Density Management Diagrams for Sweet Chestnut High-Forest Stands in Portugal

Research Article ii FF o o r r e e s s t t doi: 10.3832/ifor2411-010 Biogeosciences and Forestry vol. 10, pp. 865-870

Density management diagrams for sweet chestnut high-forest stands in Portugal

Maria Sameiro Patrício, This study aims to develop stand density management diagrams (SDMDs) for Luís Nunes pure even-aged high-forest stands of sweet chestnut in Portugal, defining the appropriate upper and lower limits of growing stock while considering the biological, technological and economic objectives that are expected for these stands. The SDMDs were developed with data collected from high-forest stands in northern Portugal, which is the main representative area of these stands in the country. Data were collected from 23 pure even-aged permanent plots with re-measurement intervals of 4-10 years, 43 semi-permanent plots and 18 even-aged temporary plots; all plots were established in chestnut high-forest stands with a broad range of ages. SDMDs were constructed by simultaneously fitting four nonlinear equations relating stand variables using the full information likelihood technique. SDMDs for the estimation of stand total volume, stand stem biomass, stand total aboveground biomass, and carbon content in aboveground biomass are presented as bivariate graphs with dominant height on the x-axis and the number of trees per hectare on the y-axis (using loga- rithmic scale). A tool is made available to define an optimal range of stand density for a silviculture oriented to single-stem selection on a tree-by-tree basis, focusing management on the most valuable trees. This tool is aimed to support forest managers in the decision-making process, enabling them to schedule thinnings on the basis of the dominant height growth of the trees with the greatest potential (frame trees), maintaining an adequate growing stock and assessing the corresponding aboveground wood volume, biomass, carbon, and mean diameter breast height.

Keywords: Castanea sativa Mill., Stand Density, Thinning, Biomass, Site Index, Dominant Height, Forest Management

Introduction wood forest products and ecosystems ser- twenties, lack proper tending. The man- The area of the sweet chestnut (Castanea vices, can become a profitable investment agement model recommended for these sativa Mill.) in Portugal increased remark- for forest owners. In Europe, the woodland areas is different from the usual models for ably over the last two decades under the area of sweet chestnut devoted to timber orchards or coppices, and it is oriented, in Community Support Frameworks that have production has been estimated at 1.78 mil- many situations, toward a silviculture sys- served as the primary funding sources for lion hectares (Conedera et al. 2004). In Por- tem that provides other forest functions afforestation. The success of these funds is tugal, the species covers an area slightly beyond the production of valuable wood. demonstrated by the sweet chestnut’s larger than 40,000 ha (ICNF/IP 2013), but These stands, while promoting forest com- contemporary afforestation rate in Portu- young plantations are poorly sampled. A partment, reduce the risk of wildfires, in- gal, northern Spain and France, estimated considerable number of recent plantations crease the diversity of the forest mosaic at 4500 ha year-1 (Alvarez-Alvarez 2004). (almost 10,000 hectares in the Bragança re- and habitats and improve landscape aes- The private sector has been the driving gion between 1994 and 2000) have been thetics. This fulfills the recommendations force behind this increase in sweet chest- established with the purpose of being man- of the Portuguese National Forest Strategy nut afforestation area because there is an aged as high-forest stands for high-quality (ENF 2006) concerning the specialization increasing trend toward high-quality wood timber production. However, many of of Portuguese forest territories. production that, when combined with non- these sweet chestnut stands, now in their The only known old chestnut high-forest stands in northern Portugal were studied to analyze the species productive potential Mountain Research Centre (CIMO), School of Agriculture, Polytechnic Institute of Bra- (Patrício 2006). These stands are located in gança. Campus de Santa Apolónia, 5300-253 Bragança (Portugal) communal areas under collaborative management with the National Forest Service. @ Maria Sameiro Patrício ([email protected]) These old growth sweet chestnut high-forest stands are healthy and are already Received: Feb 15, 2017 - Accepted: Aug 11, 2017 older than the optimal rotation age; thus, the maximum sustainable revenue and the Citation: Patrício MS, Nunes L (2017). Density management diagrams for sweet chestnut high- decrease in stumpage value are offset by forest stands in Portugal. iForest 10: 865-870. – doi: 10.3832/ifor2411-010 [online 2017-11- other functions of the forest. Although 06] there may be the so-called “memory problem” (Drew & Flewelling 1979, Jack & Long Communicated by: Andrea Cutini 1996) associated with changes in stand structure over time (Barrio-Anta & Alvarez-

