Savannas occur where trees and grasses interact to create a biome that is neither grassland nor forest. Woody and gramineous plants interact by many mechanisms, some negative (competition) and some positive (facilitation). The strength and sign of the interaction varies in both time and space, allowing a rich array of possible outcomes but no universal predictive model. Simple models of coexistence of trees and grasses, based on separation in rooting depth, are theoretically and experimentally inadequate. Explanation of the widely observed increase in tree biomass following introduction of commercial ranching into savannas requires inclusion of interactions among browsers, grazers, and fires, and their effects on tree recruitment. Prediction of the consequences of manipulating tree biomass through clearing further requires an understanding of how trees modify light, water, and nutrient environments of grasses. Understanding the nature of coexistence between trees and grass, which under other circumstances...

Tree-grass interactions in Savannas

Herbivory by domestic and wild ungulates is a major driver of global vegetation dynamics. However, grazing is not considered in dynamic global vegetation models, or more generally in studies of the effects of environmental change on ecosystems at regional to global scale. An obstacle to this is a lack of empirical tests of several hypotheses linking plant traits with grazing. We, therefore, set out to test whether some widely recognized trait responses to grazing are consistent at the global level. We conducted a meta-analysis of plant trait responses to grazing, based on 197 studies from all major regions of the world, and using six major conceptual models of trait response to grazing as a framework. Data were available for seven plant traits: life history, canopy height, habit, architecture, growth form (forb, graminoid, herbaceous legume, woody), palatability, and geographic origin. Covariates were precipitation and evolutionary history of herbivory. Overall, grazing favoured annual over perennial plants, short plants over tall plants, prostrate over erect plants, and stoloniferous and rosette architecture over tussock architecture. There was no consistent effect of grazing on growth form. Some response patterns were modified by particular combinations of precipitation and history of herbivory. Climatic and historical contexts are therefore essential for understanding plant trait responses to grazing. Our study identifies some key traits to be incorporated into plant functional classifications for the explicit consideration of grazing into global vegetation models used in global change research. Importantly, our results suggest that plant functional type classifications and response rules need to be specific to regions with different climate and herbivory history.

Plant trait responses to grazing – a global synthesis

Fire shapes the distribution of savanna and forest through complex interactions involving climate, resources and species traits. Based on data from central Brazil, we propose that these interactions are governed by two critical thresholds. The fire-resistance threshold is reached when individual trees have accumulated sufficient bark to avoid stem death, whereas the fire-suppression threshold is reached when an ecosystem has sufficient canopy cover to suppress fire by excluding grasses. Surpassing either threshold is dependent upon long fire-free intervals, which are rare in mesic savanna. On high-resource sites, the thresholds are reached quickly, increasing the probability that savanna switches to forest, whereas low-resource sites are likely to remain as savanna even if fire is infrequent. Species traits influence both thresholds; saplings of savanna trees accumulate bark thickness more quickly than forest trees, and are more likely to become fire resistant during fire-free intervals. Forest trees accumulate leaf area more rapidly than savanna trees, thereby accelerating the transition to forest. Thus, multiple factors interact with fire to determine the distribution of savanna and forest by influencing the time needed to reach these thresholds. Future work should decipher multiple environmental controls over the rates of tree growth and canopy closure in savanna.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1461-0248.2012.01789.x

Ecological thresholds at the savanna-forest boundary: how plant traits, resources and fire govern the distribution of tropical biomes

Summary


1 The savanna–forest boundary in the tropics is marked by a discontinuity not only in tree density, but also in species composition, with few tree species regularly occurring in both savanna and forest environments.



2 We performed comparative growth analysis for nine congeneric pairs, each containing one savanna species and one forest species, grown in a factorial design involving two light and two nutrient levels.



3 Contrary to predictions, there was no difference in relative growth rates (RGR) between savanna and forest species. However, there were clear differences in allocation patterns and in phenotypic responses to light intensity. Savanna species allocated more biomass to roots and maintained lower leaf area per unit plant mass (LAR), and lower leaf area per unit leaf mass (SLA).



4 Savanna species also exhibited greater phenotypic plasticity in specific leaf area, leaf area ratio and net assimilation rate in response to light intensity. An increase in LAR in response to shading of savanna species offset a decrease in net assimilation rate per unit leaf area (NAR), such that RGR was largely unaffected.



5 For most plant traits measured, more of the interspecific variation could be attributed to differences among genera than to differences between the two functional types, indicating that these seedling traits are highly conserved within the congeneric species pairs. Many of these traits were correlated to seed mass, which is itself highly conserved within genera.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2745.2003.00777.x

Comparative growth analysis of tropical forest and savanna woody plants using phylogenetically independent contrasts

C4 plants are directly affected by all major global change parameters, often in a manner that is distinct from that of C3 plants Rising CO2 generally stimulates C3 photosynthesis more than C4 ,b ut C 4 species still exhibit positive responses, particularly at elevated temperature and arid conditions where they are currently common Acclimation of photosynthesis to high CO2 occurs in both C3 and C4 plants, most notably in nutrient-limited situations High CO2 aggravates nitrogen limitations and in doing so may favor C4 species, which have greater photosynthetic nitrogen use efficiency C4 photosynthesis is favored by high temperature, but global warming will not necessarily favor C4 over C3 plants because the timing of warming could be more critical than the warming itself C3 species will likely be favored where harsh winter climates are moderated, particularly where hot summers also become drier and less favorable to C4 plant growth Eutrophication of soils by nitrogen deposition generally favors C3 species by offsetting the superior nitrogen use efficiency of C4 species; this should allow C3 species to expand at the expense of C4 plants Land-use change and biotic invasions are also important global change factors that affect the future of C4 plants Human exploitation of forested landscapes favors C4 species at low latitude by removing woody competitors and opening gaps in which C4 grasses can establish Invasive C4 grasses are causing widespread forest loss in Asia, the Americas and Oceania by accelerating fire cycles and reducing soil nutrient status Once established, weedy C4 grasses can prevent woodland establishment, and thus arrest ecological succession In sum, in the future, certain C4 plants will prosper at the expense of C3 species, and should be able to adjust to the changes the future brings Abbreviations: A – the rate of net CO2 fixation; gc – leaf conductance; PNUE – photosynthetic nitrogen use efficiency; WUE – water use efficiency

/pdf/quo-vadis-c4-an-ecophysiological-perspective-on-global-4rc51ewf7g.pdf

Quo vadis C4? ∗ An ecophysiological perspective on global change and the future of C4 plants

Temporal changes in the structure of a Trachypogon savanna protected for 25 years

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

J.J. San Jose

Author Tools

Chat about Author

Papers

Temporal changes in the structure of a Trachypogon savanna protected for 25 years