Visitor preferences of thinning practice in young even-aged stands of pedunculate oak (Quercus robur L.): comparing the opinion of forestry professionals in six European countries

This study compared visitor preferences of forestry professionals across six European countries (Sweden, Denmark, Great Britain, Austria, Romania and Portugal) using a questionnaire survey. The 598 interviewees were asked to rank photographs depicting recently thinned experimental plots in a 13-year old stand of pedunculate oak (Quercus robur L.) according to the criterion: “Which forest environment do you prefer as a visitor?” The plots represented five different residual stem densities: 7000 (no thinning, very high stem density), 5300 (heavy thinning, high stem density), 1000 (very heavy thinning, medium stem density), 300 (extremely heavy thinning, low stem density/open stand) and 100 (solitary trees, very low stem density/very open stand) stems ha^?1. The results indicated geographical variation in the preferences for different thinning practices in young stands of oak. Portuguese, Austrian and Romanian respondents generally favoured thinned, but dense stands, whereas Danish and British respondents preferred very heavily thinned stands. Swedish respondents preferred open stands resulting from extremely heavy thinning. Photographs taken along rows were favoured to photographs across rows, indicating a preference for scenes offering perspective and accessibility. The results indicate a variation of visitor preferences among forestry professionals for different silvicultural regimes. We interpret this in the context of national traditions and forestry paradigms that influence the shaping of preferences.     

Effects of pruning and stand density on the productionof new epicormic shoots in young stands of pedunculate oak (Quercus robur L.)

Context

Avoidance or control of epicormic shoots is among the major silvicultural challenges for the production of high-quality oak timber. In northern Europe, contemporary oak silviculture aims to produce valuable timber on a relatively short rotation, applying early, heavy thinning combined with artificial pruning.

Aims

The aim of this study was to analyse the effects of pruning and stand density on the production of new epicormic shoots on young trees of pedunculate oak (Quercus robur L.).

Methods

The study was based on two field experiments in even-aged stands of pedunculate oak subjected to different thinning practices and early selection of potential future crop trees. From ages 13 to 15 years, stem density was reduced to 300 trees ha^?1, 1,000 ha^?1 or stands remained unthinned. Pruning was conducted on selected trees at ages 22–24 years. At that age, the stem density in unthinned control plots ranged from 2,500 to 3,100 ha^?1. All treatments were replicated twice within each experiment.

Results

Pruning led to an overall increase in the total production of new epicormic shoots. More epicormic shoots were produced in the lower part of the stem (0–3 m in height) than in the upper part (3–6 m). The number of new epicormic shoots increased with increasing stand density.

Conclusion

Early, heavy thinning combined with high pruning at regular intervals may help shorten the rotation length for pedunculate oak without further reduction in wood quality than that which is caused by wider annual growth rings.     

Recreational preferences depending on thinning practice in young even-aged stands of pedunculate oak (Quercus robur L.): comparing the opinions of forest and landscape experts and the general population of Denmark

The aim of this study was to investigate to which extent forestry professionals, other “green” professionals (mainly landscape architects) and natural resource students in Denmark agree with the general population regarding their recreational preferences for contrasting stem densities in young, even-aged stands of pedunculate oak (Quercus robur L.). The study was based on five pairs of colour photographs from each of the five recently thinned experimental plots in a 13-year-old stand. The plots represented five different residual stem densities: 7000 (unthinned), 5300 (traditional thinning), 1000, 300 and 100 stems ha^?1. All cut trees were left on the ground. The analysis was carried out as a survey of forest and landscape experts (n=158) and the general public (n=243) based on questionnaires. Interviewees ranked the photographs according to the criterion: “Which forest environment do you prefer as a visitor?” Principal component factor analysis showed that the general public tended to perceptually group photos according to similar overall pattern of openness, presence of row structure and stand accessibility (including presence/absence of slash). As long as a stand appeared accessible, stand density had little influence on their preferences for a wide range of stand densities (5300?300 stems ha^?1). In contrast, foresters, other “green” professionals and students seemed to perceptually group photos according to treatment type, and the presence of slash had little influence on their preferences. This suggests an influence of professional background, making experts visually analyse and evaluate stands according to contemporary management standards and paradigms within their own profession.     

