For assessing the impact of soil temperature on tree growth in remote areas such as the alpine timberline we introduce a new method for soil temperature manipulations. This new approach is based on roofing of the rooting zone and allows either soil cooling or soil warming without significantly influencing soil water availability and the above ground microclimate.
To test whether the altitudinal limit of tree growth is determined by carbons shortage or by a limitation in growth we investigated non structural carbohydrates and their components starch and total soluble sugars in Pinus cembra trees along an elevational gradient in the timberline ecotone of the Central Austrian Alps. NSC contents in needles, branches, stems, and coarse roots were measured throughout an entire growing season. At the tissue level NSC contents were not significantly more abundant in treeline trees as compared to trees at lower elevations. Along our 425 m elevational transect from the closed forest to the treeline we failed to find a stable elevational trend in the total NSC pool of entire trees and observed within season increases in the tree's NSC pool that can be attributed to an altitudinal increase in leaf mass as needles contained the largest NSC fraction of the whole tree NSC pool. Furthermore, whole tree NSC contents were positively correlated with net photosynthetic capacity. Although our observed NSC characteristics do not support the hypothesis that tree life at their upper elevational limit is determined by an insufficient carbon balance we found no consistent confirmation for the sink limitation hypothesis.
The study purpose selected among several candidate models for best individual tree, over bark, total volume model, volume
ratio model to any top height limit and taper model for maritime pine (Pinus pinaster Aiton) in the regions of Pinhal Interior Sul and Beira Interior Sul, Portugal. The data used in the study were collected
from 144 felled trees, corresponding to 995 diameter/height measurements. To select among the best models, several statistics
were computed during model fitting, and the independent validation procedure was used to evaluate model fitting, collinearity
and prediction performance. A ranking index was used to support the final decision. The analysis of models studentized residuals
distribution showed that some regression model assumptions, such as normality and homogeneity, were not met. To overcome this
unideal situation, the models selected were then fitted again using robust regression and weighted regression techniques.
The set of adjusted models will allow the prediction of individual tree, over bark, total volume and merchantable volume to
any merchantable limit, for both species and region to support management decisions.
KeywordsTotal volume model–Volume ratio model–Taper model–Merchantable volume–
Pinus pinaster Aiton
Skid trails of regular harvest operations with time delays up to 24years between tracking and examination were investigated in order to characterize the status of recovery of essential soil functions. The study was focused on the ability of soils to serve as an effective rooting space. The gas diffusion coefficient and the fine root distributions of comparable sensitive silty loams were used to describe the disturbances of soil functions still detectable after decades. Tracking with heavy loaded machines severely reduced the soil aeration and in consequence the ability of the soil to act as a rooting space. Reduction of gas diffusivity and rooting was found on the whole skidding trail area and even expanded to the close vicinity of the margin zone. Up to 14years after machine impact, gas diffusion coefficients and root densities beyond 4cm depth under wheel tracks showed no signs of restoration. Soil aeration and root densities comparable to the control plot were found in the top soil layer 18years after tracking at the site Ettenheim. At that location 24years after machine impact, significantly reduced root densities occurred only in soil depths beyond 54cm. In the long run, only concentration of machine traffic on permanent skid trail systems guarantees an adequate soil preservation. This applies especially under Middle European site conditions and management practices. This prescription must be underlined in guidelines for machine use in forests.
