Tom Gittings

Identifying practical indicators of biodiversity for stand-level management of plantation forests

Identification of valid indicators of biodiversity is a critical need for sustainable forest management. We developed compositional, structural and functional indicators of biodiversity for five taxonomic groups—bryophytes, vascular plants, spiders, hoverflies and birds—using data from 44 Sitka spruce (Picea sitchensis) and ash (Fraxinus excelsior) plantation forests in Ireland. The best structural biodiversity indicator was stand stage, defined using a multivariate classification of forest structure variables. However, biodiversity trends over the forest cycle and between tree species differ among the taxonomic groups studied. Canopy cover was the main structural indicator and affected other structural variables such as cover of lower vegetation layers. Other structural indicators included deadwood and distances to forest edge and to broadleaved woodland. Functional indicators included stand age, site environmental characteristics and management practices. Compositional indicators were limited to more easily identifiable plant and bird species. Our results suggest that the biodiversity of any one of the species groups we surveyed cannot act as a surrogate for all of the other species groups. However, certain subgroups, such as forest bryophytes and saproxylic hoverflies, may be able to act as surrogates for each other. The indicators we have identified should be used together to identify stands of potentially high biodiversity or to evaluate the biodiversity effects of silvicultural management practices. They are readily assessed by non-specialists, ecologically meaningful and applicable over a broad area with similar climate conditions and silvicultural systems. The approach we have used to develop biodiversity indicators, including stand structural types, is widely relevant and can enhance sustainable forest management of plantations.

A review of competition in north temperate dung beetle communities

Abstract. 1. Studies of north temperate dung beetle communities frequently invoke competition as an influential ecological process. In this review, the evidence for competition in north temperate dung beetle communities is evaluated and the role of competition as a factor affecting community structure is assessed.

Effects of growth stage and tree species composition on breeding bird assemblages of plantation forests

Capsule Bird species assemblages are strongly dependent on growth stage and forest structure, but do not appear to be greatly affected by tree species composition. Aims To investigate changes in bird species composition of plantation forests in relation to crop tree species and forest growth stage. Methods We surveyed populations of birds in 44 plantation forests throughout Ireland in the summers of 2001 and 2002. Our study sites represented three combinations of tree species (pure Sitka Spruce Picea sitchensis, pure Ash Fraxinus exelsior, and Sitka Spruce/Ash mixed at inter-stand level) at five ages (4–8 years, 9–17 years, 23–29 years, 35–50 years and 50+ years). We used ordinations and indicator species analyses to explain the influence of growth stage and tree species composition on the bird assemblages of these forests. Results Bird species assemblage is dependent on growth stage. Changes in bird species composition over the commercial forest cycle are related to shrub layer and proximity to the forest edge. The bird assemblages of pre-canopy closure forests are typical of open habitats, some of the constituent bird species being of conservation concern within Ireland. As forests mature, these are replaced by commoner, more generalist species. We found no significant effect of tree species on bird species assemblage. Possible reasons for this include the relatively narrow range of tree species mixtures studied, and the paucity of forest specialist birds in Ireland. Conclusions Forest management for bird diversity in Ireland should promote the shrub layer in and around forest plantations, and ensure that new afforestation does not take place in areas with diverse communities of open-habitat birds. Opportunities for Irish forest plantations to provide habitat for bird forest specialists may be limited.

Spatial and temporal variation in species composition of dung beetle assemblages in southern Ireland

Abstract. 1. This study attempts to identify the main community characteristics that contribute to variability in dung beetle assemblage composition and structure across a range of spatial and temporal scales.

Aphodius dung beetle assemblage stability at different spatial and temporal scales

Abstract The stability of north temperate Aphodius assemblages was analysed at four spatial scales: geographical, regional, local and between-field and three temporal scales: inter-annual, seasonal and between-day. Greatest variability in assemblage composition occurred at the geographical scale. The similar level of variability at the regional, local and between-field spatial scales and the inter-annual temporal scale, inferred some degree of spatio-temporal stability at these scales. DCA analyses indicated that assemblage composition was as variable at the smaller between-field scale as at the regional scale. The marked seasonal variability in assemblage structure over the year exceeded variability from one year to the next. At the daily scale, species abundances within a field displayed high variability, but there was relatively little variability in assemblage structure.