r González 2005), these sweet chestnut and Castanea sativa coppices (Menéndez- ported in Tab. 1. t

s woodlands are a legacy for forest manage- Miguélez et al. 2016). In general, these The dominant height of each stand e

r ment and can be studied to develop tools tools are less available for broadleaves (hdom) was computed as the average o for sustainable management. Young stands than for conifers. height of the 100 thickest trees per hectare F are mostly found on land belonging to pri- Despite the economic, ecological, and so- (Assmann 1970). The stand total volume d n vate landowners. In both situations, the cial importance of the sweet chestnut, (V) was calculated by calculating and sum- a development of practical tools to assist in high-forest system management tools for ming the individual-tree volume (v) inside s e sustainable forest management in these ar- quality timber production are not numer- each plot using the individual-tree volume c

n eas would be very useful. Stand density ous, which justifies an increase in growth equation from Patrício (2006): v = 0.015160

e 2 2 i management diagrams (SDMDs) are an ex- and yield research. Additionally, public ad- + 0.0000324 d h (R adj = 0.98; RMSE = c 3 3 -1 3 s ample of such a tool: they are intuitive ministration and stakeholders are demand- 0.00057 m ; d - cm; h - m; v - m tree ). V (m o graphical models of even-aged stands dy- ing management tools to implement and ha-1) was obtained by extrapolation meth- e g namics and reflect the fundamental rela- optimize the effective management of ods that varied with plot area. Similarly, o i tionships among tree size, stand density, chestnut high-forest woodlands in terms of the stand stem biomass (Ws) and the stand B site occupancy and self-thinning (Jack & profitability and sustainability. total aboveground biomass (WT) were cal- – Long 1996, Long & Shaw 2005). The dia- The main aim of the present study is to culated using the individual-tree equations t s grams are constructed by characterizing develop practical SDMDs for pure even- developed by Patrício (2006) for the sweet e r the growing stock, using indices that relate aged high-forest stands of sweet chestnut chestnut with data collected from the o

F the average tree size (e.g., mean weight, in Portugal, defining the appropriate upper same stands used in the present study. Pa- i volume, height or diameter) to density and lower limits of growing stock for a silvi- rameter estimates for these equations (e.g., number of trees per hectare – Barrio- culture based on single-stem selection on a were obtained from a simultaneous fit us- Anta & Alvarez-González 2005). The most tree-by-tree basis, thus maximizing individ- ing iterative seemingly unrelated regres- commonly used density indices are the ual-tree value and promoting the develop- sion (ITSUR – eqn. 1 to eqn. 5): stand density index (Reineke 1933), the ment of natural regeneration and site sus- w =0.00033 d2 h self-thinning rule (Yoda et al. 1963), the rel- tainability. These tools would support for- L (1) ative density index (Drew & Flewelling est managers in the decision-making proc- w =0.00440d 2 h 1979), and the relative spacing index (Clut- ess, enabling them to schedule thinnings Br (2) ter et al. 1983, Gadow & Hui 1999). based on the dominant height growth of w =0.06574d 1.84096 SDMDs have been widely used because the trees with the greatest potential B (3)

