problem-solving in conservation biology and wildlife management (gibbs/problem-solving in...

CHAPTER 17

Plant Reintroductions:ReestablishingExtirpated Populations

Richard B. Primack andBrian Drayton

Simply buying conservation land and then guarding it against external threatsrepresents only part of an overall conservation strategy. Isolated conservationareas lose species over time due to a combination of human impact, randomenvironmental events, and population processes. The species that are lost tend tobe the ones with the greatest conservation value. For example, the Middlesex Fells,a conservation area in Massachusetts, has lost one-third of its native plant speciesover the last 100 years, including most of its orchids and lobeliads. Even when suchareas are carefully monitored and protected, the lost species are often not ableto return because of a fragmented landscape. Conservation biologists workingwith plants and animals are increasingly attempting to reintroduce species intoimpoverished sites within their historical range. The assumption is that many plantspecies are not capable of dispersing back to the original sites on their own andthat biologists have to assist in the dispersal process. However, this field of plantreintroduction is still in its infancy, and there are few documented examples ofsuccess, as defined as a reproducing population that is stable or expanding innumbers. Active investigations are underway to determine the most effectiveways to carry out reintroductions. Is it better to start new populations fromseeds, seedlings, or adult plants? How many seeds, seedlings, or adults need tobe used? Do the sites need to be modified before planting to increase the possi-bility of success? Do plants need to be taken care of after being planted (a ‘‘softrelease’’), for example, by being watered, being fertilized, or having competingspecies removed?

Objective

. To design and implement a reintroduction plan for a plant species and to deter-mine the effectiveness of reintroduction as a tool to establish new populations ofplant species.

Gibbs / Problem-Solving in Conservation Biology 9781405152877_4_017 Final Proof page 174 11.10.2007 1:48pm Compositor Name: PAnanthi

Problem-Solving in Conservation Biology and Wildlife Management: Exercises for Class, Field, and LaboratoryJames P. Gibbs, Malcolm L. Hunter, and Eleanor J. Sterling© 2008 James P. Gibbs, Malcolm L. Hunter, Jr., and Eleanor J. Sterling ISBN: 978-1-405-15287-7

Procedures

Initial Considerations

This plant-based project provides a practical introduction to many fundamentalquestions that arise in all reintroduction and restoration work, whether of plantsor other organisms. Plants are generally easier to work with than animals at manypoints in the reintroduction process. However, if your particular interest is in animalspecies, you should evaluate how the project would have to be different if you wereworking with an animal species.

Choosing a Target Site and Target Species

For this exercise, you need to identify two field sites. First, you should choose a sitethat appears to be recovering from past human activities as the target site for yourexperiment. These habitats might include heavily logged forests, degraded wetlands,over-used dune systems, isolated city parks, vacant lots, overgrazed rangelands,abandoned mines, or old industrial sites.

Second, you should choose a less-disturbed reference site that appears to besimilar in terms of such variables as soil type, soil moisture, the amounts of herb-aceous plant cover and woody vegetation, and the degree of shading. A comparisonof the target site with this nearby reference site could reveal one or more nativespecies that could potentially grow at the target site, but are currently absent.Human activity may be responsible for the loss of species from this site. What canyou do to get those missing native species to grow at the target site?

Designing the Reintroduction Plan

Your basic task is to determine the best possible way of creating a new population(or several populations) of a plant species on your target site. You need to designan experiment that will yield useful information. Be aware as you think aboutthis that although the data from your projects first year will be interesting andimportant, it will probably be a multi-year project. This means that others willcontinue your work at some point, and you should bear these future collaborators inmind when keeping records and in designing the monitoring and maintenance ofsites. Experiments that compare effects at more than one site, or from more than onemethod, often yield valuable results. A comparison might be made between usingseeds versus adults (assuming both are available); planting the plants into the intactground versus digging up the ground with a spade to reduce plant competition; orleaving the plants on their own after transplanting (‘‘hard release’’) versus watering,fertilizing, or weeding out competing plants (‘‘soft release’’). Other questionsof current research interest include: How many seeds do you need to create a newpopulation? How many plants do you hope to have growing at the target site? Howlong should the monitoring continue, and at what frequency?

In the Field

Material for the reintroduction, whether by seed or transplanting, should becollected from an area as close to the target site as possible, preferably the reference

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site. If the species is a perennial, you may be able to collect some seedlings or adultplants and transplant them to the target site. Good horticulture is the key to success,in particular, not damaging the root system or other plant parts in the process.The best method might be to dig up a whole clump of soil around and including theplant, and then place this into a hole dug at the target site. Discussions with peoplewho have gardening experience may be helpful. Such transplanting is often best doneearly or late in the growing season, or during periods of wet weather. It is importantnot to remove so many plants from the reference site that the original populationis damaged; as a rule of thumb, probably less than 20% of the seeds should beremoved, or less than 10% of the plants dug up.

