Tree Architecture

Structural Data from dtd Measurement

During the late winter of 2013/2014 the structure of multiple trees was manually measured with the dtd approach at the ProLoc trial site pl17 Unterrieden. The measuring took place from January to March 2014 with the rotational second harvest in Unterrieden. An overall amount of n = 51 trees were examined. 3 different levels of detail and different types of measurement were differentiated:

1. Detailed morphological measurement

2. Specific measurement with focus on stems from resprouting 3. Summary measurement with focus on main stem

Following the dtd methodology the first type of measurement included data acquisition according to the variables in Table 3.1. During the modeling process,

the branch age was additionally re-coded to the year t that the shoot formed in.

This is basically the inverted age sequence: At the time of measurement (after the third vegetation period) shoots from year 1 are 3 years old, shoots from year 2 are 2 years old and shoots that have lengthened during the last vegetation period, which is the third one, are 1 year old. In contrast to the yield model, the years are referred to here as the within rotation years. Since the structural model focuses on the second rotation the years that are numbered 4 to 6 in the yield model are here referred to as 1 to 3.

Table 3.1: All parameters that where measured for branching architecture during early 2014 on a single growth unit level.

Variable Description Unit

idGU Identifier of GU incorporating plot-ID, tree-ID, stem-ID and GU-ID idMother Identifier of mother GU, incorporating the same data as idGU

l GU Length [mm]

d GU mid-diameter [mm]

A Position of insertion / insertion height on mother [mm]

V Whether the GU is a prolongation of another GU

W Branching angle [° ]

E Number of internodes [n]

K Number of living internodes [n]

order Branch order (only recorded for order 0, rest computed afterwards) age Branch age (only recorded for order 0, rest computed afterwards) [a]

t Year that the shoot lengthened in (re-coded from age [a]

R Directional angle in classes (see Figure 3.2) [° ]

R1 R2

R3

R4 R5 R6 R7

R8 0°

45°

90°

135°

180°

225°

270°

315°

Figure 3.2: Scheme for dividing the directional angle into 8 sectors. When look-ing along a GU sector 1 resembles the upward faclook-ing direction. For vertically upward pointing GUs sector 1 is aligned with the northern compass direction (Graph and description adapted from Kurth, 2010).

On the basis of Figure 3.3, a short example should illustrate the basic function-ality of the dtd format. The graphical output of GroIMP from an imported dtd file is shown and has been annotated afterwards. The depicted upper part of a tree originates from actual structural measurement of a tree from trial site pl17 Unter-rieden (Main stem of tree 1.4.175). Each row of a dtd file contains information for a single growth unit. The data is whitespace-delimited. The focus is set on GU number 98 to exemplify how structural information is stored within dtd files:

ID98 L1192 #3 A1100 R6 W61 D5.95

The GU has a length of 1192 mm. Its mother is GU number 3, the insertion point on its mother GU is at a length of 1100 mm (GU 3 has a total length of 1304 mm).

The directional sector along the mother GU is 6 (not labeled in figure 3.3) and the branching angle is 61°. If a growth unit is a prolongation of its mother, imply-ing that it inherits the same branchimply-ing order, a "V" is noted and specifications on branching angle and directional sector are omitted. The latter applies for growth units 3 and 4 in 3.3 as they belong to the main stem. Length or diameter data does not need to be specified in mm, other units are valid as well. However all data has to be stored with the same unit, different units for diameter and length e.g. cause contorted visualizations.

ID97 ID101

ID102

ID100

ID99

ID98 L1192 #3 A1100 R6 W61 D5.95

ID3 L1304 #2 V D24.05 ID4 L1947 #3 V D11.90

Angle: 61°

Length: 1192 mm

Insertion: 1100 mm Diameter 5.95 mm

Figure 3.3: Example for dtd coding for tree 1.4.175 stem 1 in pl17 Unterrieden. 8 growth units are displayed, other growth units were deleted for better visibility.

(a)

(b)

(c)

(d)

Figure 3.4: Exemplary display of some steps in manual measuring. Panel (a) shows a tree of the clone ’Max 1’ photographed from the southern direction facing north. The trees in the plot margin have already been removed. Panel (b) contains a close up of the root stock of a ’Hybride 275’ tree. The pole on the left marks the north direction. In panel (c) a cut off stem of one of the trees is fixed horizontally for measurement. Some of the labels that were applied to the GUs for identification are visible. Panel (d) shows further marks made directly on the stem for orientation. Shown is the scar left at the shoot base between a prolongation GU and its mother GU.

