Nere Amaia Laskurain

Seed bank spatial pattern in a temperate secondary forest

Abstract Seed bank spatial pattern was studied in a secondary forest dominated by Fagus sylvatica and Betula celtiberica in the Urkiola Natural Park (N Spain). Soil samples were taken every 2 m in a regular grid (196 points) and divided into two fractions (0-3 cm and 3-10 cm deep). The viable seed bank was studied by monitoring seedling emergence for ten months. The effect of different factors on seed bank composition and patterning was analysed using constrained ordination as a hypothesis testing tool. Furthermore, the existence of spatial autocorrelation was evaluated by geostatistical analysis. Seed density was high, 7057 seed.m−2, with a few species dominating. Species composition in the various layers were significantly correlated. The seed bank showed significant spatial structure, which was partially explainable by the spatial structure of the canopy and understorey vegetation. Spatial clumping from 0-8 m was observed in seed bank density and composition, mainly due to the pattern of two abundant taxa Juncus effusus and Ericaceae. The Ericaceae seed bank was related to the spatial distribution of dead stumps of Erica arborea. J. effusus was not present in the above-ground vegetation, which indicates that its seed bank was formed in the past. As expected, the seed bank of this forest reflects its history, which is characterized by complex man-induced perturbations. The seed bank appears to be structured as a consequence of contrasting driving forces such as canopy structure, understorey composition and structural and microhabitat features. Abbreviations: TVE = Total variance explained. Nomenclature: Aizpuru et al. (1999).

Why and where do adult trees die in a young secondary temperate forest? The role of neighbourhood

Abstract• The density and identity of tree neighbourhood is a key factor to explain tree mortality in forests, especially during the stem exclusion phase.• To understand this process, we built a logistic model for mortality in a spatially explicit context, including tree and neighbourhood predictors. Additionally, we used this model to build mortality risk frequency distributions. Finally, we tested this model against a random mortality model to predict the spatial pattern of the forest.• Annual mortality rate was high for pedunculate oak (Quercus robur, 6.99%), moderate for birch (Betula celtiberica, 2.19%) and Pyrenean oak (Q. pyrenaica, 1.58%) and low for beech (Fagus sylvatica, 0.26%). Mortality risk models for pedunculate oak and birch included stem diameter, tree height, canopy position and neighbourhood. Mortality was affected by the specific nature of the neighbourhood showing a clear competitive hierarchy: beech > pedunculate oak > birch. Models based on random mortality and logistic regression model were able to predict the spatial pattern of survivors although logistic regression predictions were more accurate.• Our study highlights how simple models such as the random mortality one may obscure much more complex spatial interactions.Résumé• La densité et l’identité des arbres du voisinage sont un facteur clé pour expliquer la mortalité d’arbres dans les peuplements forestiers, surtout pendant la phase d’exclusion du tronc.• Pour comprendre ce processus, nous avons construit un modèle logistique pour la mortalité dans un contexte spatialement explicite, en incluant l’arbre et des prédicteurs de voisinage. De plus, nous avons utilisé ce modèle pour construire des distributions de fréquence de risque de mortalité. Finalement, nous avons évalué ce modèle par rapport à un modèle de mortalité aléatoire pour prédire la structure spatiale de la forêt.• Le taux de mortalité annuelle était élevé pour le chêne pédonculé (Quercus robur, 6.99 %), modéré pour le bouleau (Betula celtiberica, 2.19 %) et le chêne tauzin (Q. pyrenaica, 1.58 %) et faible pour le hêtre (Fagus sylvatica, 0,26 %). Les modèles de risque de mortalité pour le chêne pédonculé et le bouleau intégraient le diamètre du tronc, la hauteur de l’arbre, la position du houppier et le voisinage. La mortalité a été affectée par la nature spécifique du voisinage montrant une hiérarchie claire dans l’aptitude compétitive : hêtre > chêne pédonculé > bouleau. Les modèles basés sur une mortalité aléatoire et le modèle logistique ont été capables de prédire la répartition spatiale des survivants bien que les prédictions du modèle logistique étaient plus précises.• Notre étude montre comment des modèles simples basés sur une mortalité aléatoire peuvent obscurcir des interactions spatiales beaucoup plus complexes.

Sucesión secundaria en un abedular-hayedo en el Parque Natural de Urquiola (Vizcaya)

By means of tree-ring analysis of beeches (Fagus sylvatica) and birches (Betula celtiberica) the history of a young forest in the Natural Park of Urquiola (Vizcaya) has been reconstructed. The original forest was cut down in the mid-forties to establish a Pinus radiata plantation. The plantation was rather heterogeneus, with many birches and beeches subsequently becoming established, which were at least partly spared when the pine forest was felled in 1967. A huge number of birch established themselves just after the felling, and it is now the most abundant species. Beech trees established themselves continuously over time, whereas birch establishment was concentrated in the periods following disturbance. Our results corroborate a dynamic model for these ecosystems, with birch as the pioneer species and beech becoming dominant later.

