Theconservation and restoration of herbaria includes the preventive care, repair, and restoration ofherbarium specimens. Collections of dried plant specimens are collected from their native habitats, identified by experts, pressed, and mounted ontoarchival paper. Care is taken to make sure majormorphological characteristics are visible. Herbaria documentation provides a record of botanical diversity.[1]
Professionals who make decisions about the conservation-restoration of botanical specimens includeregistrars,curators, andconservators who work on herbarium collections in universities and museums. Herbarium specimens may be susceptible towater damage,mold,pests, unattached specimens,dust,dirt, and damage from improper storage conditions.Preventive conservation can prevent much of the damage that could occur.
Aherbarium is a collection of preserved plant specimens and associated data used for scientific study.[2] Originally, the word "herbarium" referred to books about medicinal plants. In 1700, FrenchbotanistJoseph Pitton de Tournefort used the word to describe a collection of dried plants andCarl Linnaeus continued to use this term in his work which is where the term caught on. Initially, herbarium collections were bound in volumes instead of on individual sheets as it is done today.[3] It is not exactly known how long dry plant specimens last in storage, but with proper conservation, they have been able to last many centuries. Specimens collected by Linnaeus in the eighteenth century and by Banks andSolander on theEndeavour voyage in 1788 are still excellently preserved.[4] The specimens may be whole plants or plant parts. These will usually be dried and pressed and mounted on a sheet of paper but, depending upon the material, may also be stored in boxes or kept in alcohol or other preservatives.[5]
The practice of preventive conservation is the management of fluctuations in temperature, light, relative humidity, pests, and pollutants that can deteriorate museum collections.[9] These factors are considered agents of deterioration. Understanding the practice of preventive conservation as well as the agents of deterioration is most important when trying to protect, display, and store collections within the conservation field.
Proper storage in secure and stable shelving will allow for less stress and movement to affect plant collections. Dried and pressed plant specimens can be stored best in archival-grade boxes, or tied in bundles in cardboard folders for long-term storage. For collections that may be handled more frequently, specimens can be placed in archival-grade plastic sheets placed in ring folders.[4]
Water damage resulting from flooding can result in shrinking, distortion, or staining of plant materials.[10] Unforeseen disasters can occur at any time anddisaster recovery planning and materials for herbaria are similar tomuseums andlibraries. Little can be done with burnt specimens and fragmented specimens except to preserve and protect what is left intact. The damage most likely to occur is water damage through natural or man-made flooding, such as roof leakage orfire sprinkler malfunction. Damaged or waterlogged specimens are frozen to delay deterioration and prevent a fungal attack, which gives curators time to evaluate the situation and decide how best to approach the problem.
Common herbarium pests include:silverfish,book lice (psocids),cigarette or tobacco beetles (Lasioderma),dermestids,drugstore beetles (Stegobium paniceum)[5]A reoccurring threat to the longevity of herbarium specimens is insects, a number of which find dried plants palatable. Historically, various methods have been used to kill insects, which either come in with the plants when they are collected or are in the building where the plants are stored.[6] Pests are commonly treated with two different methods:
Anintegrated pest management program is cost-effective over time and the best preventive measure against pests.
The primary risk factor forfungal attack is incomplete drying of specimens, caused either during the specimen preparation process or afterwards, or in collections that become wet later throughflood, other water damage or improper storage conditions, especially in thetropics. Properly dried plant specimens will not suffer from fungal attack if stored in the correct conditions. During the drying process specimens are particularly at risk if they dry slowly. This happens through poor drying conditions or specimens being wet before being pressed or having water-retaining orsucculent parts. Specimens with sugaryexudations or large quantities of nectar are also particularly attractive to fungi and need special care during drying to ensure that they dry fast enough to prevent mold growth. If fungal growth occurs on specimens, it can be brushed with 95%ethanol ormethylated spirits (denatured alcohol). However, this may alter the specimen for chemical and other investigative research and only kills the fungus present on the specimen, not preventing further problems of fungal growth.[12]
Herbarium specimens are sensitive tovisible light andultraviolet radiation, which can cause fading of biologicalpigments (fading or shifts in color) and/or damage to chemical bonds (weakened or embrittled).[13]
To best establish protocols for specimen movement control, a system of documentation can be set up to monitor and control collections.[citation needed] At theNational Museum of Natural History, theft is prevented by maintaining limited access to where collections are stored. In the event of a specimen leaving the site through outgoing loans, records are kept which gather letters of request, the transmission of names, and other supporting documentation.[14]
Storage in metal cabinets is the best material to maintain herbaria collections. Metal cabinets do not releasevolatile organic compounds as wooden cabinets do. The metal shelves can be easily cleaned and a well-sealed cabinet will provide a stable microclimate for the specimen.[15]
Ensuring that every specimen has an individual accession number will reduce the risk of disassociation. The accession number relates that number to an identifiable object and the object can only be moved if its location is updated, ensuring the object is never disassociated from its data. Most herbaria utilize a standard system of organizing their specimens into herbarium cases. Specimen sheets are stacked in groups by the species to which they belong and placed into a large lightweight folder that is labeled on the bottom edge. Groups of species folders are then placed together into larger folders by genus. The genus folders are then sorted by taxonomic family according to the standard system selected for use by the herbarium and placed into pigeonholes in herbarium cabinets.[4] Locating a specimen filed in the herbarium requires knowing the nomenclature and classification used by the herbarium. It also requires familiarity with possible name changes that have occurred since the specimen was collected, since the specimen may be filed under an older name. Modern herbaria often maintain electronic databases of their collections. Many herbaria have initiatives to digitize specimens to produce a virtual herbarium. These records and images are made publicly accessible via the Internet when possible.
Before beginning the process of restoration of a herbarium sheet, best practices suggest that the original mounted specimen be photographed for reference to ensure a new sheet is as close to the original as possible. The original mounting sheet can be dried and flattened in the same manner as the plant to serve as a reference for positioning the specimen on a new sheet. Additionally, any labels or supplement information accompanying the plant should be placed in the same place.[16]
Dust and dirt are removed from herbarium sheets by using a smoke sponge. Conservators gently rub the place where the dirt is and then softly remove any excess with a fine brush. Care must be taken by conservators when dealing with older prepared specimens that may have traces of toxic chemicals. Making use ofpersonal protective equipment by professionals can reduce the risk of exposure or harm due to dangerous materials.
Broken specimens are reattached to the herbaria sheet using thinly cut strips of archival pre-gummed linen tape. Detached materials such as seeds or leaves are placed in an acid-free card fragment packet, which is secured onto the sheet with the original specimen.
Unattached specimens are removed from the herbaria sheet by humidifying it to make them pliable and removing the plant with a paper lifter (smooth wooden spatula). They are then placed to dry and flatten along with the original mounting sheet and written documentation (label and annotations). The specimen and original documents are then remounted to a new sheet using the original sheet as reference.