Lioret F., Solé A., Pino J., Vayreda J., Font X., Terradas J. (2009) Patterns of species impoverishment in managed forests of Catalonia (NE Spain). Journal of Vegetation Science. 20: 675-685.EnllaçDoi: 10.1111/j.1654-1103.2009.01059.x
Question: In managed forests, woody plant richness shows great variations in pattern. Herein we try to elucidate the role of major factors, such as successional status, to explain this variation. Assuming that less competitive or disturbance-sensitive species will be systematically more prone to disappear, we investigate the existence of nonrandom patterns of species impoverishment - i.e., the number of species unable to attain maximal richness and the ecological and successional status of species associated with impoverishment in relation to a regional climatic gradient. Methods: We explored species composition in approximately 7500 forest plots in Catalonia (NE Spain). We evaluated non-random patterns of species impoverishment by analyzing their nestedness. Multivariate analysis was used to relate environmental variables and impoverishment to species occurrence. Plot successional status and ecological range were also estimated from species composition, and species impoverishment was then correlated to these estimators. Results: Most forests show a non-random pattern of species loss: poor stands tend to retain the same species, and the species determining high richness tend to be the same. Late successional species tend to be more common in impoverished plots of drier and warmer forests, while species typical of open or disturbed habitats are more common in impoverished plots of moister and colder forests. Communities dominated by early or late successional species are mostly impoverished, while the richest stands are constituted by species of intermediate stages. Forests dominated by species with a narrow or wide ecological range showed high impoverishment levels, while the richest stands had species with an intermediate ecological range. Discussion: In warmer Mediterranean forests, impoverishment tends to be associated with late successional stages, while in moister and colder forests, species loss is more closely related to disturbance and exploitation. This study reveals the difficulties involved in using species richness as a simple descriptor of the degree of forest conservation. Identification of dominant species and species indicative of ecological processes would constitute an easily applicable practice that would consolidate assessment of forests status. © 2009 International Association for Vegetation Science.
Estevan H., Lloret F., Vayreda J., Terradas J. (2007) Determinants of woody species richness in Scot pine and beech forests: climate, forest patch size and forest structure. Acta Oecologica. 31: 325-331.EnllaçDoi: 10.1016/j.actao.2007.01.003
We analysed patterns of woody species richness in Pinus sylvestris and Fagus sylvatica forests in Catalonia (NE Spain) from forestry inventory databank in relation to climate and landscape structure. Both types of forests are found within the same climatic range, although they have been managed following somewhat different goals. Overall, woody species richness significantly increased when conditions get closer to the Mediterranean ones, with milder temperatures. Differences between the two types of forests arose when comparing the relationship between richness and forest patch size. Woody species richness increased in pine forests with patch size, while the opposite trend was observed in beech forests. This pattern is explained by the different behaviour of structural canopy properties, since leaf area index and canopy cover showed a steeper increase with increasing forest patch size in Fagus forests than in Pinus ones. Accordingly, richness decreased with canopy cover in Fagus plots, but not in Pinus ones. We suggest that these differences would be related to management history, which may have enhanced the preservation of beech stands in larger forest landscape units. © 2007 Elsevier Masson SAS. All rights reserved.
