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Plant Evaluations

Comparison of Plant Establishment and Persistence of Sedum spp. and Native Taxa

In 2001, nine roof platforms containing three commercially available drainage systems were planted with 18 Michigan native species planted as plugs and nine Sedum spp. planted as either seed or plugs. Each platform received 10 cm of growing substrate composed of 60% heat-expanded slate (PermaTill®; Carolina Stalite; Salisbury, NC) with a particle size ranging from 7.9 mm to 9.5 mm, 25% USGA grade sand, 5% aged compost, and 10% Michigan peat.

Within the platform partitions, three groups of plants were cultivated to evaluate the effect of drainage system on plant establishment, growth, and survival. One group consisted of seven Sedum spp. propagated from seed.  Taxa included S. acre, S. album, S. kamtschaticum, S. ellacombeanum, S. pulchellum, S. reflexum, and S. spurium ‘Coccineum’.  Seed was applied at a rate of 1.0 g×m-2 and was mixed with 250 ml×m-2 of dry sand to ensure even distribution.  All seed was obtained from Jelitto Staudensamen, GmbH (Schwarmstedt, Germany). A second group consisted of two Sedum spp. planted from plugs (116.3 cm3, 38/flat): S. middendorffianum ‘Diffusum’ and S. spurium ‘Royal Pink’.  These plugs were supplied by Hortech, Inc. (Spring Lake, MI) and the study contained 108 plugs of each taxa.  The third group consisted exclusively of 18 taxa of Michigan native plants: Agastache foeniculum (lavender hyssop), Allium cernuum (nodding wild onion), Aster laevis (smooth aster), Coreopsis lanceolata (lanceleaf coreopsis), Fragaria virginiana (wild strawberry), Juncus effusus (spikerush), Koeleria macrantha (junegrass), Liatris aspera (rough blazingstar), Monarda fistulosa (bergamot), Monarda punctata (horsemint), Opuntia humifusa (prickly pear), Petalostemum purpureum (purple prairie clover), Potentilla anserina (silver feather), Rudbeckia hirta (black-eyed Susan), Schizachyrium scoparium (little bluestem), Solidago rigida (stiff goldenrod), Sporobolus heterolepis (prairie dropseed), and Tradescantia ohiensis (spiderwort).  All native plants were planted from plugs (150.8 cm3, 38/flat) obtained from Wildtype Nursery Inc. (Mason, MI) except for Potentilla anserina, which was planted from stolons supplied by Hortech, Inc.  There were 27 plugs of each native taxa included in the study. All plugs and seed were planted or sown on the platforms 15 June 2001.  An automated overhead irrigation system (Rainbird; Azusa, CA) was utilized to support seed germination, plant establishment, and plant coverage.

Plants were evaluated over three years (2001-2004) for growth, survival during establishment and overwintering, and visual appearance. During the first season, growth of most native plants peaked in September, and then declined with the onset of dormancy. Optimum growth and appearance during the entire first season was possible because irrigation was provided during the plant establishment phase.  Supplemental irrigation was much reduced during the second season and was terminated completely by 10 July of the second season.  Therefore, after this date plants had to rely on natural rainfall, the likely scenario on most extensive green roofs. The termination of supplemental irrigation was fatal to many of the native taxa. At the end of the 2002 growing season, there were no surviving plants of A. foeniculum, A. laevis, F. virginiana, L. spicata, M. fistulosa, M. punctata, P. purpureum, P. anserina, R. hirta, S, scoparium, and S. rigida.  Likewise, there were high mortality rates for C. lanceolata, J. effusus, K. macrantha, and S. heterolepisAllium cernuum, O. humifusa, T. ohiensis, but all of the Sedum proved to be drought tolerant.

Ideal plant selections for extensive green roofs in northern climates such as Michigan that lack irrigation must be heat and cold tolerant, drought resistant, have a high growth index in order to provide quick coverage, and must be self-generating by seed, root systems, or some other means. When the study was terminated in 2004, of the species tested, all nine species of Sedum along with A. cernuum, C. lanceolata, and T. ohiensis were the most suitable for unirrigated roofs. Although, Opuntia humifusa survived, it lacked the ability to provide quick surface coverage. If irrigation is available, then other native species are potential selections. No significant differences were found among the commercial drainage systems.

Complete results are published in:
Monterusso, M.A., D.B. Rowe, and C.L. Rugh. 2005. Establishment and persistence of Sedum spp. and native taxa for green roof applications.  HortScience 40(2):391-396.

