Article Biological Durability of Sapling- Products Used for and Outdoor Decoration

Christian Brischke *, Lukas Emmerich, Dirk G.B. Nienaber and Susanne Bollmus

Wood Biology and Wood Products, University of Goettingen, D-37077 Goettingen, ; [email protected] (L.E.); [email protected] (D.G.B.N.); [email protected] (S.B.) * Correspondence: [email protected]

 Received: 28 November 2019; Accepted: 13 December 2019; Published: 17 December 2019 

Abstract: Sapling-wood products from different wood such as (Salix spp. L.) and Common ( L.) are frequently used for gardening and outdoor decoration purposes. Remaining bark is suggested to provide additional biological durability. Even for temporary outdoor use it seemed questionable that durability of juvenile sapwood can provide acceptably long service lives of horticultural products. Therefore, sapling-wood from seven European-grown wood species was submitted to laboratory and field durability tests. In field tests, specimens with and without bark were tested in comparison and submitted to differently severe exposure situations, i.e., in-ground contact, and above-ground situations with and without water trapping. All materials under test were classified ‘not durable’ independently from any potential protective effect of remaining bark, which contradicted their suitability for outdoor applications if multi-annual use is desired.

Keywords: basidiomycetes; fungal decay; horticulture; juvenile wood; resistance; sapwood

1. Introduction The biological durability of most European-grown wood species is often insufficient for outdoor applications and wood needs protection either by design, wood modification, or as pointed out in prEN 460 (Durability of wood and wood-based products—Natural durability of solid wood—Guide to the durability requirements for wood to be used in hazard classes [1]). Nevertheless, more recently, some wood species were advertised and customized for gardening and outdoor decoration purposes, although their durability is generally considered low, but had been rarely studied systematically. Among those, Common hazel (Corylus avellana L.) and different willow species (Salix spp. L.) are suggested for climb supports for clamberers [2,3], paling and woven fences [4], fascines, screens, flower bed edgings, raised beds, and other decoration items (Figure1). Frequently, such products are manufactured from sapling-wood (here defined as roundwood from stems of less than 10 years of age) and bark is not removed since it is suggested to provide additional biological durability. Goat willow (Salix caprea) is classified as ‘non-durable’ (DC 5, [5]), although some previous studies indicated slightly higher durability [6], i.e., DC 4. The durability of Common hazel is not classified within EN 350 (Durability of wood and wood-based products—Testing and classification of the durability to biological agents of wood and wood-based materials [5]). However, sapling-wood is juvenile wood. The latter has previously been reported to be less durable than adjacent mature wood for different wood species [7–11]. In addition, sapling-wood is exclusively sapwood, which is per definition ‘non-durable’ according to EN 350 [5], independent from the wood species. Consequently, it is hypothesized that sapling-wood is the least durable kind of xylem and manufacturing sapling-wood

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products for outdoor use appears questionable, especially when ground contact is proposed such as Forests 2019, 10, x FOR PEER REVIEW 2 of 9 for fences and fascines.

