Spruce Site Index Research Articles

Tree improvement increases the growth of white spruce (Picea glauca): Evidence from 15-year-old operational plantations in Alberta

The timber producing forest land-base in Alberta, Canada, is decreasing due to the increase in allocation of land to other uses such as agriculture, infrastructure, energy development and conservation areas, while the demand for forest products continues to increase. Tree improvement, first implemented in Alberta in 1975, is one strategy used for increasing forest productivity to meet an increasing demand for fibre and forest products. To quantify the operational impact of tree improvement on white spruce productivity, we collected data from 15-year-old white spruce stands in Alberta: 11 stands planted with seedlings from improved (seed orchard) seedlots and seven stands planted with seedlings from wild (unimproved) seedlots. Eight plots (100 m2 circular plots) within each stand were randomly established for measurement (18 × 8 = 144 plots). Diameter at breast height (DBH), tree height, crown width, and branch diameter for each tree inside the plots were measured. Mixed effects models, with site and plot considered random, were used to evaluate the effect of tree improvement on the growth of white spruce. Basal area per ha of competitor species was used to develop a non-spatial competition index, and to compare the growth of improved and unimproved white spruce response to competition. Individual trees from improved stands showed 17% greater DBH and height compared to individual trees from unimproved stands. Individual trees of improved stands also had a greater height and smaller branch diameter for a given DBH than the trees grown in unimproved stands. Overall, tree improvement increased the site index of white spruce by 2 m while both improved and unimproved stands were similarly, and negatively, affected by competition. The application of tree improvement in white spruce resulted in an increase in growth rate, site index, and quality of timber, which will help offset the increasing demand for forest products.

Anamorphic Site Index Curves for Central Appalachian Red Spruce in West Virginia, USA

Traditional site index curves are frequently produced for shade-intolerant species but are scarce for shade-tolerant species. Red spruce (Picea rubens Sarg.) can be found in three distinct geographic regions (northern, central, and southern) within the Appalachian Mountains. The one commonly used set of red spruce site index curves is over ninety years old. A definite need exists for a modern, regionally applicable set of site index curves. This research sampled 83 plots randomly located in the central Appalachians of West Virginia. Three sets of anamorphic site index curves were created after careful examination of height models built using Chapman-Richards and Meyer functions. One set of curves was constructed with traditional age height pairs. The second utilized a suppression-corrected age and height pair. The third set examined diameter at breast height (DBH) and height pairs. Fit statistics indicated better performance for the suppression-corrected age–height pair site index and the DBH–height pair site index versus the traditional age–height pair models. Site index conversion equations were also investigated for the red spruce age-corrected site index. Linear regression was used to determine significant geographic and climate variables and the utility of including site index values for red maple (Acer rubrum L.) and yellow birch (Betula alleghaniensis Britton) in the model to predict red spruce site index. Significant models were found for varying combinations of species site index, climate, and geographic variables with R2adj in the range of 0.139–0.455. These new site index curves and conversion equations should provide utility for site productivity estimation and growth and yield modeling while aiding in restoration efforts for this important central Appalachian species.

Analyzing and modelling effects of climate on site productivity of white spruce plantations

Effects of climate on site productivity of white spruce (Picea glauca) plantations were examined. Stem analysis data collected from 93 dominant or co-dominant white spruce trees sampled from 93 plots (1 tree/plot) in even-aged monospecific plantations on 31 sites (three plots/site) in the Canadian boreal forest region of Northern Ontario were used to examine effects of climate on site productivity and to develop stand height models. Site index was used as an estimate of site productivity. Effects of site and climate on site productivity were examined by regressing site index against site and climate variables. The site specific attributes explained 33% of the variability in site index for white spruce. Stand height models were then developed by incorporating climate variables. Climatic effects specifically those of projected increased warming and rainfall on stand height growth were evaluated by predicting stand heights for three randomly selected locations (in eastern, western, and southern Ontario) for ...

