Journal of Biogeography
SUPPORTING INFORMATION
Origin of the forest steppe and exceptional grassland diversity in Transylvania
(central-eastern Europe)
Angelica Feurdean, Elena Marinova, Anne B. Nielsen, Johan Liakka, Daniel Veres, Simon M.
Hutchinson, Mihaly Braun, Alida Timar-Gabor, Ciprian Astalos, Volker Mosburgger and
Thomas Hickler
Appendix S2 Description of the REVEALS model and biomization at Lake Stiucii REVEALS
model.
The REVEALS model (Sugita, 2007) is designed to obtain estimates of regional, i.e. within
50–100 km (Hellman et al., 2008) vegetation from pollen data from lakes or bogs. The model
has been empirically validated in Sweden, Switzerland and the USA (Hellman et al., 2008;
Soepboer et al., 2010; Sugita et al., 2010) and has been applied in different parts of Europe
(e.g. Nielsen & Odgaard, 2010; Soepboer et al., 2010; Nielsen et al., 2012; Fyfe et al., 2013;
Marquer et al., 2014; Abraham et al., 2014) including in the Czech Republic (Mazier et al.,
2012), which is the closest to our study region in terms of geography and climate. The
REVEALS model has also been applied in the Tibetan Plateau to reconstruct changes
between steppe forest and meadow/steppe since the late glacial (Wang & Herzschuh, 2011).
Pollen productivity estimates (PPE) and the fall speed (FSP) for each of the 28 pollen types
(15 woody and 13 herb taxa) we employed were obtained from the literature. Most of these
estimates originate from nine study areas in Europe, which were averaged after the removal
of outlying values (Mazier et al., 2012). However, in the case of Quercus, Tilia, Alnus,
Artemisia, Plantago lanceolata, the PPE and FSP were taken from the agricultural
landscapes of the Czech Republic (Abraham & Kozáková, 2012), as this area shares similar
environmental conditions to our study area. Furthermore, in the model test run this produced
closer estimates to the observed vegetation composition, based on the most recent sediment
samples, than the averaged European PPE values (Table 1 in the main paper). PPE and
FSP for Chenopodiaceae, Sambucus and Urtica were also taken from the Czech Republic,
as these were the only existing European values (Abraham & Kozáková, 2012). We decided
not to include Asteraceae (other than Artemisia) in our reconstruction, although there are
PPE available for Asteraceae Liguliflorae (from southern Sweden, Norway, Estonia and the
Swiss Plateau) and A. Tubuliflorae (from Norway), because the test run produced
unrealistically high vegetation estimates for both groups of Asteraceae due to their low PPE.
The mean lake radius used for Lake Stiucii was 350 m and the extent of the regional
vegetation reconstruction was set to 50 km in the REVEALS model. Wind speed was set to 3
m/s and atmospheric conditions were assumed to be neutral. The use of 28 taxa in our
REVEALS model represents between 81% and 100% of the total terrestrial vegetation cover
types observed in the profile, but with a lower representation towards the last 100 years. The
vegetation cover reconstructed using REVEALS always adds up to 100%, which means that
taxa not included in the model as well as non-pollen producing areas (such as lakes and
fields of non-pollen producing crops) are ignored. Cyperaceae, which grow on hygrophilous
meadows were not included in the grassland group. We decided to exclude Cyperaceae from
the REVEALS reconstruction because Cyperaceae may be overrepresented due to the
prevalence of wetland conditions.
Pollen productivity has been seen to vary between regions, partly because of
differences in climatic conditions (Broström et al., 2008). Therefore, the most reliable
estimates of past vegetation are likely to be achieved using pollen productivity estimates
from the study region. However, no such estimates are available from Romania. Previous
studies have applied REVEALS with north-western European PPEs to other regions of
Europe (e.g. Mazier et al., 2012; Fyfe et al., 2013) or to periods with different climatic
conditions, such as the Eemian, Holsteinian, Harreskovian interglacials in southern
Scandinavia (Kuneš et al., 2011). Many of the available pollen productivity estimates
originate from cultural grasslands within a region that would naturally be forested. Few pollen
productivity estimates are available from steppe regions. An exception is the study by Wang
& Herzschuh (2011) from the Tibetan Plateau, where PPEs were obtained for Artemisia,
Chenopodiaceae and Cyperaceae (relative to Poaceae). Interestingly, their values for
Artemisia (2.08 ± 0.43) and Chenopodiaceae (5.38 ± 1.08) are rather similar to the estimates
from the Czech Republic (Abraham & Kozáková, 2012; Table 1 in the main paper), lending
some support to the application of these estimates in a dry semi-natural grassland setting.