Figure 1. Examples of using Common hazel wood for gardening, outdoor decoration, and historical Figure 1. Examples of using Common hazel wood for gardening, outdoor decoration, and historical use for stabilization of soil. Left: climb support for roses; Center: miniature woven ; Right: use for stabilization of soil. Left: climb support for roses; Center: miniature woven fence; Right: reproduction trench during World War I in Belgium. reproduction trench during World War I in Belgium. Bark tissue of various wood species is known for containing substantial amounts of extractives Bark tissue of various wood species is known for containing substantial amounts of extractives which can have inhibitory effects on fungal growth and wood degradation. Bark extractives such as which can have inhibitory effects on fungal growth and wood degradation. Bark extractives such as different organic acids, , and alkaloids have, therefore, been used to improve the biological different organic acids, tannins, and alkaloids have, therefore, been used to improve the biological durability of wood and other lignocellulosic products as previously reported by different authors [12–15]. durability of wood and other lignocellulosic products as previously reported by different authors Bark itself has been used for application where biological durability is requested, that is, such as [12–15]. Bark itself has been used for application where biological durability is requested, that is, such for roofing [16,17], boats [18,19], and mulch [20]. Recommendations to leave bark on sapling-wood as for roofing [16,17], boats [18,19], and mulch [20]. Recommendations to leave bark on sapling-wood products could therefore be meaningful, although it contains rather thin layers of bast and thick layers products could therefore be meaningful, although it contains rather thin layers of bast and thick of secondary bark. The latter contains usually significantly more extractives than bast, but the ratio as layers of secondary bark. The latter contains usually significantly more extractives than bast, but the well as the total amount of extractives is species specific [21]. Apart from potential biocidal or ratio as well as the total amount of extractives is tree species specific [21]. Apart from potential inhibitory effects of extractives, bark might serve as a chemo-mechanical barrier for moisture and can biocidal or inhibitory effects of extractives, bark might serve as a chemo-mechanical barrier for protect the wood tissue beneath from wetting for instance due to hydrophobic substances (e.g., suberin, moisture and can protect the wood tissue beneath from wetting for instance due to hydrophobic resin acids) or the formation of thyloses. In contrary, re-drying of once wetted wood is inhibited by substances (e.g., suberin, resin acids) or the formation of thyloses. In contrary, re-drying of once bark layers as well. wetted wood is inhibited by bark layers as well. This study aimed at examining the natural biological durability of sapling-wood comprehensively. This study aimed at examining the natural biological durability of sapling-wood Therefore, sapling-wood from seven European-grown wood species was submitted to laboratory and comprehensively. Therefore, sapling-wood from seven European-grown wood species was field durability tests. In field tests, specimens with and without bark were tested in comparison and submitted to laboratory and field durability tests. In field tests, specimens with and without bark submitted to differently severe exposure situations, i.e., in-ground contact and above-ground situations were tested in comparison and submitted to differently severe exposure situations, i.e., in-ground with and without water trapping, to fully reflect the anticipated in-use conditions of gardening products contact and above-ground situations with and without water trapping, to fully reflect the anticipated available in specialized trade. in-use conditions of gardening products available in specialized trade. 2. Materials and Methods 2. Materials and Methods 2.1. Wood Specimens 2.1. Wood Specimens For laboratory decay resistance tests, sapling-wood was sampled from young (less than 10 yearsFor laboratory old) of English decay resistance (Quercus tests, robur ,sapling Oak), Common-wood was hazel sampled (Corylus from avellana young, Hazel), trees (less Black than cherry 10 years( old) serotina of English), White oak willow (Quercus (Salix robur alba, ,Oak), Willow), Common European hazel (Corylus (Fagus avellana sylvatica, Hazel),, Beech), Black Silver cherry ((PrunusBetula pendulaserotina,), Birch), White Rowan willow (Sorbus (Salix aucupariaalba, Willo), andw), European Scots beech (Pinus ( sylvestrisFagus sylvatica) at diff, erentBeech), stands Silver in birchLower (Betula Saxony, pendula Germany., Birch), For Rowan laboratory (Sorbus decay aucuparia tests,) specimens, and Scots with pine a ( lengthPinus sylvestris of 50 1) at mm different and an ± standsaverage in diameter Lower Saxony, (without Germany. bark) between For laboratory 17.3 and decay 20.9 mm. tests, The specimens target diameter with a length of the sapling-woodof 50 ± 1 mm anspecimensd an average at a given diameter length (without of 50 mm bark) was betweendtarget = 21.9 17.3 mm and according 20.9 mm. to The Equation target (1). diameter However, of the the saplingdiameter-wood of the specimens collected at samples a given varied length around of 50 mm the targetwas dtarget value = 21.9 as shown mm according in Table1 .to Equation (1). However, the diameter of the collected samples varied around the target value as shown in Table 1.