Environmental and plant-based controls of water use in a Mediterranean oak stand

In this work, new information is reported on water relations of the Mediterranean oak species Quercus pyrenaica based on environmental and physiological measurements carried out during the growing seasons of 2006 and 2007. The interest in this species has increased due to its use in reforestation programs and its impacts on the water resources due to the extensive spontaneous afforestation after the abandonment of forest (firewood, charcoal, livestock, etc.) and agricultural activities, in general in some areas in the Mediterranean region and in particular, in the studied area (Sistema Central range, Spain). The objectives were to evaluate the long-term water use of this stand and its limit and to analyse the specific traits to cope with summer drought, especially the use of stem water storage and deep soil water reserves. Tree water stress associated with depletion of soil water reserves was not observed since the oak trees appeared to avoid a marked water stress using water reserves from deeper soil layers as summer drought progresses. The contribution of mean daily stem water storage to transpiration was low (4%), although it could be greater under dryer conditions. Only at the end of summer of 2006, the transpiration and canopy conductance were reduced due to soil drought. Despite the absence of marked water stress an upper limit was found in transpiration (slightly higher than 3 mm day⁻¹). The heavy use of soil water resources by this species (75% of available soil water in this study) should be considered when evaluating the impact of spontaneous afforestation and reforestation programs on water resources.     

Canopy density in stands of Picea abies and Pinus sylvestris after different thinning methods

Altogether 82 plots (261 estimations) of Picea abies (L.) Karst, and 193 plots (360 estimations) of Pinus sylvestris (L.) stands were estimated by a vertical tube. The “crown free projection”, CFP, of stands thinned in three methods with different thinning grades was measured: unthinned, heavily and very heavily thinned, heavily thinned delayed first thinning, extra heavily thinned and thinned from the top. Basal area (m²ha^?1) density (stems ha^?1) and diameter sum (m ha^?1) were plotted against CFP. Basal area was the best practical measure of stand in this study. Generally Scots pine stands have higher CFP and the curves are steeper than in Norway spruce stands. Depending on the grade of thinning, heavily and very heavily thinned spruce stands, delayed first thinning included, have CFP values of 10–15% and stands thinned from the top, 20–40%, compared with 30–80% and 30–60% respectively in pine stands. Extra heavily thinned stands have the highest CFP, 20–80% in spruce and 50–90% in pine stands. The CFP levels after thinning are too high in pine stands for avoidance of sucker and sprout production of aspen and birch. In dense Norway spruce stands thinned from the top or heavily and very heavily thinned, the CFP values are low enough (≤30%) to diminish the production of suckers.     

Evaluation of carbon sequestration and thinning regimes within the optimization framework for forest stand management

Due to the urgent demand for thinning in planted forests and the tend towards sustainable forest resource management, the forest stand age class eligible for the thinning subsidy in Japan was expanded during the period from 2000 to 2004. Currently, further expansion is under consideration in line with meeting the Kyoto Protocol target of carbon sequestration. In this paper, we conducted evaluation analyses of carbon sequestration and subsidy effects within the optimization framework for the forest stand management. The optimal forest stand management model called Dynamic Programming model for Kyushu Stand Simulator (DP-KYSS) was utilized for the analysis of the target sugi (Cryptomeria japonia) forest stand in the Kyushu region, Japan. Our results showed that the thinning subsidy was effective to stimulate thinning activities at the eligible age class for the subsidy, and that 20% of the current or proposed payment was appropriate to give an incentive to forest owners for conducting the same optimal thinning regime. The amount of carbon sequestered in remaining trees at final harvest was not always shown to increase over time. Depending upon the subsidy condition, it could decrease. The average annual amount of carbon sequestered under no subsidy showed its maximum at age 35, while under the other subsidy conditions, it was shortened to age 25. The net present value of cost per unit carbon loss associated with subsidy became the highest for the rotation age of 35 years for all subsidy policies considered here.     

