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Ann. For. Sci. 64 (2007) 333343 333cINRA, EDP Sciences, 2007DOI: 10.1051/forest:2007010

Original article

Climatic signal in annual growth variation of silver fir

(Abies albaMill.) and spruce (Picea abiesKarst.) fromthe French Permanent Plot Network (RENECOFOR)

Franois L*

UMR INRA-ENGREF 1092 Laboratoire dtude des Ressources Fort-Bois (LERFOB) quipe cologie Forestire, 54042 Nancy Cedex, France

(Received 23 May 2006; accepted 13 October 2006)

Abstract This paper explores the growth/climate relationships in earlywood, latewood and total ring-width chronologies of five Norway spruce (Picea

abies) and six silver fir (Abies alba) stands sampled in the French permanent plot network (RENECOFOR) (327 trees). The relationships betweenclimate and ring widths were analyzed using extreme growth years, simple correlations and response functions analysis (bootstrapped coefficients).Monthly climatic regressors were derived by a physiological water balance model that used daily climatic data and stand parameters to estimate soilwater deficits. Pointer years underline the high sensitivity to winter frosts (1956, 1986) and exceptional annual droughts (1962, 1976, 1991) for bothspecies. For those years, growth variations were higher for Abies alba than for Picea abies. For each species, the climate information of tree ringseries is not modified by local site characteristics (altitude, slope, aspect, soil water reserve). Moreover, strong specific differences appear amongspecies. Earlywood and latewood spruce growth mainly depends on current summer soil water deficit conditions. For silver fir, winter and early summertemperatures, as well as the water supply of the previous year (August to October) play a major role for the production of earlywood, after which thecurrent early summer water supply influences mainly latewood width.

Abies alba /Picea abies/tree ring /water balance/drought /pointer years /response functions

Rsum Rponse au climat du sapin pectin (Abies albaMill.) et de lpica commun (Picea abies Karst.) dans le Rseau National de suivi long terme des cosystmes Forestiers (RENECOFOR). Cet article prsente les relations entre le climat et les variations des largeurs du bois initial,du bois final et du cerne complet pour cinq peuplements dpica commun (Picea abies) et six peuplements de sapin pectin (Abies alba) chantillonnsdans le rseau national de suivi long terme des cosystmes forestiers (RENECOFOR) (327 arbres). Leffet du climat sur la largeur des cernes a tanalys partir de ltude des annes caractristiques et ltablissement des fonctions de rponse. Les rgresseurs climatiques mensuels pris en comptesont issus dun modle de bilan hydrique base cophysiologique qui utilise comme variables dentre des donnes mtorologiques journalireset les caractristiques du peuplement. Les annes caractristiques montrent la forte sensibilit aux froids extrmes (1956, 1986) et aux scheressesintenses (1962, 1976, 1991) des deux espces avec nanmoins des variations de croissance plus marques pour le sapin pectin. Pour chaque espce,les caractristiques cologiques locales (altitude, pente, exposition, etc.) ne modifient pas la rponse au climat. Cependant, le comportement des deuxespces apparat trs diffrent. Pour lpica, la mise en place du bois initial et du bois final dpend essentiellement du dficit hydrique estival de lanneen cours. Pour le sapin, la largeur du bois initial dpend la fois du rgime thermique hivernal et du dbut dt de lanne en cours et de la scheressede la fin de saison prcdente (aot octobre). Par la suite, la scheresse estivale de lt en cours influence la mise en place du bois final.

Abies alba /Picea abies/cerne/bilan hydrique /scheresse/anne caractristique/fonctions de rponse

1. INTRODUCTION

Silver fir (Abies alba Mill.) and Norwayspruce (Picea abies[L.] Karst.) are widely distributed species in Europe and have

provedto be important species for dendrochonologicalstudies.In France, the natural distribution areas correspond to moun-tainous regions (Alps, Pyrenees, Vosges). In these contexts,natural mixed or pure coniferous forests cover a wide rangeof substrate, topographic and climatic conditions. The habitatof both species is quite comparable, but silver fir is absent atthe upper level [4,9, 10, 41,42, 46]. From an ecophysiologicalpoint of view, the shade tolerant silver fir species appears to berather a more frost and drought-sensitive species than Norwayspruce which behaves as a pioneer species [2,24].