High Resolution Site Index Prediction in Boreal Forests Using Topographic and Wet Areas Mapping Attributes

The purpose of this study was to evaluate the relationships between environmental factors and the site index (SI) of trembling aspen, lodgepole pine, and white spruce based on the sampling of temporary sample plots. LiDAR generated digital elevation models (DEM) and wet areas mapping (WAM) provided data at a 1 m resolution for the study area in Alberta. Six different catchment areas (CA), ranging from 0.5 ha to 10 ha, were tested to reveal optimal CA for calculation of the depth-to-water (DTW) index from WAM. Using different modeling methods, species-specific SI models were developed for three datasets: (1) topographic and wet area variables derived from DEM and WAM, (2) only WAM variables, and (3) field measurements of soil and topography. DTW was selected by each statistical method for each species and, in most cases, DTW was the strongest predictor in the model. In addition, differences in strength of relationships were found between species. Models based on remotely-sensed information predicted SI with a root mean squared error (RMSE) of 1.6 m for aspen and lodgepole pine, and 2 m for white spruce. This approach appears to adequately portray the variation in productivity at a fine scale and is potentially applicable to forest growth and yield modeling and silviculture planning.

Nutrient limitation and site-related growth potential of Norway spruce (Picea abies [L.] Karst) in the Bavarian Alps

The hypothesis that soil chemistry is a main constraint for the vigour of Norway spruce trees on calcareous soils is scrutinised based on data from 60 existing and new intensive study sites in the Bavarian Alps, where comprehensive information on soils, climate, foliar nutrient concentration, ground vegetation, and tree growth is available. We characterised ecological gradients of the response variables site index (SI), foliar nutrient level and needle weight by constrained ordination, identified nutrient limitations based on regression trees and modelled SI based on vegetation-based mean Ellenberg indicator values. Our study confirms the assumption that soil development and concurrent acidification are key determinants for the vitality and growth of spruce in the Bavarian Alps, which surpass the importance of climate on nutrition and growth. Pools and availability of P and N are limiting nutrition and growth of spruce in this region. We hypothesize that N-limitation persists despite considerable deposition inputs because N tends to be locked up in organic horizons with low biological activity. K and trace elements, especially Fe, can also be deficient in some cases but do not appear as major limiting factors. High foliar Mn concentrations are a reliable indicator of mature soils and favourable site conditions in the Bavarian Alps, but Mn itself is usually not limiting. P must be regarded as the most critical macronutrient in the Bavarian Alps, particularly in the face of biomass harvesting. Consequently, at sites with shallow soils forest, management should focus on sustaining or restoring humus stocks. SI of spruce can be predicted from composition of ground vegetation and Ellenberg indicator values with remarkable precision (R 2 = 0.75).

Ecologically based height growth model and derived raster maps of Norway spruce site index in the Western Carpathians

The purpose of this study was to find the ecological factors that most affect height growth of Norway spruce (Picea abies Karst.) over the Western Carpathians. The specific aim was to find climate and soil parameters which are influenced by climate change and can thus be used to make a forest growth model more sensitive to climate. From the results, a regression model was built which can predict top height growth of Norway spruce from ecological parameters. Data collected on 201 plots established within National Forest Inventory of Slovakia were used. The plots selected for the study were distributed almost over the whole Western Carpathians. Mean height of the 20 % largest spruce trees was used as dependent variable. From all investigated ecological factors, the growing season length explained as the number of days with temperature over 5 °C, the carbon-to-nitrogen ratio and soil acidity were shown to have the major impact on top height growth of Norway spruce. Finally, 76 % of total variability in top height was explained by the mentioned site variables. To obtain a user-friendly output, a probability matrix was developed showing the likelihood of a discrete site index to occur on different combinations of site factors. Moreover, raster maps showing the site index of spruce and its probability distribution were developed.

Modelling the top-height growth and site index of Norway spruce in Southern Belgium

Top-height growth in even-aged stands of Norway spruce (Piceaabies (L.) Karst.) from Southern Belgium was modelled using functions which provide an algebraic solution for site index (SI) calculation. 16 well known growth model formulations were parameterized using a method which accounts for heterogeneous variance and autocorrelation on a dataset composed of stem analysis data completed by measuring the heights of all the branch whorls to allow for accurate height–age estimates. Comparison of the parameterized models showed that the oblique asymptotic function known as the Duplat and Tran-Ha III model was the most efficient on our dataset.Validation of the selected model on permanent sample plot data showed no evidence of bias over the full range of possible age, height, site index and densities encountered in Norway spruce stands of Southern Belgium.The new height growth model described represents a significant improvement over the previous model of Dagnelie et al. (1988), which was found to be unreliable and required the use of an iterative process to estimate SI.