Variation in the radial patterns of sap flux density in pubescent oak (Quercus pubescens) and its implications for tree and stand transpiration measurements

Radial variation in sap flux density across the sapwood was assessed by the heat field deformation method in several trees of Quercus pubescens Wild., a ring-porous species. Sapwood depths were delimited by identifying the point of zero flow in radial patterns of sap flow, yielding tree sapwood areas that were 1.5-2 times larger than assumed based on visual examinations of wood cores. The patterns of sap flow varied both among trees and diurnally. Rates of sap flow were higher close to the cambium, although there was a significant contribution from the inner sapwood, which was greater (up to 60% of total flow) during the early morning and late in the day. Accordingly, the normalized difference between outer and inner sapwood flow was stable during the middle of the day, but showed a general decline in the afternoon. The distribution of sap flux density across the sapwood allowed us to derive correction coefficients for single-point heat dissipation sap flow measurements. We used daytime-averaged coefficients that depended on the particular shape of the radial profile and ranged between 0.45 and 1.28. Stand transpiration calculated using the new method of estimating sapwood areas and the radial correction coefficients was similar to (Year 2003), or about 25% higher than (Year 2004), previous uncorrected values, and was 20-30% of reference evapotranspiration. We demonstrated how inaccuracies in determining sapwood depths and mean sap flux density across the sapwood of ring-porous species could affect tree and stand transpiration estimates.     

Timing and intensity of precommercial thinning in Pinus sylvestris stands

The effects of timing and intensity of precommercial thinning were studied in three Scots pine artificially regenerated stands on Vaccinium forest sites in southern Finland. A two-level factorial design (3×3) was used in each stand: thinning at dominant height of 3, 6 and 9 m to 1000, 1600 and 2200 stems ha^?1. The effects of the treatments were analysed after a period of 23–25 yrs when the dominant height was 14–15 m. Early thinning resulted in the highest standing volume and amount of merchantable wood, and also in slightly accelerated height development. Thinning to 1000 stems ha^?1 caused a considerable production loss, but there were no differences between the densities of 1600 and 2200 stems ha^?1. Branches became thicker after early thinning, but the differences between the treatments were negligible for crop trees. Crown ratio was lowest as the result of early or moderate thinning (2200 stems ha^?1).     

Differences of raw cork quality in productive cork oak woods in Sicily in relation to stand density

Differences of raw cork quality, in terms of thickness and porosity, were observed in productive cork oak (Quercus suber L.) stands in the Nebrodi and Iblei mountains of Sicily in relation to stand density. Five study areas were chosen across a range of different stand density satisfying specific sampling requirements among two managed cork oak woods.Analysis of variance using Fisher–Snedecor‘s F test (p < 0.05) were used to identify statistically significant differences of cork quality and sylvicultural, dendrometric and cork stripping parameters between study areas within each stand. Relationships between cork quality and sylvicultural and dendrometric parameters were also tested using Pearson's correlation coefficient (r). Results shown that sylvicultural practices are a key factor influencing cork quality: statistically significant differences in cork thickness and crown area were observed between areas at different stand density; positive correlations were found between cork thickness and crown area in lower density study areas favouring a significant vegetative activity; negative correlations were found between parameters of cork stripping (cork stripping coefficient, cork stripping surface, maximum height of cork stripping) and cork thickness. No correlations were found between cork porosity and dendrometric or sylvicultural parameters, demonstrating the probable genetic origin of cork porosity. Results shown that cork quality parameters and stand attributes may be used in sustainable management models of cork oak forests.     

Forest structure,habitat and carbon benefits from thinning floodplain forests: Managing early stand density makes a difference

