effects of coppicing in temperate deciduous forests on ecosystem nutrient pools and soil fertility

Effects of coppicing in temperate deciduous forests on ecosystem nutrient pools and soil fertility

Dirk Hölscher, Elke Schade, Christoph Leuschner*

Plant Ecology, Albrecht-von-Haller-Institute of Plant Sciences, University of Göttingen, 37073 Göttingen, Germany

Received August 16, 2000 · Accepted December 6, 2000

Abstract

Coppice forestry has been practised in the deciduous broad-leaved forests of Central Europe formany centuries until its replacement by high forest systems in the 18th and 19th century. Littleknowledge exists on the consequences of this management system for nutrient stores and nutrientturnover in soil and phytomass. In the Siegerland (Western Germany), we studied the nutrient poolsin the above-ground phytomass, the organic layers on the forest floor, and the mineral soil in three20-yr-old coppice woods on acid soils that were composed by 9 woody species and dominated byBetula pendula, Quercus petraea and Corylus avellana. The results were compared to two nearby140-yr-old monospecific high forests of Fagus sylvatica, the species that dominates the natural for-est vegetation in the region.

The mean above-ground phytomass of the two high forests (31.2 kg dry mass m–2) was 4 timeslarger than that of the coppice woods (7.3 kg m–2) and stored 2 to 3 times larger amounts of Ca, K,Mg and N. The soil organic layers (forest floor) of the high forests were thicker and contained 6times more organic matter than those of the coppice woods (6.8 vs. 1.1 kg m–2) and stored 3 to 7times more nutrients. In contrast, the coppice woods showed a higher pH value, larger salt-ex-changeable Ca, K and Mg pools, (35–95% higher) and larger Ntot stores (23%) in the mineral soil(0–20 cm depth) compared to the high forests. The higher nutrient availability in the coppice woodsoils is mainly confined to the uppermost horizons (0–5 cm) and is thought to result from (1) ashdeposition after biomass burning, (2) nitrogen fixation by broom (Sarothamnus scoparius) whichtypically colonises the clearcut sites, (3) higher soil temperatures under a less shading coppice woodcanopy, and (4) the presence of tree species with high leaf nutrient contents in the coppice woods. We conclude that coppicing does not reduce soil nutrient availability of the Siegerland forests de-spite short rotation periods and a largely reduced ecosystem nutrient capital (i.e. phytomass plussoil nutrient pools) of the coppice woods compared to the high forests. Frequent disturbance of soiland stand structure by cutting and burning apparently accelerates nutrient turnover and results inhigher storage (and probably supply) of Ca, K, Mg and N in the mineral topsoil. However, reducednutrient pools in phytomass and soil organic layers are likely to limit the capacity of coppice woodecosystems to regenerate if heavy disturbance such as topsoil erosion occurs.

Die Niederwaldwirtschaft wurde in den mitteleuropäischen Laubwaldgebieten für viele Jahrhun-derte betrieben, bis sie im Laufe des 18. und 19. Jahrhunderts von der Hochwaldwirtschaftabgelöst worden ist. Die Auswirkungen dieser Bewirtschaftungsform auf die Nährstoffvorräte undNährstoffumsätze im Boden und in der Phytomasse sind weitgehend unbekannt. Wir haben im

Corresponding author: Christoph Leuschner, Plant Ecology, Albrecht-von-Haller-Institute of Plant Sciences, University ofGöttingen, Untere Karspüle 2, 37073 Göttingen, Germany, Phone: +49 551 395718, Fax: +49 551 395701, E-mail:[email protected]

1439-1791/01/2/02-155 $ 15.00/0

Basic Appl. Ecol. 2, 155–164 (2001)© Urban & Fischer Verlaghttp://www.urbanfischer.de/journals/baecol

Basic and Applied Ecology

Introduction

In the temperate deciduous forests of Central andWestern Europe, coppicing has been practised for atleast 2000 (probably 6000) years serving as a sourceof fuel wood, charcoal and tan-bark for the local pop-ulation (Rackham 1980, Pott 1992). Coppice was cer-tainly widespread by 1000 AD, if not the principalform of forest management in this region (Buckley1992, Peterken 1996). From about the 15th centuryonwards, a coppice forestry system was introduced inthe woodland of Western Germany (North-RhineWestfalia, Hesse and Rhineland-Palatinate) whichused fire for land clearing and included an intermedi-ate period of cereal cropping. After clearcut barelyand rye were grown for a few years, followed typicallyby the spread of nitrogen-fixing broom (Sarothamnusscoparius (L.) Koch) on the abandoned fields. Subse-quently, forest regrowth by sprouting from the stumpswas allowed for a 10- to 20-yr-long period until thestart of a new rotation cycle. This medieval forestmanagement system existed until the 18th and 19thcentury when, in most regions, it was replaced by highforest systems with trees grown from seedlings and ro-tation periods lasting for more than 100 years.