In the last century, many calcareous soils in Castilla León (northwestern Spain) have been transformed from natural Quercus ilex forest to cropped land. Reforestation with Pinus halepensis has been taking place during the past 40years. In order to obtain a better understanding of how these disturbances affect
ecosystem functioning, we studied the quantity and quality of soil organic matter (SOM) in natural forest ecosystems, cropland
and Pinus plantations. Density fractionation combined with ultrasonic dispersion enables separation and study of SOM fractions:
free organic matter (OM), OM occluded into aggregates and OM stabilized in organo-mineral complexes, considered on the basis
of the type of physical protection provided. We separated SOM density fractions and determined the concentrations of C and
N, C/N ratios and the natural isotopic abundance (δ13C and δ15N values). Transformation of Quercus forest to cropland resulted in major losses of SOC and N, as expected. However, subsequent
reforestation with Pinus resulted in good recovery of the original SOC and soil N pools. This indicates the potential for
enhanced C storage in agricultural soils by their reversion to a forested state. Study of the density fractions and their
13C and 15N signatures enabled better understanding of the high stability of OM in calcareous soils, and analysis of δ13C variations throughout the profile also enabled identification of past C3/C4 vegetation change. Despite the different OC
contents of soils under different land use, OM stabilization mechanisms were not significantly different. In calcareous soils,
accumulation of SOC and N is mainly due to organo-mineral associations, resulting in physicochemical stabilization against
KeywordsLand use change-Density fractions-δ13C-δ15N
The objectives of this study were to quantify the amount of the stream discharge, nutrient fluxes, suspended sediment loss,
and to define the relationship between streamflow and these parameters in a forest-covered watershed. The study was carried
out in an experimental watershed, which has been monitored since 1979 in the Belgrad forest in Istanbul. Significant linear
regressions were obtained between streamflow and discharge of selected water quality parameters. Mean monthly losses were
10.01kg/ha for HCO3
−, 5.92kg/ha for CI−, 0.07kg/ha for total N, 1.29kg/ha for Mg2+, 3.59kg/ha for Ca2+, 2.59kg/ha for Na+, 1.82kg/ha for K+, 0.0113kg/ha for P-PO4
3−, and 35.82kg/ha for suspended sediments. Among the monitored water quality parameters, HCO3
−, CI−, and Ca2+ had greater losses than the rest of the chemical parameters studied in the watershed. Net gains (influx exceeded outflux)
calculated for total N, Mg2+, K+, and P-PO4
3− in the annual basis can be considered as an addition to the ecosystem’s organic nutrient pool. In contrast, net losses occurred
−, CI−, Ca2+, and Na+.
The paper deals with the issue of the spontaneous development of Central-European floodplain forests. The research object
was the Cahnov–Soutok National Nature Reserve situated on the confluence of Dyje R. and Morava R. in the Czecho–Slovak-Austrian
borderland area. This locality has been left to spontaneous development since the beginning of the 1930s. In the years 1973,
1994 and 2006, the surveyed site was subjected to the measurement of standing and lying, live and dead trees reaching a diameter
at breast height of 10cm and the whole area regeneration of woody species. The work objective is to describe the most pronounced
trends in tree layer changes having occurred in the period of study and to capture changes in the total tree volume and production
of dendromass during the disintegration of the old grazing oak layer. The survey into the near-natural floodplain forest of
Cahnov–Soutok showed that (1) the most significant trend is a decreased representation of Quercus robur in all monitored indicators and conversely an expanding representation of Acer campestre, Carpinus betulus and Tilia cordata and (2) that the floodplain forest ecosystem demonstrates a high-level stability in the total volume of tree biomass with
an essential change in the tree species composition, spatial structure and average stem volume of individual trees.
A model of public cost-sharing in private forest investment is proposed to describe the substitution between the private financing of investments and public investment assistance. The substitution depends on the curvature conditions of the forest investment function on forest stock. When the second-order investment effects are close to zero or when they do not exist, the funding substitution will not take place. A simultaneous econometric model for private and public funding employing forest incomes, forest income taxes, interest rates, investment scale and market wood price expectations as exogenous variables is estimated. The model estimation based on Finnish regional data in 1983–2000 rejects the substitution alternative. A 10% increase in private investment funding increases the demand for public funding at the same rate, but a 10% increase in public funds will increase the private funds supply by 2.5%. Significant income effects are found only in the case of private funding. In northern Finland, the scale effects are large for public financial assistance. The effects of the income tax reform on the private supply of funds are positive, especially for the new wood-sales profit taxation, whereas the interest rate and price expectation effects are negative.
Since the year 2000 mature beech and spruce trees were treated in a field experiment with double ambient ozone concentrations.
Elevated ozone had no influence on average single leaf biomass and there were also no ozone effects on leaf nutrient concentrations
in climatic normal years. However, the extraordinary dry summer 2003 triggered significant differences between the fumigated
and control trees. For beech in the year after the drought event the control trees surprisingly had significantly lower foliar
levels of K and P than in former years, whereas the ozone exposed trees showed no significant nutritional effects. There are
indications, that the trees exposed to double ambient ozone were already adapted to higher ozone values, whereas the control
trees experienced extraordinary high ambient ozone concentrations in the dry and sunny summer 2003. For spruce in autumn 2003
and 2004 ozone treated trees had significantly higher foliar levels of K in current year needles than control trees, an effect
which cannot be thoroughly interpreted yet on the basis of the dataset available.
