How to write an Introduction that is effective and relatively easy

Notes: 

1. This advice is for my field and the type of journals I publish in which fall under ecological and biological sciences. Different fields likely have different definitions or expectations. 
2. My advice is strongly influenced by, but not identical to, writing advice provided to me by Tom Whitham during a graduate class. I internalized it and find that I still largely follow it to this day. Thanks, Tom.
3. One size does not fit all, but these suggestions will help you get a first draft on paper that can be modified in any way you or your coauthors wish. 

General advice:

1. An introduction involves some review of the literature but is not in itself an exhaustive review of the literature.
2. An introduction must lay out the rationale, context, and basis for understanding a study. Information not directly germane to the coming study does not belong.
3. Practice thinking bigger than the particulars of your study. 
4. Don’t get derailed struggling for the perfect sentence structure or working in a first draft, or that you can’t remember the year of that citation. Just write according to a well-defined structure, and clean it up later. Get words on paper.
5. An introduction seldom requires more than 4 paragraphs. Really. 3 might be fine. Save some blab for the discussion or your next paper, or just skip it.
6. Introduction structure is an inverted triangle, broad at the top, narrow at the base (except for the very last sentence which gets broad again….Ok it’s a short-stemmed martini glass).

A structure to begin with:

Paragraph 1: Must establish the broad context of the study, the general topic. 

If you are doing basic science it should involve a scientific theory which you wish to test, refine, debunk, etc. If you are doing applied science, this is the problem affecting nature or people that you hope your work might solve.

Sentence 1- State the central theme in a clear, uncomplicated topic sentence. Since it is an overall summary of an area of inquiry, it will probably have multiple citations.

Examples: “The stress gradient hypothesis predicts that as abiotic stress increases, the prevalence of facilitative species interactions also increases.”

“Since the 1990s, a consensus has emerged that greater richness of ecological communities tends to be positively related to ecosystem functions”

“The extent and severity of western wildfires have rapidly increased in recent decades and has been linked to climate change and management legacies”

The next few sentences will flesh out some details and logical outcomes of the central theme. For example we might point out that in the American southwest, specifically changing vapor pressure deficit is linked to fire behavior, and climate predictions suggest the vapor pressure deficit is likely to decline even further by mid-century. It may be appropriate to highlight any alternative hypotheses or models about how the world works here, or that there is controversy in the literature. Do cite studies, just don’t feel like you have to cite everything ever written. Focus on the most important citations, and do not get into study details here.

Last sentence – You will state something general that is still not known, and that is in a general sense the knowledge that you wish to contribute. If you are doing basic science, this is the chink in the armor of our knowledge, the missing piece. If you are doing applied science, this is a possible solution to a problem (broad sense).

Examples: “Despite the hundreds of studies establishing a clear link between terrestrial plant richness and productivity, there have been only a handful of studies and no consensus on whether the richness of other communities also affect ecosystem functions.”
“To date all research has addressed the influence of vascular plant seeding of post-fire erosion, and there is a paucity of information about the utility of non-vascular plants for this purpose” 

Since paragraph 1 is such a tone setter, here’s a real example, consistent with the advice above:
The drylands of the world present some of the more challenging land degradation problems, driving the expansion of the desert biome (Millennium Ecosystem Assessment 2005). It can be exceptionally difficult to rehabilitate degraded drylands for various reasons (Allen 1995), including: 1. The scarcity of resources–especially water– that recovering biota need (Bainbridge 2007), 2. Persistent dominance of invasive plants (Miller et al. 2011), and 3. The propensity for soil erosion to become a self-reinforcing process that precludes the recovery of desired biota (Ludwig and Tongway 2000; Miller et al. 2012). Rehabilitation approaches may have to focus not just on reintroducing desired biota, but also restoring a system’s ability to both capture and retain resources (Tongway and Ludwig 1996; Jacobs 2015) and resist invasion (Chambers et al. 2014). Drylands also are distinct in that there can be substantial interspaces between the canopies of grasses and shrubs, even when they are not degraded (Kéfi et al. 2007). The soil surface of these interspaces is the habitat of a highly functional assemblages of soil-aggregating organisms (cyanobacteria, mosses, lichens, fungi), which together compose biological soil crusts (biocrusts). Rehabilitation of biocrusts could benefit degraded drylands by increasing erosion resistance (Chaudhary et al. 2009), by creating and maintaining soil fertility (Reynolds et al. 2001; Belnap 2002), influencing the capture or redistribution of water (Eldridge et al. 2010; Chamizo et al. 2012), and discouraging some problematic exotic invasive plants (Serpe et al. 2006; Peterson et al. 2013). A real or perceived weakness of biocrusts in a rehabilitation context is their variable but often slow natural recovery from disturbance (Weber et al. 2015), but recent research indicates that assisted recovery of biocrusts can be achieved (Wang et al. 2009; Lan et a. 2014; Liu et al. 2013). Development of viable and economical biocrust rehabilitation techniques can be viewed as an opportunity and a pathway to enhance the function of degraded drylands (Bowker 2007). 