In Germany, one of the regions with coppiceforestry being practised until today is the Siegerland ineastern North-Rhine Westfalia. Pott (1990) estimatedthat about 305 km2 still are covered by coppice woodsin this area. The stands are managed at rotation peri-ods of 20 years and mainly consist of Quercus petraea(Matt.) Liebl., Quercus robur L., Betula pendulaRoth, Sorbus aucuparia L. and Corylus avellana L..European beech (Fagus sylvatica L.) which is the dom-inant tree species of the potential natural forest vege-tation of the region occurs at only low abundance incoppice woods due to its very limited capacity for re-sprouting from stumps. However, beech and the intro-duced Norway spruce (Picea abies Karst.) dominatethe widespread high forests which are harvested at in-tervals of about 140 and 100 years, respectively.

Short rotation cycles in forest management mayhave profound impacts on both community structureand ecosystem function due to a much higher distur-bance frequency than high forest systems (Buckley1992). Coppice woods of temperate regions includingthe Siegerland have been studied with respect to theirtree and herb layer composition, vegetation history,and successional dynamics in the direction of naturalcommunities (Groos 1953, Meisel-Jahn 1955, Pott

156 Hölscher et al.

Basic Appl. Ecol. 2, 2 (2001)

Siegerland die Nährstoffvorräte in der oberirdischen Phytomasse, der Humusauflage und dem Mi-neralboden in drei 20-jährigen Niederwäldern auf saurem Boden untersucht. Diese Bestände wur-den von 9 holzigen Arten aufgebaut, wobei Betula pendula, Quercus petraea und Corylus avellanadominierten. Die erzielten Ergebnisse wurden mit zwei benachbart gelegenen, 140 Jahre altenHochwäldern verglichen, die beide Reinbestände der Buche (Fagus sylvatica) waren.

Die mittlere oberirdische Phytomasse der zwei Hochwälder (31.2 kg Trockengewicht m–2) war 4mal größer als die der Niederwälder (7.3 kg m–2) und enthielt 2 bis 3 mal größere Mengen anNährstoffen (Ca, K, Mg, N). In den Hochwäldern waren die Humusauflagen deutlich mächtiger,wiesen eine 6 mal höhere Masse auf (6.8 vs. 1.1 kg m–2) und speicherten 3 bis 7 mal mehrNährstoffe. Im Unterschied hierzu hatten die Niederwälder im Mineralboden (0–20 cm Bodentiefe)höhere Vorräte an austauschbar gebundenem Ca, K und Mg (35–95% höher) und größere Ntot-Vorräte (23%). Auch die pH-Werte des Bodens waren in den Niederwäldern höher als in denHochwäldern. Das höhere Nährstoffangebot in den Niederwäldern befindet sich überwiegend inden oberen Bodenbereichen (0–5 cm). Mögliche Gründe liegen (1) in der Aschedeposition nach demVerbrennen der Biomasse, (2) in der Stickstofffixierung durch Besenginster (Sarothamnusscoparius), der häufig die Kahlschläge besiedelt, (3) in höheren Bodentemperaturen unter derweniger schattenwerfenden Krone der Niederwälder, und (4) in dem Auftreten von Baumarten mithohen Nährstoffkonzentrationen in den Blättern.

Wir ziehen die Schlussfolgerung, dass die Niederwaldwirtschaft im Siegerland nicht zwangsläu-fig die Bodennährstoffgehalte reduziert. Die häufigen Störungen des Bodens und der Be-standesstruktur durch Kahlschlag und Brand können vielmehr den Nährstoffumsatz beschleunigenund zu höheren Bodenvorräten an Ca, K, Mg und N führen. Der Vergleich von Hoch- und Nieder-wäldern zeigte aber, dass die Nährstoffgesamtvorräte bestehend aus Mineralboden, Humusauflageund Phytomasse in den Niederwäldern deutlich geringer waren. Die geringen Nährstoffvorräte inder Humusauflage und der Phytomasse können die Regenerationsfähigkeit von Niederwäldernbeeinträchtigen, wenn es zu schwerwiegenden Störungen kommt, wie es etwa eine Erosion desOberbodens darstellt.

Key words: above-ground phytomass – coppice wood – high forest – mineral soil – nutrient pools –organic layers – Western Germany

1985). Dohrenbusch (1982a, b) has analysed treegrowth in coppice woods of the Siegerland from ayield perspective. Little information, however, existson the consequences of coppicing for ecosystem prop-erties and function such as nutrient and water avail-ability, and associated resource fluxes.

More research has been conducted in shifting culti-vation systems in the Tropics (Sanchez & Hailu 1996)which in many ways are comparable to the traditionalcoppice forestry of temperate Central Europe. A num-ber of tropical studies revealed that shifting cultivationsystems with short rotation periods exhibit negativebudgets for most nutrient elements irrespective of siteconditions (Sanchez 1976, Scott 1987, Juo & Manu1996, Hölscher et al. 1997a). However, the nutrientpools in soil and phytomass responded differently tothe application of a forest use at short intervals. Alarge reduction of the nutrient storage of the above-ground phytomass was observed in recovering forestsfollowing the conversion of primary forests (Uhl &Jordan 1984). In contrast, the mineral soils typicallyshowed no net depletion of their nutrient stores sincethe soil receives nutrient-rich ash deposits from burn-ing immediately after clearcut (Stromgaard 1984, An-driesse & Schelhaas 1987, Hölscher et al. 1997b).

