Vertical gradients in population characteristics of canopy lichens in boreal rainforests of Norway

Abstract

All specimens of three foliose lichens (Lobaria pulmonaria (L.) Hoffm., n = 725; Lobaria scrobiculata (Scop.) DC., n = 6613; Pseudocyphellaria crocata (L.) Vain., n = 1237) and two pendulous lichens (Alectoria sarmentosa (Ach.) Ach., n = 441; Ramalina thrausta (Ach.) Nyl., n = 990) were collected from 160 random Picea abies (L.) H. Karst. branches (2–15 m above the ground) in three spruce-dominated boreal rainforests in Norway. Maximum diameter (foliose lichens), length (pendulous lichens), and reproductive structures were quantified in each thallus. The effects of measured tree and branch variables on abundance and reproduction were tested by generalized linear mixed models with binomial errors (binomial GLMM) and zero-altered (over-dispersed) Poisson generalized linear mixed models (ZAPGLMM). Lobaria pulmonaria, P. crocata, and R. thrausta occurred predominantly in the lower canopy, whereas the remaining species were also common at higher levels. The portions of thalli producing soredia and (or) isidia were 60%, 22%, and 14% for P. crocata, L. scrobiculata, and L. pulmonaria, respectively. Isidiate and (or) sorediate L. pulmonaria thalli occurred mainly on low, dead branches, whereas sorediate L. scrobiculata and P. crocata occurred at all heights. The occurrence of small P. crocata, <5 mm, decreased by branch height and small L. scrobiculata, <5 mm, increased with branch length and decreased with tree age. Upper branches supported a significant part of the total populations of studied lichens and are, thus, important when evaluating epiphyte conservation status.

Intraspecific life history variation in contrasting habitats: Insights from an obligate symbiotic organism

“…In agreement with other studies in boreal (Hilmo et al, 2011a, 2013) and Mediterranean climates (Merinero et al, 2017), the probability of asexual reproduction by L. scrobiculata was size dependent (Fig. 3).…”

“…75% of the established individuals. Similar life stage distribution patterns have been documented in other lichen species in various climates (e.g., Hestmark, 1992; Hilmo et al, 2013; Rubio‐Salcedo et al, 2015). This structure may reflect that (1) populations are expanding and the local habitat has not yet been saturated (Hestmark, 1992); and (2) mortality is higher in large individuals, so a large population of small individuals may enhance the persistence of the species in a given environment (Hutchings, 1997).…”

“…Using a digital caliper, we (4) measured the largest diameter (mm) of each individual (hereafter referred as to size) and (5) visually estimated the soralia cover (%), which was equivalent to the reproductive allocation. To describe the population structure, we established three life stage categories according to Hilmo et al (2013): reproductive (thalli with soralia), juvenile (thalli without soralia), and recruit (juveniles ≤ 5 mm) (see Fig. 1C).…”

“…For instance, lichen growth depends on water, light, and the nutrient availability balance (Palmqvist, 2000). Growth is important because the onset of both sexual and asexual reproduction is known to depend on size in a few foliose species (e.g., Hestmark, 1992; Ramstad and Hestmark, 2001; Pringle et al, 2003; Hilmo et al, 2013; Rubio‐Salcedo et al, 2015; Merinero et al, 2017). Contrasting habitats can vary in terms of their microclimate; thus, the patterns of lichen growth and reproduction may differ (e.g., Sillet and McCune, 1998; Hilmo et al, 2011a; Merinero et al, 2015).…”

Estimation of metapopulation colonization rates from disturbance history and occurrence‐pattern data

“…Additionally, as there is a strong increase in occurrence of dispersal propagules with increasing thallus size in L. pulmonaria (Hilmo et al. ), we assumed that sites with a low local abundance are recently colonized, and that sites with a high local abundance are dispersal sources. We thus split the data into two parts (recent colonizations and colonization sources) to fit the dispersal function of our model species (see Q2) as in Snäll et al.…”