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Esseen, Per-Anders
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Publications (10 of 27) Show all publications
Grafström, A., Ekström, M., Jonsson, B. G., Esseen, P.-A. & Ståhl, G. (2019). On combining independent probability samples. Survey Methodology, 45(2), 349-364
Open this publication in new window or tab >>On combining independent probability samples
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2019 (English)In: Survey Methodology, ISSN 0714-0045, E-ISSN 1492-0921, Vol. 45, no 2, p. 349-364Article in journal (Refereed) Published
Abstract [en]

Merging available sources of information is becoming increasingly important for improving estimates of population characteristics in a variety of fields. In presence of several independent probability samples from a finite population we investigate options for a combined estimator of the population total, based on either a linear combination of the separate estimators or on the combined sample approach. A linear combination estimator based on estimated variances can be biased as the separate estimators of the population total can be highly correlated to their respective variance estimators. We illustrate the possibility to use the combined sample to estimate the variances of the separate estimators, which results in general pooled variance estimators. These pooled variance estimators use all available information and have potential to significantly reduce bias of a linear combination of separate estimators.

Place, publisher, year, edition, pages
Statistics Canada, 2019
Keywords
Horvitz-Thompson estimator, Inclusion probabilities, Linear combination estimator, Variance estimation
National Category
Probability Theory and Statistics
Identifiers
urn:nbn:se:umu:diva-161592 (URN)000473107900009 ()
Funder
Swedish Research Council, 340-2013-5076
Available from: 2019-07-22 Created: 2019-07-22 Last updated: 2019-07-22Bibliographically approved
Esseen, P.-A. (2019). Strong influence of landscape structure on hair lichens in boreal forest canopies. Canadian Journal of Forest Research, 48(8), 994-1003
Open this publication in new window or tab >>Strong influence of landscape structure on hair lichens in boreal forest canopies
2019 (English)In: Canadian Journal of Forest Research, ISSN 0045-5067, E-ISSN 1208-6037, Vol. 48, no 8, p. 994-1003Article in journal (Refereed) Published
Abstract [en]

This study examines how island size, isolation, and orientation influence epiphytic hair lichens in old-growth boreal spruce forests within a naturally heterogeneous landscape with approximately 1000 forest islands distributed in open wetland matrix. Forest structure, length of Alectoria sarmentosa (Ach.) Ach., Bryoria spp., and Usnea spp., and mass of Alectoria in the lower canopy (0–5 m) of Picea abies (L.) Karst. were quantified in 30 islands (0.11–10.9 ha). Length and mass of Alectoria were also studied in 25 edges with different orientation and fetch (wind exposure). Island area had a strong positive effect on length of Alectoria but a minor effect on Bryoria and Usnea. Edge orientation influenced length and mass of Alectoria, with the strongest reduction in wind-exposed western edges, whereas fetch size had no effect. Edge influence on microclimate drives hair lichen response to landscape configuration. The gradient from Bryoria in small islands to Alectoria in large islands is caused by the same mechanisms that influence vertical canopy gradients in large homogeneous stands, with Bryoria in the upper canopy and Alectoria in the lower canopy. Genus-specific, sun-screening pigments contribute to this niche differentiation, but thallus fragmentation by wind and water storage are also important. Our findings imply that lichen conservation must consider the spatial structure of the landscape.

Place, publisher, year, edition, pages
Canadian Science Publishing, 2019
Keywords
edge influence, epiphytic lichen, island area, isolation, landscape configuration
National Category
Forest Science
Identifiers
urn:nbn:se:umu:diva-161979 (URN)10.1139/cjfr-2019-0100 (DOI)000476833200015 ()
Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-20Bibliographically approved
Ekström, M., Esseen, P.-A., Westerlund, B., Grafström, A., Jonsson, B. G. & Ståhl, G. (2018). Logistic regression for clustered data from environmental monitoring programs. Ecological Informatics, 43, 165-173
Open this publication in new window or tab >>Logistic regression for clustered data from environmental monitoring programs
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2018 (English)In: Ecological Informatics, ISSN 1574-9541, E-ISSN 1878-0512, Vol. 43, p. 165-173Article in journal (Refereed) Published
Abstract [en]

