New paper out

Tomlinson KW*, Sterck FJ, Barbosa ERM, de Bie S, Prins HHT, van Langevelde F. Seedling growth of savanna tree species from three continents under grass competition and nutrient limitation in a greenhouse experiment. Journal of Ecology.DOI: 10.1111/1365-2745.13085

https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.13085

Abstract: Changes in savanna tree species composition, both within landscapes and across climatic gradients, suggest that species differ in their ability to utilize resources and cope with grass competition. Linking trait variation among species to their relative performance under resource limitation and competition treatments could provide mechanistic understanding of species’ turnover across environmental gradients in savannas. We investigated how tree species differ in response to competition from grasses and nutrient supply, and whether these responses can be related to plant traits. As humid savannas are often associated with low fertility, species of humid savannas may grow more efficiently under nutrient suppression than species from semi-arid savannas. In heterogeneous grass swards, fast-growing, resource-wasteful species may be found in low grass biomass patches and slow-growing, conservative species in high biomass patches. We compared seedlings of 40 tree species sampled from humid and semi-arid savannas of three continents (Africa, Australia, South America) with and without grass competition and with high and low nutrient supply. We measured traits related to soil resource capture, light capture, and growth, and tested whether these traits were related to performance under the four treatments. All tree species were suppressed by grass competition and most by nutrient limitation. Only species from humid savannas in Australia grew better under nutrient limitation than their semi-arid counterparts. Deciduous species from semi-arid climates were more negatively impacted by grass competition than deciduous species from humid climates whereas the reverse pattern was observed among evergreen species. Faster growing species were more severely suppressed by grass competition and low nutrients than slower growing species. Traits associated with soil resource capture and seed mass supported growth under grass competition and nutrient limitation, but the traits differed by continent and by leaf habit. Synthesis. We found limited evidence that tree seedlings from humid savannas grow better under nutrient limitation than species of semi-arid savannas. We confirmed that fast-growing species may be advantaged in low grass biomass patches and conservative species in high biomass patches. Traits that improved performance under grass competition differed by continent, which may relate to differences in leaf habit and constraints on seed size.

NEw paper out

Roeder MYang WTomlinson KW. Influence of smoke, heat and fire on germination of woody species occurring in the dry valleys of southwest China. Journal of Plant Ecology.

https://doi.org/10.1093/jpe/rtz030

Abstract:

Aims

Savannahs depend on fire for their persistence. Fire influences regeneration from seeds in several ways: it converts the environment into a more open space which can benefit the establishment of seedlings, and fire itself can also enhance germination by chemical and physical cues, such as smoke and heat. There is limited information as to how seed of Asian savannah species respond to fire, even though Asia has several dry vegetation types that are associated with fire. Our main question was whether fire enhances or triggers the germination of woody species occurring in southwest Chinese dry valleys, which have savannah vegetation.Methods

We conducted tests with heat (80°C) and smoke solution treatments, and tests with real fire by burning grass on top of sand trays containing seeds. We tested 35 species, including savannah species, and gully and forest species. Depending on seed availability, not all species were tested for all treatments. Twenty-six species had total germination >4% and these were used for analysis.Important Findings

Heat increased germination of three species (strongest reaction: Dodonaea viscosa), smoke increased germination of five species (strongest reaction: Calotropis gigantea). Both treatments decreased germination for five and seven species, respectively. Real fire was detrimental for most species, except for D. viscosa, which is known to respond positively to heat shock. Even though fire-related cues were not a trigger for germination for most species in our study, fire could still be crucial for regeneration by competition release.