Despite covering only a small area in present-dayCentral Europe, the remaining coppice woods arehighly regarded woodland types due to their conser-vation value for rare plant and animal species, andtheir role in preserving a historic forest managementsystem (Peterken 1996). Moreover, recent coppicestands may help to understand the role that historicalforest use has played in determining the current acid-ity and base-saturation status of Central Europeanforest soils. However, precise data on the conse-quences of coppicing for soil and phytomass nutrientpools and nutrient turnover rates are still lacking fortemperate forests. The objective of this study was toanalyse the nutrient pools in mineral soil, organic

layers and above-ground phytomass in coppicewoods on acid soils and to compare them with near-by high forests on similar substrate. We tested the hy-pothesis that coppicing reduces soil fertility in tem-perate forests on acid soils. Indeed, studies on the nu-trient losses associated with whole tree harvestingsuggest that short rotation forestry systems signifi-cantly reduce the available stocks of Mg, Ca, K and Pin acid soils (Silkworth & Grigal 1982, Mroz et al.1985).

Methods

Study sites

Three coppice wood and two high forest stands werestudied in summer 1998 in the Siegerland, North-Rhine Westfalia (Germany), close to the village ofHilchenbach (50°59′52′′ N, 8°6′46′′ E). The data ofa third high forest had to be omitted when it turnedout that soil liming had been conducted by forestry.The sites are located at 460 m to 610 m a.s.l. (Tab.1). Average annual precipitation is 1043 mm andmean air temperature 7 °C. At all sites, 20–40 cmdeep soil profiles (Spodo-dystric Cambisols) havedeveloped on Devonian slate as a parent material.With ages of 18 to 25 years (coppice woods) and128 to 148 years (high forests) the stands had ap-proached the time of harvest. The sites are located at500 m to 2000 m distance from each other; an ex-ception is the high forest stand HW2 with a distanceof 6 km. The coppice woods were built by variousbroad-leaved species including Betula pendula,Corylus avellana, Quercus petraea, Quercus roburand Sorbus aucuparia. A patchy herb layer ofAvenella flexuosa (L.) Drejer, Holcus mollis L., Teu-crium scorodonia L. and other species with an aver-age cover of 20% existed in all three stands. Thehigh forests were monospecific stands of Fagus syl-

Effects of coppicing in temperate deciduous forests on ecosystem nutrient pools and soil fertility 157


Table 1. Dominant shrub and tree species and selected site parameters of the studied coppice wood and high forest stands.

Dominant species Max. tree Stand Elevation Slope Aspectheight age a.s.l.[m] [years] [m] [°]

Coppice Wood 1 Betula pendula, 7.6 18 480 22 East-Corylus avellana Southeast

Coppice Wood 2 Betula pendula, 5.9 25 460 21 NorthwestQuercus petraea

Coppice Wood 3 Betula pendula, 6.8 18 480 18 East-Quercus petraea Southeast

High Forest 1 Fagus sylvatica 30 128 460 14 SouthwestHigh Forest 2 Fagus sylvatica 30 148 610 13 Northwest

a.s.l. - above sea level

vatica (community type: Luzulo-Fagetum) thatlacked a herb layer.

Analysis of stand structure and phytomass

In the three coppice woods, each two plots of 100m2 were placed at random in the stands to analysethe abundance of woody stems per species and theirdiameters at breast height (dbh). The number of re-sprouts per root stock was also counted in the plots.In the two high forest stands with a low tree density,stem densities and dbh values were measured in a900 m2 plot located in the centre of the stands. Theabove-ground woody phytomass of the coppicewoods was estimated from the stem density data andallometric regressions between dbh and phytomassestablished by harvest of Betula pendula trees inLower Saxony, Northern Germany (Hagemeier, un-publ. data; see appendix). The birch data were alsoused for the other tree species in the stands sincebirch was the most abundant tree species. Harvestdata of Heller (1986) from the Solling beech forest(Lower Saxony) were used to estimate the Fagus syl-vatica phytomass. To estimate leaf dry mass, weused an average value of 0.29 kg m-2 according tomeasurements in the Solling beech forest for all fivestands (Ellenberg et al. 1986). This rough procedureseems justified because the leaf area of growingforests is known to reach its maximum typicallyafter 20 to 40 years and remains more or less con-stant thereafter (Bormann & Likens 1979). Theabove-ground phytomass of the herb layer was har-vested from plots of 100 cm2 with two replicates persite.

Soil and phytomass sampling

(i) Above-ground phytomass: In summer 1998,samples of leaf and wood phytomass were collectedfrom the dominant tree species of the five sites forsubsequent chemical analysis. In the high forests,two sun canopy branches were collected in twotrees and fractionated into branches > 7 mm or < 7mm in diameter, and leaves. Samples of stem woodwere taken with an auger of 5 mm in diameter. Ineach of the coppice woods, 6 to 10 samples weretaken from the sun canopies of the dominant treespecies. The nutrient content data of the herb layerwere multiplied by the fractional cover of a herblayer in a stand (7,35 and 40% in the coppicewoods CW1, CW2 and CW3, respectively) to ob-tain site-representative values. All phytomass sam-ples were oven-dried (70 °C, 48 h) and analysed byatomic absorption spectroscopy or C/N elementaranalysis.

