesium – occur during the first years after the clear cut and, to a lesser extent, after secondary felling on the selective-cut plot. This may temporarily affect seepage water quality due to elevated nitrate concentrations, which reached values of more than 100 mg l⁻¹. In the time span between planting and an age 20 of the beech regeneration, total losses of nitrogen from the main rooting zone reach 230 kg ha⁻¹ after clear cut. Preliminary estimates of the total nitrogen loss in the shelterwood system range between 150 and 230 kg ha⁻¹ indicating either significantly lower or equal losses of nutrients. In the second case, however, element output is distributed more equally over the 20-year-period than after clear felling where 85% of the nitrate leaching occurs during the first 3 years.     

Stand and landscape level effects of a major outbreak of spruce beetles on forest vegetation in the Copper River Basin,Alaska

From 1989 to 2003, a widespread outbreak of spruce beetles (Dendroctonus rufipennis) in the Copper River Basin, Alaska, infested over 275,000 ha of forests in the region. During 1997 and 1998, we measured forest vegetation structure and composition on one hundred and thirty-six 20-m × 20-m plots to assess both the immediate stand and landscape level effects of the spruce beetle infestation. A photo-interpreted vegetation and infestation map was produced using color-infrared aerial photography at a scale of 1:40,000. We used linear regression to quantify the effects of the outbreak on forest structure and composition. White spruce (Picea glauca) canopy cover and basal area of medium-to-large trees [≥15 cm diameter-at-breast height (1.3 m, dbh)] were reduced linearly as the number of trees attacked by spruce beetles increased. Black spruce (Picea mariana) and small diameter white spruce (<15 cm dbh) were infrequently attacked and killed by spruce beetles. This selective attack of mature white spruce reduced structural complexity of stands to earlier stages of succession and caused mixed tree species stands to lose their white spruce and become more homogeneous in overstory composition. Using the resulting regressions, we developed a transition matrix to describe changes in vegetation types under varying levels of spruce beetle infestations, and applied the model to the vegetation map. Prior to the outbreak, our study area was composed primarily of stands of mixed white and black spruce (29% of area) and pure white spruce (25%). However, the selective attack on white spruce caused many of these stands to transition to black spruce dominated stands (73% increase in area) or shrublands (26% increase in area). The post-infestation landscape was thereby composed of more even distributions of shrubland and white, black, and mixed spruce communities (17–22% of study area). Changes in the cover and composition of understory vegetation were less evident in this study. However, stands with the highest mortality due to spruce beetles had the lowest densities of white spruce seedlings suggesting a longer forest regeneration time without an increase in seedling germination, growth, or survival.     

Growth and carbon stocks of a spruce forest chronosequence in central Europe

Human induced changes in global environmental conditions are expected to influence or, as it is hypothesised in this study, have already influenced the biomass and growth of forest ecosystems. In this study, we reconstruct the history of tree growth and quantify the standing biomass along a chronosequence of six Norway spruce stands (Picea abies [L.] Karst; 16–142 years old) on acid soils in a mountainous region with high nitrogen deposition. The inventories of the study sites, as well as the historical stem growth of the sample trees were compared with common yield tables, representing growing conditions before 1960, to find out if and when significant changes in growth of trees had occurred. The growth at tree level (0.003–0.030 m³ yr⁻¹) was about 150–350% higher than predicted by the yield tables, independent of tree age. Because of low stand densities due to early thinning, the increase of stem growth at stand level (90% higher than yield table predictions) and the stand volume (35% higher than yield table predictions) were not as high as the increase of growth at tree level. Total biomass at stand level (including stems, branches, twigs, needles and roots) ranged between 35 and 180 t C ha⁻¹. Net primary productivity varied between 6 and 13 t C ha⁻¹ yr⁻¹. Intensive tree thinning activities probably stimulated growth of remaining trees, but the observed growth rates were beyond what would be expected from these activities exclusively. Thus it is assumed that the fertilisation effects of increased nitrogen deposition and CO₂ concentration, and improved climatic conditions due to ongoing climate change, have contributed to the observed changes in stem growth and that the thinning activities were synergetic with changing environmental conditions. The implications for carbon sinks as accountable under the Kyoto Protocol are probably small, because changes in environmental conditions are not accountable under the Kyoto Protocol and most of the observed changes in growth took place before 1990, the baseline for the Kyoto Protocol. Additionally, it is assumed that impacts on the carbon balance of forest stands due to changes in the thinning regime after 1990, which would be accountable according to article 3.4 of the Kyoto Protocol, are very small without any synergetic changes in environmental conditions.     

