Kurze Darstellung zu

0 downloads 0 Views 419KB Size Report
Projektbearbeiter: Andrew Haywood. Bachelor of Forestry Science. Institut für Waldwachstum. Tennenbacher Straße 4. 79085 Freiburg i. Br. Tel.: 0761/203-3737.
Überführung und Wertsteigerung von Bu-Beständen (A4) Projektleiter:

Projektbearbeiter:

Prof. Dr. Heinrich Spiecker Institut für Waldwachstum Tennenbacher Straße 4

Andrew Haywood Bachelor of Forestry Science Institut für Waldwachstum Tennenbacher Straße 4

79085 Freiburg i. Br.

79085 Freiburg i. Br

Tel.: 0761/203-3737 Fax.: 0761/203-3740 Email: [email protected]

Tel.: 0761/203-3737 Fax.: 0761/203-3740 Email: [email protected]

Introduction Problem Statement In recent years close-to-nature forestry has been favored by many forest owners and the public. In the state forest administration of Baden-Württemberg, a concept of close-to-nature forestry involving species enrichment, structural diversity and other ecological benefits through the conversion of even-aged into multi-layered uneven-aged forest stands is being implemented (MLR (MINISTERIUM FÜR LÄNDLICHEN RAUM) 1993). To transform the stands in the southern Black Forest into this well structured mixed species uneven-aged system, some of the present stands require transformation from their current species mix and diameter distributions. The successful application of this transformation system in such stands requires a better understanding of the growth responses of individual trees than is currently available. Forest practitioners responsible for this transformation management process require more insight into growth dynamics than that required for other classic management systems. In particular, such practitioners require detailed information concerning the growth responses and spatial arrangements of individual trees both before and after release and whether release can be effective in accelerating the development/stabilization of advanced European beech trees in transformation forests. The ideal approach to investigate the response of old aged trees to release would be to conduct replicated long-term experimental trials. However, such plots would have to be monitored for a long period of time in order to obtain meaningful results on the magnitude of the response and to answer the question of whether treatments could substantially shorten the time required to promote the growth of large trees in transformation. Before making a commitment to long-term experiments, it may be desirable to evaluate growth responses in stands that have received a variety of treatments in the past.

1

Therefore, this study attempts to conduct a retrospective analysis of the reaction of basal area increment, height increment and crown expansion of trees with different dimensions that have experienced changes in competition. This research project mainly focuses on the transformation of single-layered, even-aged stands of Norway spruce (Picea abies (L.) Karsten), silver fir (Abies alba Mill.) and European beech (Fagus sylvatica) into mixed species close-to-nature forests. The quantification of the growth responses of mature trees of different dimensions to different changes in competition was the central focal point of this study.

Conditions for the Execution of the Project The investigation described above was conducted at Institut for Forest Growth of the Albert Ludwig University, Freiburg. The Institute for Forest Growth, with its existing specialized knowledge and experience in similar investigations (SPIECKER, 1991; HAHN, 1995; BÖRNER, 1997; EPP, 2003) provided an excellent environment for the execution of the project.

Planning and Expiration of the Project The investigation one completed during the the period of 1.4.1999 up to 31.9.2002 as a planned three-year project. The following are some points of interest further discussed:

Method The investigation was carried using a two stage sampling procedure. In the first stage, using non-destructive measures, the range of past and current competition scenarios within each of the four study sites was estimated from 300 trees per site. During the second stage, a smaller sample of 50 trees per study site, uniformly representing the initial sample, were selected for destructive measurement. This two stage-sampling scheme was successful in ensuring a wide range of competition scenarios. In the process of measuring this secondary sample, 30 trees were damaged during the felling process. The remaining 170 tree were analyzed using dendrochronology and branch analysis to test the posited hypotheses.

2

Material Study sites were established in four European beech stands in the southern Black Forest, that had been subjected to a range of cutting intensities over the last 25 years. The sites were located on fresh brown earth. Species composition was primarily European beech, Norway spruce and silver fir in the overstory, with European beech and Norway spruce dominating the understory. The location of these sites can be seen in Figure 4

Figure 1: Location of the four study sites in the southern Black Forest

Transferability of the Results into Forestry Practice An important goal of the work was to give the forest manager a basis for decisions in converting/transferring stands from even-aged into uneven-aged structures. Therefore the basis of the study was conducted using available growing space to predict the response of basal area and height increment to intervention.

For the Conversion of Transfer to Literature and Practice Selective thinning and target diameter harvesting are two different concepts for transformation that can be singled out in the literature. The aim of both these strategies is the same; to convert a regular structure into an irregular structure with a range of tree sizes and maintain some tree cover in perpetuity. The basis of the selection thinning concept is to partition the transformation process into distinct phases, characterized by pre-defined targets. However, this is not the case with the structural target-diameter harvest concept. This concept is usually associated with silvicultural systems applicable for even-aged management. 3

However, by ensuring a long phase of single tree, target diameter harvesting causes a vertical differentiation within the stand. In both systems, trees are selected for release. Therefore, to increase the likelihood of the results of this study being implemented into practice the focus was on the response of individual trees to release.

Co-operation with Others This investigation in terms of methodology and content was strongly linked with the project A3 . Close cooperation with the project worker occurred in terms of developing appropriate methodology and analysis techniques. A similar cooperation occurred with with project D3 to ensure compatability in terms of results.

Representation of the Results and their Conversion to Forestry Practice Representation of the Results The specific null-hypotheses (NH) posited for testing in the study were as follows: NH1) There is no significant difference, at the 0.05 level of statistical confidence, in the basal area increment of advanced European beech trees during the period from before to after heavy release; NH2) There is no significant difference, at the 0.05 level of statistical confidence, in the height increment of advanced European beech trees during the period from before to after heavy release; NH3) There is no significant difference, at the 0.05 level of statistical confidence, in the increment of an exposed branch to that of an unexposed branch for advanced European beech trees; NH4) A gap diameter of 10 m is insufficient in size, at the 0.05 level of statistical confidence, to assure the recruitment of a 4 m high gap tree into the canopy. The results for each hypothesis are provided in more detail below.

4

RESULTS Basal Area Increment Both a direct analysis of the basal area at 1.3 m increment rates of subject trees before and after treatment and comparisons of the post-treatment increment for treated and untreated trees indicate the basal area increment rates of advanced European beech can be increased by an average of 70-100% through heavy release. Under conditions of low competition even relatively old trees appear to be able to maintain rapid increment rates (>3.5mm radial increment/year) for long periods.

200 180 160 140 120 100 80 60 40 20 0 -20 -40 -60 -80 -100 0

20

40

60

80

100 120 140 160 180 200 220 240 260 280 300

Bad Säc k i ngen St . Mär gen

Sc hopf ei m Todt moos

Figure 2: Percent change in basal area increment rate of individual canopy trees for the 4-10-year posttreatment period compared with increment of the same trees in the 10-year pre-treatment period

Percent increment change after treatment was calculated using the following equation: % BAI =

BAI after − BAI before BAI before

× 100 Equation 1

Where

%BAI BAIbefore

= =

BAIafter

=

percent basal area increment (%); 10 year mean annual basal area increment before release (cm2.year-1); 10 year mean annual basal area increment after release (cm2.year-1).

5