Pattern of tree species co-occurrence in an ecotone responds to spatially variable drivers

• Published in: Landscape ecology 2022-09, Vol.37 (9), p.2327-2342
• Main Authors: Shea, Monika E., Mladenoff, David J., Clayton, Murray K., Berg, Stephen, Elza, Hayden
• Format: Article
• Language: English
• Subjects: Biomedical and Life Sciences; Climate change; Ecological function; Ecology; Ecosystems; Ecotones; Environmental Management; Forests; Historical structures; Land surveys; Landscape Ecology; Landscape/Regional and Urban Planning; Life Sciences; Nature Conservation; Plant species; Public lands; Research Article; Soil water; Soils; Species; Sustainable Development; Tension; Variables; Vegetation; Water availability
• ISSN: 0921-2973; 1572-9761
• DOI: 10.1007/s10980-022-01485-x

Context Ecological structure in ecotones, defined by how species from adjacent systems co-occur, affects ecosystem functions and climate change responses. Ecotone structure can vary spatially, yet variability in broader-scale ecotones is poorly understood. In Wisconsin (USA) the Tension Zone is an ecoregional ecotone, separating northern and southern ecosystems. Objectives Characterize ecotone structure in the Tension Zone, examine how structure varied spatially, and identify how environmental drivers affected structure. Methods Using historical (1800s) tree occurrence data, we examined co-occurrence of northern and southern species at multiple scales (1.0 km to 7.5 km) at different locations in the Tension Zone, identifying the finest scale at which co-occurrence was detected. We assessed relationships between co-occurrence and environmental variables. Results Co-occurrence emerged at different scales, related to interacting climate and soil variables and location within the ecotone. Northern and southern trees co-occurred at broader scales near ecotone center and at locations with higher climatic water availability and sandier soils; they co-occurred at finer scales in locations with higher climatic water availability and richer soils. Sites with xeric tree species were associated with broader-scale co-occurrence. Conclusions We detected spatially variable structure within the Tension Zone, resulting from multi-scale processes among underlying environmental drivers. Finer-scale co-occurrence may have resulted from competition in high-resource environments, while broader scale co-occurrence may have been driven by fire and associated feedbacks. Characterizing structure in an ecoregional ecotone adds to a growing body of evidence that finer-scale factors play a role in defining the characteristics, functions, and responses of broader-scale ecotones.