We present a field study on the drought effects on total soil respiration (SRt) and its components, i.e., “autotrophic” (SRa: by roots/mycorrhizosphere) and “heterotrophic” respiration (SRh: by microorganisms and soil fauna in bulk soil), in a mature European beech/Norway spruce forest. SRa and SRh were distinguished underneath groups of beech and spruce trees using the root exclusion method. Seasonal courses of SRa and SRh were studied from 2002 to 2004, with the summer of 2003 being extraordinarily warm and dry in Central Europe. We (1) analyzed
the soil temperature (T
s) and moisture sensitivity of SRa and SRh underneath both tree species, and (2) examined whether drought caused differential decline of SRa between spruce and beech. Throughout the study period, SRa of beech accounted for 45–55% of SRt, independent of the soil water regime; in contrast, SRa was significantly reduced during drought in spruce, and amounted then to only 25% of SRt. In parallel, fine-root production was decreased during 2003 by a factor of six in spruce (from 750 to 130mgl−1a−1), but remained at levels similar to those in 2002 in beech (about 470mgl−1a−1). This species-specific root response to drought was related to a stronger decline of SRa in spruce (by about 70%) compared to beech (by about 50%). The sensitivity of SRa and SRh to changing T
s and available soil water was stronger in SRa than SRh in spruce, but not so in beech. It is concluded that SRa determines the effect of prolonged drought on the C efflux from soil to a larger extent in spruce than beech, having potential
implications for respective forest types.
Tree rings from the Alpine area have been widely used to reconstruct variations in summer temperature. In contrast, estimates
of changes in the hydrological cycle are rather scarce. In order to detect altitudinal and species-specific patterns of growth
responses to anomalous dry and wet conditions, a large network of 53 tree-ring width site chronologies along the Rhone valley
(Valais, Switzerland) covering the 1751–2005 period was compiled and analyzed. A total of 1,605 measurement series from four
conifer species—pine, larch, spruce, fir—were detrended to allow inter-annual to multi-decadal scale variability to be preserved.
Site chronologies were combined to four altitudinal (colline: <800m asl, sub-montane: 800–1,000m asl, montane: 1,000–1,450m
asl, sub-alpine: >1,450m asl) and species-specific mean time-series. These records were compared with temperature, precipitation,
and drought (scPDSI) data. Among the altitudinal records, the colline chronologies showed highest correlation with June precipitation
and scPDSI (0.5 and 0.7). Altitudinal effects, via control on climatic conditions, were superimposed upon species-specific
characteristics in affecting tree growth and response to moisture variations. In particular, species-specific differences
affected the significance level of drought response, with decreasing drought sensitivity towards higher elevations. Growth
conditions were found to be optimal at ~1,300m asl, with precipitation/drought limiting tree growth below and temperature
above. Common years of extreme drought and low growth for the colline sites occurred in 1921, 1944, 1976, 1992, and 1998.
Our results demonstrate the potential of lower elevation conifers for reconstructing long-term changes in Alpine hydro-climate.
KeywordsAlpine drought-Tree-ring width-Hydro-climate-Dendroclimatology
COST (COST is an intergovernmental framework for European cooperation in science and technology. COST funds network activities,
workshops and conferences with the aim to reducing the fragmentation in European research) Action E47, European Network for
Forest Vegetation Management—Towards Environmental Sustainability was formed in 2005 and gathered scientists and practitioners
from eighteen European countries with the objective of sharing current scientific advances and best practice in the field
of forest vegetation management to identify common knowledge gaps and European research potentials. This paper summarizes
the work of the COST action and concludes that although diverse countries have by necessity adopted different means of addressing
the challenges of forest vegetation management in Europe in the 21st century, some common themes are still evident. In all
countries, there is a consensus that vegetation management is a critical silvicultural operation to achieve forest establishment,
regeneration, growth and production. It appears that herbicides are still in use to some degree in all the countries reviewed,
although at a lower intensity in many of the northern countries compared to other regions. The most common alternatives to
herbicides adopted are the use of mechanical methods to cut vegetation and achieve soil cultivation; overstorey canopy manipulation
to control vegetation by light availability; and in some instances the use of mulches or biological control. Any reductions
in herbicide use achieved do not seem to have been driven solely by participation in forest certification schemes. Other factors,
such as national initiatives or the availability of additional resources to implement more expensive non-chemical approaches,
may be equally important. The development of more cost-effective and practical guidance for managers across Europe on non-chemical
control methods can best be brought about by future collaborative research into more sustainable and holistic methods of managing
forest vegetation, through the identification of silvicultural approaches to reduce or eliminate pesticide use and through
gaining a better understanding of the fundamental mechanisms and impacts of competition.
