Estimates of stem wood increments in forest resources: comparison of different approaches in forest inventory: consequences for international reporting: case studyof European forests

Key message

Quality and reliability of forest resource assessments depend on the ability of national forest inventories (NFIs) to supply necessary and high-quality data. Over the last decades and especially since the 1990s, the NFIs in European countries have been rapidly developing. Possibilities for obtaining reliable and accurate data on annual increment from different inventory types were evaluated, and sample-based inventories have been found to be superior to standwise inventories in providing reliable data. Simplified methods may be employed when increment cannot be directly estimated from inventory data.

Context

An increasing intensity of forest resource use requires more accurate, detailed and reliable information, not only on forest area and growing stock but also on forest stand productivity, wood increment and its components.

Aims

The main objectives were to assess the capacities of forest inventories, the methods used for estimation of gross increment and its components and their accuracy and to demonstrate an effective method for estimation of increment when direct inventory methods are not available.

Methods

Data about national forest inventory methods were obtained from 30 responses to a questionnaire, distributed amongst national correspondents of all European countries; reports of COST Actions E43 and FP 1001, databases of Temperate and Boreal Forest Resource Assessment (TBFRA) 2000 and State of Europe’s Forests (SoEF) 2011 were used as well. Analysis and comparison of results from different forest inventories were used for evaluation of data reliability. Relationships between growing stock and gross increment in European forests were also analysed, and corresponding models were proposed.

Results

Seventy-nine percent of European forest area is covered by national forest inventories (NFIs) based on sampling methods and the rest on stand-level inventory and other inventory methods. Data obtained by aggregating standwise data usually underestimate growing stock by 15–20 % and gross increment even more. Almost half of the European forest area (47 %) is monitored using permanent plots, measured twice or more, allowing the estimation of gross increment and its components to be made directly.

Conclusion

Implementation of NFIs based on sampling methods, especially with permanent plots, resulted in an improvement of data quality and in most cases an increase of growing stock and gross increment. The estimation of natural losses is the weakest link in today’s NFIs and in the current assessment of European forest resources. The proposed default values for gross increment and its components is an option to be used in countries not having NFI at all or those which have started it only recently.

     

The role of competitors for <Emphasis Type="Italic">Chrysomela lapponica</Emphasis>, a north Eurasian willow pest,in pioneering a new host plant

The Palaearctic leaf beetle Chrysomela lapponica usually feeds upon willows in the northern region of its occurrence. However, in Central Europe, some populations are known that have specialised on birch. In this study, we investigated the significance of other herbivores occurring together on the same host plants as possible exploitative competitors of C. lapponica. Two populations were studied: a population from Finland specialised on the willow Salix borealis, and a population from the Czech Republic, specialised on the birch Betula pubescens. Abundances of folivorous and suctivorous insects on both host plants were recorded at both population sites. The willow leaf beetle Phratora vitellinae was the most abundant herbivorous insect at both study sites on willow. A field study was conducted to examine the effects of P. vitellinae on the performance of C. lapponica. The presence of P. vitellinae larvae on the same twig upon which C. lapponica larvae were feeding did not affect increase of body weight in C. lapponica larvae. Thus, the high resource availability of both willows and birches suggest that interspecific competition is unlikely to be a selection factor driving the evolution of host shift in C. lapponica.     

Root parameters of forest trees as sensitive indicators of acidifying pollutants: a review of research of Japanese forest trees

The root parameters of forest trees can be indicators of a changing environment. We summarize the results of root studies with regard to the effects of acidifying pollutants, especially soil acidification and aluminum toxicity, on various root parameters of Japanese forest trees under experimentally controlled conditions. All root parameters such as biomass, morphology, nutritional status, and physiology can be regarded as indicators, because, under laboratory conditions, root responses occur prior to the responses in the aboveground parts. However, considering the conditions of forest sites, the nutritional status and physiological changes are better indicators of soil acidification and Al stress than the biomass and morphological response. The currently available data suggest that the most important indicator is the Ca/Al molar ratio in roots of Japanese tree species. In order to predict and detect the initial effects of soil acidification, we postulate that the specific root response to the Ca/Al molar ratio of tree roots should be considered as a parameter for use in long-term forest monitoring sites.     

Comparing the model forms estimating generalised diameter-height relationships in Tecomella undulata plantations in hot arid region of India

Four generalised diameter-height equations were developed and compared for pure and even-aged stands of Tecomella undulata in hot arid region of Rajasthan State in India. The data used to fit the equations consisted of 1 540 diameter-height observations collected from the plots laid out in uniformly stocked stands of varying age and density. The performance of four equations was tested by non-linear least squares regression and evaluated using different statistical criteria. Finally, these equations, with the same values of coefficients ob- tained during the fitting phase, were validated by an independent data set consisting of 854 diameter-height observations. Overall, equation （4） （Hui and Gadow function） was found to perform best for both the fitting data set as well as validation data set.     

