Archives For Julianne Beck

Embracing Trees for Our Future

Undercover Science

Julianne Beck —  July 13, 2015 — Leave a comment

If you spot a Chicago Botanic Garden volunteer wrapping their arms around a tree trunk this summer, don’t be surprised—what looks like a loving hug is actually a scientific measurement in process.

Using a specially designed tape measure, volunteers are recording the diameter of each tree before calculating the amount of carbon dioxide it stores. The study, launched by the Living Plant Documentation department five years ago, records the amount of the pervasive greenhouse gas stored by the Garden’s trees. The research team is interested in determining which trees are able to hold the most carbon for the longest amount of time.

PHOTO: Boyce Tankersley is researching the trees' response to increased carbon in the atmosphere, using data such as the growth rate of the particular tree species.

Boyce Tankersley and volunteers measure the diameter of each tree on the Garden campus.

The Tall and Short of It

It is one of the first such studies underway in a botanic garden setting. “We know carbon is increasing but we don’t have the numbers on how much carbon is being locked up by the urban forest,” said Boyce Tankersley, director of the Living Plant Documentation department. “This is where the Garden can play a role.”

Although similar studies have been completed by the lumber industry and others, it is important to understand how increased levels of carbon dioxide in the atmosphere are mitigated by cultivated trees, explained Tankersley. It’s also essential to document how those trees fare long term in evolving conditions.

The Garden has an especially diverse number of taxa, Tankersley said, positioning it perfectly to document how numerous species behave in locations from the McDonald Woods to the English Walled Garden to the parking lot. “The Garden is among the first to look at the trees in a Garden setting and at the diversity of taxa,” said Tankersley. “That’s a piece we’d like to shed more light on.”

This summer marks the second time the trees have been measured since the original data was gathered in the first year. Measurements will continue to be taken for another 15 to 20 years.

“We hope, when the data is analyzed, to be able to identify not only the trees that are best but the Garden settings that support their efforts in this regard,” anticipated Tankersley.

PHOTO: Tree canopy.

The Living Plant Documentation department is calculating the amount of carbon dioxide stored in each of the Garden’s trees.

Deep in the Woods

Trees are lauded for coming to our rescue in the face of climate change, but scientists have learned that these strapping heroes may not be infallible. “One thing we are looking for is the influence of carbon on the growth rate,” said Tankersley. His research team is paying close attention to the trees’ response to increased carbon levels in our atmosphere.

According to Tankersley, it has been documented that trees are growing more quickly than they have in the past, which comes with positive and negative repercussions. “Trees are providing an environmental service in a major way by absorbing carbon, but there’s a point of diminishing returns,” he explained. The wood of a fast-growing tree is softer, for example, which has a negative impact on the lumber industry, he explained. In addition, “with an increased growth rate, you also get increased susceptibility to insects and diseases.”

The concern underscores the need to observe the Garden’s trees for many years to take all such factors into consideration.

In addition, the team is watching the impact of weather on the trees, and taking dry spells or rainy periods, for example, into account when documenting tree growth over a given time frame. The Garden hosts a National Weather Service monitor on-site, which allows for weather-related calculations to be even more precise.

The Zipline

When the measurement phase of the study is complete, Tankersley plans to provide the data to a doctoral student in the Garden’s joint degree program with Northwestern University for formal analysis. “My take-home would be a list of the six best trees, perennials, and shrubs for sequestering carbon in the landscape in Chicago,” he said.

“We expect to find that trees like oaks, elms, and hickories—trees that are long-lived—provide a greater environmental service in this regard,” he added.

For homeowners who would like to assist with the issue now rather than wait for the final analysis, he suggests that they begin planting longer-lived trees. It may help mitigate, or reduce, the amount of carbon in the air and resulting climate change impacts such as extreme weather.

Our 2013 adaptive planting study carefully selected 60 suitable trees to plant for future generations. View the full list of suggested trees here.
PHOTO: Fastigiate English Oak acorns (Quercus robur).

It takes more than one year for the Garden volunteers to check the diameter of the 13,493 trees on-site, and enter the estimated carbon storage into a specialized database. The calculations are made using a formula developed by the U.S. Forest Service, said Tankersley.

