Seasonal facilitative and competitive trade‐offs between shrub seedlings and coastal grasses

Sinclair, Michael N.; Woods, Natasha N.; Zinnert, Julie C.

doi:10.1002/ecs2.2995

Cited by 6 publications

(3 citation statements)

References 53 publications

(73 reference statements)

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“…The VCR is experiencing shrub encroachment by Morella cerifera on a landscape scale [42]. M. cerifera is a N-fixing shrub that dominates later successional swales and may be facilitated by the presence of a grass canopy [43,44]. Due to extensive shrub cover on the northern end of Hog Island, plots were established on the southern end in a recently developed swale (i.e., dune slack) composed of perennial grass and annual/biennial forb species.…”

Section: Study Sitementioning

confidence: 99%

Trait-Based Investigation Reveals Patterns of Community Response to Nutrient Enrichment in Coastal Mesic Grassland

Brown

Zinnert

2021

Diversity

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Despite recent advances, we still do not understand how chronic nutrient enrichment impacts coastal plant community structure and function. We aimed to clarify such impacts by testing for differences in ecosystem productivity and multiple community metrics in response to fertilization. We established plots in 2015 consisting of control (C), nitrogen (N), phosphorus (P), and nitrogen + phosphorus (NP) treatments in a mid-Atlantic coastal grassland. In 2017 we collected aboveground biomass, functional traits, and species abundance for each plot. Our findings indicate a synergistic co-limitation, such that NP plots were more productive than all other treatments. A combination of traits responsible for competition and nutrient uptake (i.e., height and δ15N) caused trait-based divergence of N and NP plots from C and P plots. Functional trait-based composition patterns differed from species composition and lifeform abundance patterns, highlighting complexities of community response to nutrient enrichment. While trait-based functional alpha-diversity did not differ among nutrient treatments, it was positively correlated with biomass production, suggesting nutrients may impact functional alpha-diversity indirectly through increased productivity. Increased functional alpha-diversity could be a mechanism of co-existence emerging as productivity increases. These results have important implications for understanding how plant communities in low-productivity coastal systems are altered by fertilization.

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Section: Study Sitementioning

confidence: 99%

Trait-Based Investigation Reveals Patterns of Community Response to Nutrient Enrichment in Coastal Mesic Grassland

Brown

Zinnert

2021

Diversity

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“…Forested plots on other nearby islands have transitioned to dominance by M. cerifera (Zinnert, unpublished data). Once established, seedlings grow rapidly and shrub thickets persist on the landscape unless lost due to shoreface erosion from sea-level rise 33,55 . www.nature.com/scientificreports www.nature.com/scientificreports/ experimental design.…”

Section: Study Sitementioning

confidence: 99%

Decreased temperature variance associated with biotic composition enhances coastal shrub encroachment

Wood

Hays

Zinnert

2020

Sci Rep

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Regime shift from grasslands to shrub-dominated landscapes occur worldwide driven by altered land-use and climate change, affecting landscape function, biodiversity, and productivity. Warming winter temperatures are a main driver of expansion of the native, evergreen shrub, Morella cerifera, in coastal landscapes. Shrub establishment in these habitats alters microclimate, but little is known about seasonal differences and microclimate variance. We assessed influence of shrubs on microclimate variance, community composition, and community physiological functioning across three vegetation zones: grass, transitional, and shrub in a coastal grassland. Using a novel application of a timeseries analysis, we interpret microclimatic variance modification and elucidate mechanisms of shrub encroachment at the Virginia Coast Reserve, Long-Term Ecological Research site. As shrub thickets form, diversity is reduced with little grass/forb cover, while transpiration and annual productivity increase. Shrub thickets significantly reduced temperature variance with a positive influence of one day on the next in maximum air, minimum air, and maximum ground temperature. We also show that microclimatic temperature moderation reduces summer extreme temperatures in transition areas, even before coalescence into full thickets. Encroachment of Morella cerifera on the Virginia barrier islands is driven by reduced local exposure to cold temperatures and enhanced by abiotic microclimatic modification and biotic physiological functioning. This shift in plant community composition from grassland to shrub thicket alters the role of barrier islands in productivity and can have impacts on the natural resilience of the islands. Woody vegetation is rapidly encroaching into grassland globally as a result of altered environmental drivers 1-3. The abrupt conversion to shrub-dominated habitats includes drivers such as altered fire or grazing pressures, increased atmospheric CO 2 , and altered temperature ranges 3-6. Warming temperatures associated with macroclimatic change, particularly in winter minima, can expand the range limits of cold-intolerant shrub species 3,6-8 while macroclimatic variance in precipitation enhances success of woody vegetation, particularly in the transition ecotones 9,10. Thus, no single factor provides dominant influence on woody encroachment. Increased annual temperatures may improve physiological functioning of encroaching species, possibly as a feedback between abiotic microclimatic conditions and shrub success to promote range expansion for woody shrubs 3,7. On smaller scales, encroaching woody vegetation frequently modifies microclimatic conditions resulting in intra-and interspecific facilitation 11-14. Changes in microclimatic temperatures within shrub thickets include temperature moderation with diminished instances of extreme temperatures that can decrease productivity and cause physiological damage of xylem structures 3,6. In areas with warming winter temperatures, thicket-forming species that are vulnerable to cold...