Three platforms with different levels of growth.
Left: Sedum from cuttings; Center: Sedum planted as plugs; Right: native herbaceous perennials and grasses from plugs (Year 1)

Effect of Substrate Depth on Crassulacean Plant Succession

A plant establishment, competition, and survival study was conducted on 24 roof platforms (4’ x 4’) over a period of seven years. The study was initiated in 2003 when cuttings of 25 succulent plant species were propagated on platforms with substrate depths of 2.5 cm, 5.0 cm, and 7.5 cm (1 in, 2 in, and 3 in). Species included Graptopetalum paraguayense, Phedimus spurius ‘Leningrad White’, Rhodiola pachyclada, Rhodiola trollii, Sedum acre, Sedum album ‘Bella d’Inverno’, Sedum clavatum, Sedum confusum, Sedum dasyphyllum ‘Burnati’, Sedum dasyphyllum ‘Lilac Mound’, Sedum diffusum, Sedum hispanicum, Sedum kamtschaticum, Sedum mexicanum, Sedum middendorffianum, Sedum moranense, Sedum pachyphyllum, Sedum reflexum, Sedum sediforme, Sedum ‘Rockery Challenger’, Sedum ‘Spiral Staircase’, Sedum spurium ‘Summer Glory’, Sedum surculosum, Sedum x luteoviride, and Sedum x rubrontinctum. Succulents such as sedum root easily from leaf and stem cuttings and are often propagated by dropping the cutting material on top of the substrate. Cuttings were propagated on 20 cm (8 in) centers with 25 plants per platform. The study was a split-plot on a completely random design with substrate depth as the main plot factor and species as the sub-plot factor. Each species was replicated eight times within each substrate depth for a total of 600 plants.

Species were evaluated at the three substrate depths for propagation success, rate of establishment, growth and survival, groundcover density, ability to exclude invasive weeds, competition among species, persistence over several years, tolerance to low winter temperatures, and drought tolerance. Rate of establishment and initial plant growth were determined by utilizing SigmaScan Pro 5.0 image analysis software (SPSS Science, Chicago, Ill.). A camera stand was constructed to suspend a digital camera equipped with a 0.8X wide conversion lens approximately 163 cm (5’4”) above the platforms. These pictures were taken weekly until the plants entered dormancy in late fall and then picture taking resumed the following Spring. The SigmaScan program analyzed these digital photographs to determine percentage of plant canopy that could be attributed to each individual species.

Absolute cover was determined using a point-frame transect every two weeks during the first three growing seasons and monthly during years four through seven to measure community composition and change.  The stainless steel point-frame had ten strings spread horizontally and vertically to create a fish line grid.  At each of the 100 intersection points, leaf area index was measured by recording all species that came in contact with a vertical needle.  Every species that intersected was recorded based on their origin in the canopy layer. It was essential to determine the tendency of neighboring plantings to displace and possibly eradicate adjacent species. Susceptibility to plant competition is important to predict the long-term stability of planted communities as well as preservation of the aesthetic goals of the roof design. Equally critical was determination of resilience and seasonal fluctuation of each species over the growth season and after winter dormancy.

Results highlight the effect of substrate depth on plant performance, as well as the importance of long-term evaluation of species as plant community can influence roof function.  In general, deeper substrate depths promoted greater survival and coverage, however, in the shallowest depth of 2.5 cm, stable plant communities were established as species most suited to those environmental conditions expanded into open space.  At 5.0 cm and 7.5 cm, Phedimus spurius and Sedum middendorfianum were the dominant species, but at 2.5 cm, Sedum acre and Sedum album covered the most area. Regarding time, at the 7.5 cm depth, 22 species were present at the end of the first growing season, but these numbers were reduced to 13, 8, and 7 after two, three, and five years, respectively.  Similar results occurred at the shallower depths except that the number of species was reduced at a faster pace.  For the most part, species present did not change after four years, but the relative abundance for each species continued to change. Plants that initially survive may eventually experience reduced coverage or disappear completely due to competition, variability in climate, and other factors.  Knowledge of how a species will perform at various substrate depths is important when choosing a green roof system to ensure viability and success, especially where substrate depth must be kept to a minimum because of building weight restrictions.  All of these factors must be considered during the design and planning phase of a green roof.

