CPC Plant Profile: Koehler's Rockcress
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Plant Profile

Koehler's Rockcress (Boechera koehleri)

Arabis koehleri var. koeleri grows out of cracks and crevices in the bare rock. Photo Credit: Ed Guerrant
Description
  • Global Rank: T1 - Critically Imperiled
  • Legal Status: N/A
  • Family: Brassicaceae
  • State: OR
  • Nature Serve ID: 145645
  • Date Inducted in National Collection: 01/01/1986

On a dry hill high above the rushing Umpqua Riverprecariously perched on a steep rocky outcrop tucked into a small crack. That's where you will find the diminutive shrub, Arabis koehleri var. koehleri. Looking like something out of a Dr. Suess book, this tough, tufted member of the mustard family clings tenaciously to the rocky outcrops it calls home. Koehler's rockcress has most likely always been a narrow endemic, whose overall range has probably not changed much since European settlement. While the range probably has not contracted much in the last 150 years, the number of populations and individuals has greatly decreased. Road construction, quarrying, livestock grazing, herbicide drift, and the construction of an electricity generating facility have all impacted populations. To offset these losses, the Bureau of Land Management (BLM) and The Berry Botanic Garden are attempting a population augmentation. In 2001, researchers grew hundreds of plants in The Berry Botanic Garden greenhouse-using seeds collected by BLM staff from the wild. During the cool fall rains, researchers battled the slippery slopes and clung to the steep cliffs to place plants and directly sow seeds into appropriate habitat near existing Koehler's rockcress plants, carefully mapping and photographing their locations. Researchers collected data on the specific microhabitat that each plant or seed was placed in. Valuable knowledge about seed germination and plant growth in the wild as well as habitat and microhabitat requirements will be gained when researchers return in subsequent years and monitor the success of the introduced plants.

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Updates
Center for Plant Conservation
  • 12/02/2021
  • Reintroduction

An experimental augmentation of Arabis koehleri var. koehleri was outplanted in fall 2007 on land owned and managed by the BLM, and has been monitored twice yearly, spring and fall. This project is designed to see if it is more effective in terms of establishment, survival and/or growth, to use seeds or small plants as founders (Guerrant, 1996; Guerrant and Kaye, 2007). Secondary questions include possible genetic effects among 55 maternal plants available for use as seed donors, as well as of habitat characteristics that were recorded at planting (e.g. slope (over 1 dm and 1 m), aspect, planting substrate, plant size), which, with potential block (replicate) effects, are intended yield information on microhabitat characteristics that might influence survival. Three people participated in the outplanting, and possible effects of planter were also examined.

The basic experimental design is a randomized complete block design (Yandell, 1997). This is a balanced design, insofar as each block has equivalent numbers and kinds of experimental units (i.e. seeds and plants). Each block (i.e. experimental replicate) was designed to be comprised of 64 Experimental Units 32 plants and 32 groups of 3 seeds, from a variable number of maternal lines. Thus, a block is comprised of a total of 128 propagules (32 plants, and 96 seeds, in 32 batches of three each). A total of 6 blocks, or replicates, were planted, each on a different ‘hill’ or rocky outcrop. Because some seeds were lost, a total of 748 propagules were planted.

By the first spring after outplanting, seventy three of the 190 plants placed out in the field (38%) and zero seeds (i.e. seedlings from seeds) were alive. Only 7 (4%) of the plants survived their first summer. Similar to the 2001 outplanting, propagule type had a profound effect on establishment and survival. Coincidentally, the summers of 2002 and 2008 were by far the driest in the period 2001 through 2008, which may have been an important causal factor in low seedling establishment and plant survivorship. Effects on survival of replicate (fall), slope 1M (fall), and substrate (spring) were seen during one monitoring period. Maternal parent (spring) and slope 1M (fall) had an effect on growth during one monitoring period. There were significant researcher effects on survival in spring and fall, and an effect on growth rate in the spring but not fall. Experience appears to have been an important contributing factor.