of their utility in terms of the design, devel- (frame trees); maintain an accurate grow- 1.76603 1.16402 w S =0.02044d h (4) opment and evaluation of alternative den- ing stock; and assess the corresponding u sity management regimes for even-aged aboveground wood volume, biomass, car- w Tot=w L +w Br+w B+w S (5) stands (Newton 1997). Managing density bon, and mean diameter breast height. u involves manipulating and controlling the growing stock to achieve specific manage- Material and methods where d (cm) and h (m) are defined as be- ment objectives (Kumar et al. 1995). Manip- fore and wL, wBr, wB, wS_u, and wTot are indi- ulating stand density by thinning will affect Data vidual-tree biomass from leaves, branches, stand structure, yield, tree size, and rota- Data were collected from a network of 23 bark (of the stem), stem under the bark tion length. According to Long (1985), thin- pure even-aged permanent plots com- and total aboveground biomass, respec- ning is probably the single most influential posed of young and mature chestnut high- tively (kg). The biomass of the stem over activity a silviculturist can perform be- forest stands with re-measurement inter- the bark (ws) was obtained by adding the tween successive regeneration periods; vals of 4-10 years, 43 semi-permanent plots results of eqn. 3 and eqn. 4. Finally, Ws and -1 thus, it is often the most effective tech- (each plot was measured at least twice) WT (Mg ha ) were calculated as the sum of nique for achieving a wide range of stand and 18 even-aged temporary plots, all es- the values predicted for individual trees management objectives. In areas where sil- tablished in old-growth chestnut high-for- (from ws and wTot) by using a scaling-up ap- vicultural practice must be implemented est stands. Plot dimensions ranged from proach. under severe budget limitations, SDMDs 100 to 3000 m2, and ages ranged from 4 to can be a cost-effective approach for the 73 years. The plots covered the existing SDMD construction management (Valbuena et al. 2008). SD- range of sites, ages and stand densities The stand density management diagram MDs have been constructed for several for- most representative of sweet chestnut proposed in this study included the relative est species worldwide to achieve diverse stands in North Portugal. The soils in the spacing index (RS) and a system of four management objectives. For traditional stands have developed over metamorphic nonlinear equations as basic components. broadleaved species SDMDs are available, rocks (schist). Total height (h) and diame- The RS was chosen to characterize the for example, for Quercus robur (Barrio-An- ter at breast height (d) were measured for growing stock level. Under the assumption ta & Alvarez-González 2005), Q. pyrenaica all trees inside the plots. Descriptive statis- of square spacing, expressing RS as a per- (Castaño-Santamaría & Barrio-Anta 2013), tics for the main stand variables are re- centage was obtained using eqn. 6, where N is the number of trees per hectare and hdom is the dominant height: Tab. 1 - Summary statistics for the stand variables. (hdom): stand dominant height; (t): 100 stand age; (N): number of trees per hectare; (dg): quadratic mean diameter; (V): stand RS (%)= ⋅100 (6) √ N hdom total volume; (Ws): stand stem biomass; (WT): stand total aboveground biomass; (SD): standard deviation. Several authors have articulated why RS is a useful and efficient index to character- Variables (units) ize growing stock levels in SDMDs (Barrio-

Parameter hdom t N dg V Ws WT Anta & Alvarez-González 2005, Castedo-Do- (m) (years) (trees ha-1) (cm) (m3 ha-1) (Mg ha-1) (Mg ha-1) rado et al. 2009). For example, RS is inde- Mean 17.3 42 759 24.3 284.16 140.23 180.41 pendent of site quality and stand age, ex- Maximum 29.9 73 2133 53.6 798.27 386.92 502.81 cept in very young stands. Additionally, Minimum 2.5 4 157 1.5 0.10 0.10 0.10 dominant height is one of the best criteria for determining thinning intervals from a SD 9.5 26 410 16.0 255.55 125.45 161.94 biological point of view, and the associa-

866 iForest 10: 865-870 SDMDs for sweet chestnut high-forest stands in Portugal y r