Initial results regarding establishment are published in:
Durhman, A.K., D.B. Rowe, and C.L. Rugh.  2007.  Effect of substrate depth on initial growth, coverage, and survival of 25 succulent green roof plant taxa.  HortScience 42(3):588-595.

Long term results are published in:
Rowe, D.B., K.L. Getter, and A.K. Durhman.  2012.  Effect of green roof media depth on Crassulacean plant succession over seven years.  Landscape and Urban Planning 104(3-4):310-319.

A wodden structure build to span a row of platforms.
A camera stand was built for taking digital photographs from above the platforms.  Images are analyzed with SigmaScan Pro software to provide a quantitative assessment of initial plant growth and coverage.

Substrate Depth Influences Sedum Plant Community

A second study was initiated in May 2005 with an additional 12 species that were planted as plugs on 8’ x 8’ platforms. Species in this study included Sedum ‘Angelina’, Sedum cauticola ‘Lidakense’, Sedum ewersii, Sedum floriferum, Sedum hispanicum, Sedum ochroleucum, Sedum reflexum, Sedum sarmentosum, Sedum sediforme, Sedum sexangulare, Sedum spurium ‘John Creech’, and Sedum stefco. In this study, each species was replicated 12 times within each of three substrate depths for a total of 432 individual plants.  This study evaluated the effect of green roof substrate depth on substrate moisture, plant stress as measured by chlorophyll fluorescence, and plant community development over four years.  Plugs of 12 species of Sedum were planted on 8 June 2005 and evaluated bi-weekly for absolute cover (AC) with a point frame as described above. 

Most species exhibited greater growth and coverage at a substrate depth of 7.0 cm and 10.0 cm relative to 4.0 cm.  For the species evaluated, substrate depths of at least 7.0 cm are highly recommended.  AC of Sedum was significantly greater at this substrate depth than at 4.0 cm.  Mean volumetric moisture content of the three substrate depths followed the same pattern as AC.  When averaged over time, the 4.0 cm substrate depth held less moisture than depths of 7.0 or 10.0 cm, while the 7.0 and 10.0 cm substrate depths were statistically the same.  Species exhibiting the greatest AC at all substrate depths were S. floriferum, S. sexangulare, S. spurium ‘John Creech’, and S. stefco. In general, species that are less suitable at these substrate depths are S. ‘Angelina’, S. cauticola ‘Lidakense’, S. ewersii, S. ochroleucum, and S. reflexum ‘Blue Spruce’.

Results of this study are published in the following two papers:
Getter, K.L. and D.B. Rowe.  2008.  Media depth influences Sedum green roof establishment.  Urban Ecosystems 11:361-372.
Getter, K.L. and D.B.Rowe.  2009. Substrate depth influences sedum plant community on a green roof.  HortScience 44(2):401-407.

Platforms with young plants
Time of planting (June 2005)

Effect of Planting Season on Establishment

The objective of was to quantify the effect of substrate depth and planting season on successful establishment of plugs of Sedum species on green roofs.  Plugs of nine species of Sedum were planted at depths of 4.0, 7.0, and 10.0 cm on green roof platforms in autumn (September 20, 2004) and spring (June 8, 2005) and then evaluated for survival on June 1, 2005 and June 1, 2006 respectively.  Overall, spring planting exhibited superior survival rates (81%) compared to autumn (23%) across substrate depths.  Sedum cauticola ‘Lidakense’, S. floriferum, and S. sexangulare were not affected by season of planting.  Sedum cauticola barely survived at any substrate depth or planting season, whereas the latter two exhibited nearly 100% survival regardless of planting season.  All other species had superior survival percentages when planted during spring. 

Complete results are published in:
Getter, K.L. and D.B. Rowe.  2007.  Effect of substrate depth and planting season on Sedum plug establishment for green roofs.  J. Environ. Hort 25(2):95-99.

Green plant with a mostly white flower.
Sedum hispanicum in flower

Influence of Substrate Moisture and Depth on Performance of Extensive and Semi-intensive Green Roof Plant Species

The objective of this study was to determine how substrate depth and watering schedule influence plant survival, performance, stress as measured by chlorophyll fluorescence, how plant selection influences substrate moisture, and if the plants tested can be used on extensive and semi-intensive roofs. Since water availability is often a limiting factor, the study explores the extent to which one can interchange substrate depth and supplemental watering to increase plant biodiversity on extensive and semi-intensive green roofs in a northern climate.

