Question
Shrub encroachment has been confirmed in the past decades all over the world and is currently viewed as a “global process” threatening many grass‐dominated biomes. In southern Europe has ...generally been related to rural depopulation, land‐use changes and grazing abandonment. Nevertheless, in several mountain ranges of the Iberian Peninsula with secular pastoralism and high shrub cover, neither stocking rate nor traditional management has substantially altered in the past decades. Within this framework, to deepen our knowledge of shrub encroachment and to adopt, if necessary, appropriate control measures, we aim to discover: (i) the overall expansion rate in the main grassland–shrub communities; (ii) the course of shrub expansion; and (iii) the consequences for grassland floristic composition, plant diversity and frequency of the main forage functional groups throughout the period of woody expansion.
Location
This study was undertaken in Moncayo Natural Park (Spain), a climate and vegetation crossroads with remarkable presence of four widespread Mediterranean shrubs: Cytisus oromediterraneus, Erinacea anthyllis, Juniperus communis and J. sabina.
Methods
To determine the expansion rates of those shrubs, we examined four distinct and sufficiently separated grazing areas (and different shrub combinations), each with four different stages of shrub cover, over a 6‐year period. To assess changes in vegetation structure between 2008 and 2014 during the different stages of shrub encroachment, we used a paired t‐test comparing 14 parameters related to the diversity, life‐form spectra and abundance of grazing plants. The influence of year, cover category and zone was jointly assessed using a Linear Mixed Model.
Results
For the whole territory, we found an increase in average yearly cover of 1.3% (with high variation between the four species), although at the zone scale (areas with a particular shrub dominance) this increase was significant in only half of them. When the four shrubs occur together, Juniperus species show faster expansion rates than the other two species, although in only a few cases was the increase significant over the 6 years of the study. We found a significant decrease in total plant diversity and a significant increase in dominance between cover categories and years. Looking at the vegetation life‐forms, the increase in chamaephytes and phanerophytes, which include invader shrubs, caused a decrease in therophytes and hemicryptophytes. Finally, grasses and leguminous plants, which constitute the main livestock food intake, showed noticeable reductions, resulting in loss of pastoral value.
Conclusions
Although cessation of grazing has been noted as the main cause of shrub encroachment in Mediterranean grasslands, our results, suggest that encroachment occurs despite the maintenance of stocking rate and livestock management, and leads to a decrease in plant diversity and grassland quality. Focusing on use of the territory and taking into account the prevalence of negative effects after shrub encroachment, additional measures to safeguard ecological and pastoral values in Mediterranean mountain grasslands should be considered, particularly on sites of nature conservation interest with a long grazing history.
Grassland encroachment is a major concern in many mountains and its causes are not yet well known; the current livestock management in the Mediterranean mountains of the Moncayo N.P. (Spain) does not seem enough to stop the process. We analyze the process when several shrub species are involved, its effects on biodiversity and pasture quality, and we propose measures for action.
The ecology and phytosociology of north-western Dinaric heaths of the association Rhododendro hirsuti-Juniperetum alpinae Horvat ex Horvat et al. 1974 nom. corr. prop. as well as the syndynamics and ...synsystematics of heaths in the Dinaric Alps are discussed. While the structure (physiognomy) of these stands is very homogenous and dominated by few species, the flora is heterogeneous, since ecotonal areas, where heaths are most frequently developed, represent a contact zone of elements of different syntaxa. Due to an abrupt reduction in pasture activities strong encroachments of shrubs and trees have become common, which additionally contribute to the floristic heterogeneity of the heaths. Although the identification and circumscription together with synecology and synchorology of heaths in general are more or less easily understood and straightforward, their floristic affinities, in relation to structure homogeneity and syndynamics, are complicated, which led to the proposal of several synsystematic schemes depending on interpretation of the relationship between flora and structure of stands. Dinaric heaths are classified into three classes, Erico-Pinetea, Vaccinio-Piceetea and Festuco-Brometea and a classification scheme is proposed together with nomenclatorial revision of the analyzed heaths with dwarf ericaceous shrubs and Alpine juniper (Juniperus alpina) in the Dinaric Alps
Three taxa have been described to study common junipers of the old world : Juniperus communis L., Juniperus alpina (Suter) Celak and Juniperus hemisphaerica Presl.. Their populations show a large ...variability and morphological criteria (habit and leaf morphology) do not always make it possible to differenciate between them. Proanthocyanic (prodelphinidin) analysis was performed on 450 specimens to better understand biological diversity within this complex. A multi-criteria approach (morphology, geography, ecology and biochemistry) yielded reference profiles for J, communis (23 specimens), J. alpina (18 specimens) and J. hemisphaerica (19 specimens).
These types were used as guidelines for the analysis of populations found in several mountain ranges which showed, depending on the area, introgression processes (J. communis x J. alpina", J. communis x J. hemisphaerica) revealing the originality of either islands (Corsica) or some mountains that function as continental biogeographic islands (Mount Ventoux, Lure Mountain, Apennines). Creeping junipers found in Mediterranean (Sierra Nevada) and peri-Mediterranean (Pyrénées, Massif Central, Mount Ventoux, Southern Alps pro parte) mountains do not generally belong to the «nana» taxon which is restricted to the Alps and some «islands» (Corsica, Apennines). They are fundamentaly linked with the «communis» taxon (sensu stricto) as are Scandinavian and Baltic populations, whatever their habit.
The very high biological diversity of Juniperus aggr. communis L. led the authors to discuss the phylogenetic origins of the main taxa and to propose a new biogeographic scheme for their distribution. Hypotheses are made concerning the ecological consequences of the studied populations’ biochemical structuration on strategies for repelling herbivores.
Trois taxons ont été décrits pour réunir les genévriers communs de l’Ancien Monde : Juniperus communis L., Juniperus alpina (Suter) Celak, Juniperus hemisphaerica Presl. Leurs populations présentent une grande variabilité et les critères morphologiques (port et feuillage) ne permettent pas toujours de les séparer sans ambiguïté. Pour parvenir à une approche plus complète de la diversité biologique au sein de ce groupe, 450 spécimens ont été soumis à l’analyse proanthocyanique (prodelphinidine). Une approche multicritères (morphologique, géographique, écologique et biochimique) a tout d’abord permis de caractériser les profils référentiels de J. communis (23 spécimens), J. alpina (18 spécimens) et J. hemisphaerica (19 spécimens).
Ces types ont ensuite guidé une analyse de populations présentes dans différents massifs montagneux, mettant en évidence selon les secteurs des processus d’introgression (J. communis x J. alpina ; J. communis x J. hemisphaerica ) qui expriment l’originalité des îles (Corse), ou de certains massifs fonctionnant comme des îles biogéographiques continentales (Ventoux, Lure, Apennins). Plus généralement, les genévriers rampants des montagnes méditerranéennes (Sierra Nevada) et péri-méditerranéennes (Pyrénées, Massif Central, Mont Ventoux, Alpes du Sud pro parte ) ne relèvent pas du taxon «nana», restreint aux Alpes et à quelques «îles» (Corse, Apennins) ; ils sont à rattacher fondamentalement au taxon communis (sensu stricto), comme d’ailleurs les populations Scandinaves et baltes, quel qu’en soit le port.
La diversité biologique très marquée de Juniperus aggr. communis L. conduit les auteurs à discuter des origines phylogénétiques des principaux taxons, et à construire un nouveau schéma biogéographique de leur répartition. Des hypothèses sont formulées quant aux conséquences écologiques de la structuration biochimique des populations étudiées sur les tactiques de dissuasion des herbivores.
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