Tab. 2 - Parameter estimates and statistics from the simultaneous fit of eqn. 7-10. Standard deviations of parameter estimates are in t s

brackets. (dfe): residuals degrees of freedom; (RMSE): root mean square error; (FIadj): fit index; (dg): quadratic mean diameter; (V): e r stand total volume; (Ws): stand stem biomass; (WT): stand total aboveground biomass. o F

d Variable Estimates of the coefficients in the models dfe RMSE FIadj n a

dg b0 = 10.26562 (3.6603) b1 = -0.3082 (0.0289) b2 = 0.973319 (0.0798) - 110 3.84 0.942 s

V b3 = 0.000031 (9.349E-6) b4 = 2.146777 (0.0966) b5 = 0.801093 (0.0974) b6 = 1.018115 (0.0348) 109 14.34 0.997 e c

Ws b7 = 0.000019 (5.672E-6) b8 = 2.039638 (0.0714) b9 = 0.855506 (0.0692) b10 = 1.019766 (0.0270) 109 7.87 0.996 n e i WT b11 = 0.000021 (6.094E-6) b12 = 2.073444 (0.0837) b13 = 0.867747 (0.0833) b14 = 1.013969 (0.0300) 109 9.51 0.997 c s o e tion between dominant height growth and sented in Tab. 1. In Tab. 2, we present the the x-axis and N on the y-axis (using loga- g o forest production adds further utility to SD- results of fitting the system of nonlinear rithmic scale). Isolines of dg and RS are pre- i B MDs used for forest management pur- equations (eqn. 7-10). sented in all SDMDs related to the vari- – poses. Furthermore, in the specific case of Every parameter was significant at the 1% ables V, Ws, WT and C . t sweet chestnut, the silvicultural model pro- significance level (p<0.01), and the fit index In Fig. 1, the SDMD outlines the silvicul- s 2 e posed by Bourgeois et al. (2004) for pro- values (FIadj), a statistic similar to R adj in lin- tural model (dashed line) proposed by r o

ducing high-quality timber in pure even- ear regression, were all above 94%. Four Bourgeois et al. (2004). As previously men- F aged high-forest stands outlined recom- SDMDs for even-aged high-forest stands of tioned, the main goal of this silvicultural i mendations for thinning according to the sweet chestnut in Portugal were con- model is to produce high-quality timber us- height growth of frame trees. structed as bivariate graphs with hdom on ing the diameter growth of the frame trees In the proposed SDMD, the y-axis con- tains the number of trees per hectare (N), and the x-axis shows the dominant height (hdom). The first step for the construction of the diagram consisted in fitting a system of four nonlinear equations (eqn. 7 to eqn. 10):

b1 b2 d g=b 0 N hdom (7)

b4 b5 b6 V =b3 d g hdom N (8)

b8 b9 b10 W s=b7 d g hdom N (9)

b12 b13 b14 W T =b11 d g hdom N (10)

Equations 7-10 were simultaneously fitted using the full information likelihood technique implemented in the MODEL procedure of SAS/ETS® (SAS Institute Inc. 2004). The procedure was selected to address the problem of dependent regressors, often called simultaneous equation bias (SAS In- Fig. 1 - Stand density management diagram for chestnut high-forest stands in Portugal stitute Inc. 2004). for estimation of stand volume (m3 ha-1). The second step in the construction of the SDMD consisted of calculating and drawing the isolines for the growing stock level (represented by RS), as well as for the stand variables: quadratic mean diameter (dg), stand volume (V), stand stem biomass (Ws), and stand total above-ground biomass (WT). These isolines were obtained by inverting eqn. 6-10 to solve for N, as ex- plained in Barrio-Anta & Alvarez-González (2005). Once the values for stem and total aboveground biomass at the stand level are known, it is possible to convert them to carbon content (C in Mg ha-1). In our study, this was done using a conversion factor of 0.50. Results and discussion After an initial exploratory data analysis, 5 observations were identified as extreme outliers and removed from the data set. Summary statistics for the data used to fit the models, namely, mean, maximum, mini- Fig. 2 - Simulation of a silvicultural prescription to define lower and upper growing mum and standard deviation, are pre- stock limits for chestnut high-forest stands for quality timber production. iForest 10: 865-870 867 Patrício MS & Nunes L - iForest 10: 865-870