Six plant species (one succulent, three herbaceous perennials, and two grasses) growing at two substrate depths (7.5 cm and 20 cm) were subjected to five watering regimes (1, 2, 7, 14, and 28 days between watering (DBW)) over a period of three months.  The study was conducted in the Plant Science Greenhouses.  Species included Sedum album ‘Coral Carpet’ (White flowered Sedum),  Allium tanguticum Balloon Boquet ‘Noneuq’ (Ornamental Chive), Liriope spicata (Creeping Lilyturf), Armeria maritima ‘Victor Reiter’ (Maritime Thrift), Sporobolus heterolepis ‘Tara’ (Dwarf Prairie Dropseed), and Festuca glauca ‘Boulder Blue’ (Fescue) planted 15cm on center. One plug of each species was used to complete one test unit for a total of 60 units, 6 plants in each unit.  Plants were supplied by Hortech, Inc. (Spring Lake, MI).

Experimental units consisted of plastic bulb crates measuring 60 cm x 40 cm.   Each tray was lined with water permeable non-woven geotextile filter fabric composed of 100% polypropylene staple filaments to retain the substrate while allowing excess water to drain through the unit. The substrate was a manufactured light weight green roof media consisting of 50% light weight aggregate (25% course and 25% fines) 35% sand and 15% organic matter. Thirty of the testing trays received 7.5 cm (3 in) of media and the other thirty trays received 20 cm (8 in) of substrate.  All units received 100g·m-2 of Osmocote, 19N-6P2O5-12K2O controlled release fertilizer hand applied at the time of planting.

After planting the units were allowed a 120 day establishment period and were watered daily for the first 30 days to keep the substrate moist and then once every other day for the next 90 days.  During both the establishment and data collection periods, natural lighting in the greenhouse was supplemented with 400-W high pressure sodium fixture for a 16-h photoperiod (Phillips Light Systems, Somerset, NJ). Average light meter (model LI-250; LI-COR, Inc. Lincoln, Neb.) measurement at canopy height ranged from 338.4 µmols·s-1·m-2 on a respectively cloudy day to 897µmols·s-1·m-2 on a sunny day. Air temperature was controlled by a thermostat set at 21 ± 1°C.

Data such as plant survival and appearance were recorded periodically for a period of three months.  Each data collection event took place before the designated watering treatments. Volumetric soil moisture was monitored by soil moisture sensors (5TE Soil Moisture, Temperature, and E.C. Sensor., Decagon Devices, Pullman, WA). Growth index was calculated on days 1, 10, 20, and 40 for each plant by averaging three individual growth measurements consisting of plant height and width in two directions.  A Hansatech plant efficiency analyzer was used to measure chlorophyll florescence (Fv/Fm) every day for the first week of the study and then again on day 9, 19, 29, and 39.  At the conclusion of the growing period plant were harvested, separated into shoots and roots, and dried to determine biomass.  This study is still in progress.

Effect of Solar Irradiance on Plant Communities

Two studies were conducted on a third-story rooftop of the Communications Arts and Sciences Building to quantify the effect of solar radiation (full sun vs. full shade) on several U.S. native and non-native species for potential use on extensive green roofs.  Plots were installed in May 2005 and instrumented with soil moisture sensors, thermocouples, pyranometers to measure irradiance levels, and a weather station to measure wind speed, ambient air temperatures, and rainfall. A data logger powered by solar energy recorded data continuously.

In the first study, plugs of six native and three non-native species were planted in May 2005 on substrates of two different depths (8.0 cm and 12.0 cm) both in sun and shade.  Absolute cover (AC) was recorded using a point-frame transect during the growing season beginning in June 2005 and every two weeks thereafter for a period of four years.  By week 174 (23 Sept 2008), most species exhibited different AC within a depth between sun and shade.  However, when all species were combined, overall AC did not differ between sun and shade within a depth.  This indicated that while species make-up was changing among solar radiation levels, that overall coverage was not significantly different between sun and shade.  For all substrate depths and solar levels, the most abundant species were Sedum acre, Allium cernuum, Sedum album ‘Coral Carpet’, and Talinum calycinum.  Less abundant species included Talinum parviflorum, Carex flacca, Sedum stenopetalum, and Sedum divergens, which all exhibited 0 or near 0 AC regardless of depth or solar radiation levels.  With the exception of T. calycinum, native species were less abundant than non-native species. 

