Release of Juniperus thurifera woodlands from herbivore-mediated arrested succession in Spain

摘要

Question: Do abiotic constraints maintain monospecificudwoodlands of Juniperus thurifera? What is the role ofudbiotic (livestock) versus abiotic (climate) drivers in theudrecruitment and growth of the different tree species?udLocation: Cabrejas range, Soria, north-central Spain,ud1200m altitude.udMethods: Stand history was reconstructed using dendroecologyudand spatial pattern analysis, combined with historicaluddata of livestock abundances and climatic records.udResults: J. thurifera establishment occurred in two distinctudpulses, with a tree component establishing in the late 1800sudto early 1900s. Quercus ilex and Pinus sylvestris establishment was evident only from the late 1970s onward.udRecruitment events were related to reductions in livestockudbrowsing. J. thurifera spatial structure was clumped and Q.udilex showed a short-scale aggregation to J. thurifera treesudand saplings. Radial growth trends of J. thurifera saplings,udQ. ilex and P. sylvestris were negatively related to livestock density. Summer drought limited the radial growth of all the study species, and P. sylvestris and Q. ilex grew faster than J. thurifera even after considering an age effect.udConclusions: The differences in radial growth patterns andudrecruitment pulses between species indicate that livestockudbrowsing and not abiotic factors is the main factorudcontrolling plant succession and structural development.udIn this process, J. thurifera acts as a nurse plant, facilitating the establishment of other tree species. Under the current low pressure from herbivores, formerly pure J.udthurifera woodlands will change towards dense stands ofudmixed species composition.