Grand Duchy of Luxembourg

Abstract

In the context of the resolutions of the Ministerial Conference on the Protection of Forests in Europe (MCPFE) and to meet the sustainable forest management commitments, the Grand Duchy of Luxembourg decided to implement a permanent National Forest Inventory (NFI) in 1990.

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1 The National Forest Inventory of the Grand Duchy of Luxembourg

1.1 History and Objectives

In the context of the resolutions of the Ministerial Conference on the Protection of Forests in Europe (MCPFE) and to meet the sustainable forest management commitments, the Grand Duchy of Luxembourg decided to implement a permanent National Forest Inventory (NFI) in 1990.

At that time the country used a full census (for public forests only), primarily at the scale of forest compartments, to provide general information on the type of stands, structure and volume per hectare. Satellite imagery and digital maps were also used to provide area estimate for small forest areas and various thematic maps.

The general aim of the NFI is to report on the state and the evolution of forests as concerning: the wooded and non-wooded area, stand composition, growing stock , regeneration, forest health and biodiversity. The inventory is becoming an important source of information for reporting to international organisations and a very pertinent tool that is relevant to the national forest policy decision-making. It facilitates monitoring the extent to which the sustainable forest management has been applied in managed forests.

Field data collection for the first inventory cycle began in 1998. Detailed results, including methodological aspects, of this first inventory cycle were published in 2003 in a well-documented textbook entitled “La forêt luxembourgeoise en chiffres” (The Luxembourgish forest in figures).

A second inventory cycle was launched in 2009 and the results were published in 2014. It was an update of the forest situation based on features and indicators relating to the whole territory in order to keep records of the sustainable management of national forest heritage.

Comparison between the data from the two cycles allowed, for the first time in Luxembourg, to identify major trends of forest evolution. It became possible to assess changes in areas and volume, both in public and private forests. Also to some extent the forest productivity could be evaluated. It was also possible to assess the impact and the sensitivity of measures applied for more than 150 years and aimed at promoting sustainable management of the forests of the Grand Duchy. In Table 29.1 the main features of the national forest inventory of the Grand Duchy of Luxembourg are described.

Table 29.1 Description of the national forest inventory of the Grand Duchy of Luxembourg

1.2 Sampling Methods and Periodicity

The inventory is based upon a single-phase, non-stratified sampling based on plots that are distributed, on a systematic basis, at the intersections of a rectangular 1000 × 500 m grid across the whole country. Nearly 1800 permanent plots were established during 1999–2001 and were remeasured during 2009–2011. One can consider that the estimates provided by the national forest inventory correspond to reference years 2000 and 2010. The sampling intensity is 0.2 %.

In the inventory each sample unit comprises different plots (Fig. 29.1) which sizes are adapted to the nature of the collected data. The main sampling unit consists of several concentric circular plots with radii varying from 2 to 30 m. All living and dead standing trees with diameters (d) of at least 7 cm are measured on the three main plots as follows:

Fig. 29.1

Design of sampling area

• plot with radius of 18 m: trees with d ≥ 40 cm

• plot with radius of 9 m: trees with 20 cm ≤ d < 40 cm

• plot with radius of 4.5 m: trees with 7 cm ≤ d < 20 cm.

Another plot of radius of 30 m is used to collect information dealing with stand structure, health conditions, main forest functions (water protection, recreation and biodiversity), sustainable management, storm and game damage. Furthermore special attention is paid to the presence of biotopes referring to the directive “Habitat” 92/43/CEE and also to wetlands, rocks, open areas.

In addition to this sample unit configuration, 4 small plots of radius of 1 m are also used; one plot has a radius of 2 m and the center of this plot is the plot center. One of them is established at the plot center and the others are located at distances of 5 m from plot center in the cardinal directions. They are used for measuring variables linked to regeneration including cover percentage and species composition for different stages of development. Saplings are defined as those trees with height >0.3 m and diameter at 1.3 m < 7 cm. The 9 m radius circle is used to measure lying dead trees (or pieces of wood) of at least 7 cm diameter and 1 m long. Edges and transition zones are observed along transects at the interception of the 18 m radius circle and the type of stands or type of land uses before shifting the plot into the dominant type (circle tangent to the intercept line).

1.3 Data Collection and Data Processing

The majority of data are collected in the field and, but for some parameters the data can be assessed from administrative and cartographic sources. The information assessed is divided in four categories:

• general data: administrative information, ownership type, plot location

• site variables: land use class, topography, soil characteristics

• stand variables: structure, age, stage of development, sylviculture, health status

• tree variables: location, species, diameter at 1.3 m, total height.

An electronic recorder is used in the field so that a first quality control can be made. The encoded data are then transferred into the database to be checked again and processed through an automated verification procedure. Numerous parameters are computed using data which refer to sample units, tree species and individual trees.

