Effect of Site Quality and Thinning Management on the Structure Ofholmoak Forests in Northeast Spain

Effect of site quality and thinning management onthe structure of holm oak forests in northeast Spain M Gracia, J Retana To cite this version: M Gracia, J Retana. Effect of site quality and thinning management on the structure ofholmoak forests in northeast Spain. Annales des sciences forestières, INRA/EDP Sciences, 1996, 53 (2-3), pp.571-584. hal-00883076 HAL Id: hal-00883076 https://hal.archives-ouvertes.fr/hal-00883076 Submitted on 1 Jan 1996 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Original article Effect of site quality and thinning management on the structure of holm oak forests in northeast Spain M Gracia J Retana 1 Centre de Recerca Ecològica i Aplicacions Forestals, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona; 2 Departament de Producciò Vegetal i Ciència Forestal, Universitat de Lleida, Rovira Roure 177, 25006 Lleida, Spain (Received 6 September 1994; accepted 20 November 1994) Summary — In the holm oak forests of NE Spain, the variability of thinning intensity, together with the great heterogeneity of site quality, due to the rough topography of the region, gives rise to important structural differences among stands. In this paper, we analyze the effect of site quality and thinning management on the structural heterogeneity of holm oak stands at the end of the cutting cycle in different areas of the Montseny and Les Guilleries massifs (NE Spain). These two factors influence the main structural variables of the stands in various ways. Height was used as an indicator of site quality, because it was relatively unaffected by thinning management, while density and total number of stems per stool were strongly affected. Mean tree diameter reflected the effect of both site quality and thinning. The type of forest management was found to be the most important factor determining forest structure. Site quality was a constraint of stand development, contributing in poor stands, to increased differences due to thinning management. holm oak / Ouercus ilex / forest structure / site quality / thinning Résumé — Effets de la fertilité de la station et de l’intensité d’éclaircie sur la structure des forêts de chêne vert du nord-est de l’Espagne. Dans les forêts de chêne vert du nord-est de l’Es- pagne, la variabilité de l’intensité d’éclaircie et la grande hétérogénéité de fertilité des stations, dues à leur topographie montagneuse, provoquent d’importantes différences de structure des peuplements. Dans cet article, nous analysons l’effet de la fertilité de la station et de la gestion sylvicole sur l’hété- rogénéité structurelle des forêts de chêne vert dans différentes zones des massifs de Montseny et les Guilleries (nord-est de l’Espagne). Ces deux facteurs influencent de différentes manières les principales variables descriptives de la structure des peuplements. La hauteur a été utilisée comme indice de fertilité de station car elle est très peu modifiée par le type de gestion sylvicole, tandis que la densité et le nombre total de brins par souche sont très affectés par le type de gestion. La diamètre moyen syn- thétise l’effet de la fertilité de la station et de l’intensité d’éclaircie. La gestion sylvicole est le facteur le plus important pour expliquer les différences de structure de peuplement, tandis que la fertilité de la station peut être un facteur limitant du développement des peuplements, contribuant, dans les stations de moindre qualité, à augmenter les différences dues à la gestion sylvicole. chêne vert / Quercus ilex / structure de la forét / fertilité de la station / éclaircie INTRODUCTION Castri, 1973; Terradas, 1991; Barbero et al, 1992). Heterogeneity is an intrinsic feature of the In this study we analyze the effect of site Mediterranean landscape (Naveh and quality and thinning management on the Lieberman, 1984; Barbero, 1988). This het- structural heterogeneity of holm oak forests erogeneity appears not only in the variation at the end of the cutting cycle. The initial of holm oak forests to different of species composition associated with gra- response fertilization and dients of aspect, elevation or soil depth thinning, irrigation practices (Aschmann, 1973; Rabinovitch-Vin, 1983; has been previously studied by measuring Quezel and Barbero, 1989; Pigott and Pig- parameters such as growth of remaining ott, 1993), but also in the changes of stand trees, production and dynamics of sprouts, structure and architecture of trees observed etc (Cartan-Son et al, 1992; Ducrey, 1992; within the same stand. It is therefore nec- Ducrey and Turrel, 1992; Floret et al, 1992; and essary to carry out a description of these