Edge Effects on an Epiphytic Lichen in Fragmented Forests

Abstract

Increased amount of edge habitat is one of several important consequences of forest fragmentation. Consequently, we must understand the responses of plants and animals to edges to formulate adequate recommendations for conservation of biodiversity. Epiphytic lichens are a well-suited subject for a study of abiotic edge effects because they gain nutrients and water directly from the atmosphere. We present a temporal model of edge effects on lichens based on empirical data for the pendulous, fruticose species Alectoria sarmentosa . Ten high-contrast edges of different age between mature Picea abies forest and large clearcuts (10-260 ha) were studied in northwestern Sweden. Abundance of A. sarmentosa (mass on 1-m branch sections and maximum thallus length per tree) was estimated in the lower canopy in four 10 ϫ 50-m 2 plots located 5-100 m into the forest. The abundance of A. sarmentosa was markedly lower at the edge compared to the interior at 9 of 10 study sites. Lichen mass constituted 22% of that in the interior at young edges (0.5-2.5 years) and 55% at old edges (8-16 years). The length of A. sarmentosa was significantly affected by both distance from the edge and site location. Maximum edge effects extended 25-50 m into the forest at moderately exposed sites. The major factor reducing lichen abundance was physical damage by strong wind. Large, pendulous lichens such as A. sarmentosa are prone to thallus fragmentation. At older edges lichen abundance had recovered inside the edge (20-30 m), probably due to increased growth in response to increased irradiance. Our analysis supports the view that edge effects may be strongly dynamic over time and caused by the interaction of several factors. We conclude that epiphytic lichens have large potential as indicators of forest edge effects. Efectos de Borde en un Líquen Epífito en Bosques FragmentadosResumen: Una de las múltiples consecuencias importantes de la fragmentación de bosques es el incremento en la cantidad de borde en el hábitat. En consecuencia, debemos entender las respuestas de plantas y animales a los bordes para formular recomendaciones apropiadas para la conservación de la biodiversidad. Los líquenes epífitos son sujetos aptos para el estudio de efectos abióticos de borde, puesto que obtienen nutrientes y agua directamente de la atmósfera. Presentamos un modelo temporal de los efectos de borde en líquenes basado en datos empíricos de la especie Alectoria sarmentosa . Diez bordes de alto contraste y diferentes edades ubicados entre bosques maduros de Picea abies y clareos grandes (10-260 ha) fueron estudiados en Suiza noroccidental. La abundancia de A. sarmentosa (masa en secciones de rama de 1 m y longitud máxima de tallo por árbol) se estimó en el dosel bajo en cuatro áreas de 10 ϫ 50 m 2 localizados de 5-100 m dentro del bosque. La abundancia de A. sarmentosa fue marcadamente menor en los bordes comparando con el interior en 9 de 10 sitios de estudio. En los bordes jóvenes (0.5-2.5 años) la masa de líquen constituyó un 22% de lo observado en el interi...

Effects of New Forestry Practices on Rare Epiphytic Macrolichens

“…Cutting of trees close to rock outcrops may also cause an edge effect. Several specialized macrolichens (e.g., E. divaricata and L. pulmonaria) are sensitive to edge effects because sudden increases of light may be detrimental (Gauslaa & Solhaug 1996Esseen & Renhorn 1998). However, the response of specialized foliose lichens on solitary trees left on clearcuts is variable: often they dry out, but some populations may survive well (Esseen et al 1997; see also Hazell & Gustafsson 1999).…”

Dispersal Limitations of Epiphytic Lichens Result in Species Dependent on Old-Growth Forests

“…We occasionally find vigorous thalli of normally old-growth restricted species in young forests. Populations of some old-growth associated lichens (e.g., Alectoria sarmentosa), however, decline when they are suddenly exposed along the edges of clearcuts (Esseen and Renhorn 1998).…”

Broad-scale distribution of epiphytic hair lichens correlates more with climate and nitrogen deposition than with forest structure

“…Mean maximum length of Alectoria across Sweden (19 cm) was half the length in northern, old-growth P. abies forests (41 cm, Esseen 2006). Alectoria can be 0.5-1 m long in optimal sites (Esseen and Renhorn 1998), thus the larger dimensions in Alectoria than in Bryoria are not surprising. The small size of Usnea (8.4 cm) across Sweden and of Alectoria and Bryoria in southern Sweden (regions 4 and 5) is remarkable.…”

“…Distance to forest edge could also be of interest, as hair lichens are sensitive to edge microclimates (Esseen and Renhorn 1998). Sweden's forests, particularly the southern and central regions, are highly fragmented by forestry and agriculture with a large extent of abrupt forest edges (Esseen et al 2016) that may strongly influence hair lichens.…”