The technique of measuring existing trees and planning for new plantings is something Tankersley hopes will have broad impact. He has already shared his process with countries in Africa through The Eden Projects and in China in an effort to help governments replace denuded forests there.

Tankersley is hopeful about the long-term implications of the study. After all, he said, when pioneers first came to the United States, they found oak trees that were about 300 years old, and had been providing benefits such as carbon sequestration for all of that time. Many of those hard-working, long-lived species have been a key part of our natural heritage since the beginning. By embracing the issue now, Tankersley and team have cleared the way for trees and their vital functions to endure.

©2015 Chicago Botanic Garden and

Wildfire. Flooding. Thirst. These issues can all be addressed through large-scale landscape restoration, according to speakers at the 2015 Janet Meakin Poor Research Symposium. Addressing a crowd of regional stewardship professionals and academics, as well as Conservation Land Management (CLM) and Research Experiences for Undergraduate (REU) interns at the Chicago Botanic Garden on June 12, they focused on solutions for ecological challenges.

The effects of strong conservation work are magnified when done on a large scale, they shared, and the theme of the day was how to magnify every step from seed-management procedures to restoration time frames and budgets to make the process as beneficial as possible. As mining, drilling, and similar industries move broadly across open lands in the United States and abroad, along with increasingly frequent and far-reaching extreme weather events, conservation practices must evolve with the times to keep pace.

PHOTO: Conservation and Land Management (CLM) interns measure species density in the field.

Conservation and Land Management (CLM) interns measure species density in the field.

As the CLM interns prepare to set off on a summer of hands-on restoration work across the United States, and potentially launch their careers shortly thereafter, these are critical issues for them to understand, according to Kay Havens, Ph.D., of the Chicago Botanic Garden, who organized the symposium. Many of the interns work in partnership with the Bureau of Land Management (BLM) on the ground in forestry, wildlife management, and habitat restoration, among others.

Fittingly, the first speaker of the day was Amy Leuders, the acting assistant director of BLM, who noted that the partnership with the Garden since 2001 has led to the training, hiring, and placement of more than 1,000 interns on federal lands. About 50 percent of those interns are later hired by a stewardship agency. “The Bureau of Land Management has had a long and successful partnership with the Chicago Botanic Garden…developing the next generation of land stewards,” she said.

In particular, she imparted to the audience the importance of developing a large scale national seed strategy, so that targeted plant seeds will be thoughtfully collected and preserved for future use. She cited examples of events in which seeds saved by chance allowed for the restoration of areas that later succumbed to natural disasters like wildfires and hurricanes. This new process would allow for seed saving to take place in a more proactive and calculated manner.

PHOTO: Seeds are collected at the Garden and stored in the Dixon National Tallgrass Prairie Seed Bank.

Collected seeds are stored in the Dixon National Tallgrass Prairie Seed Bank.

According to the second speaker, Kingsley Dixon, Ph.D., professor at Curtin University and the University of Western Australia, the current supply of wild seed cannot support global restoration demands. Innovations are helping to change that. Tools that process seeds into pellets or other small packets facilitate their successful mass delivery into recovering ecosystems, helping to achieve the level of seed performance seen in the agricultural sector. He noted that “Only by thinking at an industrial level of efficiency will ecological restoration be able to achieve the pace needed to protect and enhance natural resources.”

Drinking water quality can also be managed by restoration, said Joy Zedler of the University of Wisconsin-Madison. She shared examples of how restoration has been “scaled up” adaptively (learning while restoring) to benefit large areas. When it comes to managing water, she explained, it is essential to manage an entire watershed. One area of poor water quality will flow into every crevice in the system, for example. In the end, she explained, it is about safeguarding ecosystem services that human health and wellbeing depend on, from clean water to fresh air. “Our global society needs to redirect itself to achieve a sustainable future,” she said.

Brian Winter of the Nature Conservancy in Minnesota echoed her sentiments, as he ran through a real-life wetland restoration process for the audience. He emphasized that wetlands hold rainwater and are capable of preventing disastrous amounts of water from washing through nearby agricultural fields. The value of wetland restoration is immense and ongoing, he explained.

