Seedling emergence and establishment of Pinus sylvestris in the Mongolian forest-steppe ecotone

Abstract

The potential of Scots pine (Pinus sylvestris) for regeneration and encroachment onto dry grasslands in the forest-steppe ecotone was experimentally studied at the south-eastern distribution limit of the species in Mongolia. The experiment consisted of a sowing and planting (2-year old seedlings) assay at two different distances from the forest line and manipulation of the water supply by irrigation in one half of the replicate plots. Seedling emergence was strongly inhibited by post-dispersal seed predation (between 50 and[90 % of the seeds were apparently consumed) and by drought. Seedling survival was limited by drought and phytopathogenic fungi that infected the needles. Herbivory by insects or rodents, a key factor for seedling mortality in Larix sibirica, the most frequent tree species in Mongolia's forest-steppe ecotone, was of little importance in Scots pine, probably due to the production of efficient allelochemicals. The potential of Scots pine to regenerate in Mongolia's forest-steppe ecotone and to encroach onto the steppe is very limited and mostly restricted to the immediate vicinity of the forest; it might even decrease in future in the face of climate warming. The observed dependence of seedling emergence and survival on soil moisture suggests that regeneration outside the forest may only be successful in exceptionally moist years. Livestock grazing is certainly an additional limiting factor for Scots pine regeneration in Mongolia, but was not relevant in the present study area.

Soil-moisture conditions indicated by field-layer plants help identify vulnerable forests in the forest-steppe of semi-arid Southern Siberia

“…During dry years, however, larger pine trees exhibited stronger growth reductions (Zang et al, 2012). Studies on the regeneration of Scots pine and encroachment onto the steppe at the forest-steppe ecotone in northern Mongolia revealed that the distribution of this species was very limited, and was mostly restricted to the immediate vicinity of the forest (Dulamsuren et al, 2013). Eilmann et al (2011) concluded that Scots pine trees under drought stress build a more effective water-conducting system (larger tracheids).…”

Woodland recovery following drought‐induced tree mortality across an environmental stress gradient

“…In arid and semi‐arid forests and woodlands, cool, wet climatic conditions have historically been optimal for regional tree recruitment events (League & Veblen, ; Barger et al ., ; Shinneman & Baker, ). Experimental temperature and water manipulations further confirm the negative effects of increasing water deficits on tree recruitment (McCallum, ; Dulamsuren et al ., ). While these previous studies suggest that regional warming may alter forest and woodland composition and structure in many semi‐arid ecosystems, warming effects may vary depending on differences in local climate, soil properties, and vegetation structure.…”

Animal’s Functional Role in the Landscape

“…However, in years with good seed production (mast years), seed consumption by granivores does not threaten forest regeneration. On the other hand, in cases of low seed production, small mammals may consume all seeds on the ground, and natural regeneration may outright fail as a result (see Sukachev and Dylis 1964 ;Castro et al 1999 ;Dulamsuren et al 2013 ).…”

“…Seed removal by seed predators was also the main reason for failure of Scots pine seedling emergence in the Mongolian forest steppe. In the forest steppe, 66-92 % of the seeds were lost to seed predators, while 52-76 % were removed at the forest edge (Dulamsuren et al 2013 ).…”