Forest ecosystems are increasingly expected to produce multiple goods and services, such as timber, biodiversity, water flows, and sequestered carbon. While many of these are not mutually exclusive, they cannot all be simultaneously maximised so that management compromise is inevitable. We used a 42-year dataset from a naturally regenerating floodplain forest of the river red gum (Eucalyptus camaldulensis) to investigate the effects of pre-commercial thinning on long-term patterns in habitat quality, forest structure and rates of carbon storage (i.e. standing aboveground carbon). Estimates of habitat quality were based on the density of hollow-bearing trees because hollows are ecologically important to many species of vertebrates and invertebrates in these forests. Thinning improved habitat value by producing 20 (±8) hollow-bearing trees per ha after 42 years, while the unthinned treatment produced none. Unthinned (highest density) stands were dominated by many slender trees, mostly <25 cm in diameter, whereas thinned stands produced negatively skewed size distributions with higher median and maximum stem diameters. Moderately thinned stands (560 trees ha⁻¹) had the highest aboveground carbon storage rate (4.1 t C year⁻¹) and the highest aboveground carbon stocks (200.2 ± 9.6 t C ha⁻¹) after 42 years, while the unthinned treatment had the lowest carbon storage rate (1.6 t C year⁻¹) and an intermediate level of aboveground standing carbon (165.1 ± 31.1 t C ha⁻¹). Our results highlight the importance of early stand density as a determinant of long-term forest structure, habitat quality and carbon storage rates. We recommend that thinning be considered as one component of a broader strategy for enhancing the structure, habitat value and aboveground carbon storage of developing floodplain forests.     

Occurrence of Phytophthora species in oak stands in Italy and their association with declining oak trees

Soil‐borne species of Phytophthora were isolated from 19 of 30 examined oak forest areas in Italy. The frequency of isolated Phytophthora spp. (35.2%) was significantly correlated with soil pH and longitude of the sites. Eleven Phytophthora species were detected. Phytophthora cambivora, P. cinnamomi and P. cactorum were recovered from sites in central and southern Italy whereas P. quercina was isolated in the northern and central part of the country. Phytophthora citricola occurred all over Italy. Phytophthora quercina was the only species significantly associated with declining oak trees.     

Vegetation structure, floristic composition and growth characteristics of Aucoumea klaineana Pierre stands as influenced by stand age and thinning

The coastal forest of Gabon abounds in monospecific secondary Aucoumea klaineana stands derived from natural regeneration after shifting cultivation. This paper aims to describe the changes in the structure and dynamics of these stands with age. It then assesses the impact of selective thinning in the upper storey on both structural and dynamic parameters.

The experiment consisted of 34 Permanent Plots in stands from establishment to more mature stages (ca. 50 years old). Thirteen plots (17–45 years old) were thinned. More than 80% of the removal came from supernumerary dominant A. klaineana.

A. klaineana represented 60% of the total density in stands ca. 15 years old but >90% of the dominant trees in older stands. The changes with age in the floristic composition of the unthinned stands showed three successional stages during which pioneer species associated with A. klaineana (from establishment to ca. 15 years) were progressively replaced by mature forest species.

Basal area increased and density decreased with age before reaching stable values at ca. 40–45 years. Mortality was very high in young stands but decreased in the older ones. Mortality generally affected small diameter individuals in the dominated storey. Diameter and basal area increments showed that the stand growth resulted from the growth of dominant A. klaineana. Diameter increments of A. klaineana were elevated during the first years of colonisation (1.9 cm/year) and were still ca. 0.7 cm/year for 50-year-old dominant trees.

Thinning did not increase the mortality of the dominant population. It favoured the individual growth of A. klaineana. The gain was substantial for dominated trees and small dominant trees (from 60 to 100%) but was lower for large dominant trees (ca. 25–30%). Therefore, stimulation of individual growth did not compensate for the loss of basal area at the stand level.     

Influence of thinning time and density on sprout development, biomass production and energy stocks of sawtooth oak stumps

The high potential values of sawtooth oak (Quercus acutissima) in fuelwood or bioenergy are recognized. Sprouting ability, sprout growth, biomass production and energy stocks in coppiced plantations of sawtooth oak were evaluated at the Hongya Mountain Forest Farm in Anhui Province, China. Experimental treatments applied in a split-plot design included three sprout thinning times and four sprout numbers reserved on each stump (1 sprout, 2 sprouts, 4 sprouts stump⁻¹ and check). Sprout growth and biomass production per stump were significantly affected by the treatments and a significant positive relationship between stump basal diameter and sprout numbers produced was observed. After the third growing season, the highest total sprout biomass per stump was achieved in the treatment with thinning excess sprouts at the end of first growing season (December, 2007) and reserving 4 dominant sprouts per stump (T12S4, reaching 8.67 kg stump⁻¹), while the lowest was found in the treatment with thinning the sprouts in August of the first growing season and reserving 1 dominant sprout per stump (T8S1, only 3.40 kg stump⁻¹). Different treatments also influenced gross calorific values (GCV) of the components sampled from 3-year-old sprouts and the mean GCV of stem wood on an oven-dry weight basis was within the range of 18.45 ± 0.15 and 18.83 ± 0.12 kJ g⁻¹. Similar to the sprout biomass production, the greatest total and stem energy stocks per stump were observed in T12S4 treatment, achieving 161.6 and 110.5 MJ stump⁻¹, respectively. Based on the results from this study, thinning excess sprouts to reserve 4 sprouts per stump as early as age 1 could be proposed for the management of sawtooth oak coppice with cutting cycle of 3-5 years and stand density of 5000-6000 stump ha⁻¹.     

