Botanic Gardens Conservation International
BGCI provides a global voice for all botanic gardens, championing and celebrating their inspiring work. We are the world's largest plant conservation network, open to all. Join us in helping to save the world's threatened plants.

The Price Of Conservation: Measuring The Mission And Its Cost

Volume 7 Number 1 - January 2010

Patrick Griffith and Chad Husby

Montgomery Botanical Centre has been investigating the relationship between the conservation value and the financial costs of their living collections.


Conservation is a primary purpose of the botanic garden living collection. Recent worldwide economics have placed every aspect of botanic garden operations under closer scrutiny. So, these days, measuring success is vital, and controlling cost is critical. In a world of disappearing plants and shrinking resources, knowing real success and real costs of conservation work is essential.

The limiting element of conservation work is funding. Maximizing conservation per dollar spent is important. For plant conservation goals, straightforward metric assessments of success have been lacking – often, success is qualitatively evaluated. Modern tools allow direct measurement of conservation. DNA-based studies are increasingly less expensive and offer greater resolution.

“When funding is in short supply, maximizing conservation per dollar spent is important”

Our garden is focused on three plant groups, all with myriad conservation concerns: Cycads, Palms, and Tropical Conifers. Protocols for living conservation collections at Montgomery Botanical Center (MBC) were developed in the 1990s following isozyme-based studies of cycad genetics (Walters and Decker-Walters, 1991). Basically, within a single population, we seek to conserve at least 15 individual plants, preferably from at least 3 different mothers. In other words, maintaining 3 accessions per population, each with multiple qualifiers, is our goal.

This protocol is a good place to begin investigating the relationship between the genetics and economics of conservation collections in a botanic garden setting. To frame the question directly: how effective is our conservation strategy, as measured against the investment?

A case study

Botanical science can directly inform botanic garden management; science can guide strategy. To approach this living collections management question, we located a suitable model system. Our collections of Keys Thatch Palm (Leucothrinax morrisii) were well suited to the exercise, owing to large numbers of plants curated from a single isolated population. We maintain almost 60 palms from this population on the grounds, and curate them by accession, so we can separate them into half-sibling groups. All of these resulted from a single collecting trip in the late 1990s.

Using a recently-developed genetic assessment method, we compared these 60 plants in the collection to a broad sample of plants still surviving in the original population (Namoff et al., ined.). Stated simply, around 94% of the wild genes in that population are represented in the collection.

So, in this case a collection of 60 plants captures all but a few percent of the population diversity. Often, though, collections may contain fewer representative plants. We spent time processing these data to model how genetic capture functions over a range of collection sizes. We believe these results are useful as a point of consideration for collections planning.

Economics of the conservation collection

The data gleaned here, when compared to investment in the collection, can offer some potential insight of use for botanic garden conservation. Here, we present a simple visualization of the interplay of three variables: plants, genetic capture, and cost.

Sampling methods vary among collectors and gardens, so to offer broad applicability for the very diverse botanic garden community, we simplify the main sampling metric as “number of plants maintained in collection.” This is a straightforward count, very easy to calculate, and is perhaps the simplest benchmark for measuring an institution’s investment in a particular plant group, species, or population. Since this is such a fundamental parameter, we chose to also make it the “common denominator” for this model.

The important metric with regard to conservation success is “degree of genetic capture.” For our case study, this was measured via ISSR (inter-simple sequence repeat) data, but a broad variety of modern methods exist for the assay of genetic diversity.

The third metric examined is monetary investment. Managers and governing organisations are quite familiar with this measure. Calculating the cost of maintaining a collection of plants may be performed in a way that makes the most sense to the organization involved. The cost of obtaining the collection in its first year is almost always greater than the annual cost of keeping the collection. In our study, we calculated fixed costs (fieldwork expenses) and variable costs (cost to maintain an individual plant per year). One quick, straightforward way to estimate this cost is to divide the annual “horticulture” and “plant records” costs by the number of plants maintained.

Insights from this model

The three graphs presented at the end of the article show the interaction of these three variables. The first graph (Graph A) models the increase in genetic capture, as the number of plants is increased. Essentially, this relationship follows an inverse exponential pattern. The important consideration here is that initial increases (for example, from 1 plant to 5 plants, or from 1 plant to 10 plants) give a steep increase in genetic capture. There is a point at which additional plants in the collection do not add significant conservation value. In economics, this type of pattern is called the “law of diminishing marginal returns.”

Graph A: The conservationist’s curve: graph of collection size vs. allele capture.

Graph A: The conservationist’s curve: graph of collection size vs. allele capture.

The second graph presented here (Graph B) shows the relationship between collection size and cost. Since each plant costs the same to maintain, there are really no surprises here; more plants equal higher costs. The position of the Y-intercept is equal to the fixed cost of bringing the plants to the garden, and is never equal to zero. For most conservation work, major costs here include travel to field sites and personnel costs for the field botanist. The slope of the line reflects the efficiency of the horticulture operation. Administrators grasp this type of straight-line function easily.