Reintroductions should be made into clearly marked plots. If the plots are square(perhaps 0.5 m or 1 m on a side), then all four corners could be marked with stakes. Ifthe plots are round (perhaps 1 m in diameter), then only the center point has to beidentified with a stake. You should consider that the stakes may be removed orknocked down; exactly measure the distance and compass heading from each stake topermanent features of the landscape (e.g. ‘‘From the central stake in plot #3 to theisolated magnolia tree, the distance is 3.4 m in a direction of 838’’). For the vastmajority of species, it is not known how to create a new population. A comparisonof various methods will give you information on how to carry out a successfulreintroduction, and may well provide some new information about the biology ofthe target species.

Record-keeping

In order to evaluate the success of the experiments, careful records will have to betaken on how many seeds, seedlings, or adult plants were used, what procedures werefollowed, and the exact location of the plots that received plants. Ideally, you shouldalso note the dates of experimental work, the dates of monitoring visits, and the dateand general location of sources for your material (where you collected seeds orplants for transplant). These records will form the basis of a monitoring programover the following growing season and the coming years. All of this information willaid in the interpretation of results. Your records should include a clear description ofthe reintroduction plan as a whole, including the criteria used to choose species, therationale for the size of the experiment, the desired size of restored populations, andcriteria by which success will be measured.

Box 17.1 Equipment

. Local field guide to identify plant species

. Notebook and pencils

. Wooden or metal stakes cut to 30–40 cm lengths

. Compass

. Tape measure

. Plastic bags, ties, and labels for collecting seeds

. Trays, boxes, or large bags for transplanting adult plants

. Shovels or trowels

. Buckets and bottles for watering plants.

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Records of your activities need to be exceptionally clear and then written up asprogress reports. These materials should be photocopied and stored in electronicformat and kept in several secure, well-known places so that future classes canfollow-up on these experiments. How many seeds were used? Where were the plantsobtained? Where exactly are the plots located? What treatments were done tothe plots and when? You may wish to verify that your records are intelligibleto others besides the writers, asking classmates to examine them, and to try to locatefield sites.

Photographic records of reference site, target area, and experimental populationscan be very helpful as reminders and illustrations about the sites and the proceduresyou undertake, and can provide useful data in their own right.

A Final Comment to Future Classes Doing the Reevaluations

It is often difficult to create new populations of plant species. If no plants can befound in the experimental plots after one or two growing seasons, consider repeatingthe experiment (because some years may be better than others for reintroductions),or try using plots in different areas, more plots, or greater numbers of seeds andadult plants. Consider removing more of the competing vegetation, adding addi-tional soil or providing shading, depending on the circumstances. Something isbound to work.

Expected Products

. Rationale for choosing target site and target species

. Formal, detailed reintroduction plan

. Documentation of transplant activities sufficient to permit assessment oftransplant success in future years

. Assessment of what worked and what didn’t with recommendations for follow-uptransplant efforts (for resurvey years)

. Responses in a form indicated by your instructor to the Discussion questionsbelow.

Discussion

1 What if the classes visiting the sites in future years are unable to detect livingplants on any plots? Does it just mean that these techniques did not work at thisparticular time and place? How could the chance of success be increased?

2 What if the follow-up in one or two years shows numerous plants surviving, andeven flowering? Does this mean that the reintroduction was a success? Why orwhy not? What if only five plants survive? What if 100 plants survive, but thereare no new seedlings being produced?

3 If the goal is to create a population of 50, 500, or even 5 000 reproducing plants,how many seeds or plants should be used in the experiment?

4 On the basis of your experience with creation of new populations of plants, discussthe relative values of reintroduction versus protecting the remaining populations

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of declining species. What logistical, political, or biological considerations shouldbe taken into account?

5 On the basis of the data from your projects so far, what new information ortechniques should be incorporated in future projects of this kind?

6 If you have worked primarily with the reintroduction of locally extirpated speciesthat are not of conservation concern (i.e. not threatened or endangered), whatadditional considerations would you have to take into account if you use the sametechniques with globally threatened species?

7 What have you learned from the plant experiments that is applicable to animalreintroductions? What would be different about an animal reintroduction?

Making It Happen

Experience gained in these initial experiments can be more widely applied. As aclass project, you might consider restoring an entire biological community anddocumenting the process. The site could be abandoned farmland, a lawn, a pollutedpond, a channelized stream, a tree plantation, a vacant lot, or overgrazed rangeland.Such a project will probably take many years, but would serve as a demonstration toa wider audience. Volunteer workers from school clubs, local conservation organ-izations, and the general public could provide needed labor in creating fences,preparing the site, putting in new plants, and long-term maintenance. A goodphotographic record is useful in documenting the project and in writing populararticles about the project. Another project could be to focus on one species thatis rare or endangered in your region. Discussions with officials in the HeritagePrograms, or the regional office of state conservation agencies might help to identifysuitable species. A comprehensive project would involve study of the ecology of thisspecies in its existing populations, developing methods for propagating it in gardensor greenhouses and finally establishing new experimental populations in the wild.

In all such projects, make sure to seek the advice of local botanists or naturalists,who will have a good knowledge of local habitats and species, the locations ofpossible source populations (for seeds or transplant material), and may have valuableknowledge of recent changes in land use or the population dynamics of particularspecies.

Further Resources

The key reference in this field is Falk et. al. (1996). Guerrant et al. (2004) is also animportant supporting resource. Useful collections of articles can be found in thejournals Restoration Ecology and Restoration and Management Notes.

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