Susanna Lehvävirta

Natural regeneration of trees in urban woodlands

Abstract We studied tree regeneration, a key process for the existence of urban woodlands. We hypothesized that, besides the usual biological factors, anthropogenic ones (fragmentation, wear, pollution etc.) determine the regeneration success of tree species in urban woodlands. To test this hypothesis, within an observational setting, we collected data from 30 urban woodlands in the cities of Helsinki and Vantaa, Finland. We defined the number of living saplings (30‐200cm in height) as an indicator of regeneration success and used regression analysis to test different factors as independent variables. The results showed that different tree species responded differently to urban pressure. The regeneration of Picea abies decreased with increasing fragmentation of the forest landscape, whereas for the other most common (deciduous) species, regeneration increased. Wear, measured as total path area per study site, had a negative effect on regeneration success. An a posteriori examination of the data suggested that coarse woody debris might promote regeneration. We conclude that, although tree regeneration in general is not threatened in urban woodlands in the area we studied, the species composition may gradually change. We discuss some management implications for counteracting the urban pressures on tree regeneration. Nomenclature: Hämet‐Ahti et al. 1992.

Structural elements as barriers against wear in urban woodlands

The effect of structural elements of woodlands (trees, rocks, topography, etc.) on the spatial distribution of wear was studied in 30 sites in the cities of Helsinki and Vantaa, Finland. Discriminant analysis showed that the size of the adjacent human population and structural elements within study sites were important in distinguishing sample plots with a lot of path area (≥6 m2/30 m2) from those with little or no path area (>6 m2/30 m2). The higher the structural elements, the more effectively they functioned as barriers against wear. Thickets of small trees (dbh > 10 cm), topographical elements, and fallen trees seemed most effective, and big trees (dbh ≥ 10 cm) least effective as barriers. It was concluded that natural barriers could be used to limit wear in urban woodlands.

Effects of fragmentation and trampling on carabid beetle assemblages in urban woodlands in Helsinki, Finland

We studied the effects of fragmentation (edge effects and patch size) and trampling (path cover) on carabid beetle assemblages in urban woodland patches in Helsinki, Finland. We expected that (1) open habitat and generalist species would benefit and forest species would suffer from increased woodland fragmentation, and (2) most carabid species would respond negatively to increased levels of trampling. A total of 2088 carabid individuals representing 37 species were collected. A cluster analysis distinguished sites in the interior of large woodland patches, with low or moderate path cover, from the other sites. The other sites did not cluster meaningfully, suggesting increased variation in the carabid fauna with increasing human impact. All species and ecological species-groups decreased with increasing distance from the edge toward the woodland interior and with increasing patch size. This pattern is in accordance with our expectation for open habitat and generalist species but opposite to what we expected for forest species. The reason for these surprising results may be that (1) the species we collected are not true forest interior species, (2) urban woodland edges are optimal habitats for many forest carabids, or (3) edges are actually sub-optimal, and high catches simply reflect increased activity of beetles moving away from the edge. Trampling did not have an overall negative effect on carabids as hypothesized. Species associated with moist forest habitat responded as predicted: they decreased in abundance with increasing path cover. Furthermore, open habitat species decreased with increasing path cover but more straightforward than we had predicted. Model elaboration, by dropping the highly trampled sites from the analyses, suggested that our data of high trampling may be too scarce: the results without these sites were more in accordance with our predictions than with the full dataset.

Effects of habitat edges and trampling on the distribution of ground beetles (Coleoptera, Carabidae) in urban forests

Urban forest patches are generally small with highly contrasting edges bordering non-forest habitat, landscape features that increase with urbanisation. These forest patches are also subject to high human foot traffic resulting in trampling and other user disturbances that affect their quality as habitat for invertebrates. We studied the effects of these factors on carabid beetles in urban forests in the cities of Helsinki (Finland) and Edmonton (Canada). In both cities, the structure of carabid assemblages was affected by trampling intensity and distance to the forest edge. Moderate intensity of trail use was associated with increased beetle captures, especially in Edmonton. The effects on individual species were apparent in Edmonton but harder to demonstrate in Helsinki where forest specialist species may have been largely extirpated already. We suggest that these differences result because there has been a long history of fragmentation of urban forest patches in Helsinki, species loss from such patches is gradual, and understorey vegetation structure constrains human foot traffic in forest patches more in Edmonton than it does in Helsinki.