퐴 푑 = √ 퐶퐸푁 푇푆 15083−1 ∙ 2 (mm) 푡푎푟푔푒푡 휋 (1)

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r ACEN TS 15083 1 dtarget = − 2 (mm) (1) π · where, dtarget is the target diameter of the sapling-wood specimens, in mm; ACEN TS 15083-1 is the cross-sectional specimen area acc. to CEN/TS 15083-1 (2005) = 375 mm2. The bark was peeled off immediately after cutting the trees. In addition, sapwood specimens of 15 25 50 mm3 were cut from Beech, Hazel, Willow, Birch, and Scots pine according to CEN/TS 15083-1 × × (Durability of wood and wood-based products—Determination of the natural durability of solid wood against wood-destroying fungi, test methods—Part 1: Basidiomycetes [22]). For each test , 16 replicate specimens were used. Further detailed information about the specimens is summarized in Table1. For the di fferent field tests, sapling-wood was sampled from the same species as listed above, but separate sets of specimens were prepared with and without bark. The length of the field test specimens was 500 mm, the mid-length diameter varied between 15 and 50 mm (Table1). For each test set-up, 10 replicates with and without bark were exposed, resulting in 60 specimens per each wood species.

Table 1. Wood species and specimen mid-length diameter used in laboratory decay tests (n = 16), in-ground field tests (n = 10), above-ground tests (n = 10), and above-ground sponge tests (n = 10).

Diameter (mm)

Wood Botanical Lab Decay In-Ground Field Above-Ground Above-Ground Species Name Test Test Field Test Sponge Field Test Without With Without With Without With Without Bark Bark Bark Bark Bark Bark Bark Quercus English oak 17–22 20–38 20–29 18–36 12–32 18–33 15–37 robur European Fagus 16–18 20–37 23–38 18–35 11–36 20–40 18–39 beech sylvatica Common Corylus 17–21 21–33 17–35 17–37 18–36 15–39 18–37 hazel avellana Black Prunus 17–22 17–33 17–34 14–37 14–37 14–28 15–40 cherry serotina Sorbus Rowan 16–25 22–31 18–33 20–33 14–34 22–33 17–30 aucuparia White Salix alba 18–22 15–50 21–44 14–45 13–42 12–34 13–36 willow Betula Silver birch 16–20 20–50 22–39 22–43 21–33 17–35 19–37 pendula Pinus Scots pine 18–22 n.a. n.a. n.a. n.a. n.a. n.a. sylvestris

2.2. Durability Test with Basidiomycete Monocultures Laboratory decay resistance tests were conducted according to a modified CEN/TS 15083-1 [22] protocol as follows: all specimens were oven-dried at 103 2 C for 48 h, weighed to the nearest ± ◦ 0.001 g, and afterwards conditioned at 20 ◦C/65% relative humidity (RH) until constant mass. After sterilization in an autoclave at 121 ◦C and 2.4 bar for 20 min, two specimens of the same species were placed on fungal mycelium in a Kolle flask. To avoid direct contact between wood and overgrown malt agar (4%) stainless steel washers were used. The incubation time was 16 weeks. The following test fungi were used: Coniophora puteana = (Schum.:Fr.) P. Karsten BAM Ebw. 15 and Trametes versicolor = (L.:Fr.) Pilat CTB 863A. After incubation, the specimens were cleaned from adhering mycelium, weighed to the nearest 0.001 g, and mass loss (ML) calculated according to Equation (2). Forests 2019, 10, 1152 4 of 9