Wood volume yield and stand structure in Norway spruce understorey depending on birch shelterwood density

Wood volume yield and stand structure were investigated for Norway spruce understorey growing at 1500 trees ha⁻¹ under birch shelters of two different densities, 300 and 600 trees ha⁻¹, and Norway spruce growing without shelter, in a field trial in the boreal coniferous forest, 56 years after the establishment of the stand and 19 years after establishment of the trial.Wood volume yield in sheltered spruce (mean annual increments of 1.87 and 1.78 m³ ha⁻¹ year⁻¹ under the dense and sparse shelterwoods, respectively) was significantly lower than that of unsheltered spruce (mean annual increment 2.43 m³ ha⁻¹ year⁻¹). The loss in wood volume yield for sheltered spruce was more than compensated for by the additional wood volume yield in the shelterwoods (mean annual increments 3.26 and 1.88 m³ ha⁻¹ year⁻¹ for the dense and sparse shelterwood respectively).Shelterwood density did not produce any significant differences in inequality of the understorey stands, measured as skewness and the Gini coefficient for the wood volume distributions. This implies that two-sided competition for nutrients and water was more significant than competition for light.Immediately after trial establishment, trees in the no shelterwood treatment (i.e. where all overstory trees had been removed) showed a marked increase in diameter growth. Over time, the growth rate of unsheltered Norway spruce was reduced to a level comparable to that of sheltered spruce. The difference in average diameter has persisted during the trial period. There was no similar effect on height growth, resulting in an increased slenderness index (h/d) with increased shelterwood density for the understorey trees.     

Silvicultural measures to increase the mechanical stability of pure secondary Norway spruce stands before conversion

This study evaluates the effect of two different thinning treatments (2 and 3), and a control without thinning (1), on stand stability of secondary even-aged Norway spruce stands, in relation to the main risk factors of snow and wind, which should be considered in the period of stand conversion. Treatment 2 is a heavy thinning at top heights of 10, 12.5 and 15 m; treatment 3 starts with the first heavy thinning at the top height of 10 m, but the second and third treatments are delayed till a top height of 20 and 22.5 m are reached. The experimental stands are in secondary Norway spruce forest growing on a site considered unsuitable for that species and especially at risk from snow and storm damage. The investigated thinning variants significantly influenced the stability of the experimental stands. Both thinning treatments encouraged diameter increment and therefore their h/d ratio reached lower levels than the control. In treatment 2, the h/d ratio stabilized in the period of intensive treatment at around 80; i.e., it is the most suitable treatment from the viewpoint of stem-break resistance. Treatment 3 did not stop h/d ratio increase, but slowed it compared to the control variant without thinning. Subsequently the later interventions at the top heights of 20 m and, especially, 22.5 m stopped the increase of the h/d ratio and kept it under the critical value of 90.     

Effects of chronic nitrogen amendment on dissolved organic matter and inorganic nitrogen in soil solution

Increased atmospheric deposition of N to forests is an issue of global concern, with largely undocumented long-term effects on soil solution chemistry. In contrast to bulk soil properties, which are typically slow to respond to a chronic stress, soil solution chemistry may provide an early indication of the long-term changes in soils associated with a chronic stress. At the Harvard Forest, soil solution was collected beneath the forest floor in zero tension lysimeters for 10 years (1993–2002) as part of an N saturation experiment. The experiment was begun in 1988 with 5 or 15 g N m⁻² per year added to hardwood and pine forest plots, and our samples thus characterize the long-term response to N fertilization. Samples were routinely analyzed for inorganic nitrogen, dissolved organic nitrogen (DON), and dissolved organic carbon (DOC); selected samples were also analyzed to determine qualitative changes in the composition of dissolved organic matter. Fluxes of DOC, DON, and inorganic N were calculated based on modeled water loss from the forest floor and observed concentrations in lysimeter samples. The concentration and flux of inorganic N lost from the forest floor in percolating soil solution are strongly affected by N fertilization and have not shown any consistent trends over time. On average, inorganic N fluxes have reached or exceeded the level of fertilizer application in most plots. Concentrations of DOC were unchanged by N fertilization in both the hardwood and pine stands, with long-term seasonal averages ranging from 31–57 mg l⁻¹ (hardwood) and 36–93 mg l⁻¹ (pine). Annual fluxes of DOC ranged from 30–50 g m⁻² per year. DON concentrations more than doubled, resulting in a shift toward N-rich organic matter in soil solution percolating from the plots, and DON fluxes of 1–3 g m⁻² per year. The DOC:DON ratio of soil solution under high N application (10–20) was about half that of controls. The organic chemistry of soil solution undergoes large qualitative changes in response to N addition. With N saturation, there is proportionally more hydrophilic material in the total DON pool, and a lower C:N ratio in the hydrophobic fraction of the total DOM pool. Overall, our data show that fundamental changes in the chemistry of forest floor solution have occurred in response to N fertilization prior to initiation of our sampling. During the decade of this study (years 5–14 of N application) both inorganic N and dissolved organic matter concentrations have changed little despite the significant biotic changes that have accompanied N saturation.     

