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Observer and relocation errors matter in resurveys of historical vegetation plots

(2018) JOURNAL OF VEGETATION SCIENCE. 29(5). p.812-823
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Abstract
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.
Keywords
legacy studies, nestedness, pseudo-turnover, species richness, temperate forest, true turnover, understorey vegetation, PLANT-COMMUNITIES, ENVIRONMENTAL-CHANGE, TEMPERATE FORESTS, SPECIES RICHNESS, CLIMATE-CHANGE, GRASSLANDS, DRIVERS, ECOLOGY, BIODIVERSITY, DIVERSITY

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Chicago
Verheyen, Kris, Martin Bažány, Ewa Chećko, Markéta Chudomelová, Déborah Closset-Kopp, Patryk Czortek, Guillaume Decocq, et al. 2018. “Observer and Relocation Errors Matter in Resurveys of Historical Vegetation Plots.” Journal of Vegetation Science 29 (5): 812–823.
APA
Verheyen, Kris, Bažány, M., Chećko, E., Chudomelová, M., Closset-Kopp, D., Czortek, P., Decocq, G., et al. (2018). Observer and relocation errors matter in resurveys of historical vegetation plots. JOURNAL OF VEGETATION SCIENCE, 29(5), 812–823.
Vancouver
1.
Verheyen K, Bažány M, Chećko E, Chudomelová M, Closset-Kopp D, Czortek P, et al. Observer and relocation errors matter in resurveys of historical vegetation plots. JOURNAL OF VEGETATION SCIENCE. 2018;29(5):812–23.
MLA
Verheyen, Kris, Martin Bažány, Ewa Chećko, et al. “Observer and Relocation Errors Matter in Resurveys of Historical Vegetation Plots.” JOURNAL OF VEGETATION SCIENCE 29.5 (2018): 812–823. Print.
@article{8578128,
  abstract     = {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.},
  author       = {Verheyen, Kris and Ba\v{z}{\'a}ny, Martin and Che\'{c}ko, Ewa and Chudomelov{\'a}, Mark{\'e}ta and Closset-Kopp, D{\'e}borah and Czortek, Patryk and Decocq, Guillaume and De Frenne, Pieter and De Keersmaeker, Luc and Enr{\'i}quez Garc{\'i}a, Cecilia and Fab\v{s}i\v{c}ov{\'a}, Martina and Grytnes, John-Arvid and Hederov{\'a}, Lucia and H{\'e}dl, Radim and Heinken, Thilo and Schei, Fride H and Horv{\'a}th, Soma and Jaroszewicz, Bogdan and Jermakowicz, Edyta and Klinerov{\'a}, Tereza and Kolk, Jens and Kopeck{\'y}, Martin and Kuras, Iwona and Lenoir, Jonathan and Macek, Martin and M{\'a}li\v{s}, Franti\v{s}ek and Martinessen, Tone C and Naaf, Tobias and Papp, L{\'a}szl{\'o} and Papp-Szak{\'a}ly, {\'A}gnes and Pech, Pawe\unmatched{0142} and Pet\v{r}{\'i}k, Petr and Prach, Jind\v{r}ich and Reczy\'{n}ska, Kamila and Saetersdal, Magne and Spicher, Fabien and Standov{\'a}r, Tibor and \'{S}wierkosz, Krzysztof and Szcz\k{e}\'{s}niak, Ewa and T{\'o}th, Zolt{\'a}n and Ujh{\'a}zy, Karol and Ujh{\'a}zyov{\'a}, Mariana and Vangansbeke, Pieter and Vild, Ond\v{r}ej and Wo\unmatched{0142}kowycki, Dan and Wulf, Monika and Baeten, Lander},
  issn         = {1100-9233},
  journal      = {JOURNAL OF VEGETATION SCIENCE},
  language     = {eng},
  number       = {5},
  pages        = {812--823},
  title        = {Observer and relocation errors matter in resurveys of historical vegetation plots},
  url          = {http://dx.doi.org/10.1111/jvs.12673},
  volume       = {29},
  year         = {2018},
}

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