Forests 2019, 10, x FOR PEER REVIEW m0,i m0, f 4 of 9 ML f = − 100 (%) (2) m0,i · where, m0,i is the oven-dry mass before incubation, in g; m0,f is the oven-dry mass after incubation, where, m is the oven-dry mass before incubation, in g; m is the oven-dry mass after incubation, in g. in g. 0,i 0,f 2.3. Field Durability Tests 2.3. Field Durability Tests Specimens with and without bark, each of 500 mm length, were exposed outdoors in three different Specimens with and without bark, each of 500 mm length, were exposed outdoors in three settings. Firstly, specimens were buried to half of their length in the loamy soil on the in-ground different settings. Firstly, specimens were buried to half of their length in the loamy soil on the in- field test site at the University of Goettingen (51 33 34.6”N 9 57 19.1”E) in September 2017. At the ground field test site at the University of Goettingen◦ 0(51°33'34.6"N◦ 0 9°57'19.1"E) in September 2017. At Goettingen test site brown, white, and soft rot decay occur. To avoid the growth of grass and other the Goettingen test site brown, white, and soft rot decay occur. To avoid the growth of grass and a horticultural water permeable textile sheet was placed on the soil. Secondly, specimens were other plants a horticultural water permeable textile sheet was placed on the soil. Secondly, specimens placed horizontally on aluminum L-profiles (4 30 60 mm) with a distance of 10 mm to each other. In were placed horizontally on aluminum L-profiles× ×(4 × 30 × 60 mm) with a distance of 10 mm to each a third test setting specimens were wrapped with sponges (thickness: 5 mm, width: 100 mm), other. In a third test setting specimens were wrapped with cellulose sponges (thickness: 5 mm, width: which were fixed with two cable strips at the center of the specimens and served for water trapping 100 mm), which were fixed with two cable strips at the center of the specimens and served for water (Figure2). trapping (Figure 2).

(a) (b)

Figure 2. Field tests with sapling wood specimens. (a):): i in-groundn-ground exposure. ( b)):: s specimenspecimens with and without bark, partly wrapped with a cotton sponge.

Decay was assessed every 6 months (results (results during during first first 1.5 1.5 years years of of exposure exposure are are reported) reported).. Therefore, the specimens were evaluated according to EN 252 (Field test method for determining the relative protective protective eff effectivenessectiveness of of a wood a wood preservative preservative in ground in grou contactnd contact [23]) using[23]) using a pick-test a pick where-test wherea pointed a pointed knife was knife pricked was into pricked the specimens into the and specimens backed andout again. backed The out fracture again. characteristics The fracture characteristicsof the splinters of as the well splinters as depth as well and as appearance depth and ofappearance decay were of decay assessed were visually, assessed and visually, referred and to referredthe evaluation to the evaluation scheme according scheme according to EN 252 to [23 EN] (Table 252 [2).3] Due(Table to 2). varying Due to cross-sectional varying cross-sectional areas of areasthe specimens of the specimens and their and circular their circular shape, shape, the rating the rating system system had to had be to adjusted. be adjusted. Therefore, Therefore, based based on onthe thedepth depth of decay of decay the minimum the minimum intact cross-sectional intact cross-sectional area was area determined was determined according accor to Equationding to (3).Equation The latter (3). The was latter assigned was assigned to the five to ditheff erentfive different rating steps rating according steps according to EN 252 to EN [23 ],252 based [23], onbased the percentageon the percentage minimum minimum remaining remaining intact cross-sectional intact cross-sectional area Aintact areaas A shownintact as inshown Table 2in.A Tableintact 2.and Aintact the andcorresponding the corresponding adapted adapted decay rating decay according rating according to EN 252 to [ 23 EN] were252 [ determined23] were determined for each specimen for each specimenseparately, separately, considering considering the individual the individual mid-length mid diameters-length diameters of the specimens. of the specimens.

푑 ( 푖−푠 )2∙휋 2 2 di 푑푒푐푎푦 퐴푖푛푡푎푐푡 = ( 2 푑 sdecay) (π%) A = ( −푖)2∙휋 · (%) (3) intact 2 2 ( di ) π 2 · where, Aintact is the minimum remaining intact cross-sectional area, in %; di is the initial diameter of where, Aintact is the minimum remaining intact cross-sectional area, in %; di is the initial diameter of specimen, in mm; sdecay is the maximum depth of decay in mm. specimen, in mm; sdecay is the maximum depth of decay in mm.