KeywordsVegetation management-Alternatives to herbicides-Forest certification-Weeds
Applications of flow models to tall plant canopies are limited, amongst other factors, by the lack of detailed information on vegetation structure. A method is presented to record 3D vegetation structure and make this information applicable to the derivation of turbulence parameters suitable for flow models. The relationship between wind speed, drag coefficient (C
) and plant area density (PAD) was experimentally investigated in a mixed conifer forest in the lower part of the Eastern Ore Mountains. Essential information was gathered by collecting multi-level high-frequency wind velocity measurements and a dense 3D representation of the forest was obtained from terrestrial laser scanner data. Wind speed dependence or streamlining was observed for most of the wind directions. Edge effects, i.e. the influence of the here not regarded pressure gradient and the advective terms of the momentum equation, are assumed to cause this heterogeneity. Contrary to the hypothetic shelter effect, which would reduce the drag on sheltered plant parts, the calculated profiles of drag coefficients revealed an increasing C
with PAD (i.e. a dependence on canopy and plant structure).
Airborne laser scanning (ALS) data are not usually considered to be very informative with respect to tree species, and this information is often obtained by combining such data with spectral image material. The aim was to test the ability of height, density, intensity and applied 2D and 3D texture variables derived solely from a very high-density ALS point cloud to describe the crown shape and structure characteristics required for tree species discrimination. Linear discriminant analysis was used to find optimal combinations of variables within the predictor groups, and classifications based on variables from different groups were compared. The third power of the tree diameter was used as a stem volume approximate, and rather than examining species alone, the classification was evaluated with respect to the volume approximates assigned to the predicted species. The sensitivity of pulse density to the methodology presented here was determined by simulating thinned data sets by reducing the initial pulse density. The reliability of the estimates was analysed both with functions generated using the original data and with new functions for each thinning level. Alpha shape metrics developed for describing tree crowns constructed from the 3D point clouds proved capable of discriminating between all three species groups evaluated, and several height distribution and textural variables were found to discriminate between the coniferous tree species. The results demonstrate the importance of species interpretation in forest inventories based on allometric modelling, but then indicate that species-specific estimation could be carried out using ALS-derived variables alone.
This paper presents an assessment of the ability of the 3PG process-based model to simulate height (h) and diameter at breast height (DBH) growth in three plots located in a Eucalyptus globulus plantation on the Atlantic coast of Galicia (Northwest Spain). The obtained results show how this model estimates adequately
height (h) and DBH growth, and determination coefficients (R
2) between observed data and data predicted by the model are always higher than 0.97, root mean square error (RMSE) of 0.45–1.05cm
in DBH and 0.46–0.85 in h, and a model efficiency (EF) close to 1 (0.98–0.99). In order to improve the results predicted by the model, we propose modifying
the nS and fullCanAge parameter values given by default so as to adjust growth rates in the plantation to the weather conditions in the site. The
ability of the model to discriminate growth rates in the three plots must be noted, even when plots are located in the same
plantation and they only show differences in aspects related to site factors. Given the obtained results in the three plots
used in this study, its simplicity and the small number of parameters needed as input data, the 3PG model stands out as a
very useful tool for forest plantation management.