* Corresponding author: lebourgeois@engref.fr

Over the last few decades, damage to coniferous ecosys-tems has occurred over many regions throughout Europe andFrance [5, 47]. Sometimes, the symptoms can be explainedby well-identified agents such as insect pests, fungal attack,

mineral deficiency, etc. In addition, extreme climatic events(e.g. severe drought, winter or late frost) can play an im-portant role in promoting growth decrease and forest de-cline [36,10]. In the context of climate change and of poten-tial effects of the exceptional heat waves (such as that observedin 2003 throughout Europe [16]), questions are being raisedconcerning survival and growth of natural vegetation in re-sponse to changes in yearly weather conditions and/or extremeevents [15]. Due to land abandonment, an important increasein the establishment of both species is observed in variousmountainous regions nowadays. Thus, a better understanding

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334 F. Lebourgeois

Table I. Site description and characteristics of selected stands. Age at breast height, mean values (SD)/maximum. H and DBH = Tree height anddiameter at breast height, mean values (SD). N =number of trees per hectare. LAI = Maximum Leaf Area Index. EW: Maximum ExtractableSoil Water (mm).

Site code Latitude Longitude Alt. Slope Aspect Age H DBH N LAI EW

(m) (%) (years) (m) (cm) (n/ha) (m2/m2) (mm)Picea abies Pa 39a 46 34 47 N 5 52 37 E 970 10 SE 58 (3)/69 30.2 (2.5) 45 (4) 414 6.1 65

Norway spruce Pa 39b 46 31 00 N 6 03 44 E 1210 8 W 106 (6)/262 23.6 (2.2) 4 4 (5.1) 746 6.8 109

Pa 71 47 00 33 N 4 07 06 E 600 20 SE 48 (2)/50 27 (1.2) 41 (3.7) 460 7.4 149

Pa 73 45 35 12 N 6 47 23 E 1700 40 NW 185 (12)/209 22 (2.6) 45 (4.4) 499 6.9 118

Pa 88 48 14 02 N 7 06 14 E 660 20 SW 89 (2)/92 34.8 (2.3) 52 (4.4) 401 5.9 88

Abies alba Aa 05 44 29 25 N 6 27 33 E 1360 30 NE 99 (14)/152 28.3 (2.7) 5 0 (7.1) 375 7.7 190

Silver fir Aa 07 44 42 36 N 3 57 57 E 1300 20 W 80 (3)/86 25.7 (1.5) 58 (5.8) 315 5.9 92

Aa 09 42 51 52 N 1 20 43 E 1100 66 NW 168 (4)/183 25.1 (3) 44 (4.1) 427 6.6 80

Aa 57 48 36 36 N 7 08 02 E 400 20 NW 54 (4)/60 27.5 (1.5) 39 (5) 410 8.1 103

Aa 63 45 26 51 N 3 31 39 E 1040 25 SW 100 (14)/225 26.8 (2.7) 53 (6.4) 358 6.8 125

Aa 68 47 56 01 N 7 07 31 E 680 45 NW 104 (6)/114 29.3 (2) 53 (5.9) 322 6.2 60

of the species-specific effects of the weather conditions on treegrowth could help the foresters to direct the future forest man-agement [4, 6].

In France, dendroecological studies of fir and spruce arescare [4, 9], and comparative analyses have been mainly car-ried out in French Alpine valleys [18, 19, 43]. This studyled in high-elevation southern alpine stands (from 1400 to2000 m a.s.l.) has revealed a species-specific pattern of cli-matic response with strong effects of local conditions such asaspects and altitude levels. Spruce is successively sensitive tocurrent summer drought at the lower level, sensitive to the pre-vious hot summer at the intermediate level, and sensitive to

current cold summer at the upper level. Silver fir growth ishighly influenced by the previous summer water balance, par-ticularly on southern slopes. Ring-width is also enhanced byhot April temperatures in all stands and by hot February tem-peratures in northern slopes. Thus, at this regional alpine scale,fir appeared more thermophile than spruce. Summer weatherconditions (water balance or temperature) also highly influ-enced both species, but the influence of the year preceding ringformation appeared higher for fir than for spruce.

