COS 41-8
Initial disturbance intensity affects recovery rates and successional divergence on abandoned ski slopes
The importance of site history (including initial disturbance intensity and differential propagule arrival) in determining successional pathways and outcomes remains an understudied topic in ecology. Abandoned ski slopes present a novel system for studying successional processes following differing initial disturbance intensities. Ski slopes may be created by simply cutting and clearing tall woody vegetation (“cleared” ski slopes), or they may be further graded and levelled with heavy equipment (“graded” ski slopes). In a blocked chronosequence study of abandoned graded and cleared ski runs, I analyzed similarity between ski runs and adjacent reference forests in both plant community composition and soil function across six abandoned ski areas ranging in age from 10-43 years since abandonment in the northern Sierra Nevada mountains of California and Nevada.
Results/Conclusions
Graded (severely disturbed) ski runs exhibited reduced predictability and rates of succession compared to cleared (intermediately disturbed) ski runs over many decades following abandonment. Cleared ski runs showed increasing similarity with forest communities over time in terms of species and lifeform composition; these patterns of increasing plant community similarity were driven by overstory species, though understory species were by far more numerous and dominant during succession. In contrast, graded ski slopes lacked any predictable patterns of vegetation recovery, with no evident convergence with reference forests, and greater variability in plant community composition between sites than observed across either forests or cleared ski runs. Graded runs also exhibited reduced or no edaphic recovery, with no significant changes apparent over time in exposed bare ground, visible soil erosion, or soil depth, and had reduced soil surface litter accumulation compared to cleared ski runs. Successional divergence on graded runs is thus likely driven both by greatly reduced biotic legacies as well as worsened conditions for plant germination, establishment, and growth. Because grading ski slopes reduces ecosystem function and can result in unpredictable patterns of soil and vegetation recovery even decades after abandonment, ski slope clearing is preferable to grading to reduce long-term impacts. Active restoration of native vegetation and soils on existing graded ski slopes (both operational and abandoned) should be strongly considered.