Shrub interactions drive vegetation succession of subalpine grasslands under two climatic conditions |
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| Authors: | Paloma Nuche Concepci n L. Alados |
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| Affiliation: | Department of Biodiversity Conservation and Ecosystem Restoration, Pyrenean Institute of Ecology (IPE-CSIC), Avda. Montañana 1005, PO Box 13034, Zaragoza 50059, Spain |
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| Abstract: | Aims The abandonment of agronomic practices in subalpine systems has led to shrub encroachment, which has transformed grasslands into woodlands. The competitive and facilitative interactions among incoming shrub species might influence vegetation succession and might be affected by climate change. This study aimed to identify the nature of shrub species interactions between an early colonizer and a secondary succession shrub in the successional encroachment process and whether it differs between two contrasting climatic conditions.Methods The interactions between the two main encroaching shrub species in the Central Pyrenees (Spain), Buxus sempervirens and Echinospartum horridum, were studied at the current upper limit of the altitudinal range of B. sempervirens, where it coexists with E. horridum (high site), and in a milder location at lower elevation (low site). In the studied areas, E. horridum is the first shrub species that encroaches upon the abandoned grasslands and B. sempervirens enters the system after E. horridum has become established. A neighbor-removal experiment was used to assess the bidirectional interactions between both species, and whether those interactions differed among the life stages of B. sempervirens (seedlings, juveniles and adults), at the two study sites. Survival, annual crown growth and developmental instability (error in development caused by stress) were the performance indices used to quantify plant responses. Differences in air temperatures and soil nutrient amelioration were evaluated as possible mechanisms of facilitation of E. horridum on B. sempervirens .Important findings E. horridum enhanced the survival of B. sempervirens seedlings under its crown, whereas, B. sempervirens adults outcompeted E. horridum. Therefore, the invasion of the grasslands by E. horridum facilitated the settlement and expansion of B. sempervirens, promoting vegetation succession at the Pyrenees. In addition, climatic differences associated with elevation affected shrub interactions. Under low temperatures at the upper limit of B. sempervirens altitudinal range, the presence of E. horridum enhanced the growth of B. sempervirens juveniles. At low elevation, under a milder climate, B. sempervirens exerted a high degree of competition toward E. horridum. An increase in temperatures associated with climate change would benefit B. sempervirens juveniles growth which might affect the successional process because it would increase their competitive ability when B. sempervirens juveniles become adults. |
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| Keywords: | climate change developmental instability plant interactions subalpine ecosystems vegetation succession |
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