Sixty-year effects of deciduous removal on white spruce height growth and site index in the Western Boreal

In the boreal plains of western Canada, white spruce (Picea glauca (Moench) Voss) height−age and site index (SI) curves have been developed and applied to assess site productivity for white spruce without fully considering the competition that usually occurs between the spruce and taller deciduous trees. In this study, we evaluated the effects of deciduous removal on white spruce height growth potential using stem analysis on typical control spruce grown with deciduous neighbours and spruce that were released from deciduous competition ∼60 years prior. Due to the late application of the release treatments (at stand ages of 20–60 years), the observed site index of spruce was not affected by treatment. However, height growth in the 50 years following treatment was increased by 2.1 m. We present a height−age model to specifically estimate the change in SI required to achieve the observed height response following late release. The model indicated that the post-release SI estimate of white spruce would need to be on average 4.2 m higher than control SI to track the height response. This model is useful for estimating the true, competition-free SI for white spruce from the observed SI in natural mixed stands.

Productivity of Norway spruce compared to Scots pine in the interior of northern Sweden

Productivity of Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) was studied in 12 paired plots in the interior of northern Sweden. Stands were established between 1928 and 1959; yield plots were established between 1974 and 1983 during pre-commercial thinning of the stands. Gross stem-wood production was significantly higher for Scots pine than for Norway spruce, stem-wood production by Norway spruce being 29.4% that of Scots pine. The site index for Norway spruce was lower than for Scots pine at all sites except one; the average difference in site index was 4.8 m. The simulated maximum mean annual increment (MAI) during the rotation was 19% higher than the MAI estimated with the site index for Scots pine, whereas simulated MAI and MAI estimated from the site index was about the same for Norway spruce. The simulations also indicated that MAI peaked about 50 years later for Norway spruce than for Scots pine. More small trees were included in the diameter distribution of Norway spruce than of Scots pine resulting in a lower stem-wood volume for Norway spruce when stands with the same dominant height were compared. This study shows that the difference in growth and rotation length between Scots pine and Norway spruce has implications when choosing which species to grow in the interior of northern Sweden.maxmaxmaxmax

Sitka spruce site index in response to varying soil moisture and nutrients in three different climate regions in Ireland

We examined the relationships between Sitka spruce ( Picea sitchensis (Bong.) Carr.) site index, windspeed, former land use, soil moisture and soil nutrients with a view to identifying factors limiting the growth potential of the species in three climate regions in Ireland. We selected plantations covering three climate regions (delineated on the basis of ‘growing season’ balance of precipitation and potential evapotranspiration; representing dry, moist and wet climate regions) located on sites representing the range of soil moisture regimes (SMR), soil nutrient regimes (SNR), and land use types found throughout Ireland. Site index of Sitka spruce varied among climate region, with significantly lower site index associated with the wet climate region mainly due to the deterioration in edaphic conditions and adverse climatic conditions. The effect of edaphic variables (SMR, SNR) on site index was consistent across climate regions, site index increasing with increasing SNR, and decreasing with excess moisture or moisture deficit. Site index reached a maximum on fresh/very rich sites in the dry and moist climate regions and on moist/rich sites in the wet climate region. In the dry climate region, water supply (SMR) was the most important variable regulating growth, in wetter windier climates nutrient supply (SNR) was the most important factor, accounting for 69% of the variation in site index. The study has allowed region-specific recommendations to be made for successful plantation establishment in Ireland and for countries with similar climatic regions.

Site index of Sitka spruce (Picea sitchensis) in relation to different measures of site quality in Ireland

To examine the relationships between Sitka spruce (Picea sitchensis (Bong.) Carr.) site index and site quality variables, we sampled 201 Sitka spruce stands covering the entire range of sites supporting the growth of the species in Ireland. Site index varied significantly with climate and climate surrogate variables, some site quality variables, soil physical and chemical properties, edatopes (combinations of soil nutrient and moisture regimes), rotation types, provenance, and fertilizer regimes. We developed a series of models to predict site index using climate, site, soil physical and chemical properties, edaphic variables, and management factors as predictor variables. Soil nutrient regime (SNR) exhibited the strongest relationship of all variables examined in the study, explaining 51% of the variation in site index, with site index increasing with increasing SNR. We found that edaphic variables of soil moisture regime and SNR produced the best prediction of site index. The species showed the best development on fresh to very moist sites, with rich to very rich soil nutrient regimes. We also developed a composite model explaining 62% of the variation in site index and an elevation zone model (>300 m) explaining 74% of the variation in site index.

Climate-sensitive modelling of site-productivity relationships for Norway spruce ( Picea abies (L.) Karst.) and common beech ( Fagus sylvatica L.)