Conservation is in transition, explained speaker John Rogner of the U.S. Fish and Wildlife Service. Rogner discussed the steps involved in planning for a successful restoration, and the importance of landscape conservation cooperatives that can work together across states or even countries to identify and address issues in a given geographic area such as the Great Lakes watershed. He outlined an ongoing project to improve blockages in the Great Lakes system that impede fish migration. This can lead to a buildup of invasive plant species that create additional system blockages. A regional perspective and collaboration across entities is critical, he said. “It is absolutely essential that everyone have access to the same information to keep moving in the right direction,” added Rogner.

Issues that often fall to the side in planning are conceptual, according to James Aronson of the Missouri Botanical Garden. He urged the audience to pay attention to the economic side of their work by learning to speak and think in terms of renewable natural capital. Across land and ocean, natural capital can be restored to facilitate the flow of ecosystem services such as fresh air and clean water.

PHOTO: One of our greatest national resources and treasures: the Colorado River Basin.

One of our greatest national resources and treasures: the Colorado River Basin.

Lastly, Megan Haidet with Seeds of Success emphasized the importance of partnerships to meet the goals of the Bureau of Land Management’s National Seed Strategy for Rehabilitation and Restoration 2015–2020. She noted that increased coordination is vital to accelerate the pace and scale of restoration and provide native plant materials when and where they are needed.

The Garden’s CLM interns have now dispersed across the United States, where they will work for the next five months on public lands to put these lessons into action.

©2015 Chicago Botanic Garden and

A Taste of the Garden

Undercover Science

Julianne Beck —  May 25, 2015 — 1 Comment

On an early spring day in the offices of the Regenstein Fruit & Vegetable Garden, Lisa Hilgenberg, Garden horticulturist, is seated at a rustic conference table sorting through pencil drawings of garden beds and photos of vegetable plants. Across the Garden, in the Garden View Café kitchen, chef Peter Pettorossi is considering a cabbage slaw recipe inspired by those same plants.

The concept of serving fresh, seasonal, local food at the Garden was key to café renovations completed one year ago. Produce and fruit from the garden, as well as from Windy City Harvest plots in the area, and other local vendors, is increasingly available in many dishes including salads, calzones, daily soups, and other specials.

PHOTO: The bountiful Regenstein Fruit & Vegetable Garden in 2014.

The bountiful Regenstein Fruit & Vegetable Garden in 2014  ©North Branch Communications

Although the café and the Fruit & Vegetable Garden are physically separate, they come together in the growing season through an intricate network of connections that bring garden to table.

“It’s such a unique opportunity,” said Harriet Resnick, vice president of visitor experience and business development. “It opens people’s eyes to what we offer here.” New signage in the garden indicates which plants are on their way to the café. It also feels right, she explained. “If you are a true gardener, that’s how you live your life—by the plants of the season.” She added that the café has only grown in popularity, seeing about 200,000 unique food purchases last year.

Hilgenberg spent much of her lifetime learning how to match seeds with soil and growing conditions, perfecting each step. She lives with the rhythm of the seasons. “We are moving back in the right direction,” she said. “There’s something exciting about eating freshly grown vegetables seasonally. It’s always new and nutritious.”

Hilgenberg begins planning a year in advance for each growing season, mapping out what she will plant and how it will be arranged for display. Seeds for cool-season plants begin to grow in the Greenhouses in late winter, go into the ground in April, and are harvested in May and June. A similar cycle follows shortly after for warm-season crops.

PHOTO: Chef slicing fresh cabbage.

Fresh cabbage from the Garden is put to use at the Garden Chef Series. Join us on Saturdays and Sundays, May 23 – October 4.

This is Pettorossi’s first spring at the Garden, after beginning in his role in November. He eagerly welcomes the arrivals of produce this spring. “If you can get something at the peak of freshness it always tastes better,” he said. As for the menu, “the season definitely dictates it,” he explained. “The menu features a lot of specials, depending on what we have in house.” No matter the season, he said the menu is always “fresh, mostly organic, local, and garden-inspired.”

Cool-season crops such as heirloom Tennis Ball butterhead lettuce (Lactuca sativa ‘Tennis Ball’) are the first to be ready this year. They will soon be joined by French Breakfast radish (Raphanus sativus ‘French Breakfast’), Hakurei salad turnips (Brassica rapa ‘Hakurei’), beets, and bunching onions. “All of our ingredients are very simple based on what they tell me they can grow,” he said, indicating that the most seasonal foods can be found in daily specials that he plans a day ahead.