Quantifying the effects of trampling and habitat edges on forest understory vegetation – A field experiment

We investigated the effects of human trampling on boreal forest understory vegetation on, and off paths from suburban forest edges towards the interiors and on the likelihood of trampling-aided dispersal into the forests for three years by carrying out a trampling experiment. We showed that the vegetation was highly sensitive to trampling. Even low levels of trampling considerably decreased covers of the most abundant species on the paths. Cover decreased between 10 and 30% on paths which had been trampled 35 times, and at least by 50% on those trampled 70-270 times. On-path vegetation cover decreased similarly at forest edges and in the interiors. However, some open habitat plant species that occurred outside the forest patches and at forest edges dispersed into the forests, possibly through the action of trampling. A higher cover percentage of an open habitat species at the forest edge line increased its probability to disperse into the forest interior. The vegetation community on, next to, and away from lightly trampled paths remained the same throughout the trampling experiment. For heavily trampled paths, the community changed drastically on the paths, but stayed relatively similar next to and away from the paths. As boreal vegetation is highly sensitive to the effects of trampling, overall ease of access throughout the forest floor should be restricted to avoid the excessive creation of spontaneous paths. To minimize the effects of trampling, recreational use could be guided to the maintained path network in heavily used areas.

The effects of soil fertility on the abundance of rowan (Sorbus aucuparia L.) in urban forests

The amount of rowan saplings has increased considerably in urban forests in Finland. In this study, we investigated the effects of soil fertility on rowan abundance. Urban forests studied were more fertile than rural forests, and consequently included more rowans than reference areas. The abundance of rowan increased with increasing soil fertility in urban areas, being the highest at forest edges. Furthermore, rowan did not suffer from trampling, and the presence of other trees and saplings did not restrict its growth in relatively open urban forests. We conclude that the effects of urbanization, e.g., edge effects, and factors related to trampling (e.g., dog excrement), may increase forest soil fertility creating favorable conditions for rowan. To control the spread of rowan in urban forests, we recommend that open forest edges with a large number of broad-leaved trees should be avoided, and recreational use of forests should be guided to the maintained path network.

Dealing with varying detection probability, unequal sample sizes and clumped distributions in count data

Temporal variation in the detectability of a species can bias estimates of relative abundance if not handled correctly. For example, when effort varies in space and/or time it becomes necessary to take variation in detectability into account when data are analyzed. We demonstrate the importance of incorporating seasonality into the analysis of data with unequal sample sizes due to lost traps at a particular density of a species. A case study of count data was simulated using a spring-active carabid beetle. Traps were ‘lost’ randomly during high beetle activity in high abundance sites and during low beetle activity in low abundance sites. Five different models were fitted to datasets with different levels of loss. If sample sizes were unequal and a seasonality variable was not included in models that assumed the number of individuals was log-normally distributed, the models severely under- or overestimated the true effect size. Results did not improve when seasonality and number of trapping days were included in these models as offset terms, but only performed well when the response variable was specified as following a negative binomial distribution. Finally, if seasonal variation of a species is unknown, which is often the case, seasonality can be added as a free factor, resulting in well-performing negative binomial models. Based on these results we recommend (a) add sampling effort (number of trapping days in our example) to the models as an offset term, (b) if precise information is available on seasonal variation in detectability of a study object, add seasonality to the models as an offset term; (c) if information on seasonal variation in detectability is inadequate, add seasonality as a free factor; and (d) specify the response variable of count data as following a negative binomial or over-dispersed Poisson distribution.