Effects of experimental acidification,nitrogen addition and liming on ground vegetation in a mature stand of Norway spruce (Picea abies (L.) Karst.) in SE Sweden

During the period 1976–1991, a combined experiment of acidification, liming and nitrogen addition in a mature spruce stand was conducted at Farabol in south-east Sweden. The aim of this study was to investigate the effects of these treatments on the ground vegetation 0, 1, 5 and 15 years after experimental establishment. The treatment regimes were nitrogen (200 kg N ha⁻¹, repeated three times at 4–5-year intervals, totally 600 kg N ha⁻¹), sulphur powder (50 and 100 kg S ha⁻¹ a⁻¹, totally 600 and 1200 kg ha⁻¹), sulphur plus nitrogen (600+600 kg ha⁻¹) and limestone (500 kg ha⁻¹ a⁻¹, i.e. totally 6000 kg ha⁻¹). The results showed that nitrogen addition and liming promoted the abundance of the grass Deschampsia flexuosa, while acidification had a negative effect on D. flexuosa and herbs in the field layer. There was a negative reaction giving immediate damage to the bryophytes in connection with additions of nitrogen, sulphur powder and lime. The magnitude of damage and the capacity to recover varied among species as well as among treatments. The recovery from immediate damage after liming was much faster than after the treatments with sulphur powder and/or nitrogen. A negative interaction between sulphur powder and nitrogen was found for herbs and mosses where the combined effects were stronger than the effects of a single treatment alone. Acidification also had a negative effect on the total number of species. The results of this study showed that acidification and nitrogen deposition could negatively influence forest vegetation by changing the nutrient availability in the soils. Liming led to an improved growth of the forest ground vegetation and the flora changed towards a more nitrophilic species composition.     

The impact of six European tree species on the chemistry of mineral topsoil in forest plantations on former agricultural land

Influences on mineral topsoils of common European tree species (oak-Quercus robur L., lime-Tilia cordata Mill., ash-Fraxinus excelsior L., birch-Betula pendula Roth., beech-Fagus sylvatica L. and spruce-Picea abies (L.) Karst.) were studied in 30 to 40-year-old stands planted in adjacent plots on former arable land. Mineral soil samples from two depth layers (0–10 and 20–30 cm) under the different species were compared in terms of pH, base saturation, pools and concentrations of exchangeable macro- and micronutrients, total nitrogen and carbon. With the exception of pH (H₂O) and extractable Al and Fe, no significant differences between species were detected in the lower layer. The upper (0–10 cm) layer was, however, affected differently depending on tree species: significant differences in pH, base saturation, exchangeable base cations and other nutrients were observed. The most prominent differences were between lime and spruce. Lime had considerably higher pH, base saturation, base cation and boron pools compared to spruce, which had the most acidifying effect on the mineral topsoils. Among the deciduous species, beech had the most similar effect to spruce on the upper layer of mineral topsoils. Soil C, N and C/N ratios did not differ significantly among species.     