The importance of non‐crop vegetation for bird diversity in Sitka spruce plantations in Ireland

Capsule Open spaces and areas dominated by broadleaved trees make an important contribution to the bird diversity of conifer plantations.

Implications of afforestation for bird communities: the importance of preceding land-use type

Afforestation of open habitats is one of the principal land-use changes underway in Europe and elsewhere in the world at present, and it can have a considerable impact on local biodiversity. The sustainable expansion of global forest plantations requires an understanding of the factors that determine the ecological impacts of afforestation. This study set out to determine the importance of preceding land-use type in determining the outcomes of afforestation for bird communities. Paired comparisons of 5-year-old exotic conifer plantations and matching non-forested sites were studied in areas of low (peatland), intermediate (wet grassland) and high (improved grassland) management intensity. Afforestation resulted in an overall increase in total bird density in all three habitat types. The effects of forest planting on bird conservation were found to be positively related to prior management intensity at the site. The density of bird species of conservation concern increased in response to the planting of intensively managed grassland sites, but decreased in response to afforestation of peatlands and of grasslands under intermediate management intensity. This study shows that plantation forests can, in some contexts, offer opportunities for bird conservation, and the findings highlight the trade-offs that are an integral part of land-use change. Therefore, where afforestation planning includes consideration of its impact on bird communities, planting should take place predominantly on sites of low biodiversity value, such as agriculturally improved grasslands. Furthermore, the preservation of sites of high conservation value within areas of afforestation would confer advantages on bird communities.

Factors affecting the bird diversity of planted and semi-natural oak forests in Ireland

Capsule In Ireland, which has relatively low diversity of bird species, commercially mature plantation oak forests (aged 72–151 years old) have similar bird diversity to typical semi-natural oak woodlands, and higher bird diversity than over-browsed semi-natural oak woodland, with bird diversity related to habitat complexity. Aims To investigate whether oak plantations can support comparable bird assemblages to semi-natural oak woodlands, and to assess if high levels of ungulate browsing and grazing impact on the quality of semi-natural oak woodland habitat for birds. Methods Bird and vegetation surveys were conducted in commercially mature oak plantations (n = 4), semi-natural oak woodlands (n = 10) and intensively browsed semi-natural oak woodland (n = 4). Species richness, total bird density, warbler density and density of parids were compared between oak forest types. Variation in bird communities between sites was investigated using ordination, and relationships between bird and vegetation metrics were assessed using general linear models. Results Bird diversity in plantation oak and the semi-natural forests subject to low levels of ungulate browsing, was similar, with no difference in species richness, total bird density or density of warbler and density of parids. However, browsed semi-natural oak woods had lower species richness than either of the other two study site types, and lower density of warblers than oak plantations. These observed differences in bird communities appear to be a result of browsing mediated differences in habitat complexity between the forest types. Conclusions Plantation forests of native tree species may support comparable bird communities to semi-natural woodlands in areas that lack forest specialists. Bird diversity in woodlands subject to high levels of browsing and grazing is likely to be limited, unless ungulate populations and their access to these woodlands are managed to promote the development of a more complex understorey.

Can Malaise traps be used to sample spiders for biodiversity assessment

Malaise traps are typically used to sample a range of flying insect groups; however non-target taxa such as spiders may also be collected in large numbers. In this study, spiders were sampled in peatlands and wet grasslands and catches in Malaise and pitfall traps were compared in order to determine the adequacy of Malaise traps for use in spider biodiversity assessment. Overall, the number of species and individuals caught in Malaise and pitfall traps were comparable, although more species were sampled in Malaise traps in locations with a greater structural diversity of the vegetation. The spider fauna sampled by the Malaise traps differed from that of the pitfall traps, but both methods consistently separated the species assemblages by biotope. These results demonstrate that Malaise traps are effective at sampling spiders and indicate that they can be used in biodiversity assessment. In addition the complementary species sampled by each method mean that employing both techniques will be useful where a full inventory of the species is required. The authors do not suggest that Malaise traps should be used solely to sample spiders; however, if traps are set to collect insects, identification of the spiders sampled may reduce the need to employ additional sampling techniques.