(ii) Organic layers and mineral soil: An auger of 5cm in diameter was used to extract 12 organic layersamples per stand (L, Of and Oh horizons) for chemi-cal analysis. Mineral soil material was taken at 0–5cm and 10–15 cm depth in small soil pits (12 repli-cates per site). Mass-related nutrient content valueswere expressed as nutrient pools per soil depth usingbulk density data of the soil profiles (12 replicate sam-ples of 100 cm3 volume dried for 48 h at 105 °C). Weused the system of Green et al. (1993) to classifyhumus types.

For the mineral soil, the nutrient pools were calcu-lated to a profile depth of 20 cm since the majority offine root biomass of the stands is found in the topsoilof the shallow profiles. We averaged the 0–5 cm and10–15 cm data to estimate nutrient contents at 5–10cm depth. Since nutrient contents typically decreaseonly slightly with depth in the subsoil, the 10–15 cmdata were also used to estimate the nutrient contentsat 15–20 cm depth.

Chemical analyses

(i) Organic layers and above-ground phytomass: Thefresh humus was sieved (2 mm) and the pH valuesmeasured by a glass electrode. The ground humus andphytomass samples were analysed for total carbonand nitrogen with a C/N analyser. The calcium, mag-nesium and potassium contents were analysed byatomic absorption spectroscopy after HNO3/pressuredigestion.

(ii) Mineral soil: The concentration of salt-ex-tractable cations was determined by percolating 2.5 gsoil with 100 ml of 1 molar NH4Cl solution for 6hours. The effective cation exchange capacity (CECe)was calculated as the sum of all extractable cations(Meiwes et al. 1984). The solution concentrations ofNa, K, Mg, Ca, Mn, Al and Fe were analysed byatomic absorption spectroscopy. Fe was assumed tobe Fe2+. pH values were measured using a glass elec-trode. The concentration of hydrogen ions at thecation exchangers was calculated from the observedpH change during the percolation process, applying acorrection to allow for hydrolytic reactions involvingaluminium ions.

Statistical analyses

The chemical characteristics of the mineral soil andthe organic layers of the five stands were statisticallyanalysed by analyses of variance. The means werecompared according to Scheffé (SAS/STAT, Anon.1987). Differences were considered significant belowthe 5% probability level.



Results

Stand structure and phytomass

In the three coppice woods (CW) nine different shruband tree species occurred with silver birch (Betulapendula) having the highest abundance of root stocksat all sites (Tab. 2). The stem densities varied between12 804 and 26 120 ha–1 (coppice woods 1 and 3, re-spectively), and thus were 40 to 130 times higher thanin the high forests (200 and 311 ha–1). Large differ-ences existed among the tree species with respect tothe number of resprouts per root stock: Corylus avel-lana (9.0–14.5) and Quercus petraea (and robur;7.6–9.1) showed the highest numbers, while Betulapendula (1.8–2.4), Carpinus betulus (1.0) and Fagussylvatica (1.0) revealed only limited or no capacitiesto resprout after cut.

About 80% of the sprouts in the coppice woodshad breast height diameters smaller than 5 cm. Thelargest diameters among the 20-yr-old coppice treespecies were recorded for Quercus with a maximumof 12.1 cm, whereas in the high forests (HF), the dbh

classes 40–45 cm (site HF1) or 45–50 cm (site HF2)were most frequent. Average tree height was 5.9–7.6m in the coppice woods, and 30 m in the high forests.

The above-ground phytomass was estimated at6.3–8.6 kg m–2 in the three coppice woods and26.4–36.1 kg m–2 in the high forests. The herb layer inthe coppice woods added another 0.015 (CW1) to0.062 kg m–2 (CW3) of above-ground phytomass tothe stand totals.

Nutrient concentrations and pools in the phytomass

While all tree species had similarly low nutrient con-tents in their woody phytomass (data not shown), theleaf concentrations of N, K, Ca and Mg showed aconsiderable variability among the species. The nitro-gen content was high in leaves of Frangula alnus Mill.(2.4 mol N kg–1) and comparatively low in Fagus syl-vatica and Sorbus aucuparia (1.5 mol N kg–1, Tab. 3).Similarly, K and Mg leaf concentrations were particu-larly low in Fagus. The leaf element concentrations ofFagus did not show marked differences between thecoppice and the high forest sites (data not shown).



Table 2. Number of rootstocks (N) and resprouts per rootstock (F) of the woody species present at the coppice wood sites. The number of stems per hectare isN × F.