KeywordsForest growth model-Process-based models-3PG-Eucalyptus globulus-Site factors
Fine root dynamics in mono-specific stands of mature Fagus sylvatica L. and Picea abies Karst. was studied from December 2003 to December 2004 in a stand in Southern Germany. Minirhizotrons were used to draw between
species comparisons concerning fine root (≤1mm) longevity and temporal patterns of fine root dynamics (growth and mortality)
as related to seasonal changes in soil water content and soil temperature. In F. sylvatica, median fine root longevity from early seasonal to late-seasonal cohorts was low (77days). Fine root dynamics scaled positively
with seasonal changes in soil water and temperature indicating accelerated fine root turnover during favourable soil conditions.
In contrast, fine root longevity in P. abies (273days) was significantly higher when compared to F. sylvatica and increased from early seasonal to late-seasonal cohorts. Fine root dynamics in P. abies did not correlate with soil environmental conditions. Rather a large proportion of new fine roots occurred during the dry
season in superficial soil layers. The data suggest species inherent patterns of fine root longevity and temporal patterns
of fine root dynamics.
KeywordsEuropean beech-Norway spruce-Fine root dynamics-Fine root longevity-Soil water-Temperature
In spite of its high diversity the forests in Southern Ecuador are highly endangered by deforestation. One of the main reasons
for the loss of forests is the conversion into pastures. Due to their fast degradation, the pastures are abandoned after several
years and form an increasing area of unproductive land. The remoteness from existing forest edges is discussed as one reason
for the very slow natural reforestation of these areas. In this study we analyzed the regeneration of a secondary forest after
approx. 38years of succession in relation to the distance from the surrounding forest. We revealed that regeneration was
rather slow. Especially larger trees with dbh>10cm were very scarce. Only Dioicodendron dioicum, Graffenrieda emarginata and Clusia sp. achieved larger diameters. The basal area of the secondary forest is still far beyond the original level in the primary
forest. The number of species on plot level and the Shannon index were significantly lower in the secondary forest compared
to the primary forest. The total number of species decreased from 47 to 31 with increasing distance from the forest edge and
the similarity of species composition to the upper story declined to a level of 56.4 (Sörensen). Alzatea verticillata, Macrocarpea revoluta and Palicourea andaluciana had significantly higher abundances in the succession stages than in the natural forest. The most abundant species in all
regeneration plots, G. emarginata and Purdiea nutans, seem to be generalists as they did not show preference either to natural forest or successional stages.
Eight-year-old plantations (11) of silver birch were studied on abandoned agricultural land in Estonia. Trees were planted
on uncovered soil and on polyethylene. After eight growing seasons, the height and diameter at breast height of the trees
grown on polyethylene were significantly (P<0.001) larger than corresponding parameters of the trees grown on uncovered soil. The annual height increment of the birches
grown on the polyethylene was significantly (P<0.05) larger during six growing seasons after planting compared to that of the trees grown on uncovered soil. However,
annual height increments were not significantly different in the 7th and the 8th growing seasons. The use of polyethylene
mulching had a statistically significant effect (P<0.001) on the height of the beginning of the live crown in 8-year-old plantations. The differences between the values of
live crown ratio of the trees grown on polyethylene and the values of live crown ratio of the trees grown on uncovered soil
decreased during six growing seasons. However, by the 7th and 8th growing seasons, there was no significant difference (P>0.05) between the values of the live crown ratio. The height growth of silver birch grown without mulching as well as with
mulching was found to be more intensive on Glossic Podzoluvisol, Calcaric Cambisol, Calcaric Luvisol and Dystric Gleysol; however, the height growth was more intensive on mulched soil. The height growth of the birches was modelled on the single-tree
and stand levels for five soil types.
KeywordsSilver birch-Field soils-Polyethylene mulching-Height growth model-Crown characteristics
The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics
of a 8-year-old silver birch (Betula pendula) natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current
annual production after eight growing seasons was 31.2 and 11.9tDMha−1, respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass
of the stand. Carbon sequestration in tree biomass reaches roughly 17.5tCha−1 during the first 8years. The biomass of the fine roots (d<2mm) was 1.7±0.2tDMha−1 and 76.2% of it was located in the 20cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7m2m−2 and specific leaf area (SLA) 15.0±0.1m2kg−1. The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared
with the lower part. The short-root specific area (SRA) in the 30cm topsoil was 182.9±9.5m2kg−1, specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry mass
unit of short roots were 145.3±8.6mg−1, 58.6±3.0kgm−3 and 103.7±5.5tipsmg−1, respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6,
25.0 and 56.6kgha−1, respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7kgha−1yr−1 (55 and 27%), respectively, of which 29.1kgha−1 N and 2.8kgha−1 P were accumulated in the above-ground part of the stand.