Lloret F., Lobo A., Estevan H., Maisongrande P., Vayreda J., Terradas J. (2007) Woody plant richness and NDVI response to drought events in Catalonian (northeastern Spain) forests. Ecology. 88: 2270-2279.EnllaçDoi: 10.1890/06-1195.1
The role of species diversity on ecosystem resistance in the face of strong environmental fluctuations has been addressed from both theoretical and experimental viewpoints to reveal a variety of positive and negative relationships. Here we explore empirically the relationship between the richness of forest woody species and canopy resistance to extreme drought episodes. We compare richness data from an extensive forest inventory to a temporal series of satellite imagery that estimated drought impact on forest canopy as NDVI (normalized difference vegetation index) anomalies of the dry summer in 2003 in relation to records of previous years. We considered five different types of forests that are representative of the main climatic and altitudinal gradients of the region, ranging from lowland Mediterranean to mountain boreal-temperate climates. The observed relationship differed among forest types and interacted with the climate, summarised by the Thorntwaite index. In Mediterranean Pinus halepensis forests, NDVI decreased during the drought. This decrease was stronger in forests with lower richness. In Mediterranean evergreen forests of Quercus ilex, drought did not result in an overall NDVI loss, but lower NDVI values were observed in drier localities with lower richness, and in more moist localities with higher number of species. In mountain Pinus sylvestris forests NDVI decreased, mostly due to the drought impact on drier localities, while no relation to species richness was observed. In moist Fagus sylvatica forests, NDVI only decreased in plots with high richness. No effect of drought was observed in the high mountain Pinus uncinata forests. Our results show that a shift on the diversity-stability relationship appears across the regional, climatic gradient. A positive relationship appears in drier localities, supporting a null model where the probability of finding a species able to cope with drier conditions increases with the number of species. However, in more moist localities we hypothesize that the proportion of drought-sensitive species would increase in richer localities, due to a higher likelihood of co-occurrence of species that share moist climatic requirements. The study points to the convenience of considering the causes of disturbance in relation to current environmental gradients and historical environmental constraints on the community. © 2007 by the Ecological Society of America.
Lloret F., Estevan H., Vayreda J., Terradas J. (2005) Fire regenerative syndromes of forest woody species across fire and climatic gradients. Oecologia. 146: 461-468.EnllaçDoi: 10.1007/s00442-005-0206-1
Community resilience after fire is determined by species' ability to regenerate through two main mechanisms growth of new sprouts (resprouter species) and germination from surviving seed banks or from seeds arriving from neighbouring populations (seeder species). Both the mechanisms are present in Mediterranean communities. The occurrence of both the types in a community depends on fire history and the bio-geographical history determining the available species pool. Regenerative traits also covary with other functional attributes associated with resource acquisition and stress tolerance. As post-fire regenerative responses can be related to various ecological factors other than fire, we tested the hypothesis of a different proportional representation of post-fire regenerative syndromes in forest woody species along a climatic gradient in Catalonia (NE Spain) ranging from Mediterranean to temperate-boreal climates. Specifically, we expected seeder species to become less common with colder and moister conditions while resprouters would not be so influenced by the climatic gradient. We also tested the hypothesis of change in the relative abundance of regenerative syndromes in relation to recent fire history. We analysed a large database obtained from extensive forestry surveys and remote sensing fire records. After correction for spatial autocorrelation, we found an increase in the proportion of seeder species under more Mediterranean conditions and a decrease in fire-sensitive species (with no efficient mechanisms of post-fire recovery) in moister conditions. Resprouter species were similarly present across the whole gradient. A similar pattern was observed after excluding recently burnt plots. Therefore, post-fire regenerative syndromes segregate along the climatic gradient. Recent fires reduced the occurrence of fire-sensitive species and increased the proportion of seeder species. No significant effect was observed on resprouter species. Fire has a sorting effect, shaping the occurrence of species with different regenerative traits. Overall, fire seems to explain better the variability of the proportion of fire-sensitive species and climate the variability of seeder species. In addition, other factors (forestry practices and the covariation between regenerative and functional attributes) are likely to contribute to the regional pattern of regenerative syndromes. © Springer-Verlag 2005.
Terradas J, Salvador R, Vayreda J, Lloret F (2004) Maximal species richness: an empirical approach for evaluating woody plant forest biodiversity. Forest and Ecology and Management 189:241-249.
Vayreda J, Ibàñez JJ, Gracia C, Terradas J (2001) Patrón geográfico de la riqueza de especies leñosas según el sistema de información de los bosques de Cataluya. In Actas del Congreso de Ordenación y Gestión Sostenible de Montes. Tomo II:691-699.
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