PHOTO: Staff and volunteers plant the Fruit & Vegetable Garden terraces with fall season crops.

Staff and volunteers plant the Fruit & Vegetable Garden terraces with fall crops.

The connection from garden to table extends to connect people as well, from garden mentor to student, or from an individual to their culture or family traditions, for example. Hilgenberg loves hearing from garden visitors about their connections to the garden crops. She spent much of her childhood on her Norwegian grandparent’s farm in Iowa, building her own such connections.

Hilgenberg makes a point to grow widely recognized plants in the garden each year, including herbs, edible flowers, and vegetables. She grows annual small fruits such as strawberries, gooseberries, and currants in addition to blueberries and bramble fruit. She also grows less common plants such as Marshall strawberries (Fragaria × ananassa ‘Marshall’), which she and her team propagated from three donated plants. Everything grown in the garden is done so organically. “I think it’s interesting for people to try different local varieties,” she said. Many, she explained, cannot be found in a typical grocery store, especially in organic form.

This year, several beds have been planted in the French potager style, and others laid out to mirror the gardens of Monticello. There are two beds planted with vegetables people may have seen in seed houses in 1890, the same year the Chicago Horticultural Society was founded. In honor of the Society’s 125th anniversary, seeds were made available through seed catalogs, the Seed Savers Exchange, and other sources. Edible flowers, such as Empress of India nasturtium (Nasturtium ‘Empress of India’), artfully border beds of radish, rutabaga, and turnips, for example. In addition, she included carrots, kale, collard, and three varieties of cabbage (Brassica oleracea): ‘Mammoth Red Rock’, ‘Early Jersey Wakefield’, and ‘Perfection Drumhead Savoy’. Each one was selected because it is adapted to our local growing conditions, a process Hilgenberg and her staff, volunteers, and interns have mastered over the years. Last year, they grew and harvested two tons of produce. The year before, that was combined with a bumper apple crop for 6,000 pounds of production.

PHOTO: The Herbs de Provence garden bed in the Fruit & Vegetable Garden.

The Herbes de Provence garden bed in the Fruit & Vegetable Garden: what is not used fresh can be dried in one batch at the end of the season.

How does the chef manage to find a way to serve even the most unusual varieties with style? “I always try to add a little acid [such as lemon or vinegar] to food because acid makes flavors pop,” he advised. “A lot of lettuces are sweet, but others have a bitterness to them,” he added, “so you would have to find that perfect vinaigrette to go with that bitterness,and maybe add a touch of honey or something sweet.”

In addition to growing and preparing food at the Garden, “we are also this amazing workforce and training program for underserved youth and adults,” said Resnick, who explained that participants in the Windy City Harvest program, with large growing beds off-site, provide a significant amount of produce for the Garden View Café and learn to sell their produce at farmers’ markets. On-site each year, a few Windy City Harvest interns work directly with Hilgenberg.

Anyone walking through the Fruit & Vegetable Garden today may see the beginnings of a dish they can enjoy in the café by early summer. The season will continue to evolve in coming months, with the Garden Grille opening in late May. In June, warm-season crops such as heirloom corn, Japanese Nest Egg summer squash (Cucurbita pepo ‘Japanese Nest Egg’), White Patty Pan squash (Cucurbita pepo var. melopepo ‘White Patty Pan’), Yellow Pear tomatoes (Solanum lycopersicum ‘Yellow Pear’), and Blueberry Blend tomatoes (Solanum lycopersicum ‘Blueberry Blend’) will replace the spring plantings in the Fruit & Vegetable Garden, giving way to new edible discoveries.

©2015 Chicago Botanic Garden and

Unfolding the Mysteries of the Ravines

Undercover Science

Julianne Beck —  March 29, 2015 — Leave a comment

Standing guard along the western shore of Lake Michigan, the ravines are a naturally engineered filtration system from land to water.

Curving up from the flat lands of Illinois and arching alongside the coast into Wisconsin, their hills and valleys are filled with an abundance of foliage, plants, and animal life unlike any other ecosystem in the Chicago Wilderness region. Among other benefits, they help to filter rainwater. Rare plants, migratory birds, remnant woodlands, and fish are a part of this shadowed world that has long been entrenched in mystery for local residents and scientists alike.