Effects of wood-ash on the tree growth,vegetation and substrate quality of a drained mire: a case study

The effects of wood-ash fertilisation on tree stands, soil characteristics and ground vegetation were studied on a drained pine mire in Finland (64°51′N, 26°04′E, 62 m a.s.l.). The original site type was a treeless, mesotrophic Sphagnum papillosum fen. The site was drained in 1933 and the wood-ash fertilisation experiment was started in 1947. The treatments were: (i) unfertilised, (ii) wood-ash 8 t ha⁻¹, and (iii) wood-ash 16 t ha⁻¹.Drainage and ash application had radical and long-lasting consequences on the biological activity on the site and the vegetation compartments studied. The understorey vegetation had been profoundly affected by the ash with almost complete transformation of the species and other life forms. Even 50 years after the ash treatment the changes in vegetation/site type and the tree stand were clearly visible. On the unfertilised plot, the biomass of ground vegetation consisted mostly of mosses and dwarf shrubs, but on the ash-treated plots it consisted mostly of herbs and grasses typical of upland forests.Ash treatment had promoted stem volume growth of Scots pine (Pinus sylvestris L.) substantially and for a long time. The total wood production on the ash plots during 1947–1994 was 13 and 17 times over that of the control plot. Unfertilised pine trees suffered from P and K deficiency throughout the study period. The concentrations of some plant nutrients (P, K) decreased during the past years on Ash8. No nutrient shortage afflicting the tree stand was observed on Ash16 during the study period.Ash application has also led to increased concentration of nutrients in the peat. A sizeable proportion of the mineral nutrients applied were still in the 0–20 cm peat layer. On the ash-treated plots the amount of soil nitrogen (0–20 cm) was 18 and 29 times and the amount of soil phosphorus 9 and 13 times over the amount bound by the tree stand and the ground vegetation (Ash8 and Ash16, respectively). The stock of potassium was generally small in the surface peat—only 60–90% of the amount of potassium bound in the tree stand and the ground vegetation.It was concluded that wood-ash had powerfully influenced the biological processes in surface peat. The decomposition of cellulose was significantly accelerated by both ash treatments. Ash fertilisation also increased the emissions of CO₂. The intensified decomposition rate in the litter, vegetation and peat explained to a large extent the accelerated growth of the Scots pine stands studied.     

Carbon sources and sinks in high-elevation spruce–fir forests of the Southeastern US

This paper examines carbon (C) pools, fluxes, and net ecosystem balance for a high-elevation red spruce–Fraser fir forest [Picea rubens Sarg./Abies fraseri (Pursh.) Poir.] in the Great Smoky Mountains National Park (GSMNP), based on measurements in fifty-four 20 m × 20 m permanent plots located between 1525 and 1970 m elevation. Forest floor and mineral soil C was determined from destructive sampling of the O horizon and incremental soil cores (to a depth of 50 cm) in each plot. Overstory C pools and net C sequestration in live trees was estimated from periodic inventories between 1993 and 2003. The CO₂ release from standing and downed wood was based on biomass and C concentration estimates and published decomposition constants by decay class and species. Soil respiration was measured in situ between 2002 and 2004 in a subset of eight plots along an elevation gradient. Litterfall was collected from a total of 16 plots over a 2–5-year period.The forest contained on average 403 Mg C ha⁻¹, almost half of which stored belowground. Live trees, predominantly spruce, represented a large but highly variable C pool (mean: 126 Mg C ha⁻¹, CV = 39%); while dead wood (61 Mg C ha⁻¹), mostly fir, accounted for as much as 15% of total ecosystem C. The 10-year mean C sequestration in living trees was 2700 kg C ha⁻¹ year⁻¹, but increased from 2180 kg C ha⁻¹ year⁻¹ in 1993–1998 to 3110 kg C ha⁻¹ year⁻¹ in 1998–2003, especially at higher elevations. Dead wood also increased during that period, releasing on average 1600 kg C ha⁻¹ year⁻¹. Estimated net soil C efflux ranged between 1000 and 1450 kg C ha⁻¹ year⁻¹, depending on the calculation of total belowground C allocation. Based on current flux estimates, this old-growth system was close to C neutral.     

Regeneration of Norway spruce in canopy gaps in Sphagnum-Myrtillus old-growth forests

Gap-associated spruce (Picea abies (L.) Karst.) regeneration in Sphagnum-Myrtillus stands of south taiga forests (Central Forest Biosphere reserve, Tver region, Russia) was studied to evaluate the role of different disturbances in spruce dynamics. Sampled gaps (n=70) ranged from 40 m² to 1.7 ha in size, and from 1 to 70 years since disturbance moment. Formation of gaps lead to increase in the number of stems per ha in all gap size classes (small: 40–200 m², medium: 200–3000 m², and large: >3000 m² gaps). Spruce was the most important species in gap refilling, although its role was not the same in different gap classes. The highest values of relative abundance (compared to other species) were recorded in small gaps, and much lower values – in middle and large gaps. However, as refilling of gaps proceeded, spruce showed rather active regeneration in middle and large gaps and partly regained its abundance in middle-age disturbances. In general, all types of gaps studied supported spruce regeneration into the forest canopy. Almost perfect correlation between predicted outcome of spruce dynamics in gaps and its current role in the canopy of Sphagnum-Myrtillus stands suggests a good adaptation of this species to the current disturbance regime and a steady state of the these forests.     