  • 08/30/2020
  • Propagation Research

Germination trials conducted at The Berry Botanic Garden. A constant 68F (20C) temperature, with or without 8 weeks of cold stratification, yielded 100% germination (BBG File).

  • 08/30/2020
  • Reintroduction

Seeds and plants grown in the greenhouse from 9 different parent plants were planted in the wild in the fall of 2001.

  • 08/30/2020
  • Orthodox Seed Banking

Seed from five populations is stored at the Berry Botanic Garden Seed Bank.

Nature Serve Biotics
  • 05/02/2017

Endemic to the Umpqua River Valley in Douglas County, Oregon. Only nine known element occurrences and fewer than 1000 total individuals; threatened by highway construction, grazing, railroad operation and herbicide drift.

Edward Guerrant, Ph.D.
  • 01/01/2010

Road construction (Holmes, pers. comm.). Railroad operations (Meinke 1982). Grazing by goats, cattle and other livestock (Holmes, pers. comm.). Herbicide drift (Meinke 1982). Rock quarry operations (Holmes, pers comm.). Fire (Holmes, pers. com

Edward Guerrant, Ph.D.
  • 01/01/2010

9 occurrences (ONHP Data Base, 2000) with an unknown number of individuals. Only two sites are on federal land. Seven are on private property and are not protected (Holmes, pers comm.).

Edward Guerrant, Ph.D.
  • 01/01/2010

Experimental population augmentation. Seeds and plants grown in the greenhouse from 9 different parent plants were planted in the wild in the fall of 2001. Researchers expect to gain valuable knowledge about seed germination and plant growth in the wild as well as habitat and microhabitat requirements. Ultimately, researchers hope to increase the population size and develop successful reintroduction methods (Berry Botanic Garden/BLM project). Germination trials conducted at The Berry Botanic Garden. A constant 68F (20C) temperature, with or without 8 weeks of cold stratification, yielded 100% germination (BBG File).

Edward Guerrant, Ph.D.
  • 01/01/2010

Sites on BLM land are contained within the ""North Bank Habitat Management Area."" The area is managed for the continued survival and proliferation of Arabis koehleri var. koehleri. No management activity that would damage the population is allowed, including grazing, prescribed fire, and herbicide application (Holmes, pers. comm.). Seed from five populations is stored at the Berry Botanic Garden Seed Bank.

Edward Guerrant, Ph.D.
  • 01/01/2010

Determine successful and practical reintroduction techniques (Holmes, pers. comm.). Augment existing populations. Reintroduce plants at historic sites (Holmes, pers. comm.). Analyze genetic variation within and between populations (Holmes pers. comm.). Study general ecology of this species, including: habitat requirements, life history, reproductive biology, etc.

Edward Guerrant, Ph.D.
  • 01/01/2010

Collect and store seeds from all known populations. Keep maternal lines separate.

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Photos
Nomenclature
Taxon Boechera koehleri
Authority (Howell) Al-Shehbaz
Family Brassicaceae
CPC Number 180
ITIS 823181
USDA ARKOK
Common Names Koehler's rock cress | Koehler's rockcress
Associated Scientific Names Arabis koehleri var. koehleri | Boechera koehleri | Arabis koehleri | Arabis koehleri var. stipitata
Distribution Oregon: Umpqua River Valley, Douglas County
State Rank
State State Rank
Oregon S1
Habitat

Cracks and crevices on rocky bluffs and cliffs between approximately 730 and 1250 ft (225 and 280 m) in elevation. Found growing along with Phacelia sp., Sedum sp, and various mosses, selaginellas, and lycopodiums.

Ecological Relationships

Little is known about the ecology of this species. It grows on southwest- to northeast facing rock slopes, but most commonly on west-facing slopes (Holmes, pers. comm.). It is not known why the plant is a narrow endemic, inhabiting rock faces within only a short section of the Umpqua River Valley.

Pollinators
Common Name Name in Text Association Type Source InteractionID
Reintroduction
Lead Institution State Reintroduction Type Year of First Outplanting
Berry Botanic Garden Oregon Reinforcement 2001

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