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Table 2. Decay rating scheme according to EN 252 [23], corresponding maximum depth of decay sdecay,

and remaining minimum intact cross-sectional area Aintact. Table 2. Decay rating scheme according to EN 252 [23], corresponding maximum depth of decay sdecay, and remaining minimum intact cross-sectional area A . Rating Description intact sdecay Aintact Aintact

Rating Description sdecay(mm) Aintact (mm²)Aintact (%) 0 No attack (mm)0 (mm2)1250 (%) 100 1 0Slight No attack attack 01 12501104 100 88 1 Slight attack 1 1104 88 2 Moderate attack 3 836 67 2 Moderate attack 3 836 67 3 3Severe Severe attack attack 55 600600 48 48 4 Failure 50 0 0 4 Failure 50 0 0

3. Results and Discussion 3. Results and Discussion 3.1. Durability against Basidiomycetes 3.1. Durability against Basidiomycetes The average mass loss (MLf) caused by C. puteana was between 32% and 50%, and between 24% The average mass loss (MLf) caused by C. puteana was between 32% and 50%, and between 24% and 48% after incubation with T. versicolor (Figure3). The median ML f caused by C. puteana was well and 48% after incubation with T. versicolor (Figure 3). The median MLf caused by C. puteana was well above 30% corresponding to durability class 5 (DC 5, ‘not durable’) according to CEN/TS 15083-1 [21] above 30% corresponding to durability class 5 (DC 5, ‘not durable’) according to CEN/TS 15083-1 [21] and EN 350 [5]. Sapwood of any wood species is ‘not durable’ as defined in EN 350 [5], although and EN 350 [5]. Sapwood of any wood species is ‘not durable’ as defined in EN 350 [5], although several studies showed that sapwood of different wood species showed less than 5% median MLf several studies showed that sapwood of different wood species showed less than 5 % median MLf in in laboratory decay tests according to CEN/TS 15083-1 [22] or similar test protocols such as Atlas laboratory decay tests according to CEN/TS 15083-1 [22] or similar test protocols such as Atlas cedar cedar ( atlantica (Endl.) Manetti,[24]), Red ( L., [25]), Douglas fir (Pseudotsuga (Cedrus atlantica (Endl.) Manetti, [24]), Red maple (Acer rubrum L., [25]), Douglas (Pseudotsuga menziesii Franco., [26]) and different other American conifers [27]. However, in most cases where menziesii Franco., [26]) and different other American conifers [27]. However, in most cases where durability was assigned better than DC 5 might be related (1) to its within-species variation and (2) to durability was assigned better than DC 5 might be related (1) to its within-species variation and (2) varying virulence of the respective test fungus with respect to discrete MLf boundaries for the different to varying virulence of the respective test fungus with respect to discrete MLf boundaries for the DC according to CEN/TS 15083-1 [22]. different DC according to CEN/TS 15083-1 [22].

Mass loss [%] - minimum/maximum x mean [] ± s ▒ ± 95% confidence 80 C. puteana 70

60

50

40

30

20

10 0

▒ 80 T. versicolor 70

60

50

40

30

20

10

0 Scots Scots Beech Beech Hazel Hazel Willow Willlow Birch Birch Rowan Black Oak pine pine sw slw sw slw sw slw sw slw slw cherry slw sw slw slw

Figure 3. Mass loss (MLf) of sapwood (sw) and sapling-wood (slw) specimens after 16 weeks of Figureincubation 3. Mass with lossConiophora (MLf) of puteana sapwoodand Trametes(sw) and versicolor sapling-wood. (slw) specimens after 16 weeks of incubation with Coniophora puteana and Trametes versicolor. In most cases, MLf of sapling-wood was significantly higher compared to sapwood of the same wood species, which underpins the hypothesis that juvenile wood, which has still not undergone any heartwood formation, can be considered less durable than regular sapwood. Forests 2019, 10, x FOR PEER REVIEW 6 of 9