Large-scale surveys, such as national forest inventories and vegetation monitoring programs, usually have complex sampling designs that include geographical stratification and units organized in clusters. When models are developed using data from such programs, a key question is whether or not to utilize design information when analyzing the relationship between a response variable and a set of covariates. Standard statistical regression methods often fail to account for complex sampling designs, which may lead to severely biased estimators of model coefficients. Furthermore, ignoring that data are spatially correlated within clusters may underestimate the standard errors of regression coefficient estimates, with a risk for drawing wrong conclusions. We first review general approaches that account for complex sampling designs, e.g. methods using probability weighting, and stress the need to explore the effects of the sampling design when applying logistic regression models. We then use Monte Carlo simulation to compare the performance of the standard logistic regression model with two approaches to model correlated binary responses, i.e. cluster-specific and population-averaged logistic regression models. As an example, we analyze the occurrence of epiphytic hair lichens in the genus Bryoria; an indicator of forest ecosystem integrity. Based on data from the National Forest Inventory (NFI) for the period 1993-2014 we generated a data set on hair lichen occurrence on > 100,000 Picea abies trees distributed throughout Sweden. The NFI data included ten covariates representing forest structure and climate variables potentially affecting lichen occurrence. Our analyses show the importance of taking complex sampling designs and correlated binary responses into account in logistic regression modeling to avoid the risk of obtaining notably biased parameter estimators and standard errors, and erroneous interpretations about factors affecting e.g. hair lichen occurrence. We recommend comparisons of unweighted and weighted logistic regression analyses as an essential step in development of models based on data from large-scale surveys.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Bryoria, Cluster-specific model, Complex sampling design, Correlated data, Logistic regression, tional forest inventory, Population-averaged model
National Category
Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-145390 (URN)10.1016/j.ecoinf.2017.10.006 (DOI)000424721000015 ()
Available from: 2018-03-01 Created: 2018-03-01 Last updated: 2018-06-09Bibliographically approved
Eriksson, A., Gauslaa, Y., Palmqvist, K., Ekström, M. & Esseen, P.-A. (2018). Morphology drives water storage traits in the globally widespreadlichen genus Usnea. Fungal ecology, 35, 51-61
Open this publication in new window or tab >>Morphology drives water storage traits in the globally widespreadlichen genus Usnea
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2018 (English)In: Fungal ecology, ISSN 1754-5048, E-ISSN 1878-0083, Vol. 35, p. 51-61Article in journal (Refereed) Published
Abstract [en]

Links between lichen morphology, internal/external water storage and distribution patterns are poorly known. We compared mass- (WC, % H2O) and area-based (WHC, mg H2O cm−2) hydration traits in seven pendent or shrubby Usnea species from oceanic to continental climates. All species held more external than internal water. Internal WHC and WC increased with specific thallus mass (STM, mg cm−2), while external WC decreased. Shrubby species had higher STM and total WHC than pendent ones. The continental Usnea hirta (shrubby) had the highest total and external storage; the suboceanic Usnea longissima (pendent) had the lowest internal storage. Morphology drives hydration traits and explains distributions of some Usnea species, but such traits did not distinguish oceanic from widespread species. Shrubby species maximize water storage and thus prolong hydration after rainfall events and/or hydration by dew. The low internal WHC in pendent species is likely an adaptation to frequent hydration in humid air.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Epiphytic lichens, Functional traits, Specific thallus mass, Water-holding capacity, Water content
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-151932 (URN)10.1016/j.funeco.2018.06.007 (DOI)000444930900006 ()2-s2.0-85050654829 (Scopus ID)
Funder
Swedish Research Council Formas, 2016-00553
Available from: 2018-09-18 Created: 2018-09-18 Last updated: 2018-10-05Bibliographically approved
Esseen, P.-A., Rönnqvist, M., Gauslaa, Y. & Coxson, D. S. (2017). Externally held water: a key factor for hair lichens in boreal forest canopies. Fungal ecology, 30, 29-38
Open this publication in new window or tab >>Externally held water: a key factor for hair lichens in boreal forest canopies
2017 (English)In: Fungal ecology, ISSN 1754-5048, E-ISSN 1878-0083, Vol. 30, p. 29-38Article in journal (Refereed) Published
Abstract [en]

Lichens hold water inside (internal pool) and outside their body (external pool). Yet, external pool size is not known in hair lichens dominating boreal forest canopies. Here we quantify morphological traits and internal/external water in two widespread Bryoria species along Picea abies canopy-height gradients: Bryoria fuscescens at 5-20 m and Bryoria capillaris at 15-20 m. Dry mass and specific thallus mass (STM) of intact B. fuscescens increased with height, while STM of individual branches did not. Maximum water holding capacity (mg H2O cm-2) increased with height, but did not differ between the species. Bryoria had much larger external (79-84% of total) than internal water pools, trapping water by dense clusters of thin, overlapping branches. They thus increase water storage in boreal forest canopies and influence hydrology. High external water storage extends hydration periods and improves lichen performance in upper canopies, and thereby contributes to the success of these hair lichens. 