Stand development and production dynamics of loblolly pine under a range of cultural treatments in north-central Florida USA

The objectives of this study were to examine the effects of stand development and soil nutrient supply on processes affecting the productivity of loblolly pine (Pinus taeda L.) over a period approximately equal to a pulpwood rotation (18 years). The experiment consisted of a 2×2 factorial combination of complete and sustained weed control and annual fertilization treatments (C: control treatment, F: fertilization, W: weed control, FW: combined fertilization and weed control), located on a Spodosol in north-central Florida, USA. The reduction of soil nutrient limitations through fertilization or control of competing vegetation resulted in dramatic increases in almost every measure of productivity investigated, including height (19.7 m in the FW treatment versus 12.5 m in the C treatment at age 18 years), basal area (FW=44.2 m² ha⁻¹, F=39.6 m² ha⁻¹, W=36.6 m² ha⁻¹, C=19.9 m² ha⁻¹ at age 16 years), stemwood biomass accumulation (114 Mg ha⁻¹ in FW versus 42.8 Mg ha⁻¹ in C at age 18 years), foliar nitrogen concentration (1.53% in plots receiving fertilization versus 1.06% in unfertilized plots at age 17 years) and leaf area index (age 16-year peak projected of approximately 3.3 at age 9–10 years in F and FW plots, 2.5 in the W treatment and 1.5 in the C plots). Cultural treatments also decreased the growth ring earlywood/latewood ratio, and accelerated the juvenile wood to mature wood transition. While soil nutrient supply was a major determinant of productivity, production changes that occurred within treatments over the course of stand development were equally dramatic. For example, between age 8 and 15 years, stemwood PAI in the FW treatment declined by 275%; similarly large reductions occurred in the F and W treatments over the same time period. The reductions in PAI in the treated plots were linearly related to stand BA, suggesting the decline in productivity was associated with the onset of inter-tree competition. Responses of stemwood PAI to re-fertilization treatments at age 15 years suggests that the declines in growth and growth efficiency with time were partially attributable to nutrient limitations.     

Applicability of a forest simulation model for estimating effects of nitrogen deposition on a forest ecosystem: Test of the validity of a gap-type model

Ecosystem models have been used to compile scattered information on various ecosystem processes and to test the hypotheses about ecosystem responses to various simultaneously changing environmental factors. In spite of the widespread use of models, there have been comparatively few quantitative evaluations of model projections compared to long-term observations under changing environmental conditions (e.g. increased nitrogen deposition). In this study we tested the validity of a gap-type forest simulation model (SIMA) in order to extend the applicability of the model for the prediction of how nitrogen deposition influences the production of a boreal forest ecosystem. The validity of the model was tested by comparing the prediction of the model with independent data from long-term fertilization experiments. The predictions provided by the SIMA model agreed fairly well with the results of long-term fertilization experiments. Both the experiments and the model simulations showed similar increases in stem-wood production and in growing stock as a consequence of repeated nitrogen fertilization over the 30-year study period. The addition of nitrogen increased the total production by 30–53% according to field experiments and by 39–63% according to model computations. In both the model calculations and the field experiments, organic matter accumulated in the soil after the addition of nitrogen. The increase in the amount of soil organic matter can be explained as being due to the increased biomass production and the resulting increase in litterfall. According to the model computations, annual litterfall of needles on the mesic site varied from 970 kg ha⁻¹ to 3050 kg ha⁻¹ and this agreed well with measured litterfall of the stand.     

Factors affecting stand structure in forests – are there climatic and topographic determinants?

Multi-aged stands are not a common structural type of mountain-ash forest in the Central Highlands of Victoria, southeastern Australia, but they are nevertheless important, particularly as habitat for wildlife. Extensive field data and information generated from spatial models of climate, topography and radiation regimes were examined to identify factors which related to the occurrence of stands of multi-aged mountain-ash forest. The probability of occurrence of multi-aged stands increased significantly (p < 0.001) with the age of the forest. There also was evidence that multi-aged stands were more likely to occur on steeper slopes (p = 0.01). When actual on-ground field measurements were ignored and program-generated climate, topography and radiation data only were modeled, a decrease in the shortwave radiation ratio (a measure of the estimated solar radiation budget) was associated with a significantly increased probability of occurrence (p = 0.03) of multi-aged stands. Our analyses indicated there are particular parts of mountain-ash forest landscapes where complex multi-aged stand structures are more likely to develop. This has implications for the methods used to harvest mountain-ash forests for timber and pulpwood, particularly the need for increased retention of structural components of stands targeted for logging.     