y -1

r (≥ 1 cm year ) as a reference to achieve the t

s desired diameter (≥ 45 cm) within a reason- e

r able time (i.e., thinnings are intended to o improve the growth rate of the frame F trees). Until a dominant height of 9 m is d n reached, a slight decrease in the number of a stems per hectare is attributed to natural s e mortality. From this point on, we assumed c

n that no mortality occurs, which is not inap- e i propriate if silviculture is regularly prac- c

s ticed. With respect to growing stock levels, o the silviculture prescribed in the model of e g Bourgeois et al. (2004) results in a range of o i relative spacing index values between 32 B (lower limit) and 24 (upper limit). We rec- – ommend 32% as the lower limit of growing t s stock for producing high-quality timber in e r Portuguese chestnut high-forest stands, o

F according to the existing yield tables (Patrí- i cio et al. 2005). Below this limit, there will be considerable losses in management effi- Fig. 3 - Stand density management diagram for chestnut high-forest stands in Portu- -1 ciency, with negative consequences for gal for estimation of stand stem biomass (Mg ha ). stumpage value and potential revenue. Thus, descending below this level should be avoided. Furthermore, below this threshold, there will be increased risk of fire ignition due to the accumulation of combustible vegetable material. To define the upper limit of growing stock, we simulated a silvicultural model that, according to our experience studying these stands, adequately achieves the objective of high-quality timber production and is representative of a silviculture based on the dominant height growth of the trees with the greatest potential (frame trees). This simulation is presented in Fig. 2 (solid ladder-shaped line), starting with ap- proximately 1250 trees per hectare. The first thinning occurs (pre-commercial thinning) at a dominant height of 11 meters, reducing density to 800 trees per hectare, re- sulting in a relative spacing of 32%. After this point, the upper limit of growing stock that was most appropriate in achieving a Fig. 4 - Stand density management diagram for chestnut high-forest stands in Portu- -1 rhythm of thinnings in accordance to wise gal for estimation of stand aboveground biomass (Mg ha ). values of dominant height growth – that al- lowed obtaining adequate target diame- ters and number of trees per hectare at the end of the rotation – was the one corresponding to a relative spacing of 26%. Fol- lowing the simulation (solid ladder-shaped line in Fig. 2), three more thinnings will occur successively, reducing the number of trees per hectare to 530, 350, and approxi- mately 230. Rotation can end when the trees have either a dominant height slightly above 21 meters and a quadratic mean diameter of 36 cm or a dg above 40 cm, al- lowing management to be flexible according to market opportunities. In these conditions, values of stand stem biomass (Fig. 3), total aboveground biomass (Fig. 4) and total aboveground carbon content (Fig. 5) will achieve values in the ranges of 100-175, 125-225, and 60-110 Mg ha-1, respectively. The thinning cycle is regulated by the height increment of frame trees. A new thinning should occur when there is a 2-2.5 Fig. 5 - Stand density management diagram for chestnut high-forest stands in Portu- -1 m height increment in young stands. In gal for estimation of carbon content in stand aboveground biomass (Mg ha ). older or slower growing stands, the gaps