In most cases, MLf of sapling-wood was significantly higher compared to sapwood of the same woodForests species,2019, 10, which 1152 underpins the hypothesis that juvenile wood, which has still not undergone any6 of 9 heartwood formation, can be considered less durable than regular sapwood. 3.2. Durability against Fungal Decay in Field Tests 3.2. Durability against Fungal Decay in Field Tests All in-ground specimens failed after only 1 year of exposure (Figure4), which coincides with All in-ground specimens failed after only 1 year of exposure (Figure 4), which coincides with decay rates determined for beech wood in a test field in Hannover, Germany, where the average service decay rates determined for beech wood in a test field in Hannover, Germany, where the average life of standard graveyard test specimens was between 0.6 and 0.9 years [28]. In-ground decay was service life of standard graveyard test specimens was between 0.6 and 0.9 years [28]. In-ground decay initiated generally faster in specimens without bark, but different decay rates between sets with and was initiated generally faster in specimens without bark, but different decay rates between sets with without bark were equalized during the second half-year of exposure. and without bark were equalized during the second half-year of exposure.

Mean decay rating [0-4] 4 4 In ground - with bark In ground - without bark Hazel Beech 3 3 Oak Birch

2 2 Rowan Black cherry Willow 1 1

0Mean decay rating [0-4] 0Mean decay rating [0-4] 0,0 0,5 1,0 1,5 2,0 0,0 0,5 1,0 1,5 2,0 4 4 Above ground - with Exposurebark time [years] Above ground - withoutExposure bark time [years]

3 3

2 2

1 1

0Mean decay rating [0-4] 0Mean decay rating [0-4] 0,0 0,5 1,0 1,5 2,0 0,0 0,5 1,0 1,5 2,0 4 4 Above ground sponge - withExposure bark time [years] Above ground spongeExposure - without time bark [years]

3 3

2 2

1 1

0 0 0,0 0,5 1,0 1,5 2,0 0,0 0,5 1,0 1,5 2,0 Exposure time [years] Exposure time [years] Figure 4. Mean decay rating of field test sapling-wood specimens with and without bark in-ground Figure 4. Mean decay rating of field test sapling-wood specimens with and without bark in-ground and and above-ground exposed as single specimens with and without sponge wrapping for moisture above-ground exposed as single specimens with and without sponge wrapping for moisture trapping. trapping. Specimens exposed 1 m above ground showed first signs of decay at least after 1.7 years of exposure,Specimens and exposed earlier in 1most m above cases. ground Specimens showed with first bark signs decayed of decay slightly at least faster after than 1.7 those years where of exposure,bark had and been earlier removed in most before cases. exposure. Specimens Wrapping with a bark sponge decayed around slightly the center faster of thethan specimens those where led to barkhigher had decaybeen removed rates only before in specimens exposure. without Wrapping bark. a sponge Similar around acceleration the center measures of the werespecimens previously led toapplied higher decay to L-joint rates specimens only in specimens by Van Acker without and Stevensbark. Similar [29] and acceleration led to increased measures decay were rates previously compared appliedto specimens to L-joint without specimens water capturing. by Van Acker In contrast, and Stevens within [2 this9] and study led permanent to increased moistening decay rates of the comparedbark might to have specimens improved without the performance water capturing. of the bark In envelope contrast, around within the this cylindrical study permanent specimens. moisteningEspecially of on the Beech, bark severe might flaking have of improved bark was the observed, performance as shown of the in Figure bark 5 envelope, which then around led to the an cylindricalincreased specimens. formation ofEspecially cracks. Consequently, on Beech, severe the flaking expected of bark negative was eobservedffect of wetting, as shown on thein Figure durability 5, whichof the then specimens led to an was increased superposed formation by positively of cracks. affecting Consequently, the integrity the of expected the protective negative bark effect layer. of In wettingspecimens on the without durability bark, of decay the specimens was significantly was superposed accelerated by positively by wrapping affecting sponges. the integrity of the Forests 2019, 10, x FOR PEER REVIEW 7 of 9

Forestsprotective2019, 10 bark, 1152 layer. In specimens without bark, decay was significantly accelerated by wrapping7 of 9 sponges.