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Bryoria, Epiphytic lichens, Specific thallus mass, Morphology, Vertical zonation, Water content, Water holding capacity
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-143574 (URN)10.1016/j.funeco.2017.08.003 (DOI)000417009400004 ()
Available from: 2018-01-04 Created: 2018-01-04 Last updated: 2018-06-09Bibliographically approved
Ståhl, G., Ekström, M., Dahlgren, J., Esseen, P.-A., Grafström, A. & Jonsson, B.-G. (2017). Informative plot sizes in presence-absence sampling of forest floor vegetation. Methods in Ecology and Evolution, 8(10), 1284-1291
Open this publication in new window or tab >>Informative plot sizes in presence-absence sampling of forest floor vegetation
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2017 (English)In: Methods in Ecology and Evolution, ISSN 2041-210X, E-ISSN 2041-210X, Vol. 8, no 10, p. 1284-1291Article in journal (Refereed) Published
Abstract [en]

1. Plant communities are attracting increased interest in connection with forest and landscape inventories due to society’s interest in ecosystem services. However, the acquisition of accurate information about plant communities poses several methodological challenges. Here, we investigate the use of presence-absence sampling with the aim to monitor state and change in plant density. We study what plot sizes are informative, i.e. the estimators should have as high precision as possible.

2. Plant occurrences were modelled through different Poisson processes and tests were developed for assessing the plausibility of the model assumptions. Optimum plot sizes were determined by minimizing the variance of the estimators. While state estimators of similar kind as ours have been proposed in previous studies, our tests and change estimation procedures are new.

3. We found that the most informative plot size for state estimation is 1.6 divided by the plant density, i.e. if the true density is 1 plant per square metre the optimum plot size is 1.6 square metres. This is in accordance with previous findings. More importantly, the most informative plot size for change estimation was smaller and depended on the change patterns. We provide theoretical results as well as some empirical results based on data from the Swedish National Forest Inventory.

4. Use of too small or too large plots resulted in poor precision of the density (and density change) estimators. As a consequence, a range of different plot sizes would be required for jointly monitoring both common and rareplants using presence-absence sampling in monitoring programmes.

Place, publisher, year, edition, pages
Hoboken: British Ecological Society, 2017
Keywords
density, intensity, optimum plot size, plant monitoring, point pattern, Poisson model, sample plots, vegetation change, vegetation survey
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-141551 (URN)10.1111/2041-210X.12749 (DOI)000412858600012 ()
Projects
Statistical methods for ecological research on data from national monitoring programs. Funded by the Swedish Research Council. Grant Number 340-2013-5076.
Funder
Swedish Research Council, 340-2013-5076
Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2019-03-06Bibliographically approved
Esseen, P.-A., Ekström, M., Westerlund, B., Palmqvist, K., Jonsson, B. G., Grafström, A. & Ståhl, G. (2016). Broad-scale distribution of epiphytic hair lichens correlates more with climate and nitrogen deposition than with forest structure. Canadian Journal of Forest Research, 46(11), 1348-1358
Open this publication in new window or tab >>Broad-scale distribution of epiphytic hair lichens correlates more with climate and nitrogen deposition than with forest structure
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2016 (English)In: Canadian Journal of Forest Research, ISSN 0045-5067, E-ISSN 1208-6037, Vol. 46, no 11, p. 1348-1358Article in journal (Refereed) Published
Abstract [en]

Hair lichens are strongly influenced by forest structure at local scales, but their broad-scale distributions are less understood. We compared the occurrence and length of Alectoria sarmentosa (Ach.) Ach., Bryoria spp., and Usnea spp. in the lower canopy of > 5000 Picea abies (L.) Karst. trees within the National Forest Inventory across all productive forest in Sweden. We used logistic regression to analyse how climate, nitrogen deposition, and forest variables influence lichen occurrence. Distributions overlapped, but the distribution of Bryoria was more northern and that of Usnea was more southern, with Alectoria's distribution being intermediate. Lichen length increased towards northern regions, indicating better conditions for biomass accumulation. Logistic regression models had the highest pseudo R-2 value for Bryoria, followed by Alectoria. Temperature and nitrogen deposition had higher explanatory power than precipitation and forest variables. Multiple logistic regressions suggest that lichen genera respond differently to increases in several variables. Warming decreased the odds for Bryoria occurrence at all temperatures. Corresponding odds for Alectoria and Usnea decreased in warmer climates, but in colder climates, they increased. Nitrogen addition decreased the odds for Alectoria and Usnea occurrence under high deposition, but under low deposition, the odds increased. Our analyses suggest major shifts in the broad-scale distribution of hair lichens with changes in climate, nitrogen deposition, and forest management.