868 iForest 10: 865-870 SDMDs for sweet chestnut high-forest stands in Portugal y

between thinnings are extended up to 4 m r t

of height growth. The thinning cycle ad- s e

justs to the growth rate of the stand over r time, and the considered height incre- o F ments are consistent with the thinning d practice. The usual length of the thinning n a cycle is shorter in young or fast-growing s crops because younger trees react quickly e c

to competition reduction and longer for n e older or slower growing crops. Because i c

these values are similar to current values s within the management practice and the o e yield tables already available for chestnut g o high-forest in Portugal (Patrício et al. i B 2005), we suggest that growing stock – should adhere to intervals of relative spac- t ing between 32% and 26%. These values are s e suitable for a silviculture focused on ob- r o

taining high revenues from quality timber F production in chestnut high-forest stands. i These percentages represent the optimal Fig. 6 - Site index curves with reference age of 45 years (SI 45) for chestnut high-forest range of densities that will control compe- stands, established by Patrício (2006). tition in chestnut stands for high-quality timber production. Moreover, we suggest Age of thinning can be obtained by locat- MSP. Data used in this study were col- that practitioners go beyond the simple ing the stand height on the dominant lected under financial support of AGRO density reduction suggested by SDMDs by height-over-age curves for a given site in- Program, Project 267: Sustainable Manage- applying a silviculture based on the selec- dex (Fig. 6). ment of Chestnut Forested Areas in High- tion of the best trees in the stands using The prescribed silviculture for high-forest Forest and Coppice Systems, and Project matrix trees (“accompanying trees”) as a chestnut based on single-stem selection on PTDC/AGRCFL/68186/ “Mixed forests: Mod- complement of management that will be a tree-by-tree basis encourages the devel- eling, dynamics and geographical distribu- removed once they hinder the frame trees. opment of natural regeneration by seed tion of productivity and carbon storage in Therefore, the management objective is and coppice. However, we recommend fa- mixed forest ecosystems in Portugal”, not to maximize volume production per voring the continuity of the stand by the funded by the Portuguese Science Founda- hectare but rather to maximize the growth seedling’s natural regeneration process to- tion (FCT) and FEDER - COMPETE Program. of valuable single-stems. wards site sustainability using the shoots Based on our results, a slight modification as “accompanying stand” (matrix trees) References in the model outlined by Bourgeois et al. only. We can select the best trees by crown Alvarez-Alvarez P (2004). Viveiros forestales y (2004) is proposed (dashed ladder-shaped thinning followed by low thinning in the fi- uso de planta en repoblación en Galicia [Forest line in Fig. 2) to adapt the prescribed silvi- nal stages of stand growth or by the appli- nurseries and plant use in afforestations in Gali- culture to the lower and upper limits of cation of the final crop tree thinning. This cia]. Doctoral thesis (electronic publication), growing stock we defined. If a stand starts type of thinning focuses management on Universidad de Santiago de Compostela, Santi- with an initial density of 1250 trees per the most valuable trees in a stand in order ago de Compostela, pp. 261. [in Spanish] hectare and assuming some natural mortal- to achieve maximum value per tree, to de- Assmann (1970). The principles of forest yield ity in young stages, the first thinning would velop adequate stability of individual trees study. SH Gardiner, Pergamon Press Ltd., Ox- occur at a dominant height of 12 m, reduc- and to make sure that the best individuals ford, UK, pp. 506. ing the number of trees to 700 per hectare. will have the opportunity to regenerate Barrio-Anta M, Alvarez-González JG (2005). De- Once a dominant height of 14.6 m is (Kerr & Haufe 2011). The SDMDs now avail- velopment of a stand density management dia- reached, density will be reduced to 460 able for chestnut high-forest stands allow gram for even-aged pedunculate oak stands trees per hectare, and again, at hdom 17.9 managers to set the upper and lower limits and its use in designing thinning schedules. m and 21.9 m, density will be reduced to within which the density range should oc- Forestry 78: 209-216. - doi: 10.1093/forestry/cpi 305 and 205 trees per hectare, respec- cur and estimate the corresponding stump- 033 tively. age value in volume, biomass, carbon and Bourgeois C, Sevrin E, Lemaire J (2004). Le châ- To determine the age at which thinning mean breast height diameter dg. The pro- taignier un arbre, un bois [The sweet chestnut: and harvesting should be carried out, the posed density limits are guidelines for man- a tree, a wood]. IDF, 2nd edn, Paris, France, pp. site index curves developed by Patrício agers to consider when setting thinning 347. [in French] [online] URL: http://books. (2006) can be used. These curves were ob- regimes; we propose that thinning regimes google.com/books?id=-KGxQ0ra-zUC tained using an algebraic difference ap- should focus on single-stem selection on a Castaño-Santamaría J, Barrio-Anta M (2013). Re- proach (ADA) of the McDill & Amateis tree-by-tree basis, enabling best trees to gional-scale stand density management dia- (1992) equation with stem analysis data regenerate by seedling and preserving the grams for Pyrenean oak (Quercus pyrenaica (eqn. 11): most valuable trees for final cut, ultimately Willd.) stands in northwest Spain. iForest 6: 113- improving the stand’s quality and revenue. 122. - doi: 10.3832/ifor0880-006 y = 34.85593 SDMDs are a helpful tool for manage- Castedo-Dorado F, Crecente-Campo F, Alvarez- 2 1.61604 ment, but the ultimate management tool is Alvarez P, Barrio-Anta M (2009). Development 34.85593 t1 1− 1− (11) the eye of the technician who makes the of a stand density management diagram for hdom t ( 1 )( 2 ) single-stem selection in the field to identify radiate pine stands including assessment of trees that have the greatest potential. stand stability. Forestry 82 (1): 1-16. - doi: 10.109 (FIadj = 0.996; RMSE = 0.46 m) where y2 rep- 3/forestry/cpm032 resents both the dominant height hdom2 at Acknowledgments Clutter JL, Fortson JC, Pienaar LV, Brister GH, age t2 and the site index at the reference Conception of the study, data analysis, Bailey RL (1983). Timber management: a quan- age of 45 years (SI45) and hdom1 represents drafting of the manuscript and critical revi- titative approach. Krieger Publishing Co., New the dominant height at age t1. sion: MSP and LN. Contributed materials: York, USA, pp. 333. [online] URL: http:// iForest 10: 865-870 869 Patrício MS & Nunes L - iForest 10: 865-870 y