Coppice Wood 1 Coppice Wood 2 Coppice Wood 3–––––––––––––––––––––––––––––––––––––– –––––––––––––––––––––––––––––––––––––– ––––––––––––––––––––––––––––––––––––––root- sprouts / root- sprouts / root- sprouts /stocks rootstock stocks rootstock stocks rootstock[n ha–1] [n] [n ha–1] [n] [n ha–1] [n]

Betula pendula 1595 1.8 1337 1.9 1455 2.4Fagus sylvatica 100 1.0 708 1.0 73 1.0Sorbus aucuparia 0 708 1.6 436 3.5Quercus petraea (robur) 0 865 7.6 582 9.1Populus tremula 598 1.5 0 0Frangula alnus 0 550 3.9 582 3.0Carpinus betulus 100 1.0 0 0Corylus avellana 1495 14.5 550 9.0 0

All species 3888 4717 3128

Table 3. Leaf element concentrations of the woody species at the coppice wood sites.

N C/N K Ca Mg––––––––––––––––––––––––– ––––––––––––––––––––––––– ––––––––––––––––––––––––– ––––––––––––––––––––––––– –––––––––––––––––––––––––

n mean cv mean cv mean cv mean cv mean cv[mol kg–1] [%] [mol mol–1] [%] [mmol kg–1] [%] [mmol kg–1] [%] [mmol kg–1] [%]

Betula pendula 6 1.74 8 23 8 218 14 96 29 70 14Fagus sylvatica 5 1.50 13 27 11 188 40 118 41 48 21Sorbus aucuparia 2 1.47 26 449 205 95Quercus petraea (robur) 4 1.63 12 25 11 207 40 85 31 52 40Populus tremula 2 1.63 25 209 84 81Frangula alnus 2 2.36 17 404 181 111Corylus avellana 4 2.01 23 20 21 270 26 128 44 111 23

cv – coefficient of variation

The nutrient pools in the phytomass were 2 to 3times larger in the high forests compared to the cop-pice woods due to an about 4.3 times greater above-ground phytomass. The differences were largest forCa (ratio HF:CW = 3.2) and smallest for N (2.1, Tab.4).

Nutrient concentrations and pools in the soil

Large and significant differences existed among thestands studied with respect to the exchangeable Cacontents at 0–5 cm mineral soil depth. High valueswere found in coppice woods (10–17 mmolc kg–1) andlow values were measured in high forests (2–4 mmolckg–1 Tab. 5). Similar differences between CW and HFwere found for the K and Mg concentrations whereasthe cation exchange capacity (CECe) was equal forthe two management systems reflecting similar geo-logical substrates. Larger topsoil concentrations ofCa, K and Mg correspond to a higher proportion ofCa, K, Mg and Na (‘basic cations’) in the cation ex-change capacity of the coppice wood soils compared

to the high forest soils (14–18% and 5–6% in CWand HF, respectively). Total carbon and nitrogen oc-curred at significantly larger concentrations, and theC/N ratio was smaller, in the topsoil of the coppicewoods compared to the high forests (Tab. 6). In con-junction with a higher mean pH(H2O) value (4.24 and3.85 for CW and HF, respectively) these data indicatea better plant nutrient availability at 0–5 cm depthunder the coppice woods than the high forests. Inlower soil horizons (10–15 cm depth), differences insoil chemistry between the two management systemswere less pronounced than in the topsoil, or did notexist (data not shown).

The soil organic layers on the forest floor differedgreatly in thickness and morphology between the cop-pice woods (2–4 cm thick Mull layers) and the highforests (6–8 cm thick Moder layers). The Mull layersof the coppice woods contained about 6 times smalleramounts of organic matter (1.1 kg m–2) than theModer layers of the high forests (6.8 kg m–2). Similarto the upper horizons of the mineral soil, a significant-ly higher pH(H2O) value and higher Ca and Mg concen-



Table 4. Mean element pools in the the above-ground phytomass, the organic layers and the mineral soil (0–20 cm depth) of coppice wood and high forestsites. For nitrogen Ntot values are given while, for the other elements, totals in humus and biomass, and the salt-exchangeable fraction of the mineral soil arepresented. The total element pools for each stand are given in brackets.

C N K Ca Mg[mol m–2] [mol m–2] [mmol m–2] [mmol m–] [mmol m–2]

Coppice Woods Phytomass 295 2.4 360 267 116Humus layer 38 1.6 93 109 78Mineral soil 461 28.0 236 213 109

794 32.0 689 589 303Stand total (877, 795, 708) (37, 29, 29) (713, 751, 606) (652, 594, 519) (339, 299, 271)

High Forests Phytomass 519 5.0 753 841 314Humus layer 229 9.2 635 272 264Mineral soil 491 22.8 126 109 81

1239 37.0 1514 1222 659Stand total (1214, 1265) (36, 38) (1093, 1937) (1188, 1256) (533, 786)

Table 5. Exchangeable cations in the mineral soil (0–5 cm depth) at the coppice wood and the high forest sites. Significantly different values within a manage-ment system are indicated by different letters (analysis of variance, p < 0.05).

