Forensic Botany or the uses of plants in criminal investigations
Forensic botany is the application of plant sciences to criminal investigations. A relatively new discipline, forensic botany incorporates several subdisciplines: palynology (the study of pollens), dendrochronology (the study of tree rings), limnology (the study of aquatic environments), systematics (the classification of plants), ecology (the study of ecosystems), and molecular biology.
Unlike forensic anthropologists, forensic botanists do not normally deal with human remains. Their primary role in an investigation is in making connections between evidence and a crime. For example, pollen can be used to connect a suspect to a victim or scene. Pollen is a powder-like substance released by plants as part of their reproductive cycle. Since it is produced in large volumes and is easily transported by wind, pollen grains are often found on clothes, hair or skin. If investigators find a rare plant type near a murder victim, the presence of its pollen on a suspect could place them at the scene. Even for common plants, each environment has its own unique combination of pollens, and this 'signature' can link an individual or object to a location. Pollen signatures may also indicate that a body has been moved or suggest the type of area where the original crime took place.
Botanical evidence and clandestine graves
Botanical evidence can also be used to identify clandestine graves. When soil is disturbed, certain plants quickly invade the fresh surface. Other species follow in succession until the area recovers. However, the composition and distribution of the new assemblage is never exactly the same as the original community. In addition, the presence of a buried body may chemically change the soil and either promote or inhibit growth. Either way, the disturbed area will be at a different stage than its surroundings. These differences may be visible for decades.
Botanical evidence and estimating time elapsed since death
Aquatic species can also be helpful. For example, algae and diatoms can be used to diagnose death by drowning in freshwater. To establish drowning, botanists identify the number and species of diatoms present in the lungs and other tissues and correlate them with the flora from the location the individual was found. Because algae and diatoms vary seasonally, their abundance and diversity in an area can also approximate time since death or generate a 'signature' of an aquatic habitat that can match a body to a given location.
Trees and roots are useful for determining elapsed time since death, time since a body was placed at a given location or the season in which a death occurred. Because woody plants and trees grow in annual cycles that vary with environmental conditions, growth rings can be counted to provide the timing of an event, sometimes centuries later. This is particularly accurate if the roots grow through clothing or bone. Even partial damage to root growth can suggest the period since an interruption occurred.
Despite many benefits, forensic botany has limitations. Because pollen is so common, it can be difficult to associate particular pollens with a specific area. In addition, investigators must ensure that buried evidence is not contaminated by fresh pollen at the scene. If the evidence is not protected, it is impossible to determine whether the pollen was there at the time of death or not. Root evidence must also be used cautiously. Extra, false, or distorted rings can lead investigators to over or under-estimate the actual length of time a body has been in a location. If a body is covered by some of the original vegetation at the time of burial, it could look as if the plant has been at the scene longer than the body below. In contrast, decomposition processes may delay the growth of a plant and cause a plant younger than the burial to be present on the surface. Like all forensic investigators, botanists must collect, document, and preserve their evidence very carefully to ensure their interpretations are valid and admissible in court.
A report is a formal description of an event or investigation. A forensic report explains what an investigator did, how they did it and what they think the evidence shows. A forensic investigator's report is especially important because it must be able to explain the results of the investigation to a judge and possibly a jury who would not be able to attend a crime scene and observe an investigation first-hand. There are no agreed-upon protocols or standards for writing forensic reports in Canada, but most forensic scientists use a scientific format that includes the following:
- Report summary
- Background (how the author became involved in the case)
- Qualifications of the author (what makes the author an authority on the subject)
- Materials, methods and limitations (what work was done, how and why it was conducted, and any barriers to further investigation/analysis)
- Results (what the evidence found)
- Interpretation of results (what the evidence means, within the area of expertise)
- Conclusions (another short summary of the case, the findings and their importance)
- Bibliography (what sources of information - professional literature, interviews etc - were used).