(a) (b)

Figure 5. Visual appearance of above-groundabove-ground specimensspecimens afterafter 66 monthsmonths ofof exposure.exposure. (aa):): severesevere flakeflake ooffff ofof barkbark onon BeechBeech specimensspecimens withwith spongesponge wrapping.wrapping. ((bb):): formationformation of cracks in HazelHazel specimensspecimens without bark.

After 2 years of exposure,exposure, all above-groundabove-ground specimens showed at least moderate decay, most specimens were severely decayeddecayed oror hadhad failed.failed. Provided that mechanical strength is not an issue for the respectiverespective application, the service life of all sapling-woodsapling-wood specimens was less than 1 year when exposed inin ground,ground, andand lessless than than 2 2 years years when when exposed exposed above above ground. ground. The The serviceability serviceability of of fences fences or load-bearingor load-bearing items items such such as climbingas climbing supports supports would would have have been been lost lost earlier. earlier. Diff erencesDifferences in decay in decay rate betweenrate between wood wood species species were were statistically statistically insignificant, insignificant, which which can alsocan also be related be related to their to their general general low durabilitylow durability and thusand thus to short to short service service lives lives of all of tested all tested materials. materials.

4. Conclusions Sapling-woodSapling-wood from seven didiffefferentrent tree species turned out to be not durable, both in laboratory and di differentfferent field field tests. tests. Against Against advertisement advertisement promises promises and as and expected as expected from studies from on studies the durability on the ofdurability sapwood of and sapwood juvenile and heartwood juvenile ofheartwood various wood of various species, wood the durability species, the of sapling-wood, durability of whichsapling is- consideredwood, which juvenile is considered sapwood, juvenile was even sapwood lower than, was common even lower sapwood. than common Protective sapwood. effects of remainingProtective barkeffects were of remaining not observed. bark It were is therefore not observed. expected It that is therefore service lives expected of gardening that service and outdoorlives of decorationgardening accessoriesand outdoor made decoration from sapling-wood accessories made are generally from sapling low. In-wood particular, are generally under Central low. In European particular, climatic under conditionsCentral European the service climatic life isconditions barely 2 the years service in above-ground life is barely and2 years 1 year in above in in-ground-ground and contact. 1 year The in einff-ectground of additional contact. waterThe effect capturing of additional seemed towater be negligibly capturing small seemed due to to be the negligibly very low small durability due to of the materialvery low itself.durability of the material itself. Author Contributions: C.B. was mainly responsible for the conceptualization, methodology used, data evaluation, dataAuthor validation, Contributions: and formal C.B. analysis. was m Investigationsainly responsible and data for curation the conceptuali were conductedzation, methodology by D.G.B.N. and used L.E., data The originalevaluation, draft data of validation this article, wasand formal prepared analysis. by C.B., Investigations S.B. and L.E. and who data was curation also responsible were conducted for the by review D.G.B. andN. editingand L.E process. The origin of thisal draft article. of C.B.this andarticle L.E. was did prepared care for theby visualization.C.B., S.B. and L.E. who was also responsible for the Funding:review andThis editing research process received of this no article. external C.B. funding. and L.E. did care for the visualization. Acknowledgments:Funding: This researchMartin received Rosengren, no external Mirko funding. Küppers, and Rainer Henke are acknowledged for providing sapling-wood test material and corresponding sapwood portions. Acknowledgments: Martin Rosengren, Mirko Küppers, and Rainer Henke are acknowledged for providing Conflictssapling-wood of Interest: test materialThe authors and corresponding declare no conflict sapwood of interest. portions.

Conflicts of Interest: The authors declare no conflict of interest. References

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