Influence of Snowmelt Timing on the Diet Quality of Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Implications for Reproductive Success

The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) is the southernmost subspecies of the species in Europe and is considered threatened as a consequence of changes in landscape, human pressure, climate change, and low genetic diversity. Previous studies have shown a relationship between the date of snowmelt and reproductive success in the Pyrenean ptarmigan. It is well established that birds laying early in the breeding season have higher reproductive success, but the specific mechanism for this relationship is debated. We present an explicative model of the relationship between snowmelt date and breeding success mediated by food quality for grouse in alpine environments. From microhistological analyses of 121 faecal samples collected during three years in the Canigou Massif (Eastern Pyrenees), and the assessment of the chemical composition of the main dietary components, we estimated the potential quality of individual diets. Potential dietary quality was correlated with free-urate faecal N, a proxy of the digestible protein content ingested by ptarmigan, and both were correlated with phenological stage of consumed plants, which in turn depends on snowmelt date. Our findings suggest that the average snowmelt date is subject to a strong interannual variability influencing laying date. In years of early snowmelt, hens benefit from a longer period of high quality food resources potentially leading to a higher breeding success. On the contrary, in years of late snowmelt, hens begin their breeding period in poorer nutrient condition because the peaks of protein content of their main food items are delayed with respect to laying date, hence reducing breeding performance. We discuss the possible mismatch between breeding and snowmelt timing.

Grazing exclusion unleashes competitive plant responses in Iberian Atlantic mountain grasslands

Questions Does the absence of equalizing mechanisms after cessation of grazing unleash strong aboveground competitors to create large patches in the community? Do these competitive intraspecific aggregations displace and exclude other species, thereby reducing species diversity? Location Atlantic grasslands in the Aralar Natural Park, Basque Country, Northern Iberian Peninsula. Methods Large herbivores were experimentally excluded from three sites (50 m × 50 m exclusion fences) during nine years in a productive semi-natural grassland system with long history of grazing, using adjacent grazed plots as experimental controls. Sampling was carried out by placing systematically one hundred quadrats (0.5 m × 0.5 m) in each of the six plots. Floristic composition and abundance, as well as eight hydrological and chemical soil properties, were measured in each quadrat. The spatial structures created by competitive species were analysed using Redundancy analysis in conjunction with Morans Eigenvector Maps, and soil variables were simultaneously included in the analyses, thus disentangling the structures likely created by niche effects. Competitive exclusion was further determined using linear regressions between species richness and abundance of competitive species. Results Grazing exclusion unleashed competitive species such as Festuca rubra and Agrostis capillaris, which became dominant in the exclusion plots and created large spatial patches. Furthermore, a negative linear relationship, consistent across exclusion plots, was observed between species richness and abundance of competitive species, indicating that strong aboveground competitors outcompeted other species when herbivores were excluded. However, the outcome of grazing exclusion across sites depended to some extent on local environmental conditions (niche effects). Conclusions This work confirms that the powerful equalizing mechanism of disturbance by herbivores is crucial for species co-existence in productive grasslands. However, important differences observed in environmental effects across sites suggest that, even in highly productive grasslands, plant traits and local environmental characteristics (niche effects) do matter for species co-existence. This article is protected by copyright. All rights reserved.

Iberian Atlantic Forest Restoration: An Experiment Based in Vegetation Succession

Restoration of European Atlantic forest has been taking place in the Basque Country since 1994. For this study three plots were selected, each for restoration of one of the three main types of natural forest common in the area: Mesophytic Oak Forest, Eutrophic Beech Forest and Oligotrophic Beech Forest. In order to find the most appropriate method for successful restoration, the plots were planted with three different densities and three species combinations of indigenous trees and shrubs. In the species selection, mature forest and seral-stage trees and shrubs were chosen, as it was intended to investigate whether planting seral-stage species was a better option than planting mature-forest tree species directly. The results after 14 years of monitoring show that, in spite of the low overall survival rate, using seral-stages shrubs improves the biodiversity of the restored forests and accelerates succession by controlling the invasion of some shrubs, such as Rubus and Ulex, which have inhibitory effects on secondary succession in degraded lands. A selection of saplings with good root systems contributes effectively to higher survival rates and to more successful results. As a general rule, a combination of trees and shrubs is recommended for ecological restorations, and in any case, it is recommended to improve soil conditions before initiating the restoration.