Impacts of horse grazing on botanical composition and diversity in different types of heathland

Plant dynamics under horse grazing was studied in a three-year field experiment in heather-gorse shrublands in NW Spain. The experimental design consisted of three vegetation types with four replicates (paddocks): (1) heather (Ericaceae)-dominated (H), (2) gorse (Ulex gallii Planch.)-dominated (G), and (3) co-dominated by gorse and heath-grasses (GG). Each paddock (1.2 ha) was grazed from May to October by two crossbred mature mares (310 ± 52 kg bodyweight), one dry and one lactating (plus foal). Two other paddocks (one in H and one in GG) were excluded from grazing. Plant cover and height were sampled three times a year (spring, summer, and autumn) with a point-quadrat method. Floristic composition and diversity were annually sampled at 10 25-m2 quadrats per paddock. Data were subjected to mixed models for repeated-measures and redundancy analyses. Horse grazing resulted in overall increases (P < 0.001) in heather and herbaceous cover (from 13% to 27%, and from 16% to 23%, respectively), and decreases (P < 0.001) in gorse cover and height (from 35% to 17%; from 30 to 25 cm), with scarce differences among vegetation types. Floristic diversity (species richness and Shannon index) increased more over time in grazed than in ungrazed paddocks. Redundancy analyses revealed that grazing effects on plant species assemblages depended on vegetation type, and that plant communities evolved differently between grazing treatments for both abundance and frequency data. Some herbaceous species characteristic of heathlands were favoured by horse grazing. Horse grazing reduced gorse dominance in G and GG vegetation, controlling excessive accumulation of combustible material and reducing fire risk, and promoted the presence of species of conservation interest, so it offers a promising management tool for the restoration of heathlands and their biodiversity.

Candidate insect vectors of apple proliferation in Northwest Spain

The apple proliferation (AP) disease is spread mostly by two psyllids. Each species plays a predominant role as AP vector that changes regionally. Thus, there is an urgent need to identify the AP vectors in each region where the disease is present. This research aimed at identifying the psyllid community in apple orchards from Asturias (NW Spain) and studying their possible role in AP transmission. Yellow sticky traps were used to monitor psyllid community in five cider-apple orchards during 2 years. 3678 individuals belonging to 22 species were identified. We confirmed the presence of the two known vectors, Cacopsylla picta and Cacopsylla melanoneura, although they occurred in relatively low numbers (2.1 and 0.7 % of total catches, respectively). Most collected psyllids are not supposed to use apple as host, and their occurrence is likely favoured by landscape structure and an insect-friendly management. Phytoplasma detection was performed by squash-capture real-time PCR. The pathogen was detected in six species (Cacopsylla crataegi, Cacopsylla mali, Ctenarytaina spatulata, Ctenarytaina eucalypti and the two known AP vectors). Based on abundance and AP-detection rate C. picta is likely the main species spreading AP in our region. However, the low density of the known vectors does not match the widespread and high tree damage level observed in Asturias. The discovery of other four psyllid species carrying the phytoplasma reveals that our knowledge on the potential vectors is limited and that more research is clearly needed to unravel the role of the psyllid fauna in disease transmission in our orchards.

The occurrence and abundance of two alien eucalypt psyllids in apple orchards

BACKGROUND

The arrival of alien insects is frequently associated with the introduction of alien plants. Two exotic Psylloidea native to Australia [Ctenarytaina eucalypti (Maskell, 1890) and Ctenarytaina spatulata Taylor, 1997] were recorded during a two-year survey in five apple orchards located in Asturias, on the northern coast of Spain. Both species develop on Eucalyptus, but our results suggest that the adults feed also on apple.

RESULTS

The captures of adult Ctenarytaina, particularly C. spatulata (2191 individuals vs 100 of C. eucalypti) were higher than those of the psyllids that develop on apple. Both species occurred in all sites, including those most distant from the eucalypt plantations. Their abundance peaks matched with two crucial periods in the apple tree cycle: sprouting and leaf drop. The hypothesis that the adult eucalypt psyllids feed on apple is supported by the presence of a phytoplasma, the causal agent of the apple proliferation disease, in one specimen of each species. This phytoplasma can be only acquired after feeding on an infected apple tree. This is the first report of continuous captures of these psyllids in apple orchards.

CONCLUSIONS

This study suggests that adults of the two Ctenarytaina species feed in apple orchards in Asturias.

Responses of arthropod fauna assemblages to goat grazing management in northern Spanish heathlands

Changes in arthropod fauna assemblages after different goat grazing treatments (breeds and stocking rates) and responses to grazing cessation were studied in a heath-gorse shrubland located in northern Spain. Three treatments (low grazing pressure and high grazing pressure with Cashmere breed and high grazing pressure with local Celtiberic breed) with three replicates were randomly allocated to nine plots. Fauna data were collected three times per year during 3 grazing yr (2003, 2004, and 2005) and three times during 2007, i.e., 2 yr after grazing cessation. Arthropods were collected by 12 pitfall traps per plot, whereas vegetation cover and height were estimated by 100 random contacts per plot. Arthropod community composition was mostly affected by sampling year during the grazing period (between 2003 and 2005) but also between 2005 and 2007 (after cessation). Species composition differed between treatments, although the differences were not attributed to the stocking rates or to the goat breeds along those periods. Differences between treatments remained constant from 2003 to 2005 and between 2005 and 2007. Heather height explained most of the variance in arthropod species data during the last grazing year (2005), whereas heather cover was the most explanatory environmental variable 2 yr after grazing cessation (2007). Grazing effects still remained on both vegetation and fauna 2 yr after grazing cessation.