CECe K Ca Mg Al––––––––––––––––––––––––– ––––––––––––––––––––––––– ––––––––––––––––––––––––– ––––––––––––––––––––––––– –––––––––––––––––––––––––

n Mean cv mean cv mean cv mean cv mean cv[mmolc kg–1] [%] [mmolc kg–1] [%] [mmolc kg–1] [%] [mmolc kg–1] [%] [mmolc kg–1] [%]

Coppice Wood 1 12 173 a 20 6.06 a 28 16.9 a 72 8.85 a 57 112 a 18Coppice Wood 2 12 134 b 10 4.67 b 6 10.0 b 22 4.46 b 25 94 b 10Coppice Wood 3 12 140 b 16 3.99 c 17 10.3 b 52 4.64 b 44 105 ab 15All Coppice Woods 36 149 4.91 12.4 5.99 104

High Forest 1 12 161 a 7 2.39 c 28 3.9 c 44 3.31 bc 26 124 a 12High Forest 2 12 135 b 11 1.42 d 18 2.4 c 29 1.83 c 14 91 b 19All High Forests 24 148 1.58 3.1 2.57 103

cv – coefficient of variation

trations indicate a more favourable nutrient status inthe organic layers of the coppice woods compared tothe high forests (Tab. 7).

Data on bulk soil density were used to calculate theexchangeable nutrient pools in the mineral soil up to aprofile depth of 20 cm. The exchangeable pools of themajor plant nutrients K, Ca and Mg were substantial-ly higher in the soil under coppice woods than highforests (Tab. 4). This is also true for the Ntot pool. Thedifference was larger for K and Ca than for N andMg. In the organic layers, in contrast, the coppicewoods contained 2.5–6.9 times smaller nutrient stores(total pool) than the high forests due to a larger massof ectorganic material being present in the latter. Thisdifference existed despite the fact that the Ca and Mgconcentrations were substantially higher in the Mullmaterial of the coppice woods than in the Moder ma-terial of the high forests (Tab. 7).

Adding of the nutrient pools in mineral soil, organ-ic layers and phytomass yields an estimate of the totalecosystem nutrient pools for the two forest manage-ment systems. The high forests contained about 2times larger K, Ca and Mg stores than the coppice

woods whereas the difference between the two man-agement systems was small for N.

Discussion

This study revealed remarkable differences in thenutrient pools of phytomass and soil between highforests and nearby coppice woods. Three reasons maybe responsible for these patterns, (i) differences inmanagement practices, (ii) differences in tree speciescomposition (Betula/Quercus/Corylus vs. Fagus), and(iii) differences in tree age (20 vs. 140 yrs) of the twoforest types studied. Indeed, early- and late-succes-sional trees can differ substantially with respect toproductivity and nutrient economy (Bazzaz 1979)and, thus, may cause different phytomass and ecosys-tem nutrient pools in a stand. The selected Fagusstands are dominated by a late-successional speciesand resemble the potential natural forest vegetation.In contrast, the Betula/Quercus/Corylus coppicewoods represent stands of early- to mid-successionalspecies that are in the thinning phase of stand devel-



Table 6. Concentrations of total carbon and nitrogen in the mineral soil (0–5 cm depth) at coppice wood and high forest sites. Significantly different valuesbetween the two management systems within a soil depth are indicated by different letters (analysis of variance, p < 0.05).

pH(H2O) Ctot Ntot C/N––––––––––––––––––––––––––––––––––– ––––––––––––––––––––––––––––––––––– –––––––––––––––––––––––––––––––––––

n Mean mean cv mean cv mean cv[mol kg–1] [%] [mol kg–1] [%] [mol mol–1] [%]

Coppice Wood 1 12 4.21 c 12.75 a 27 0.71 a 25 17 c 4Coppice Wood 2 12 4.19 c 9.18 b 14 0.54 b 13 16 c 4Coppice Wood 3 12 4.34 c 8.92 b 16 0.53 b 13 16 c 5All Coppice Woods 36 4.24 10.29 0.59 17

High Forest 1 12 3.95 b 8.75 b 21 0.40 c 23 25 a 6High Forest 2 12 3.76 a 6.02 c 11 0.24 d 9 21 b 8All High Forests 24 3.85 7.39 0.32 23

Table 7. Element concentrations of the organic layers at coppice wood and high forest sites. Significantly different values are indicated by different letters(analysis of variance, p < 0.05).

pH(H2O) N C/N K Ca Mg––––––––––––––––––– ––––––––––––––––––– ––––––––––––––––––– ––––––––––––––––––– –––––––––––––––––––

n Mean mean cv mean cv mean cv mean cv mean cv[mol kg–1] [%] [mol mol–1] [%] [mmol kg–1] [%] [mmol kg–1] [%] [mmol kg–1] [%]

Coppice Wood 1 12 5.00 c 1.55 a 6 22 c 3 80 ab 20 101 a 22 73 ab 11Coppice Wood 2 12 4.67 c 1.29 b 6 24 b 5 90 a 20 98 a 15 62 b 13Coppice Wood 3 12 4.78 c 1.32 b 10 25 ab 5 79 ab 25 86 ab 20 74 a 12All Coppice Woods 36 4.80 1.39 24 83 96 70

