Magne Sætersdal

How to maximize biological diversity in nature reserve selection: Vascular plants and breeding birds in deciduous woodlands, western Norway

Abstract One aim in nature reserve selection is to identify a set of reserves that includes all species of interest. Three possible quantitative methods to obtain this goal are presented here, using plant and bird lists from 60 deciduous woods in western Norway. The first method concentrates on the number of so-called endemic species (i.e. those present at only one site). The second repeatedly selects a chosen number of sites at random, aiming at maximising the number of species for that number of sites. The third procedure finds the smallest set of sites that will include each species at least once. Seventy-five per cent of the total area surveyed is needed to preserve all plant species, but only 20% to ensure total representation of the bird species. The existing reserve system in the area (12 woods), selected by traditional non-quantitative procedures has not maximised biological diversity because the sites, to a large extent, duplicate each other. Results from the three methods are discussed and compared with related broad-scale studies in Australia.

Effects on avian diversity of introducing spruce Picea spp. plantations in the native pine Pinus sylvestris forests of western Norway

Abstract We compared diversity of birds in 35 study plots of equal size (58 ha) and productivity in western Norway, ranging from pure native pine Pinus sylvestris forests ( n = 7), through different mosaics of native pine forests and spruce Picea spp. plantations ( n = 21), to pure spruce plantations ( n = 7). Diversity was evaluated by means of species richness, diversity indices, relative abundance curves and rarefaction. The diversity indices appeared to be less suitable for our purpose. Species richness was higher in pine forest than in spruce forest. However, a peak in species richness was found in mosaic forest. For pooled samples (408 ha), 11 bird species recorded in pine forest were not found in spruce forest, seven species were found in spruce forest but not in pine forest, and seven species were confined to the medium mosaics of pine and spruce forest (on average 56% pine and 44% spruce). We argue that, when mixing two habitat types A and B, the ratio of these habitats that maximize avian diversity depends on the ratio of species confined to habitat A and B, as well as the number of species favoured by the mixture of A and B. Existing spruce plantations (13% of the area) in native pine forests of western Norway have reduced the diversity of birds locally, but increased the diversity of birds on the landscape and regional scale.

Assessing the representativeness of nature reserves using multivariate analysis: Vascular plants and breeding birds in deciduous forests, western Norway

Multivariate analyses were used as a tool for delimiting representative types of 60 deciduous woods in western Norway based on vascular plants and breeding birds. The relationships between the species assemblages and 47 environmental and other explanatory variables were investigated Environmental variables considered included climate, area, habitat features, landscape attributes, and disturbances.Two-way-indicator-species-analysis was applied to the data and revealed four representative types of deciduous forests based on the plants, but only one representative type based on the bird data. Detrended correspondence analysis, canonical correspondence analysis, and canonical variates analysis suggested that the major gradients of floristic variation are primarily related to climatic variables such as July temperature and humidity, reflecting the strong west-east gradient in oceanicity in western Norway.One of the four representative plant groups is not represented in the existing reserve system, showing that additional reserves are needed to ensure a fully representative system. The differences between representativeness based on plants and birds are discussed

Abundance of two threatened woodpecker species in relation to the proportion of spruce plantations in native pine forests of western Norway

In a comparative study we investigated woodpecker abundance in forest landscapes with different proportion of native pine forest and spruce plantations in western Norway. In 100 circular study plots of 100 ha each we recorded 38 white-backed –Dendrocopos leucotos, 22 grey-headed –Picus canus, 13 great spotted –Dendrocopos major, 6 green –Picus viridis, and 2 lesser spotted –Dendrocopos minor woodpeckers in the breeding season. The mean number of recorded woodpecker species peaked at 20–40% spruce plantations. The two most common species in the study, the white-backed and the grey-headed woodpeckers are both Red-listed species in Norway and among the rarest woodpeckers in Europe. The white-backed woodpecker preferred plots with higher than average proportions of standing dead trees and deciduous trees, and low proportions of spruce plantations in the plots. The grey-headed woodpecker preferred plots in the western (coastal) parts of the study area with presence of large aspen Populus tremula trees. Logistic regression models did not reveal any clear threshold values with respect to proportion of spruce plantations in plots, although both woodpecker species were extremely rare in plots with >60% spruce plantations. We recommend spruce plantations to be kept at moderate levels to ensure viable populations of woodpeckers in western Norway.

Observer and relocation errors matter in resurveys of historical vegetation plots

Aim: Revisits of non-permanent, relocatable plots first surveyed several decades ago offer a direct way to observe vegetation change and form a unique and increasingly used source of information for global change research. Despite the important insights that can be obtained from resurveying these quasi-permanent vegetation plots, their use is prone to both observer and relocation errors. Studying the combined effects of both error types is important since they will play out together in practice and it is yet unknown to what extent observed vegetation changes are influenced by these errors. Methods: We designed a study that mimicked all steps in a resurvey study and that allowed determination of the magnitude of observer errors only vs the joint observer and relocation errors. Communities of vascular plants growing in the understorey of temperate forests were selected as study system. Ten regions in Europe were covered to explore generality across contexts and 50 observers were involved, which deliberately differed in their experience in making vegetation records. Results: The mean geographic distance between plots in the observer+relocation error data set was 24m. The mean relative difference in species richness in the observer error and the observer+relocation data set was 15% and 21%, respectively. The mean pseudo-turnover between the five records at a quasi-permanent plot location was on average 0.21 and 0.35 for the observer error and observer+relocation error data sets, respectively. More detailed analyses of the compositional variation showed that the nestedness and turnover components were of equal importance in the observer data set, whereas turnover was much more important than nestedness in the observer+relocation data set. Interestingly, the differences between the observer and the observer+relocation data sets largely disappeared when looking at temporal change: both the changes in species richness and species composition over time were very similar in these data sets. Conclusions: Our results demonstrate that observer and relocation errors are non-negligible when resurveying quasi-permanent plots. A careful interpretation of the results of resurvey studies is warranted, especially when changes are assessed based on a low number of plots. We conclude by listing measures that should be taken to maximally increase the precision and the strength of the inferences drawn from vegetation resurveys.