Graph B: A manager’s view: graph of collection size vs. cost

Graph B: A manager’s view: graph of collection size vs. cost

The third graph brings all three variables together (Graph C). Again, we use the number of plants as the basic benchmark. Our metric, “unit cost of conservation,” is simply the % genetic capture divided by the cost of that collection. The behavior of this curve has much to say about the economics of botanic garden conservation. First, there is significant decrease in the unit cost as the collection increases above one individual. This is followed by a steady increase in the unit cost as the collection is increased further. Ultimately, the unit cost more or less increases linearly.

Graph C: reconciling cost and conservation: graph of collection size vs. “unit cost” of genetic capture.

Graph C: reconciling cost and conservation: graph of collection size vs. “unit cost” of genetic capture.

Two primary points are meaningful here. First, there is a collection size at which there is a maximum efficiency for conservation. This is at the lowest Y-value on the curve. Second, there is a maximum collection size where the unit costs are equal to the lowest collection size. Simply stated, “if you would grow one, you may as well grow twenty,” as the unit cost of conservation is the same.

Going forward

This study compares the conservation value of a living plant collection, and its monetary cost over time. What does this mean for the botanic garden? Space, staffing, funding, and priority are all important considerations for any project. For conservation, a direct metric of success is helpful for evaluation and future planning. From the managerial perspective, knowing projected outcomes relative to investment is the key to most decisions. In very broad terms, this model provides one potential starting point for the Comptroller and the Curator to sit down at the same table.

Like all models, this one is best when it is used with accurate data. Our case study of Leucothrinax employed a long-lived, polycarpic perennial palm, with a monoecious breeding system and a straightforward life history. The targeted population shows healthy recruitment, and is easily circumscribed by the boundaries of Big Pine Key, an island. We selected it as a case study for these reasons, as it is more or less generalized in its biology.

Within the palm family alone, there are many other life histories, habits, phytogeographies, conservation concerns, and breeding systems. One prominent example is Corypha taliera. This species is known from perhaps fewer than 20 living individuals, and is extinct in the wild. Its century-long, hapaxanthic life history adds another level of complexity to its management. One high-profile species, Wollemia nobilis, has no discernable genetic variation in the wild (Peakall et al., 2003), so any single-specimen garden collection is perhaps a more-or-less complete genetic collection.

Examining our protocol with this model system, we found that our existing target of 15 individuals does provide for a healthy level of genetic capture, consistent with our goals. We found that our highest efficiency in conservation versus cost occurs at around 5 individuals.

“In many cases it is prudent to grow as many plants as you can afford.”

The upper limit to a conservation collection need only be limited by resources, though. There are certainly many cases where it is prudent to grow as many plants as you can afford, and examine the genetics when you get a chance. Here at Montgomery, we recently planted our most extensive single-species cycad collection, 79 individuals of Cycas micronesica, representing 29 accessions from 2007. This cycad has a high likelihood of going extinct in the wild, and our recent conservation efforts may have obtained some of the last seed that will be produced in situ. As the genetic information becomes available (Cibrian et al., 2008), we can consider thinning any potential genetic duplicates if space is needed. Since unforeseen circumstances can also cause the loss of individuals in a collection (Griffith et al., 2008), some redundancy is important. In such cases, it is absolutely worth the extra cost to grow a large collection.


Cibrian, A., Marler, T. and Brenner, E.D. 2008. Development of EST-microsatellites from the cycad Cycas rumphii, and their use in the recently endangered Cycas micronesica. Conservation Genetics.

Griffith, M. P., Noblick, L. R., Dowe, J. L., Husby, C. E. and Calonje, M. 2008. Cyclone tolerance in New World Arecaceae: biogeographic variation and abiotic natural selection. Annals of Botany 102: 591-598.

Namoff, S., Husby, C. E., Francisco-Ortega, J., Noblick, L. R., Lewis, C. E. and Griffith M. P. Ined. Evaluating a botanic garden conservation protocol: Case study of an ex situ plant collection via molecular means.

Peakall, R., Ebert, D., Scott, L.J., Meagher, P.F. and Offord, C.A. 2003. Comparative genetic study confirms exceptionally low genetic variation in the ancient and endangered relictual conifer, Wollemia nobilis (Araucariaceae). Molecular Ecology 12:2331–2343.

Walters, T. W. and Decker-Walters, D. S. 1991. Patterns of Allozyme Diversity in the West Indies Cycad Zamia pumila (Zamiaceae). American Journal of Botany 78: 436-445.

Patrick Griffith
Executive Director

Chad Husby
Collections Manager and Botanist
Montgomery Botanical Center,
Coral Gables, Florida USA.


We are very grateful to the International Palm Society for funding the conservation genetic assay. The entire MBC Team, especially Palm Biologist Larry Noblick, has done a great job caring for these living treasures for over a decade. Our colleagues Carl Lewis, Sandra Namoff, and Javier Francisco-Ortega performed the labwork for the analysis. This economic model was first presented in a panel discussion organized by Andrea Kramer of the BGCI, as part of the American Public Garden Association 2009 National Meeting.