Soil properties constrain forest understory plant distributions along a
climatic elevational gradient
Abstract
Predictions of plant migration under climate warming come mostly from
models including only climate variables, neglecting the influence of
non-climatic factors, such as soil properties and dispersal limitation.
Soil properties might have a stronger effect on plant distributions in
colder environments, where plant nutrient absorption capacity is
inhibited, but this has rarely been tested. Macroecological studies of
range dynamics rely on soil data at much coarser spatial resolution than
that experienced by plants. In contrast, field studies along elevational
gradients permit detailed soil data, while still covering a wide
climatic gradient. Here, we first report an intensive field survey of
four spring forest herbs and soil properties along an elevational
gradient in southern Québec, Canada, testing the hypothesis that soil
properties contribute to defining upper elevational range limits. We
then report a seven-year transplant experiment with one species,
Trillium erectum, testing the hypothesis that climate warming has
already created suitable sites at high elevation, with its near-absence
explained by dispersal limitation. In our field survey, soil properties
had substantial impacts on the occurrence or abundance of all four
species, and soil effects were more pronounced at higher elevations. For
two species, T. erectum and Claytonia caroliniana, very
infrequent occurrences at high elevation (>950m) were
strongly associated with rare microsites with high pH or nutrients.
After transplantation to high-elevation sites, T. erectum
individuals grew to much smaller size and with very low probability of
flowering (<10%) compared to individuals at low or
mid-elevations (>60% flowering), suggesting that
environmental factors rather than dispersal limitation constrain the
species’ upper elevational range limit. Our study highlights that soil
factors interact strongly with climate to determine plant range limits
along climatic gradients. Unsuitable soils for plants at high elevations
or latitudes may represent an important constraint on future plant
migration.