As urbanization, erosion, increasingly intense weather events, and invasive plants begin to peel away at the perimeter of the ravines, it has become increasingly urgent for us to unwrap those mysteries and help protect the system that has long protected us.

New volunteers are welcome to dig in this spring and summer. Register to begin by attending a new volunteer workshop.

Volunteers and staff sample vegetation along a bluff transect at Openlands Lakeshore Preserve.

Volunteers and staff sample vegetation along a bluff transect at Openlands Lakeshore Preserve.

“The ravines are one of Illinois’s last natural drainage systems to the lake,” said Rachel Goad, manager of the Chicago Botanic Garden’s Plants of Concern program. “They are delicate landscapes. It can be challenging to get in to them. It can be challenging to move around on the steep slopes.” Those challenges have not deterred Goad and a team of citizen scientists from digging in to look for solutions.

For 15 years, the many contributors to Plants of Concern have been collecting data in the ravines, with a particular focus on the rare plant species that can be found there. The data, now quite valuable due to its longevity, is a treasure chest for land managers and others who are trying to better understand the system and how to save it.

Goad and her team are now in the final stages of testing a vegetation assessment connected to a virtual field guide for the ravines. She hopes it will be completed by the end of this year. Its purpose is to serve as a resource for ravine restoration and management long term. The plant-focused sampling method, called a rapid assessment, is the third piece of a larger ravine-management toolkit that includes a way to evaluate erosion and stream invertebrates considered to be indicator species. The toolkit has been assembled by Plants of Concern and partner organizations in recent years.

“The idea is that a land manager or landowner could pull these tools off of the Internet—there would be data sheets and an explanation for how to use them, and these resources would provide a practical, tangible way for people to better understand the ravines,” explained Goad. She and her volunteers will test the protocol this summer, as they meander through the ravines with their notebooks, cameras, and GPS mapping equipment in hand. What they learn could benefit managers trying to determine whether to focus on vegetation management or restoring the stability of a ravine, for example. The toolkit, according to Goad, “is complementary to restoration and understanding these plant communities.”

The data, however, is only one piece of the solution. Goad believes the connections people make when monitoring the ravines are what will impress upon them the significance and urgency of the issue. Her goals are to create connections between people and their local natural communities, and to engage a more diverse representation of volunteers in the program.

“What Plants of Concern is doing is engaging local citizens, introducing them to ravines, and getting them interested in what’s happening in these mysterious V-shaped valleys around them,” said Goad.

In all, Plants of Concern monitors 288 species across 1170 populations in 15 counties, covering 13 habitat types.

Rachel Goad monitors rare plants in a ravine.

Rachel Goad monitors rare plants in a ravine.

Goad hopes that by growing connections between these ravines and those who live nearby, she can increase the chances that this system will continue to protect rare plant species and one of the largest sources of drinking water in the world. As a recent recipient of a Toyota TogetherGreen Fellowship, administered by Audubon, Goad is intent on better understanding how to build such connections.

“We are working to make connections between monitoring and stewardship,” she said. “Monitoring can be a transformative experience.” Once a volunteer is in the field, navigating the terrain and gaining familiarity, they learn to see existing threats, such as encroachment by invasive species. Documenting these threats is important, but can feel disempowering if they’re not being addressed. Goad wants to show volunteers that there is something that can be done about the problems they encounter, and build a proactive understanding of conservation. “I believe in citizen science, which is the idea that anybody can do science and get involved in research,” she said.

Goad stepped in as manager of Plants of Concern just last year, after earning her master’s degree. It was like returning home in some ways, as she had previously helped to manage natural areas at the Garden.

In part because of that initial experience, “I knew I wanted to work in plant conservation,” she said. “It felt pretty perfect to get to come back and work with Plants of Concern. It’s an amazing experience to live in Chicago and to be able to work in some of the most beautiful natural areas in the region.”

Early spring ephemerals in bloom on a ravine bluff.

Early spring ephemerals bloom on a ravine bluff.

Plants of Concern has been a mainstay at the Garden for 15 years, dispatching committed volunteers to the ravines and other key locations across the Chicago Wilderness region to monitor and collect data on endangered, threatened, and rare species. The mounting data collected by the program is often used as baseline information for shifting or struggling species, and is shared with land managers. Through special projects, such as with one of the Garden’s recent REU interns, they have also contributed to habitat suitability modeling for rare species.