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“…While rapid depletion of shallow water (Davis et al., 1999; Holdo & Brocato, 2015; Riginos, 2009) and interception of light (Rugemalila et al., 2020) are important mechanisms by which grasses influence savanna tree seedlings' growth and survival, it is unclear how seedlings respond to grasses that vary in morphological and physiological properties such as height, rooting depth, leaf area, photosynthesis, growth rates and defoliation tolerance. For example, tall grasses with a high leaf area index reduce light but may improve the temperature and moisture environment for young seedlings (Sinclair et al., 2020). Alternatively, high‐quality grasses preferred by herbivores may experience reduced leaf surface area due to grazing, leading to lower transpiration and higher soil moisture for tree seedlings (Thapa et al., 2021; Treydte et al., 2013).…”

Section: Introductionmentioning

confidence: 99%

Tree and grass competition in savannas: Interactive effects of soil moisture, grass defoliation and grass species identity on the growth and survival of tree seedlings

Rugemalila,

Sarakikya,

Anderson

2024

Austral Ecology

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We experimentally examined the influence of grass competition, grass species identity (taxa) and water availability on the seedling growth and survival of two dominant tree species (Vachellia (formerly Acacia) robusta and V. tortilis) of the Serengeti National Park in Tanzania. Despite being widely distributed, the species have an opposing overstorey dominance across a rainfall and productivity gradient, with V. robusta dominating the more productive mesic sites and V. tortilis in the lower productivity, drier sites. We investigated the role of different grass species, which vary in distribution and abundance across the rainfall gradient, in influencing the growth and survival of Vachellia seedlings. We found a significant effect of grass competition but no effect of grass species identity on the growth or survival of seedlings. Seedling survival was highest in the absence of grass competition, intermediate when grasses were defoliated to simulate grazing and lowest when grown with ungrazed grasses. Grass competition had a more negative effect on the stem diameter of V. tortilis than V. robusta. All V. tortilis seedlings grown under a combination of drought conditions and unclipped grasses died by the end of the experiment. However, reduced grass competition by simulated grazing improved V. tortilis seedling survival to comparable levels achieved by V. robusta species. Our study advances our understanding of tree and grass competition across environmental gradients and suggests that the presence of grass and soil moisture have species‐specific effects on tree seedling growth and survival in African savannas.

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Seasonal facilitative and competitive trade‐offs between shrub seedlings and coastal grasses

Cited by 6 publications

References 53 publications

Trait-Based Investigation Reveals Patterns of Community Response to Nutrient Enrichment in Coastal Mesic Grassland

Trait-Based Investigation Reveals Patterns of Community Response to Nutrient Enrichment in Coastal Mesic Grassland

Decreased temperature variance associated with biotic composition enhances coastal shrub encroachment

Tree and grass competition in savannas: Interactive effects of soil moisture, grass defoliation and grass species identity on the growth and survival of tree seedlings

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