{If I engage in some self-critique here it would be that my paragraphs tend toward the lengthy side. But, they flow well in my biased opinion.  I really want to focus on the structure and  flow in this post; you can go for brevity in your writing if you like, and I'll work on being less wordy in the future}


Paragraph 2: Must establish the specific topic of the study. 

Supply key facts, and some relevant details about what you identified in the last sentence of paragraph 1.

“Like plant communities, corals may also be highly diverse communities of sessile organisms that potentially contribute to a different set of ecosystem functions. These functions include…….{pertinent details here}.  Also like plant communities, corals are threatened by anthropogenic stressors which compromise biodiversity. The identity of the stressors is again different from vascular plants…{pertinent details here}”

Last 1 or 2 sentences will identify more specific unknowns about your specific topic.

Here’s a continuation of the previous real example:
Biocrust rehabilitation is a young field that has only become a common research topic in the last ~15 years. A recent proliferation of research on this topic has emerged, especially from China (Tian et al. 2006; Li et al. 2010; Liu et al. 2013), but many questions remain unresolved (Zhao et al. 2015). Biocrusts can be rehabilitated in dryland ecosystems using salvaged natural biocrust material as inoculum (St. Clair et al. 1984; Belnap 1993). This practice may result in enhancement of ecosystem functions such as soil aggregation, and the creation of soil fertility (Maestre et al. 2006; Chiquoine et al. in press). However, it is uncommon to have a ready supply of salvageable biocrust materials on hand. To fully realize the potential of biocrusts as a rehabilitation tool, ex-situ cultivation techniques must be developed and optimized (Bowker 2007; Zhao et al. 2015). With a few exceptions (Xu et al. 2008; Xiao et al. 2011), most work in this arena has focused on culture of biocrust cyanobacteria with notable successes (Liu et al. 2013). Cyanobacteria may be isolated and grown in liquid media, which can be scaled up to produce inoculum in large quantities (Rao et al. 2009; Liu et al. 2013). Research on the other common biocrust autotrophs, mosses and lichens, has not progressed as far as the research on cyanobacteria (Zhao et al. 2015). Despite this, mosses are also generally culturable, either vegetatively from fragments of gametophytes or from spores, and can be grown on sand or agar substrates (Stark et al. 2004; Xu et al. 2008; Bu et al. 2011). Despite this knowledge, there remains much work to do to optimize the moss culture process to make it efficient enough to produce sufficient quantities of material for use in field applications. To our knowledge, rapid culture of dryland soil lichens has never been achieved and was therefore a much more notable research gap. Because some lichens are nitrogen fixers (Belnap 2002), it would be especially beneficial to overcome the technological hurdle of lichen culture, so that they may be artificially grown as a rehabilitation material (Bowker et al. 2010).

{Did you catch that? We went from talking generally about the challenges of rehabilitating drylands, to the specific state of knowledge about biocrust rehabilitation for ecosystem outcomes.}

Paragraph 3: Establishes why your study system is ideal to address this topic. 

Note: There is often but not always a need for this paragraph. 

Example topic sentences:
“The widespread woody plant mortality observed during the 2003 drought in Northern Arizona, across broad elevational and edaphic gradients, make it the ideal location to identify determinants of different mortality rates.”

“The 2011 Wallow fire was the most extensive wildfire in Arizona state history, burning in a mosaic of high, moderate, and low intensities. Thus, it affords us an opportunity to explore the variation in hydrological outcomes of wildfire in a heterogeneous landscape”

Just lay out your reasoning for the selection of either your study organism, community, location, whatever. There ought to be good reasons, and you know them.

Paragraph 4: Must state your questions or hypotheses

Sentence 1: Summarize what you did in the study in 1 or 2 sentences
“We conducted a meta-analysis of the effects of biochar on crop productivity and soil fertility”

“We sought to determine the relative importance of community richness, evenness and spatial patterning on nutrient cycling rates in Northern Arizona.

Next few sentences: State your specific hypotheses and questions. 1 – 5 is a good number usually.

You may use a numbered list format if it’s useful. It helps readers follow too.
“Specifically, we tested the hypotheses that: 1. Blue, but not red skittles, correlate with lower cancer incidence in rural counties, and 2. This positive benefit is contingent upon navel width.”

The above may be sufficient, but in cases where hypotheses need a little explanation or justification, follow each with a statement explaining some nuance or novelty of the hypothesis.

Specifically we tested the hypotheses that:
1. Blue, but not red, skittles correlate with lower cancer incidence in rural counties. Previous research has overlooked this factor, focusing on genetics and environmental exposure to carcinogens.
2. The positive benefit of blue skittles is contingent upon navel width. Since wider navels can accommodate more blue skittles, subjects with wider navels can benefit from higher dosage”

Final sentence: An impact statement. State what we might gain from this study. It should link back to the general topic in the beginning.

“If these hypotheses are correct, we may begin to apply skittles to navels as an inexpensive yet effective cancer treatment in impoverished rural areas”.