©2015 Chicago Botanic Garden and

Mapping the Future of the Wild West

Undercover Science

Julianne Beck —  March 6, 2015 — Leave a comment

Silvery-green sagebrush cascades over the canyons of the Great Plains and Great Basin in numbers that would strike envy into the hearts of most rare and endangered plants. The abundant species keeps the wheels turning in a system where struggling plant and animal species rely on it for life-sustaining benefits.

As the climate changes and brings new rainfall levels and other environmental conditions, will this important species transition to new locations? What are the potential consequences for its current neighbors? These questions concern Shannon Still, Ph.D., postdoctoral research associate at the Chicago Botanic Garden.

PHOTO: Dr. Shannon Still looks over the area of his research.

Dr. Still looks over the area of his research.

“Sagebrush is a very big part of the ecosystem in the West, and we need to see what is going to happen,” said Dr. Still. “It’s a workhorse species that is important for pygmy rabbits, sage grouse, and mice that live around it, and it helps to stabilize soils.”

Still made several trips into states including Colorado, Wyoming, Idaho, and Nevada in 2014 to investigate the likelihood of such a transformation and to help prepare land managers for the potential results. “When a climate changes, species often shift their location within it,” he explained. When that species has already become an integral part in the lives of its neighbors, it can mean a ripple of changes across the entire system.

It’s All About That Brush

PHOTO: Wyoming big sagebrush, the focus of the study.

Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis), the focus of the study

Standing in a thicket of Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis), the focus species of his study, Still reaches into a 3-foot tall plant with his Felco 8 pruners to take a sample. (He’ll later send this sample to his collaborator in Utah who will confirm the subspecies identification through a genetic test.)

Still plots the location of the plant with his GPS unit, which he also uses to track his route through the dusty wilderness in the Garden research vehicle. He snaps a few photos for visual reference and makes notes in his computer tablet before moving on to the next site.

There are millions of plants out there now, Still estimates. So, he strategically collects information from 150 key locations during multiple visits. He then returns to the Garden to add the new information to his database, which also holds data from herbaria records he collected earlier.

At his desk in the Garden, he inputs new data. He then uses a software workflow he built himself to compare a map of the plants with a map of how the climate will look in those locations in future years. He runs models that overlay one map on top of the other to see where climate shifts will occur in the current species range. This allows him to predict where Wyoming big sagebrush will continue to prosper, and where it may disappear due to a lack of rain, too much rain, or temperature shifts, for example.

Staking a Claim

Still is excited about the ability of the software to provide climate-related analysis on sagebrush and other species. In fact, it’s the second study he has run with the program in the last two years since it was developed, using specialized algorithms for each.

PHOTO: Chicago Botanic Garden research vehicle parked in the field.

Colorado Rockies in the background; research subjects all around

First, he developed the software workflow to better understand how more than 500 rare species in the same western region might fare in the future if their environmental conditions change as predicted, and to which changes they are most vulnerable. The study results are like a crystal ball for land managers, identifying which species are most urgently in need of their care. The three-year investigation will come to a close in late 2015.

Already, both studies have received attention, with publications in the January issue of Nature Areas Journal authored by Still and his collaborators.

Still’s initial findings reveal that the Wyoming big sagebrush species already appears to be shifting. An anticipated increase in precipitation in the Great Plains and a drier climate in the Great Basin may lead to a contraction of the species into a smaller range, he explained. “By 2050, models show that 39 percent of the current climate for Wyoming big sagebrush will be lost.”

Still hopes that by identifying locations where sagebrush may fail to thrive, land managers can immediately focus on restoring areas that will continue to be suitable for the species long term.

PHOTO: Sagebrush in the canyon.

Sagebrush population in the canyon

“We don’t expect sagebrush to go extinct,” said Still. “But we may lose plants in areas where we don’t want to lose them, or more rapidly than we hoped. That could lead to more erosion or the loss of suitable habitat.”

Always moving forward, Still is continuing to work with the data, now adding details about plant locations such as the slope of the land and the direction they face. With those details, he will run new models in the future.

The wild West once again finds itself at the forefront of exploration and change. If Still has any say in the matter, its mysteries and historic charm will endure.

©2015 Chicago Botanic Garden and