Mayor Rodá, 1994). Nevertheless, these studies are and it forests based on structural, architectural relatively recent, has not been to evaluate the and physiognomic features on the different yet possible relative of these factors in the vertical strata of the canopy, that provide importance information about this dynamic environment, structural features of the stands in the medium term. which is a habitat of animal communities (Cody, 1985; De Garnica and Robles, 1991), liable to suffer disturbances (Sousa, 1984; STUDY AREA AND METHODS Lorimer, 1989; Oliver and Larson, 1990), and potentially be used and exploited in numerous ways (Ducrey, 1992). This study was carried out in three different areas: Gualba, in the southwestern sector of the Holm oak forests (Quercus ilex) coppice Montseny Massif (40 km from Barcelona, Spain), are one of the most representative com- Arbúcies, in the northern sector of the Montseny munities in the western part of the Mediter- Massif (90 km from Barcelona), and Susqueda, in ranean basin (they cover more than 120 000 the southwestern sector of the Les Guilleries Mas- ha in Catalonia alone; Montoya, 1988). In sif (110 km from Barcelona). The climate of the is subhumid Mediterranean. Mean annual this type of forest, the inherent heterogeneity region from 600 to 800 mm and of Mediterranean has precipitations range ecosystems multiple mean annual temperatures from 10 to 15 °C. origins that overlap on different temporal Soils are developed on a bedrock of granite and and spatial scales (David et al, 1979; Floret metamorphic schists. The main vegetation type of et al, 1989; Barbero, 1988; Romane et al, the area corresponds to the montane holm-oak 1988). In addition to this environmental het- forest (Quercetum mediterraneo-montanum), with Q ilex as the main at the tree there is one another caused component layer, erogeneity, by and Erica arborea and Arbutus unedo as the main human as this of forest influence, type components of the shrub layer. Holm oak forests ecosystem has been subjected for decades of this region are managed by coppicing through or even centuries to frequent coppicing (Di selective cutting at intervals of approximately 30 years (Retana et al, 1992). Together with this ning intensity. In each of the tree areas, groups of variability in management practices, there is a plots of similar site quality (plots which did not spatial heterogeneity in site quality due to the show significant differences in height from an rough topography of the region. To distinguish analysis of variance) have been established. A between the effects of management and quality, group of low quality plots and another of high plots which differed in only one of these two fac- quality plots have been distinguished in each area. tors have been compared. Circular plots with a 12 m radius (450 m2) were In each area, two adjacent stands with differ- established. In each plot, the following measures ent thinning management were chosen: one qual- were taken: ified as ’conservative and another as thinning’, — topographic factors: elevation, aspect, slope ’intense In the area of a third thinning’. Susqueda, and position on the slope (low, medium and high) stand, referred to as ’old forest’ was also included. The three stands corresponding to conservative — diameter at breast height (dbh) of all standing trees than 5 cm dbh thinning belonged to the same owner, and were larger managed by selective thinning. This practice — height of the ten tallest trees in the plot involved a period of about 25-30 years between Forest structure has been described using the harvests, a variable harvest of basal area following variables: (40-60%), and special care in the selection of — of stems above 5 cm dbh the remaining trees. These stands had a similar density age from last thinning. The three stands corre- — basal area to were intense all character- — sponding thinning mean dbh of stems above 5 cm dbh ized by a less careful management. The high cutting intensities of these stands had the — dominant height characteristics of clear felling practice in some — number of stems per stool cases. a They presented longer period between — stool equivalent diameter, which is the diameter were con- harvests than stands which thinned that has the same basal area as the sum of the The stand of old forest in servatively. Susqueda basal areas of all stems from the stool. was a portion of the conservatively thinned stand To elaborate on the diameter distributions, that was not cut in the last thinning period. There- stems of each were in width intervals fore, its age from last thinning was 70 years plot grouped instead of 35.

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