Place, publisher, year, edition, pages
NRC Research Press, 2016
Keywords
climate change, epiphytic lichens, forest structure, nitrogen deposition, temperature
National Category
Forest Science
Identifiers
urn:nbn:se:umu:diva-129029 (URN)10.1139/cjfr-2016-0113 (DOI)000386675600012 ()
Projects
Statistical methods for ecological research on data from national monitoring programs. Funded by the Swedish Research Council. Grant Number 340-2013-5076.
Funder
Swedish Research Council, 340-2013-5076
Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2018-06-09Bibliographically approved
Jonsson, B. G., Ekström, M., Esseen, P.-A., Grafström, A., Ståhl, G. & Westerlund, B. (2016). Dead wood availability in managed Swedish forests: policy outcomes and implications for biodiversity. Forest Ecology and Management, 376, 174-182
Open this publication in new window or tab >>Dead wood availability in managed Swedish forests: policy outcomes and implications for biodiversity
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2016 (English)In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 376, p. 174-182Article in journal (Refereed) Published
Abstract [en]

Dead wood is a critical resource for forest biodiversity and widely used as an indicator for sustainable forest management. Based on data from the Swedish National Forest Inventory we provide baseline information and analyze trends in volume and distribution of dead wood in Swedish managed forests during 15 years. The data are based on ≈30,000 sample plots inventoried during three periods (1994–1998; 2003–2007 and 2008–2012). The forest policy has since 1994 emphasized the need to increase the amount of dead wood in Swedish forests. The average volume of dead wood in Sweden has increased by 25% (from 6.1 to 7.6 m3 ha−1) since the mid-1990s, but patterns differed among regions and tree species. The volume of conifer dead wood (mainly from Picea abies) has increased in the southern part of the country, but remained stable or decreased in the northern part. Heterogeneity of dead wood types was low in terms of species, diameter and decay classes, potentially negatively impacting on biodiversity. Overall, we found only minor effects of the current forest policy since most of the increase can be attributed to storm events creating a pulse of hard dead wood. Therefore, the implementation of established policy instruments (e.g. legislation and voluntary certification schemes) need to be revisited. In addition to the retention of dead trees during forestry operations, policy makers should consider calling for more large-scale targeted creation of dead trees and management methods with longer rotation cycles.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
National Forest Inventory, Saproxylic species, Environmental objectives, Natura 2000, Boreal forest, Western Taiga
National Category
Forest Science
Identifiers
urn:nbn:se:umu:diva-122291 (URN)10.1016/j.foreco.2016.06.017 (DOI)000381233500018 ()
Projects
Statistical methods for ecological research on data from national monitoring programs. Funded by the Swedish Research Council. Grant Number 340-2013-5076.
Funder
Swedish Research Council, 340-2013-5076
Available from: 2016-06-16 Created: 2016-06-16 Last updated: 2018-06-07Bibliographically approved
Esseen, P.-A., Hedstrom Ringvall, A., Harper, K. A., Christensen, P. & Svensson, J. (2016). Factors driving structure of natural and anthropogenic forest edges from temperate to boreal ecosystems. Journal of Vegetation Science, 27(3), 482-492
Open this publication in new window or tab >>Factors driving structure of natural and anthropogenic forest edges from temperate to boreal ecosystems
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2016 (English)In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 27, no 3, p. 482-492Article in journal (Refereed) Published
Abstract [en]

