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  • Author or Editor: S. Cesaretti x
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Since the early 20th century Patagonian arid steppes have been subjected to overgrazing that led to the degradation of plant communities. We hypothesized that the interplay among grazing history, plant-plant spatial interactions and species traits affects recovery and assemblage of shrub community after short-term abandonment in north-eastern Patagonian arid steppe (Peninsula Valdés, Argentina). We compared six sites (two in grazed pastures, and four in short-term ungrazed pastures, two of which intensively grazed, while the other two low intensity grazed in the past) with regard to: shrub cover percentage (10 × 10 m plots); shrub patch dimension, species richness, and spatial interactions among shrub species depending on patch dimension (patches sampled along transects); species richness and composition, vertical relations among species, and traits related to avoidance strategies and disturbance (1 × 1 m plots sampled along transects). Our results indicated that recovery processes in abandoned pastures act through the increase in shrub patch size, formation of new patches, change in patch composition and richness, and in within-patch relations among shrub species. No significant differences were found between sites subjected to different past grazing intensities. The increase in shrub cover was due to a significant expansion of the dominant shrub Chuquiraga avellanedae. The mechanism of new patch formation and spread was mainly based on facilitative processes acting between the dwarf shrubs, poorly palatable and disliked by wild herbivores, and young individuals of the dominant species emerging from their canopy. As patch size increased, dwarf shrubs were covered by taller ones or grew at the edge of the patch, indicating a phase of competitive exclusion. Plant-plant spatial interactions involved changes in the composition of plant traits linked to avoidance strategies, which were indicators of grazed conditions and of plots with shrub cover lower than 50%, while less need for defence against animal browsing was highlighted in ungrazed pastures and shrub-dominated plots. As the density of herbivores is recognized as the key factor in biodiversity conservation and ecosystem recovery, management plans devoted to conservation of biodiversity and forage resources should work to recreate grazing conditions close to the wild ones or to impose a short-term period of ecosystem rest that allows the plant community to recover.

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The present research deals with the impact of the invasive species Brachypodium genuense in central Apennine meadows. The study compares meadows under different management types (mown versus abandoned). B. genuense spread in the abandoned condition alters the ecological status of the site. It lowers soil temperature, moisture and pH, while it increases soil C/N ratio and litter production. In terms of biotic features, phenological analysis indicated that the abandoned condition is less rich in flowering species and individuals in each analysed date. We observed a less affected temporal niche (during the first phase of B. genuense leaf growth) and two strongly influenced phases (in early spring and in correspondence with phases when B. genuense flowers and has full growth of leaves). Functional trait analysis indicated that species with runners, ability to form patches, and late flowering strategies benefit from B. genuense spread, whereas species marked by storage organs, small size, and early flowering strategies benefit in the mown condition. However, it seems that only low frequency species are heavily threatened, while the others can remain inside the plant community by shelter niche occupation.

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