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In montane areas, climate change can shift tree species distributions upslope over time which can affect forest ecosystem structure and functioning. Seedlings of low-elevation temperate broadleaf trees establishing beyond their ranges at high elevations need to overcome both herbivore pressure and soil nutrient limitations. To assess the influence of these two stressors, we quantified leaf and stem herbivory, soil and foliar nutrient status, and two-year survival of experimentally grown seedlings of two hardwood species, sugar maple (Acer saccharum) and American beech (Fagus grandifolia) along elevation gradients in the Green Mountains of Vermont, USA. While insect foliar herbivory was reduced on maple seedlings growing beyond range boundaries, suggesting enemy escape, the opposite pattern was observed for beech. Mammalian browsing increased with elevation for both species. In general, foliar nutrient concentrations and resource utilization (that is, the relationship between soil nutrient availability and foliar nutrient status) declined with elevation for both species (although more so for maple, especially calcium), while toxic foliar aluminum concentrations increased for maple. Survival decreased with elevation for both species, but especially for sugar maple, linked more to declining foliar nutrient status than herbivory at higher elevations. Thus, the effects of herbivory and nutrient utilization on seedling survival can be critical for shaping tree species range shifts and, ultimately, species composition and forest ecosystem functioning.
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Mycorrhizal fungi as critical biotic filters for tree seedling establishment during species range expansions
Abstract Global warming has been shifting climatic envelopes of many tree species to higher latitudes and elevations across the globe; however, unsuitable soil biota may inhibit tree migrations into these areas of suitable climate. Specifically, the role of mycorrhizal fungi in facilitating tree seedling establishment beyond natural species range limits has not been fully explored within forest ecosystems. We used three experiments to isolate and quantify the effects of mycorrhizal colonization and common mycorrhizal networks (CMN) on tree seedling survival and growth across (within and beyond) the elevational ranges of two dominant tree species in northeastern North America, which were associated with either arbuscular mycorrhiza (AMF,Acer saccharum) or ectomycorrhiza (EMF,Fagus grandifolia). In order to quantify the influence of mycorrhiza on seedling establishment independent of soil chemistry and climate, we grew seedlings in soils from within and beyond our study species ranges in a greenhouse experiment (GE) as well as in the field using a soil translocation experiment (STE) and another field experiment manipulating seedling connections to potential CMNs (CMNE). Root length colonized, seedling survival and growth, foliar nutrients, and the presence of potential root pathogens were examined as metrics influencing plant performance across species' ranges. Mycorrhizal inoculum from within species ranges, but not from outside, increased seedling survival and growth in a greenhouse setting; however, only seedling survival, and not growth, was significantly improved in field studies. Sustained potential connectivity to AMF networks increased seedling survival across the entire elevational range ofA. saccharum. Although seedlings disconnected from a potential CMN did not suffer decreased foliar nutrient levels compared with connected seedlings, disconnected AM seedlings, but not EM seedlings, had significantly higher aluminum concentrations and more potential pathogens present. Our results indicate that mycorrhizal fungi may facilitate tree seedling establishment beyond species range boundaries in this forested ecosystem and that the magnitude of this effect is modulated by the dominant mycorrhizal type present (i.e., AM vs. EM). Thus, despite changing climate conditions beyond species ranges, a lack of suitable mutualists can still limit successful seedling establishment and stall adaptive climate‐induced shifts in tree species distributions.
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- Award ID(s):
- 1759724
- PAR ID:
- 10546409
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecological Monographs
- ISSN:
- 0012-9615
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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