A sample of n = 4 trees per clone, i.e. n = 12 trees collectively, were mea-sured. Before commencing measurement, it was advisable to clear the surround-ing ground area of the tree from litter and branches. Then the compass directions were marked with wooden poles. The stool of each tree was photographed up close with a small board containing date and tree identifier. With the same board placed appropriately, the tree was then photographed as a whole from the 4 com-pass directions (see panels (a) and (b) in Figure 3.4). Next, some information on the tree level was collected like overall tree height, breast height diameter of all stems and basal diameter. Since poplars, as already stated in contrast to willows, usually tend to develop one vigorous main stem and several minor stems after coppicing (Crow and Houston, 2004; Bärwolff et al., 2012; Janßen et al., 2017) an assessment was made which was the dominant main stem for each tree. The priorities in evaluating this were primarily focused on height and secondarily on diameter. This differentiation appears arbitrary but was actually needed for the modeling procedure. The implications will be discussed in Section 5. Following up, each stem’s orientation was quantified by first consecutively numbering the stems and then assessing the directional angle R and the orientation angle (an-gle to vertical)W of all stems at root collar/stool level. Since their growth is pre-dominantly upright, the growth direction of the main stems was assumed to follow a normal vector to thexy-plane which is the ground here. This implies no value for angle R and W = 0. Before continuing the measurement two options were available: If a stem was not too tall and measurement was manageable standing upright, then the stem was left attached to the stool. For taller stems however, it was recommendable to horizontally draw a line on the stems at a fixed height of e.g. 100 mm from the ground. Alongside this line the direction towards the stool’s center was then marked with a vertical line. Along the horizontal marking the stem was then cut whilst carefully bringing the stem down without branches or twigs breaking off. The stem was then mounted in a custom built wooden fixture comparable in function to a sawbuck (see panel (c) in Figure 3.4). The branches should not touch the ground or bend in any way due to the fixing. Independently of a stem being measured as a whole still attached to the stool or after being

shoot bases and other important points were marked on the stem (see panel (d) in Figure 3.4). Additionally, a topological layout/sketch was drawn of each tree (see panel (a) in Figure 3.5).

(a) (b)

Figure 3.5: Exemplary illustration of different visualization of topology and struc-ture. Panel (a) shows the topological sketch of the middle part of the main stem of a ’Max 1’ tree (Sketch drawn by Niels Lakämper). Panel (b) shows a photo-graph of the same tree on the right and on the left the visualized dtd file from GroIMP (Illustration in panel (b) taken from Lakämper, 2014, p. 11).

All growth units are then measured regarding the variables as specified in Table 3.1. A minimal workforce should consist of 2 persons who divide the measuring itself and the data recording amongst each other. An additional person can be useful to further divide the measuring when multiple tools are needed to avoid switching.

The specific measurement mainly incorporated the same steps as the detailed morphological variant. The measurement itself however differed by recording the length and mid diameter of all GUs only from branch order 0 of all main and minor stems. Additionally the internode count and the count of lateral axes (branch

order 1) were counted. This procedure was applied to a sample ofn = 12 trees withn= 4 trees per clone.

The third summary variant of structural data acquisition applied the specific variant only to the major stem while for the minor stems only length and mid-diameter per GU were measured. A total amount ofn = 27 trees was measured here. The count of trees per group is unbalanced here due to 3 additional trees that were measured for ’Max 1’ before the plantation was harvested completely.

A list of all measured trees grouped by the measurement variant is given in Table 3.2.

Table 3.2: List of trees that were randomly selected for differently detailed DTD measuring during winter 2013/2014 in pl17 Unterrieden.

Clone Tree Identifier Type

MAX 1_1_001, 1_2_091, 1_3_121, 1_4_175 detail HYB 2_1_019, 2_2_061, 2_3_139, 2_4_181 detail AF2 3_1_043, 3_2_073, 3_3_115, 3_4_175 detail MAX 1_1_007, 1_2_073, 1_3_139, 1_4_145 specific HYB 2_1_025, 2_2_093, 2_3_097, 2_4_187 specific AF2 3_1_037, 3_2_079, 3_3_109, 3_4_169 specific MAX

1_1_019, 1_1_037, 1_1_043, 1_2_066, 1_2_080, 1_3_115, 1_3_127, 1_3_133, 1_4_163, 1_4_169, 1_4_181

summary HYB 2_1_031, 2_1_037, 2_2_049, 2_2_085,

2_3_109, 2_3_121, 2_4_163, 2_4_175 summary AF2 3_1_001, 3_1_013, 3_1_031, 3_2_049,

3_2_054, 3_2_061, 3_3_097, 3_3_121 summary

After finishing the measurement, the data was digitized and then imported into R for a full plausibility check with validating the data types and value entries.

Based on the topology, age and order were computed for all GUs as these were