Inspection of Norway spruce and Silver fir on experimental plots in south-western Germany showed that Silver fir had suffered
significantly less bark injuries than Norway spruce. Data from both federal forest inventories (1987, 2002) showed a similar
species-specific vulnerability. Additional visual inspections of the basal cross-sections of trees removed from the experimental
plots showed rather high proportions of butt rot in uninjured Norway spruce (51%). The proportion further increased to 93%
in trees, which had sustained bark injuries. In contrast, decay symptoms were almost absent in uninjured Silver fir and less
enhanced in trees with bark injuries (27%). Management implications for risk rating of tree species, as well as the necessity
of implementing low-damage harvesting regimes, are discussed.
Using a representative sample of stands from a cross section through the Bavarian portion of the northern Calcareous Alps, this study evaluates the plausibility and significance of causal hypotheses for an explanation of the poor crown condition of Norway spruce in mountain forests: (1) ozone exposure in conjunction with (a) drought and (b) ample water supply; (2) soil-borne nutrient deficiency; (3) drought; and (4) tree age. Site index and, in a subset of stands, foliar nutrient concentrations are considered as additional indicators of tree vigour. According to principal component analysis and multiple regression, crown condition was controlled by soil chemistry (transparency increased towards shallow calcareous soils), stand age and, to a smaller degree, by an interaction between ozone exposure and drought. Site index was best explained by a model including elevation, soil chemistry and drought. Tree nutrition clearly reflected the main soil chemical gradient, and P, N and Fe deficiencies were found in transparent stands, which had markedly smaller needles. The similar distributions of crown transparency, site index and nutrition present a strong argument for the hypothesis that soil chemistry has constrained the vigour of spruce trees in the Calcareous Alps for a long time. By leaving unproductive stands to age naturally, forest management has accentuated the pattern of crown condition. In the heterogeneous alpine landscape, possible effects of recent increases in ozone exposure have to be viewed extremely carefully against the background of these natural and anthropogenic covariables.
This study examined topsoil samples from the humic mineral horizon in four pure silver fir (Abies alba Mill.) and five mixed stands with beech (Fagus sylvatica L.), spruce (Picea abies L.; Karst.) and pine (Pinus sylvestris L.). In every stand, 60–70 sampling locations were chosen using a stratified random scheme that represented a gradient in
local stand density and local species composition. One working hypothesis was that stand density and species composition affect
the content of nutrients in the mineral humic soil horizon. Specifically, the analysis statistically tested for relationships
between general and species-specific local stand density measures (basal area, sum of tree diameters weighted by distance,
canopy openness) and the contents of total C, total N (in four stands), base cations (Ca2+, Mg2+, K+, Na+) and Mn2+ (in nine stands). A considerable variation in nutrient concentrations was observed; the coefficients of variation ranged
from 0.21 to 0.38 for N, from 0.20 to 0.94 for the sum of base cations and from 0.56 to 0.95 for Mn. However, no clear relationship
emerged between local stand density and the concentration of N and base cations; in five stands, manganese showed a negative
correlation with local stand density. In the mixed fir-beech stand, significantly higher concentrations of Ca, K and Mn were
found in the vicinity of beeches, and species-specific stand density explained up to 15, 29 and 34% of total variation in
the content of these elements, respectively. Similar tendencies also appeared in the mixed stands with pine, although the
relationships were weak. The results obtained for two fir-spruce stands were ambiguous. In sum, in the stands studied, small
canopy gaps and inter-crown openings might not be considered ‘‘nutrient hot spots’’, and the admixed species, except for beech,
had an insignificant effect on nutrient content in the humic mineral horizon.