High Forest 1 12 3.67 b 1.29 b 13 26 a 5 62 b 35 68 ab 9 45 c 25High Forest 2 12 4.13 a 1.34 b 9 24 bc 3 99 a 27 36 c 16 40 c 10All High Forests 24 3.84 1.39 25 80 52 41

cv - coefficient of variation

opment. To distinguish between management and treespecies or age effects, a comparison between 20-yr-old(and also 140-yr-old) Betula/Quercus/Corylus andFagus stands would be required which, however, can-not be conducted in the region since 20-yr-old Faguscoppices or 140-yr-old Betula/Quercus/Corylusstands do not exist. Thus, the above-mentioned threeinfluential factors are not independent from eachother, and can hardly be separated in the Siegerlandstudy area. Moreover, the three old-growth Fagusstands (one being omitted later) and the three Betu-la/Quercus/Corylus coppices that were studied repre-sent (together with planted Picea stands) the typicalforest communities of the study region. Thus, the fol-lowing discussion focuses rather on a comparison ofFagus high forests and Betula/Quercus/Corylus cop-pice woods than on species or age effects.

The Siegerland high forests had an estimated above-ground phytomass that was four times greater thanthat of the coppice woods. For the monospecific highforests allometric equations could be used, that weredeveloped for old-growth beech forests. The phy-tomass of the coppice woods, which were composed of9 woody species, was estimated with one species-spe-cific function for silver birch, which had the highestabundance of root stocks at all sites. Korsmo (1995)compared the weight equations established for seventree species of young stands in the hemiboreal zone,which included silver birch. Significant differences formany of the species studied were found, but silverbirch was an intermediate species. However, the use ofonly one species-specific allometric function results inuncertainties about the phytomass in the coppicewoods. But the differences among the high forests andthe coppice woods studied were large and the uncer-tainties about the phytomass in the coppice woods areunlikely to change this result significantly. Followingour results, the Siegerland high forests had larger totalecosystem pools of plant nutrients than the nearbycoppice woods which results from both substantiallygreater nutrient stocks in the above-ground phytomassand in the soil organic matter on the forest floor.

In forests, the size of the plant-available ecosystemnutrient pool is primarily dependent on the amount ofabove-ground phytomass that is present because alarge proportion of the ecosystem nutrient capital(50–69% in the studied stands) is located in this bioticcompartment. Indeed, the conversion of Fagus highforests (128–148-yrs old) to Betula/Quercus/Coryluscoppice woods (18–25-yrs old) in the Siegerland re-duces the above-ground phytomass more than 4foldand also greatly diminishes the ecosystem nutrientpool. A second, though less important, factor thatcontributes to the reduction of the ecosystem nutrientcapital is the reduction in soil ectorganic matter: the

three coppice woods had much thinner organic layersthan the high forests with a less important storagefunction for plant nutrients. However, the concentra-tion of important plant nutrients such as Ca, Mg andN was higher in the humus material of the coppicewoods than the high forests. The correspondingsmaller carbon/nutrient ratios, together with elevatedpH values, indicate a more favourable nutrient statusof the soil organic layers of the coppice woods com-pared to the high forests.

The mineral soil data (0–20 cm depth) show largerpools of Ntot and exchangeable Ca, K and Mg, and asmaller C/N ratio for the coppice woods than the highforests. This result represents additional evidence forthe conclusion that coppicing apparently leads to asignificant improvement of nutrient availability, andincreases soil biological activity, in the topsoil of thestudied Siegerland forests. Thus, our soil chemicaldata, which emphasize plant-available nutrient pools(organic layers and mineral topsoil) instead of ecosys-tem total pools, do not support the hypothesis thatcoppicing in temperate forests results in soil impover-ishment due to increased phytomass and nutrient ex-ports (e.g., Pott 1985, Manz 1995).

In order to give a rough estimation of the rate of nu-trient extraction with biomass harvest in the coppicewood and high forest stands we assumed that final har-vest takes place in the coppice forestry system at a standage of 20 years, and in the high forest system after 140years. The nutrient stores measured in the woody phy-tomass fraction > 7 mm in diameter (including bark)were assumed to be equal to the amount of nutrientswhich is exported with final harvest. To account for thedifferent length of the rotation periods, the values of thecoppice woods were then multiplied by a factor of 7.This calculation gave an export of 0.6 mol Ca, 0.3 molMg, 0.5 mol K, and 2.8 mol N m–2 for the high forestsystem, and 1.3 mol Ca, 0.6 mol Mg, 1.6 mol K, and10.8 mol N m–2 for the coppice woods during a 140-yr-period. Thus, the extraction with harvest of all studiednutrients would be larger by a factor of 2 to 3 in thecoppice woods compared to the high forests.

