DOI: 10.5061/dryad.9w0vt4bg8
title: Patterns and determinants of lichen abundance and diversity across a subarctic to arctic latitudinal gradient

description: Macrolichen abundance at the species level in 42 sites across a
 subarctic (56°N) to arctic (62°N) latitudinal gradient in Nunavik (Québec,
 Canada). Data was collected in the dominant vegetation types of
 six regions sampled along this gradient.
description: From south to north, we
 visited Clearwater Lake (CL; 56°20'N, 74°27'W), Boniface River
 (BR; 57°45'N, 76°10'W), Le Roy Lake (LL; 58°29'N,
 75°28'W), Payne Lake (PL; 59°32’N, 74°63'W), Chukotat River (CR;
 61°18'N, 75°55'W) and Deception Bay (DB; 62°05'N,
 74°16'W). For each region, the most dominant vegetation types were
 identified according to their land surface cover, based on the 2018 Québec
 Northern Vegetation Map produced by the Ministère des Forêts, de la Faune
 et des Parcs (MFFP) of the Government of Québec. Three sites in each of
 the dominant vegetation types were randomly selected in a radius of five
 kilometers around each region’s research station prior to fieldwork
 (Figure 1b). Minimal distance between sampling sites was set to 250
 meters. For each polygon of the vegetation map, a 250 m-wide buffer zone
 was excluded to ensure that sampling was conducted in the central section
 of the polygon. The final site selection consisted in a total of 42 sites
 and included three sites of each of the following dominant vegetation
 types: lichen woodland, open subarctic heathland (thereafter open area),
 and shrubland in Clearwater Lake and Boniface River (the two southernmost
 regions), open area and shrubland in LeRoy Lake and Payne Lake, herbaceous
 tundra in Chukotat River, and herbaceous tundra and shrubland in Deception
 Bay. For each of
 the study sites, a 30 m x 40 m quadrat was positioned in a representative
 portion of the site. Twenty 1 m-long linear surveys were randomly
 positioned along parallel transects placed every two meters along the
 largest (40 m) side of the quadrat . Macrolichens (fruticose, foliose and
 squamulose lichens) were identified to the species level according to the
 floras of Brodo, Sharnoff, & Sharnoff, (2001), Hinds &
 Hinds (2007), and Thomson & Brehmer, (1984). Crustose lichens were
 not identified. Terricolous and saxicolous lichen cover was measured by
 species for each 10 cm segment along every 1 m-long linear survey. The
 measurements made on these ten segments were summed to obtain a precise
 estimate of each species cover to the nearest centimeter on the 1-m long
 survey. Species for which cover was &lt; 1 cm were assigned a cover of
 0.5 cm. Vegetation cover was also evaluated for the following plant
 functional groups: erect shrubs (&gt; 15 cm-high), prostrate shrubs
 (&lt; 15 cm-high), graminoids, forbs and bryophytes. For each 1 m-long
 transect, we measured the height and evaluated the canopy closure of erect
 shrubs, using the following cover classes: 0-25%, 25-50%, 50-75%, and
 75-100%. Soil organic layer thickness was measured at the center of every
 survey transect and five soil samples were collected systematically at
 every site. Soil pH was evaluated using the mean pH value of the five soil
 samples collected during the field campain. Soil samples were first dried
 in paper bags at room temperature during the field campain and soil pH was
 measured using a pH-meter by suspending soil material in distilled water
 with a 1:1 ratio once back at Laval University (Eckert & Sims,
 1995). For each site, we also summed the cover of each vegetation
 functional group measured in the field and calculated the mean value of
 the soil organic layer thickness. <i>Cladonia
 arbuscula</i> Wallr. and <i>Cladonia mitis</i>
 Sandst.<i> </i>were both identified as <i>C.
 mitis</i>, since the PD (phenylethylenediamine) spot test necessary
 to distinguish both species was not performed during fieldwork.
 <i>Cladonia sulphurina </i>Michx. and <i>Cladonia
 deformis</i> Hoffm. were also recorded together as <i>C.
 sulphurina</i>, since the distinction between these two species is
 mainly based on the presence of squamatic acid revealed by UV light, which
 was not used during fieldwork. <i>Cladonia borealis
 </i>Stenroos<i> </i>and <i>Cladonia
 coccifera</i> Willd. were both identified as <i>C.
 borealis</i> because they are morphologically very similar. For the
 same reason, <i>Cladonia stygia</i> Ruoss and
 <i>Cladonia rangiferina </i>Wigg. were
 pooled<i>.</i> <i>Cladonia trassii </i>Ahti and
 <i>Cladonia stricta</i> Nyl. were also pooled because
 taxonomic distinction between the two species is still unclear. Finally,
 <i>Stereocaulon</i> species were only identified to the genus
 level due to the unclear taxonomy of the genus (Lavoie et al., 2020).
 Other specimens that could not be identified directly in the field were
 collected and brought back at the Louis-Marie Herbarium (Laval University,
 Québec, Canada) for further identification using dissecting microscopes
 and chemical spot tests. The cover of primary thallus of
 <i>Cladonia</i> species was measured but all specimens were
 recorded as <i>Cladonia</i> spp. and were therefore not
 included in species richness analyses. Crustose lichens cover was measured
 but species were not identified, and thereby only included in the
 abundance analyses.
description: Decsription of the variables included in the dataset.  Variables Description SurveyID Survey ID Region Region Name Site Site Name Y Latitude X Longitude Year Year of sampling Veg_type Vegetation type according to MFFP SurveyNo Survey number (from 1 to 20) Org_layer Soil organic layer thickness (cm) pH soil pH (5 samples per site) Alectoria.ochroleuca to Vulpicida.pinastri species cover (cm)  Lichen_cov Total lichen cover (cm) Shrub_cov Shrub cover (cm) Shrub_hei Shrub height (cm) Shrub_closure Shrub canopy closure using the following classes 1 (0-25%), 2 (25-50%), 3(50-75%), and 4 (75-100%) Rock_cov Rock cover (cm) Forb_cov Forb cover (cm) LowSh_cov Low shrub cover (cm) Bryo_cov Bryophyte cover (cm) Litter_cov Litter cover (cm) Tree_cov Tree cover (cm) Lyco_cov Lycopod cover (cm) HighSh_cov High shrub cover (cm) Gram_cov Graminoid cover (cm)