KeywordsForest soils-Micro-site-Stand heterogeneity-Mixed stands-Nutrients
The spatial dynamics of soil water-recharge in a forest stand is the product of a number of interacting processes. This study focuses on the role of tree species and antecedent soil water content upon horizontal and vertical patterns of soil water recharge in heavy clay soils of a mixed European beech–Norway spruce stand and of a pure Norway spruce stand after rewetting periods with different rain quantities and intensities. Volumetric water content (VWC) was measured at 194 locations across 0.5-ha plots in each stand using time-domain reflectometry (TDR) with fixed 30- and 60-cm vertical waveguides. This was repeated 28 times (as close as possible) before and after rewetting periods during the vegetation seasons in 2000 and 2001. In addition, the locations of all trees within the plots were recorded. Geostatistics was used to describe the spatial correlation between VWC measurements and to interpolate soil water recharge in space. Spatial patterns of soil water recharge were then evaluated according to antecedent soil water-content and tree species distribution. Open-field precipitation of 30mm (maximum intensity 10mmh–1) on extremely dry initial soil conditions resulted in higher subsoil (30–60cm soil depth) recharge and erratic recharge patterns. This was presumably due to preferential flow in opening shrinkage cracks of the heavy clay soil. A comparable quantity and intensity of rainfall under moderately dry antecedent soil water conditions resulted in almost exclusively topsoil (0–30cm soil depth) water recharge and patterns of recharge that were clearly related to tree species distribution. The higher recharge around beech trees can be attributed to the lower interception rates there. Spatial patterns of soil water recharge reflect patterns of antecedent soil water conditions.
For the period 2003–2006, fructification of Norway spruce (Picea abies [L.] Karst.) was recorded at the Kranzberg forest site in Southern Germany by employing a crane with access to the canopy
of more than 266 trees. For each tree, stem diameter and growth parameters were assessed annually as well as biomass of cones
and seeds, number of seeds per cone, and proportions of empty seeds for a total of 371 trees with cone crop. Genotypes at
19 enzyme coding gene loci of 110 trees were included in the study of correlations between morphological and genetic traits.
Re-scaling the observed values for a virtual pure Norway spruce stand of 1ha, cone biomass including winged seeds (oven-dried
at 38°C) varied between 706.8kg/ha in 2006 (average value per tree was 3.6kg) and values close to zero in 2005. Corresponding
values for vegetative biomass increment of the coning trees in 2006 were 9,273.0kg/ha and 10.8kg/tree. A significant higher
biomass investment was determined for dominant trees in terms of absolute cone mass as well as in terms of cone mass relative
to vegetative biomass and fructification frequency. No trade-off effects in decreased vegetative biomass growth were found
in the fructification year, compared to trees that did not grow cones. Although the dominant trees invested proportionally
considerable biomass in cones, they showed no significant reduction in vegetative biomass growth. In the following year no
decrease in vegetative growth was detected. Based on logistic regressions and homogeneity tests, respectively, significant
genetic effect became evident with respect to the gene loci AAP-B and AAT-C concerning fructification probability in the year
with maximum generative biomass investment. These and closely related loci also have been found to be indicative for growth
and viability, respectively, in other species.
A bark beetle (Ips typographus) infestation caused the death of almost all Norway spruce (Picea abies) trees in a mountain forest in the Swiss Alps. We developed a tree regeneration model, ‘RegSnag’ (=REGeneration in a SNAG stand), to project the future amount and height of tree regeneration in these snag stands. The model combines a height-class structured tree module with a microsite-based module of snag decay and ground-vegetation succession. Microsite-specific rates of germination, mortality and height growth were modelled for four tree species (Picea abies, Sorbus aucuparia, Acer pseudoplatanus and Betula pendula) in eight height classes (from seedlings to saplings 5m tall) and on 26 microsite types (e.g. moss, grass). Model tests with independent field data from 8years after the Picea die-back demonstrated that microsites had a considerable effect on the development of tree regeneration on both the montane and the subalpine level. With microsite-specific parameters, the height and frequency of Picea in each microsite could be simulated more accurately than without considering microsite effects (e.g. bias of 8 vs. 119 saplings ha−1 on the montane level). Results of simulations 40years into the future suggest that about 330–930 Picea saplings per ha out of those that germinated in 1994 and 1996 will reach a height of 5m within 30–35years after Picea die-back. This is due to differences in seed inflow and browsing intensities. Picea and not Betula or Sorbus trees will replace the current herbaceous vegetation in these snag stands.