Estimating water use of sclerophyllous species under East-Mediterranean climate: III. Tabor oak forest sap flow distribution and transpiration

The annual course of daily transpiration and the hydrological balance of a Tabor oak forest were determined. The study was done in a representative forest within the natural geographical range of the species in the lower Galilee region of Israel. The climate is sub-humid with a rainless dry season from May to October. A partial water balance of a 0.1 ha area supporting an average of 14 trees was calculated from: (a) soil water content (SWC) measured by a Neutron Probe at depths of from 0.2 to 8 m, and (b) daylight transpiration rate measured with sap flow sensors by the heat pulse technique.Soil–bedrock complex water content (%) in the first 2 m of the profile fluctuated strongly between 5 and 20% depending on the season. The water content increased with depth from about 10% at 2.0 m depth to more than 20% at 5.0 m depth. For depths exceeding 5.5 m seasonal fluctuations in water content were negligible and water content ranged from 30 to 35%. After a dry winter, water content generally decreased within the main root zone down to about 2.0 m depth. Monthly changes in water content (mm) were greatest at depths of 0.35–1.0 m. Only minor changes in the soil–bedrock complex water content were recorded at greater depths. After a very rainy winter (2002/2003), decreases in soil–bedrock complex water content in the upper 2 m were much larger than after a dry winter. Fluctuations of soil–bedrock complex water content in deeper regions were larger in the wetter year, probably the result of drainage.Sap velocity was measured at six depths in the sapwood, from 4 to 44 mm, at 8 mm intervals. Sap velocity declined with depth, hence, sap flux density too.Based on sap velocity measurements performed during 4 years, the annual average daily transpiration (T) was 0.796 mm/day. This sums up to 239 mm during ∼300 days of leaf carriage, i.e. 41.3% of the 578 mm average annual rainfall for the area in the last 50 years. In a relatively dry year (rainfall of 432.7 mm) total water withdrawal from the 8 m soil–bedrock profile was 81% of the annual rainfall; of this amount 69% were transpired by the oak trees (239.0 mm), or 55% of the annual rainfall. In a relatively wet year (annual rainfall 801.4 mm) total water withdrawal was 67%; of this amount 45% would be transpired by the oak trees, or 30% of the annual rainfall.     

Production,allocation, and stemwood growth efficiency of Pinus taeda L. stands in response to 6 years of intensive management

Loblolly pine (Pinus taeda L.) is a highly plastic species with respect to growth responses to forest management. Loblolly pine is the most planted species across the southern United States, a region with the most expansive and intensively managed forest plantations in the world. Management intensity, using tools such as site preparation and fertilization, is increasing greatly in scope over time. To better define to the productive potential of loblolly pine under intensive management, the influence of 6 years of management with weed control (W), weed control plus irrigation (WI), weed control plus irrigation and fertigation (irrigation with a fertilizer solution) (WIF), or weed control plus irrigation, fertigation, and pest control (WIFP) since plantation establishment on stand productivity in loblolly pine was examined. The site is located near Bainbridge, GA (30°48′N latitude and 84°39′W longitude) and is of medium quality (site index=18 m, base age 25). Increasing management intensity greatly accelerated stand development and biomass accumulation. At age 6 total production (above plus belowground) was nearly doubled from 50 to 93 Mg ha⁻¹ in WIFP stands compared to W stands, and standing stem biomass increased from 24 Mg ha⁻¹ in W stands to 48 Mg ha⁻¹ in response to WIFP treatment. Stem current annual increment (CAI) peaked at age 5 in the WIF and WIFP stands at 17–18 Mg ha⁻¹ per year at a basal area between 18 and 21 m² ha⁻¹. Year to year variation in CAI was better explained by previous-year leaf area index (LAI) than current-year LAI. Maximum stemwood production in loblolly pine was achieved through large increases in LAI and small decreases in allocation to woody roots (tap+coarse roots) versus woody shoots (stem+branches) associated with intensive treatments.