The aim of the presented research project is to fit a site index model capable for predicting changes in site-productivity in a changing climate. A generalized additive model is used to predict site index as a function of soil and climate variables. The climate parameter values are estimated using the regional climate model WETTREG, based on global climate simulations with the global circulation model ECHAM5/MPI-OM for the reference period from 1961 to 1990. The climate values are further regionalized on a 200 m × 200 m grid. The generalized additive model quantifies the partial linear and non-linear effects of the predictor variables on site index. The model is parameterized for Norway spruce ( Picea abies (L.) Karst.) and common beech ( Fagus sylvatica L.) in Lower Saxony, Germany. Two case studies investigate the model's ability to generate information in order to support forest management planning decisions under a changing climate. One example analyzes the possible shift in site index of spruce along a precipitation gradient under the International Panel on Climate Change (IPCC) emission scenario A1B in the period from 2041 to 2050. The other case study shows possible future changes in site index of beech along a temperature gradient.

Relationship between site index of oriental spruce [Picea orientalis (L.) Link] and ecological variables in Maçka, Turkey

Oriental spruce [Picea orientalis (L.) Link] is a species native to Turkey, covering about 350,000 ha. The species is of great importance to the production of timber as well as to the creation of social welfare in eastern Black Sea region. There are few studies about ecological variables affecting oriental spruce site productivity. Based on data from 90 sample plots, multiple regression models were developed using topographic, edaphic, soil nutrients, climatic subgroups and all factors integrated. Within the different subgroups of site factors, the integrated model with all ecological variables provided the best statistical results, which explained 77% of index variation. Other topographic, edaphic, soil nutrients and climatic subgroup models were enumerated by the success of modelling site index of oriental spruce from the related site variables. The results show that the integrated model is more successful than the models developed separately for each ecological variable. However, the integrated model included 12 different variables and thus the assessment of some of these model variables, e.g. element content of the soil (Ca2+, Mg2+, etc.), require potentially laborious soil analyses and costly applications. Therefore, the topographic model with only three variables (R 2=0.656), which can be assessed directly from digital maps by Geographical Information System (GIS), seems to be more promising and convenient, since the model can be easily applied to large areas. The results can be translated into practical recommendations to forest managers for selecting suitable site conditions for oriental spruce.

Current growth differences of Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and birch (Betula pendula and Betula pubescens) in different regions in Sweden

The choice of species in forestry is important, and a real issue as large areas of wind-damaged forest land in southern Sweden need to be regenerated. To compare the growth potential between the most common tree species in Sweden, ratios between site quality derived from site index values determined with site properties were used. A regression function to determine site index for birch from site properties was used to complement the known relationships between site properties and site index for spruce and pine. In large regions of Sweden the distribution of site quality classes was calculated to compare the special characteristics and demands of the three species. On average, the growth difference for pine compared to spruce was about 60% in southern Sweden and 95% in northern Sweden. Corresponding figures between birch and spruce were 40% and 60%. Birch was expected to produce around 60% of pine in northern Sweden and about 70% in southern Sweden. However, it must be stressed that the comparison is based on survey data encompassing mainly naturally regenerated birch, whereas spruce and pine are mainly planted.

Effect of topography and geology on the site index of Picea abies in the West Carpathian, Poland

The effects of topographic features and the soil parent rock on the site index of Norway spruce [Picea abies (L.) Karst.] were examined. Field data were collected on 347 plots located in the Polish West Carpathian. On these plots, the diameter at breast height and the height of trees were measured and the age of trees was determined. On 64 plots one dominant or codominant tree was felled for stem analysis. In addition, topographic features of each site were measured, including elevation above sea level, aspect and slope. Stem analysis data were used in the development of a local site index system, which was used for calculating the site index for particular plots. In order to interpret site index as functions of elevation, aspect, slope, size of a mountain massif and soil parent rock, the multiple regression model was used, which explained 79.0% of the variation in Norway spruce site index. Elevation above sea level was the major factor responsible for variation in site index, and was negatively correlated (R 2 adj=0.610) with site index. Site index also depended on the soil parent rock. The stands growing on the tertiary Magura sandstones had considerably higher site indices than those located on the geological substratum composed of Istebna and Godula sandstones formed during the Cretaceous period. The site index of Norway spruce is also determined by the aspect, slope and height of mountain massif.