The REVEALS model was originally intended for application to pollen records from
larger sites (Sugita, 2007). No precise definition of how large a basin needs to be can be
given, as the critical size depends on the spatial structure of the vegetation (Sugita, 2007),
something, which is rarely known for the past. Limits of 100 ha (Sugita, 2007) or 50 ha
(Mazier et al., 2012) have been suggested. Instead of large sites, multiple small sites can be
combined to obtain REVEALS estimates, which has been applied in several studies, with the
number of small sites ranging from 21 (Sugita et al., 2010) to two (Fredh et al., 2013; Poska
et al., 2014). Our current study site is at the smaller end of the range of what can be
considered a ‘large site’ in terms of REVEALS, which indicates that the pollen assemblages
may have some bias towards a local vegetation signal, in addition to the regional background
expected by the REVEALS model, and thus that our reconstructions perhaps reflect a
smaller region than the 100 km suggested by Hellman et al. (2008). Over time the site has
undergone change between lake and peatland (Feurdean et al., 2013a). We took this into
consideration when running the REVEALS model by applying the appropriate pollen
dispersal and deposition models, the Prentice (1995) model for peatland periods, and the
Sugita (1994) lake model for the open water phases. However, the choice of dispersal model
does not fully account for vegetation that grows on the site itself during peatland phase,
hence our decision to exclude Cyperaceae from the REVEALS analysis. Over-representation
of other peatland taxa, such as certain species species of Poaceae could also lead to
inaccuracies in modelled forest openness (see Discussion in the main paper), although the
Poaceae pollen percentages are not generally higher during the peatland phase 11,450–
4700 cal. yr BP than they are during the lake phases.
Kuneš et al. (2011) discuss the uncertainties that are involved in assuming constant
pollen productivity in space and time and the uncertainties in basin size, but conclude that
REVEALS can be regarded as the best available method to estimate vegetation openness
and the ratio between deciduous and conifer forest. We therefore chose to apply the model,
with the PPEs available from southern Scandinavia and Central Europe, and where possible
from the Czech Republic, to obtain a more realistic reflection of vegetation composition and
openness, than raw pollen percentages provide. These PPEs were also found to fit more
accurately with the modern vegetation from the Czech Republic (Abraham et al., 2014).
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Biomization
The diversity of plant communities in the area considered as Eastern Mediterranean–Black
Sea–Caspian Corridor Biomes (EMBSeCBIO) comprises over 1100 pollen taxa. Biomization
allows palynological data to be distilled into a small number of plant functional types (PFT)
and subsequently into biomes, producing an effective and informative summary of the
vegetation and its climatic constraints. About 885 of the pollen taxa were assigned to plant
functional types, which were then assigned to biomes. Several pollen taxa specific to the
region were assigned to PFTs with reference to the literature (Davis, 1965–1988; Tutin et al.,
1964–1980; Bohn et al., 2003).
Considering the vegetation of the region and the life form leaf form, phenology and
climate tolerances 31 PFTs and 14 biomes were defined. This was done following the
general approach of Prentice et al. (1992) and Harrison et al. (2010). In defining leaf form,
we used a functional classification independent of taxonomic or phylogenetic considerations;
thus, a photosynthetic organ is taken to be a ‘leaf’ whether it is a true leaf or a modified stem.
The form ‘needleleaf’ includes needles of conifers, but also the scale-like leaves of
Cupressaceae. Aquatic and recently introduced taxa, as well as taxa representing cultivated
plants, were excluded from the taxon-PFT allocations.
Affinity scores for any given pollen spectrum and biome are calculated as the sum of
pollen values for taxa that may occur in that biome. Prior to this calculation, the pollen values
are transformed by square-root transformation in order to increase the signal-to-noise ratio
and correct for the over-representation of taxa that produce large quantities of pollen. The
minimum threshold for inclusion of pollen is 0.5%. Each pollen spectrum was assigned to the
biome to which it has the highest affinity score. The biomization scheme used for the current
paper is set up for publication (Marinova et al., in preparation).
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