Optimizing thinning and rotation in a stand of Pinus sylvestris on a drained peatland site

A non‐linear programming algorithm was combined with a stand simulator consisting of individual‐tree, distance‐dependent diameter growth, mortality and thinning models, and a distance‐independent height growth model. The Hooke and Jeeves’ direct search method was used for determining the optimum thinning schedule and rotation length. The optimum solutions for both deterministic and stochastic optimization, with stochastic growth predictions, were calculated. In the optimization, stand density was regarded as a function of the distance to ditch. On the rather infertile site, it was most profitable to keep the stand about twice as dense near ditches and the extraction road, which was placed midway between two adjacent ditches. Stochasticity did not affect the optimum regimes markedly nor did it increase the expected returns of the optimum regimes.     

Performance and cost of a new mini-forwarder for use in thinning operations

Two tests were conducted with a new model of mini-forwarder, specifically designed for thinning operations. The tested machine resembles a conventional industrial forwarder, with tandem bogies and central articulation, but is much smaller and lighter. The machine was tested on forest plantations established on ex-farm land: such plantations offer favorable and homogeneous work conditions, which allowed reasonably accurate productivity figures to be obtained with a relatively small number of observation hours (about 10.5 h). Despite the relative inexperience of the driver, the tests indicated a productivity of between 3.1 and 3.8 m³ per scheduled machine hour (SMH) over an extraction distance of about 400 m. Extraction costs ranged from 12.4 to 15.1 € m⁻³ at the calculated machine rate of 47.6 € h⁻¹. Compared to older models derived from recreation vehicles or tracked wheelbarrows, the machine tested in this study offers a better performance and a much more comfortable workplace, with the operator sitting inside an enclosed and insulated cab. Fitted with four bogies and provided with a much longer wheelbase, the new forwarder is likely to be safer than tracked machines when surmounting obstacles, and it certainly offers a much smoother ride to the operator. Nevertheless, the tested machine is still much narrower than industrial forwarders and does not enjoy the same lateral stability. Hence, the machine is ideal for sneaking between trees and climbing over obstacles, but once on a slope it must be driven straight along the grade and never across it, unless with much caution. Like all hydrostatically driven vehicles, the tested mini-forwarder is not suited to long-distance extraction (>1 km): if run at high speed for too long, its hydrostatic transmission tends to overheat, forcing the operator to make frequent stops.     

A management planning system for even-aged and uneven-aged forests in northeast China

The most common scientific approach to numerical landscape-level forest management planning is combinatorial optimization aimed at finding the optimal combination of the treatment alternatives of stands. The selected combination of treatments depends on the conditions of the forest, and the objectives of the forest landowners. A two-step procedure is commonly used to derive the plan. First, treatment alternatives are generated for the stands using an automated simulation tool. Second,the optimal combination of the simulated treatment schedules is found by using mathematical programming or various heuristics. Simulation of treatment schedules requires models for stand dynamics and volume for all important tree species and stand types present in the forest.A forest planning system was described for Northeast China. The necessary models for stand dynamics and tree volume were presented for the main tree species of the region. The developed models were integrated into the simulation tool of the planning system. The simulation and the optimization tools of the planning system were described. The optimization tool was used with heuristic methods, making it possible to easily solve also spatial forest planning problems, for instance aggregate cuttings.Finally, the use of the system is illustrated with a case study, in which nonspatial and spatial management plans are developed for the Mengjiagang Forest District.