Species and Spacing Effects of Northern Conifers on Forest Productivity and Soil Chemistry in a 50-Year-Old Common Garden Experiment

Species and Spacing Effects of Northern Conifers on Forest Productivity and Soil Chemistry in a 50-Year-Old Common Garden Experiment

Linking juvenile growth of white spruce with site index

The goal of this study was to link the growth of juvenile white spruce stands with an estimate of their site index. We applied a previously developed technique for correcting the height bias created by dominance switching among juvenile trees before trees reached the site index base age (50 years at breast height), using stem analysis data of white spruce from five mixedwood stands in central Alberta. For white spruce of approximately 15 years total age, we found the height of the current top height trees was approximately 14% greater than the height of the top height trees that would be selected close to breast height age 50. This height correction is essential to avoid an overestimate of site index. Secondly, to avoid the difficulties of determining breast height age or growth increment required for juvenile site index determination, we developed a linkage to site index using data from 168 white spruce trees that were longitudinally sectioned along the pith, selected from juvenile (age 6–15) spruce stands. Using this new equation, coupled with the correction for bias, we found that site index for white spruce from 49 test stands in Alberta, ranged from 9.0 to 31.8 m at base age 50, with a mean of 17.8 m; these values are in the range for spruce in mixedwood stands in Alberta. Key words: juvenile stand, height age curve, height bias adjustment, site index

Site-Index Curves and Growth Intercepts for Young White Spruce Plantations in North Central Ontario

Abstract Site-index (heightߝgrowth) curves, site-index prediction equations, and growth intercepts were developed from internode measurements and stem-analysis data using dominant trees in 69 plots located in white spruce plantations aged 19 to 32 years total age. Site-index curves were based on breast-height (1.3 m) age because our analyses show that height growth below breast height is slow and erratic and is poorly related to site index (dominant height at 15 years breast-height age). The most precise model for computing heightߝgrowth curves was a Newnham constrained polymorphic expression (Newnham, R.M. 1988. A modification of the Ek-Payandeh nonlinear regression model for site-index curves. Can. J. For. Res. 18:115ߝ120) of the Ek nonlinear regression model (Ek, A.R. 1971. A formula for white spruce site-index curves. University of Wisconsin For. Res. Note 161. 2 p). Comparisons showed that site-index curves in North Central Ontario were comparable to site-index curves for white spruce plantations in southeastern Ontario. The first three to five internodes above 2.0 m gave the most precise estimates of site index based on growth intercepts. North. J. Appl. For. 23(4):257–263.

A Light-Adjusted Growth Intercept Model for Predicting White Spruce Site Index

Abstract One of the challenges of managing spruce-aspen mixedwoods in the boreal forest is the difficulty in determining site index for spruce in those stands in which it occurs primarily in the understory. A study was conducted to determine if growth increment of understory spruce, adjusted for available light, could predict spruce site index. In each of nine stands, spruce site index was determined for three dominant trees. Available light (measured as proportion transmitted) and growth increment (estimated by the growth intercept method) were recorded for three to eight understory spruce per stand. Growth increment adjusted for available light predicted spruce site index better (R2 = 0.56 or 0.63, depending on the model used) than unadjusted growth increment (R2 = 0.10), thus indicating the potential for using light-adjusted growth increment to predict site index.

Potential productivity of three interior subalpine forest tree species in British Columbia

Productivity potential of high-elevation forests in British Columbia is poorly understood despite continuing harvesting operations. We examined how site index of three principal tree species, subalpine fir ( Abies lasiocarpa (Hook.) Nutt.), Engelmann spruce ( Picea engelmannii Parry ex Engelm.), and lodgepole pine ( Pinus contorta var. latifolia Dougl. ex Loud.), were affected by climatic and edaphic conditions in the Engelmann spruce–subalpine fir zone. We deliberately selected naturally established stands with a wide range in site quality, which are described by subzones, latitude, longitude, elevation, soil moisture regime (SMR), and soil nutrient regime (SNR). Site index varied among subzones for all three species, particularly between the parkland and the forested subzones. Increasing latitude and elevation resulted in a significant decrease in site index for all study species. Site index of subalpine fir and Engelmann spruce significantly increased with SNR from very poor to very rich while site index of lodgepole pine increased with SMR from moderately dry to moist and then decreased on very moist sites. The models developed accounted for 63–70% of variation of site index. These models, tested by independent data, were unbiased with mean prediction error of ±2.3, ±2.6, and ±1.8 m in predicting site index of subalpine fir, Engelmann spruce, lodgepole pine, respectively. They are recommended for estimating site index of the study species to assist in making silvicultural decisions in the interior subalpine forest.