Coming to Terms with the Concept of Moving Species Threatened by Climate Change - A Systematic Review of the Terminology and Definitions

Intentional moving of species threatened by climate change is actively being discussed as a conservation approach. The debate, empirical studies, and policy development, however, are impeded by an inconsistent articulation of the idea. The discrepancy is demonstrated by the varying use of terms, such as assisted migration, assisted colonisation, or managed relocation, and their multiple definitions. Since this conservation approach is novel, and may for instance lead to legislative changes, it is important to aim for terminological consistency. The objective of this study is to analyse the suitability of terms and definitions used when discussing the moving of organisms as a response to climate change. An extensive literature search and review of the material (868 scientific publications) was conducted for finding hitherto used terms (N = 40) and definitions (N = 75), and these were analysed for their suitability. Based on the findings, it is argued that an appropriate term for a conservation approach relating to aiding the movement of organisms harmed by climate change is assisted migration defined as follows: Assisted migration means safeguarding biological diversity through the translocation of representatives of a species or population harmed by climate change to an area outside the indigenous range of that unit where it would be predicted to move as climate changes, were it not for anthropogenic dispersal barriers or lack of time. The differences between assisted migration and other conservation translocations are also discussed. A wide adoption of the clear and distinctive term and definition provided would allow more focused research on the topic and enable consistent implementation as practitioners could have the same understanding of the concept.

Botanic gardens in the age of climate change

We are facing an unprecedented plant diversity crisis. If current trends in habitat conversion, over-exploitation, alien species invasions, and climate change continue, up to 50% of the world’s vascular plant flora is expected to become threatened with extinction within the twenty-first century (Pitman and Jorgensen 2002; Root et al. 2003; Hahns et al. 2009). Climate change seems to rapidly have become recognized as the primary threat to many plants. In Europe, more than half of the vascular plant flora may become endangered by the year 2080 as a result of climatic changes (Thuiller et al. 2005), and the first unfavourable trends in the threat status of plant species attributable to such changes have already been observed in successive Red List evaluations (Rassi et al. 2010). The Global Strategy for Plant Conservation (GSPC; Secretariat of the CBD 2002) was adopted under the Convention on Biological Diversity (CBD) in 2002 as a policy response to the dire situation of plant life, and an updated version of the strategy up to 2020 was recently approved at the Conference of Parties to the CBD in Nagoya (Convention of Biological Diversity 2010). Botanic gardens of the world, largely through their advocate Botanic Gardens Conservation International (BGCI), were pivotal in the writing and promotion of the GSPC, and have continued in this role in the implementation, follow-up, and further development of the strategy (Secretariat of the CBD 2009). The role of botanic gardens in the creation and mainstreaming of the GSPC has been a manifestation of the fact that these time-honoured institutions have fully adopted a fourth main task—conservation—alongside their traditional responsibilities in research, teaching, and public education in the field of botany. However, the GSPC puts due emphasis also on these traditional tasks through the recognition that successful conservation must be based on a solid knowledge base and that the understanding of the value of plant diversity must also be disseminated to the widest possible audience in order to make a difference

Quantitative tools and simultaneous actions needed for species conservation under climate change–reply to Shoo et al. (2013)

We identify four issues in the decision framework for species conservation management under climate change proposed by Shoo et al. (2013) Clim Chan 119:239–246 and suggest ways to address them. First, binary-decision flow charts require Yes/No answers, which are not appropriate in most conservation decisions. A quantitative framework is preferable and action-guidance should be obtained even when the realistic answer to some questions remains “we simply do not know”. Second, the proposed flow chart imposes an a priori order of precedence and does not explicitly allow simultaneous actions. A workable framework should enable optimal allocation between multiple kinds of conservation efforts and permit complementary actions. Third, the probability of success, co-benefit to non-target species, and cost are unlikely to have a simple, consistent relationship across taxa. These variables need to be assessed case-by-case for each conservation measure and species. Finally, the decision framework disregards the legal, social, and ethical aspects pertaining to decision-making.