r www.cabdirect.org/cabdirect/abstract/198406 cultural guide - Version 1.0. Forestry Commis- Patrício MS (2006). Análise da Potencialidade t

s 91762 sion, Edinburgh, UK, pp. 54. [online] URL: Produtiva do Castanheiro em Portugal [Analysis e Conedera M, Manetti MC, Giudici F, Amorini E http://www.forestry.gov.uk/pdf/Silviculture_Thi of Sweet Chestnut Productive Potentiality in r o (2004). Distribution and economic potential of nning_Guide_v1_Jan2011.pdf Portugal]. PhD thesis, Universidade Técnica de F the Sweet Chestnut (Castanea sativa Mill) in Kumar BM, Long J, Kumar P (1995). A density Lisboa, Instituto Superior de Agronomia, Lis- d

n Europe. Ecologia Mediterranea 30 (2): 179-193. management diagram for teak plantations of boa, Portugal, pp. 273. [in Portuguese] a [online] URL: http://s3.amazonaws.com/acade Kerala in Peninsular India. Forest Ecology and Patrício MS, Tomé M, Monteiro, ML (2005). s e mia.edu.documents/40200333/ Management 74: 125-131. - doi: 10.1016/0378-1127 Tabela de produção para o castanheiro em c

n Drew TJ, Flewelling JW (1979). Stand density (94)03499-M regime de alto fuste [Yield table for sweet e i management: an alternative approach and its Long JN (1985). A practical approach to density chestnut in high-forest system]. In: Proceed- c th s application to Douglas-fir plantations. Forest management. Forestry Chronicle 61: 23-27. - ings of the “5 Portuguese National Forest o Science 25: 518-532. [online] URL: http:// doi: 10.5558/tfc61023-1 Congress” (Silva R, Páscoa F ed). Viseu (Portu- e

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