Questions What factors control broad-scale variation in edge length and three-dimensional boundary structure for a large region extending across two biomes? What is the difference in structure between natural and anthropogenic edges? Location Temperate and boreal forests across all of Sweden, spanning latitudes 55-69 degrees N. MethodsWe sampled more than 2000 forest edges using line intersect sampling in a monitoring programme (National Inventory of Landscapes in Sweden). We compared edge length, ecosystem attributes (width of adjacent ecosystem, canopy cover, canopy height, patch contrast in canopy height, forest type) and boundary attributes (profile, abruptness, shape) of natural edges (lakeshore, wetland) with anthropogenic edges (clear-cut, agricultural, linear disturbance) in five regions. Results Anthropogenic edges were nearly twice as abundant as natural edges. Length of anthropogenic edges was largest in southern regions, while the abundance of natural edges increased towards the north. Edge types displayed unique spectrums of boundary structures, but abrupt edges dominated, constituting 72% of edge length. Anthropogenic edges were more abrupt than natural edges; wetland edges had the most gradual and sinuous boundaries. Canopy cover, canopy height, patch contrast and forest type depended on region, whereas overall boundary abruptness and shape showed no regional pattern. Patch contrast was related to temperature sum (degree days5 degrees C), suggesting that regional variability can be predicted from climate-controlled forest productivity. Boundary abruptness was coupled with the underlying environmental gradient, land use and forest type, with higher variability in deciduous than in conifer forest. Conclusions Edge origin, land use, climate and tree species are main drivers of broad-scale variability in forest edge structure. Our findings have important implications for developing ecological theory that can explain and predict how different factors affect forest edge structure, and help to understand how land use and climate change affect biodiversity at forest edges.

Keywords
Agricultural edge, Boundary abruptness, Clear-cut edge, Climate, Edge influence, Edge length, Lakeshore edge, Land use, Linear disturbance edge, Patch contrast, Tree species, Wetland edge
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-121566 (URN)10.1111/jvs.12387 (DOI)000375147500007 ()
Available from: 2016-06-30 Created: 2016-06-03 Last updated: 2018-06-07Bibliographically approved
Harper, K. A., Macdonald, S. E., Mayerhofer, M. S., Biswas, S. R., Esseen, P.-A., Hylander, K., . . . Bergeron, Y. (2015). Edge influence on vegetation at natural and anthropogenic edges of boreal forests in Canada and Fennoscandia. Journal of Ecology, 103(3), 550-562
Open this publication in new window or tab >>Edge influence on vegetation at natural and anthropogenic edges of boreal forests in Canada and Fennoscandia
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2015 (English)In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 103, no 3, p. 550-562Article in journal (Refereed) Published
Abstract [en]

Although anthropogenic edges are an important consequence of timber harvesting, edges due to natural disturbances or landscape heterogeneity are also common. Forest edges have been well studied in temperate and tropical forests, but less so in less productive, disturbance-adapted boreal forests. We synthesized data on forest vegetation at edges of boreal forests and compared edge influence among edge types (fire, cut, lake/wetland; old vs. young), forest types (broadleaf vs. coniferous) and geographic regions. Our objectives were to quantify vegetation responses at edges of all types and to compare the strength and extent of edge influence among different types of edges and forests. Research was conducted using the same general sampling design in Alberta, Ontario and Quebec in Canada, and in Sweden and Finland. We conducted a meta-analysis for a variety of response variables including forest structure, deadwood abundance, regeneration, understorey abundance and diversity, and non-vascular plant cover. We also determined the magnitude and distance of edge influence (DEI) using randomization tests. Some edge responses (lower tree basal area, tree canopy and bryophyte cover; more logs; higher regeneration) were significant overall across studies. Edge influence on ground vegetation in boreal forests was generally weak, not very extensive (DEI usually <20m) and decreased with time. We found more extensive edge influence at natural edges, at younger edges and in broadleaf forests. The comparison among regions revealed weaker edge influence in Fennoscandian forests.Synthesis. Edges created by forest harvesting do not appear to have as strong, extensive or persistent influence on vegetation in boreal as in tropical or temperate forested ecosystems. We attribute this apparent resistance to shorter canopy heights, inherent heterogeneity in boreal forests and their adaptation to frequent natural disturbance. Nevertheless, notable differences between forest structure responses to natural (fire) and anthropogenic (cut) edges raise concerns about biodiversity implications of extensive creation of anthropogenic edges. By highlighting universal responses to edge influence in boreal forests that are significant irrespective of edge or forest type, and those which vary by edge type, we provide a context for the conservation of boreal forests.

Keywords
boreal forest, cut edges, edge effects, fire edges, habitat fragmentation, lakeshore edges, meta- alysis, randomization tests, wetland edges
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-103201 (URN)10.1111/1365-2745.12398 (DOI)000353640500003 ()
Available from: 2015-05-26 Created: 2015-05-18 Last updated: 2018-06-07Bibliographically approved
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