The starting hypothesis of this study was that conifer-ous growth responses observed under high-elevation alpineweather conditions differ for stands sampled at lower altitudesand growing under more various ecological conditions. In thisstudy, the relationships between tree growth and weather con-ditions were investigated in 11 natural mature silver fir andNorway spruce forests of the French Permanent Plot Networkfor the Monitoring of Forest Ecosystems network (RENECO-FOR). The ecological conditions varied from low-elevationstands with mesic and fresh weather conditions to high-elevation forests with very humid and cold weather conditions.The objectives of this study are: (1) to define the pattern ofclimatic response of each species, (2) to highlight the influ-ence of local ecological conditions on climate response, and(3) to compare the response of silver fir and Norway spruceto climate. To precise the time of the transition phase between

both components of the ring and to refine the tree-ring growthresponse to climate [28], an analysis of early- and latewoodwidths as separate variables of ring growth was also under-taken. Responses of total ring, early- and latewood ring-widthvariations to monthly climate were estimated by establishingthe mean relationships between growth and climate throughsimple correlation analysis and bootstrapped response func-tions [26]. The response to climatic variability was also as-sessed by analysing pointer years which correspond to abruptchanges in growth pattern and reveal the tree-growth responseto extreme climatic events [45]. Climatic variables were de-rived from an ecophysiological soil water balance model that

calculates daily changes of soil water content and soil waterdeficit during phenologically defined periods of the growingseason [23].

2. MATERIALS AND METHODS

2.1. Studied sites

The six silver firs and five Norway spruces stands were sampledin different French mountainous regions between 42 5 and 48 4 Nand 1 2 and 7 1 E. The mean slope was 30% (8 to 66%) with al-titude ranging from 400 to 1700 m a.s.l. (mean: 1004 m) (Tab. I andFig. 1). The pure sampled coniferous forests are composed of natu-rally regenerated even-aged stands from 48 to 185 years. The species

composition of the ground vegetation and the pedological charac-teristics of two trenches were used to define the site type for eachstand [14, 20]. Extractable soil water was calculated for each standaccording to textural properties, depth and coarse element percent-ages together with the rooting characteristics observed for each soilhorizon [14]. Soil depth averaged 150 cm unless physical or pedo-logical constraints to root penetration occurred. Soil types vary frombrunisol with low maximum extractable soil water (EWm) (65 mm)to deep calcisol with high EWm (190 mm) (mean value: 107 mm;French pedological reference) (Tab. I). Leaf area indices were esti-mated from an average value of leaf fall 1996 [12]. The range of LAIis 5.9 to 8.1 m2/m2 with a mean value of 6.8 m2/m2 (Tab. I).

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Table II.Mean climatic characteristics for each sampled stand. N= Number of meteorological stations used. Rd, rainy days (P>0 mm). Fd,number of frost days (Tmin25 C) (reference period: 19611990).

Site code N Rd Precipitation (mm) Mean temperature (C) Fd Wd

Year MaySept Year MaySept

Picea abies Pa 39a 3 167 1721 675 5.1 11.2 168 13

Norway spruce Pa 39b 3 175 1912 745 5.1 11.2 168 13

Pa 71 2 194 1283 493 10.3 16 74 49

Pa 73 1 153 971 354 9.0 15.7 121 56

Pa 88 2 178 1142 504 10.2 17.1 82 58

Abies alba Aa 05 2 97 837 362 10.0 16.6 104 61

Silver fir Aa 07 3 138 1394 489 5.8 11.7 142 14

Aa 09 2 163 1610 622 11.8 17.1 57 61

Aa 57 3 181 973 401 9.1 15.6 81 33

Aa 63 2 160 790 380 10.9 16.9 71 59

Aa 68 2 180 1860 612 10.2 17.2 82 58

water (EWM). REWc is basically a physiological threshold at whichregulation of transpiration (T) begins to occur due to stomatal clo-sure [23]. In the model, two stress indices are calculated if REW