For each tree basal area and volume to upper diameter to limit of 7 cm are estimated. Sample tree volume (stem and branches over bark) are calculated from volume equations based on regression models most commonly used in Belgium. Volume of standing and lying deadwoods are also estimated. Areas regarding to productive and non-productive forests are estimated through the dot grid method (1 sampling point falling in such areas corresponding to 50 ha).

Furthermore since 2012 growing stock increment and evolution of wooded areas are assessed from the comparison of the two successive inventories.

2 Land Use and Forest Resources

2.1 National Forest Area

The main information provided by the inventory concern the forest land area of the Grand Duchy. Conventionally forest land includes forests devoted to production, protection, conservation and multiple-use objectives. Forest land is defined as having a minimum area of 0.5 ha with tree crown cover of more than 10 %, comprising trees able to reach a minimum height of 5 m at maturity. In this respect it should be noted that the forest area is remaining stable between 2000 and 2010 amounts to 91,400 ha which corresponds to a forest cover of more than 35 % (Table 29.2). This rate has not changed during the last ten years and is lower than the European average level but higher than in neighbouring countries: France (32 %), Germany (32 %) and Belgium (23 %).

Table 29.2 Forest land classification

2.1.1 Classification of Forest Stands

Luxembourgish forest is composed of about two-thirds deciduous forest and one-third coniferous forest (Table 29.3). Despite the high proportion of beech, oak and spruce forests which represent nearly 60 % of the stands, there is a significant presence of mixed stands (mixed beech-oak-hornbeam forests, other mixed deciduous forests, mixed forests with a dominance of conifers). This proportion shows a quite remakable diversity of species at the national level in spite of the dominance of stands with a more homogenous composition.

Table 29.3 Species distribution in Luxemburg’s forests and rate of change from 2000 to 2010

2.1.2 Classification by Ownership Categories

Two types of forest owners can be distinguished: private owners and public owners. The latter include the state, municipalities, and public institutions (church councils, social insurances, companies where the state is a shareholder, etc.). The private forests are managed by private bodies and/or by private persons whereas the public forests that come under the Forestry Regime are managed by the Nature and Forest Administration (Administration de la Nature et des Forêts).

In spite of an increase of the proportion of the total area of public forests, the proportions of private and public owners of the Luxembourgish forest remain nearly the same, 54 % private and 46 % public (Table 29.4). The difference of these two types of ownership has been reduced at 7350 ha (8 % of the forest area) compared to 9350 ha in 2000 (10 % of the forest area).

Table 29.4 Forest area by type of ownership

The public forests are mainly composed of deciduous forest (80 %) whereas the private forests are divided in almost equal parts in deciduous forest (56 %) and coniferous forest (42 %) which mainly consists of spruce forest (68 %) (Table 29.5). This situation remains stable for the private owners in contrast to the public forest where the gap between deciduous and coniferous is growing, especially due an increase of beech-oak-hornbeam mixed stands.

Table 29.5 Area by type of stand and type of ownership

2.2 Wood Resources and Their Use

Wood production remains an important facet of Luxembourg’s forest policy. In this context it is essential to characterise and quantify the timber resource in terms of species, structures and growing stock or even size categories. On one hand this allows the forest manager to better plan his silvicultural interventions and on the other hand the timber industry can evaluate the potential wood supply over the short and medium term. The evaluation of carbon stocks and the description of potential forest habitats for fauna and flora are other important outcomes of the use of such data.

The standing stock volume of stem wood over bark is about more than 31 million m³ (Table 29.6). The coniferous stands and especially the mixed coniferous forests are characterised by average volumes per hectare higher than those observed in the deciduous stands. Among the latter, other mixed deciduous forests represent the lowest volumes.

Table 29.6 Volume of heavy timber by structure and type of stand

In terms of evolution over time the average volume per hectare of standing total heavy timber has increased during the period 2000–2010 as well as for the deciduous forests (+34 m³/ha, +11 %), the coniferous forests (+86 m³/ha, +26 %) and coppice (+53 m³/ha, +22 %). Heavy timber includes those stem and branches that have top diameter >7 cm in diameter.

The volume of firewood in high forests is significantly represented in the public forest: more than 80 m³/ha, thus 20 % of the volume of standing heavy timber. Only the half of this volume is found in private forest ownership, the majority of which are, covered by conifers. At stand level firewood reserves are highest in the deciduous forests, the mixed forests with a dominance of conifers and other coniferous forests. Beech forests and the beech-oak-hornbeam mixed forests supply firewood volumes which are quite higher than those generally found in other stands.

The annual volume increment of high forests amounts to 10 m³/ha/year or 758,000 m³/year (Table 29.7). The removals represent about 59 % of this increment. However, this national average is subject to local variations according to present species, age, forest site productivity, etc.

Table 29.7 Increment and removals of heavy timber by type of stand