Rapid spread of a fleshy-fruited species in abandoned subalpine meadows - formation of an unusual forest belt in the eastern Carpathians

Abstract

In recent decades, most subalpine hay meadows and pastures have been abandoned, and trees have been recolonizing these sites where forest existed before agricultural activity. This study examined how woody vegetation, dominated by the deciduous fleshy-fruited tree Sorbus aucuparia (rowan), expanded on subalpine meadows in the Western Bieszczady Mountains (eastern Carpathians, Poland) after the cessation of agricultural use. The aims were to determine the abundance of rowan in the woody vegetation, to estimate the rate of rowan expansion in the studied area, and to characterize the variability of rowan stands and growth forms. Rowan dominated the current plant community of abandoned subalpine meadows, though this species is not considered a rapid colonizer of open areas and was not frequent in the uppermost forest belt before the colonization. The whole area was encroached by rowans in a very short period of time 60-70 years ago. Rowan tree density was similar throughout the elevational gradient but the growth form changed, becoming more shrub-like with increasing elevation. Rowan stands will likely be the main element of the subalpine belt in this region in the upcoming decades. At present, no tree species can be considered a rapid successor to rowan in the area.

Subalpine woody vegetation in the Eastern Carpathians after release from agropastoral pressure

“…Shrub overgrowth in alpine pastures after the cessation of economic use has been observed, for several decades, in many European mountain systems 7 , 11 , 14 , 20 , 58 – 60 . In the Bieszczady Mts, the rate of colonization of subalpine pastures by woody species was also attributed to global climate change 34 , 35 . However, climate change in the Carpathians at locations higher than 1200 m is slower than at lower altitudes 61 .…”

“…S4 ) 74 – 76 . Trusches ( Turdidae ) use protruding rocks on open slopes eating rowan fruits, which favours sowing seeds 35 , 77 , 78 . In addition, insolation was significant, positively correlated with the occurrence of cold spot clusters, and pointed to a negative influence on the growth of subalpine thicket.…”

“…The succession stage of beech is limited only to a narrow zone at the upper forest limit 19 , 21 , 34 , 35 . Generally, the upper forest limit forms a diffuse treeline with ‘krummholz’ of shrubby thwarted tree individuals that survive only in a few microsites (spatial heterogeneity).…”

“…We used 12 variables (10 continuous and two categorical) that are expected to affect the distribution of subalpine thicket patches (Table 1 ). They were characterized as to the location with respect to human settlements, past land use (both categorical), distance from the contemporary upper forest border, snow cover and other climatic related variables, and parameters determining the topographic diversity of the terrain, according to the high-resolution DTM 21 , 22 , 26 , 32 – 35 .

Figure 2 Flow diagram of the data handling.

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