Effect of maleic anhydride grafted styrene-ethylene-butylene-styrene （MA-SEBS） on impact fracture behavior of polypropylene / wood fiber composites

MA-SEBS as compatibilizer and impact modifier was incorporated into Polypropylene/Wood Fiber （PP/WF） to enhance interface adhesion and impact strength of the composite. The effect of MA-SEBS content on the impact fracture behavior of PP/WF composites was studied. The impact properties of composites with 8% MA-SEBS reached the maximum value. And further increasing of MA-SEBS content to 10% did not improve the fracture toughness, but improved the stiffness of composites by DMA analysis. This was attributed to the improved PP/WF adhesion. As the MA-SEBS content is more than 8%, the molecule interaction of PP and WF was expected to much stronger than lower MA-SEBS. Scanning electron microscopy （SEM） was performed to analyze the impact fracture surface and showed a stronger affinity for the wood surfaces.     

Use and effectiveness of Washington state’s extension forest stewardship program

This paper describes the use by family forest landowners of educational programs provided by Washington State University Cooperative Extension (WSUCE), and the associated use of technical assistance programs provided by state and federal agencies and the private sector. Approximately 100,000 family forest owners controlled 19% or over 1.2 M ha of Washington’s forestland and accounted for 29% of the timber harvested in the state on a volume basis in 1998. A variety of public and private assistance and education programs are available to encourage and help family forest owners manage their forests. In 1999 a mail survey was conducted to evaluate use and effectiveness of Washington’s family forest assistance and education programs. Over half of the 872 responding family forest landowners had contact with an extension educator, program or educational material, and about three quarters of these respondents gave an overall rating of the usefulness of extension programs and materials as good or excellent. Respondents attending WSUCE forestry educational programs have larger median land ownership size, are older, have owned their forests longer, have a higher rate of absentee ownership, and are better educated than non-users. They are more likely to actively manage their forests for timber production and exhibit a clearer understanding of the multiple-use capabilities of their forests.     

Root architecture might account for contrasting establishment success of <Emphasis Type="Italic">Pseudotsuga menziesii</Emphasis> var. <Emphasis Type="Italic">menziesii</Emphasis> and <Emphasis Type="Italic">Pinus sylvestris</Emphasis> in Central Europe under dry conditions

Key message

Pinus sylvestris seedlings quickly expand their roots to deeper soil layers while Pseudotsuga menziesii concentrates its root system in the topsoil, thereby running the risk of desiccation during long dry spells, as indicated by lower survival after simulated summer drought.

Context

Pseudotsuga menziesii (Douglas-fir) is regarded as a promising species to maintain the productivity of Central European lowland forests given the projected increase of long dry spells.

Aims

Will the species be able to regenerate from seed and spread outside plantations in a drier temperate Europe?

Methods

We measured the relative growth rate, biomass allocation, root architecture, and phenotypic plasticity of Pseudotsuga menziesii seedlings sown in a common garden and grown under current precipitation and prolonged drought, respectively. The species’ competitive ability with respect to Pinus sylvestris L., the most drought-tolerant native conifer in Central Europe, was assessed during three growing seasons.

Results

Pinus sylvestris seedlings had higher relative growth rates than did Pseudotsuga menziesii seedlings, first in terms of aboveground biomass and later in terms of shoot height. This resulted in heavier and taller seedlings after three growing seasons under both moist and dry conditions. Shorter vertical roots corresponded with lower survival of Pseudotsuga menziesii seedlings under dry conditions.

Conclusion

Fast root proliferation allows Pinus sylvestris seedlings to reach deeper water pools that are less rapidly depleted during transient drought. By contrast, the shallow root system might put Pseudotsuga menziesii seedlings at the risk of desiccation during prolonged dry spells.

     

What is new about new forest owners? A typology of private forest ownership in Austria

With structural changes in agriculture, new types of forest owners have become increasingly important. This article develops an empirically-based typology of forest owners in Austria. Based on a representative survey and by means of cluster analysis, seven types of forest owners are identified. These types form a sequence, ranging from forest owners with a strong agricultural background to forest owners with no agricultural background at all. The latter exhibit markedly different behaviour in various respects, e.g. in their interest in forest-related information. The increasing number of ‘new’ forest owners raises important questions for forest policy, especially how policy instruments can reach these owners and how extension services can address them.     

Effects of acorn attack by curculio weevils on the germination and early growth of <Emphasis Type="Italic">Pasania edulis</Emphasis> (Makino) seedlings

We conducted field studies to evaluate the impact that curculio weevil attacks on Pasania edulis (Fagacea) acorns have on the regeneration of this tree. The germination ratio of weevil-attacked acorns was significantly lower than that of sound acorns. The number and position of the attacks on acorns affected the germination ratio. The seedlings from weevil-attacked acorns were shorter and had a smaller leaf area than those from sound acorns. The negative effects on seedling height lasted for at least three years after germination. We also studied the handling of the two types of acorns by granivorous Apodemus mice in a broad-leaved forest dominated by P. edulis. The mice picked up, transported, hoarded, and recovered sound and weevil-attacked acorns similarly. In the study site, the seedlings from weevil-attacked acorns were estimated to account for 1.5–20.4 % of the total seedlings for cohorts of mast years and 0–3.7 % for those of poor or medium acorn production. From these results, we conclude that acorns with the lower part of their cotyledons slightly damaged by weevil larvae might still be able to contribute to the regeneration of P. edulis in the field but that their contribution would be negligible or small even in mast years in this study site.