These calculations represent an overestimation forboth management systems since only larger diametersare extracted while thinner branches usually remain inthe forest. Additionally, thinning is regularly practisedin Central European high forests which should lowerthe differences in nutrient export between the twomanagement systems. However, the calculation indi-cates that nutrient export with harvest is greater incoppice than in high forest systems as a result of (a)higher amounts of phytomass harvested by coppicing,and (b) a higher bark/stemwood ratio with elevatednutrient concentrations in the extracted wood. Thus,the observed comparably high soil nutrient availabili-



ty under the coppice woods is even more astonishing. A more favourable nutrient status and pH in the min-

eral topsoil of the coppice woods is thought to resultfrom (i) ash deposition after burning (which can explainelevated pH values and higher Ca, K and Mg concentra-tion in the soil), (ii) N fixation by Sarothamnus scopar-ius, a leguminose that often dominates clearcut sitesprior to forest regrowth, and (iii) the abundance of treespecies with particularly high N and Mg contents intheir leaves (Corylus and Frangula, see Tab. 3). Morefavourable soil chemical conditions together with elevat-ed soil temperatures due to a less shading canopy willenhance the activity of soil microbes and soil fauna inthe coppice woods. A consequence would be a morerapid decomposition and a more efficient transfer of nu-trients from the organic layers to the mineral soil below.

The biologically more active Mull layers under cop-pice wood contrast with the less favourable Moderlayers of the Fagus high forests. No evidence of burn-ing, which greatly reduces soil organic matter but mayrelease nutrients, has been found at the high forestsites. Chronosequence studies in other forest ecosys-tems on acid soils in NW Germany have shown thatorganic matter accumulates at rates of 40 (–140) g drymass m–2 yr–1 in secondary successions after major dis-turbance (Leuschner & Gerlach 2000). From thesedata it is estimated that the regrowth of the organiclayers to their pre-disturbance level must take at least50 or, more likely, 120 to 170 years. The widespreadand century-old practice of coppicing, thus, may wellhave contributed to the reduction of the organic mat-ter pools in the Siegerland and other Central Euro-pean forest soils. On the other hand, it is unlikely thatthis forestry practice has accelerated acidification offorest soils, rather it should have mitigated it.

Our soil chemical data from coppice systems in thetemperate region compare well with results obtainedin shifting cultivation systems in tropical and subtropi-cal regions. Most of such studies have reported an in-crease in soil pH and in the concentration of exchange-ably bound nutrients as a consequence of ash deposi-



AppendixAllometric regressions used to estimate the above-ground woody biomass based on the diameter at breast height(dbh). Equation 1 (Heller 1986) was used for the high forest sites (Fagus sylvatica). The tree species at the birch-dom-inated coppice wood sites were calculated with equation 2 derived for Betula pendula (Hagemeier, unpubl. data).

Equation 1:wood < 7 mm in diameter [kg] = –22.5485 + 21.4402 * exp (0.0471 * dbh [cm])wood > 7 mm in diameter [kg] = –71.3104 + 47.0308 * exp (0.0798 *dbh [cm])

Equation 2:wood < 7 mm in diameter [kg] = 0.2507 * exp (0.1933 * dbh [cm])wood 7–70 mm in diameter [kg] = 0.5937 * exp (0.1811 *dbh [cm])wood > 70 mm in diameter [kg] = –25.5787 + 19.8925 * exp (0.0838 * dbh [cm])

tion following burning (Stromgaard 1984, Khanna etal. 1994, Hölscher et al. 1997b). The persistence ofthis fertilisation effect may vary between 20 and morethan 80 years in Amazonia (de Moraes et al. 1996).

Our findings in temperate coppicing systems con-tradict the view that forestry systems with short rota-tion periods necessarily impoverish forest soils. Onthe contrary, the frequent disturbance of soil andstand structure by cutting and burning apparently ac-celerates nutrient turnover and results in higher stocks(and probably supply rates) of Ca, K, Mg and N. Onthe other hand, ecosystem nutrient pools are greatlyreduced by coppicing due to a reduction in bothabove-ground phytomass and soil organic matterstores. This reduction may limit the ecosystem’s ca-pacity to regenerate after catastrophic disturbancesuch as topsoil erosion or catastrophic fires.

Future studies in temperate short rotation forestrysystems should investigate nutrient status and produc-tivity of other coppice and high forest systems in orderto better understand the impact on ecosystem function-ing of this historic management practice. Furthermore,additional data on past changes in coppice wood man-agement practice are needed which are not well docu-mented for most regions. In the Siegerland, for exam-ple, the remaining coppice woods are primarily usedfor fuel wood production in our days. During past cen-turies, however, rye and barley are likely to have playeda role as an intermittent crop after clearcut, a practicethat was abandoned in the beginning of the 19th centu-ry at most sites (Pott 1990). This change could have in-fluenced the present-day ecosystem nutrient budgets ofthe coppice woods as may have recent anthropogenicnitrogen deposition. Finally, studies in lowland coppicewoods and stands on base-rich parent material are re-quired in order to show whether our results can be gen-eralised for Central Europe.

Acknowledgements. This study was supported by a grantof the Landesanstalt für Ökologie, Bodenordnung undForsten / Landesamt für Agrarordnung Nordrhein-Westfalen.

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effects of coppicing in temperate deciduous forests on ecosystem nutrient pools and soil fertility

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