In the second study, six common extensive green roof species of Sedum established from seed in May 2005 on a 10.0 cm (3.9 in) substrate depth were compared in both sun and shade over four growing seasons.  AC was evaluated as in the previous study.  Solar radiation did not affect AC, but over all species composition differed between sun and shade levels.  The most abundant species in full sun were Sedum acre (0.57 AC) and Sedum album ‘Coral Carpet’ (0.51 AC).  Sedum kamtschaticum (0.57 AC) and Sedum spurium ‘Coccineum’ (0.35 AC) performed the best in the shade.  For both solar levels, the least abundant species at week 174 were Sedum pulchellum (0.0 AC) and Sedum album ‘Coral Carpet’ (0.1 AC).

Complete results are published in:
Getter, K.L., D.B.Rowe, and B.M. Cregg.  2009.  Solar radiation intensity influences extensive green roof plant communities.  Urban Forestry and Urban Greening 8(4):269-281.

a Gravel roof top with sun and shade platforms; A brick building and many windows in the background
Research plots on the Communication Arts and Sciences Building are comparing plant responses at various substrate depths in full sun and shade.

Changes in Plant Cover and Species Diversity on a Steep Green Roof

The objective of this study was to measure plant species composition and coverage changes that occurred on an extensive green roof systems exposed to direct solar exposure and steep roof conditions over time.  An extensive green roof system (XeroFlor America, Durham, NC) was installed in August 2005 on a timber frame barn located on the Old Mission Peninsula, Grand Traverse County, Michigan. The barn, a gable-end, steep-roofed structure with a 45% slope, was oriented in a due east-west direction along its main axis. The roof surface area is non-insulated and covers approximately 98 m2 (1,050 ft2) on a side. In 2009, a point frame transect was used to record species composition and absolute plant cover on the north and south faces of the roof, as well as a flat control area at ground level. The control plot provided baseline data for the extensive green roof system on the barn roof because it represented the growing conditions that would normally be found on a flat roof system. During the interim between installation and data collection, no maintenance, fertilizer, or irrigation was applied.

Originally, twelve plant species were present when the vegetated mats were installed in 2005. By April 2009, only five sedum species and two invasive species, Centaurea maculosa and a moss were recorded. This was a reduction in plant diversity of over 50% during the time between installation and measurement. When evaluating differences between the three study areas in terms of the presence or absence of the remaining plant species, significant differences existed between the study areas. The north face of the roof barn had five different sedum species identified at one or more points within the sampling frames, whereas the south face had only two sedum species reported for one or more of the1089 possible points within the nine sampling frames. The control area had four sedum and one invasive herbaceous species present. All three areas recorded moss present at one or more points within the sampling frames. The north face of the roof had the greatest amount of plant coverage (89%), whereas the flat control and south face had 67% and 36% coverage, respectively.

In terms of frequency of occurrence, distinct patterns occurred for different species. Among the species remaining, only two sedum species (Sedum album and Sedum sexangulare) were common to all three study areas. Of these two, S. album appears to be the sedum of choice for sites where direct solar incidence produces both high temperatures and droughty conditions, since it was the predominant species on the south aspect of the roof. Under more favorable slope and solar incidence conditions, such as those found on the control, it appeared as the predominant species as well. S. sexangulare occurred to a lesser degree on the south aspect and the control area, but predominated on the north aspect where no direct solar incidence occurred and smaller moisture extremes were likely. This suggests that it will compete well with other sedums under a variety of conditions, but it is particularly well suited for use under conditions of low direct sunlight, where other sedums are less competitive. Sedum acre appears to be a good companion species for S. sexangulare, since it was the second most common species recorded on the north aspect of the barn roof. Sedum album rounded out the species predominating on the north study area. Therefore, under roof conditions where high shade and steep slope would prevail, a combination of S. sexangulare, S. acre, and S. album are likely to give long-lasting, nearly complete plant coverage on the roof.

Complete results are published in:
Jones, E., T. Miller, J. Monsma, J. Puszykowski, and J. Westphal.  2011.  What happens to plant cover and species diversity when an extensive green roof is tilted? A case study on green roof design, Old Mission Peninsula, MI.  Michigan Academician 40(2):175-196.

Four men installing green mats on a roof.
Pre-vegetated mats installed in 2005 on barn located on the Old Mission Peninsula, Grand Traverse County, MI

Salt Tolerance

Detrimental effects of road deicing salt on vegetation are well known and have been well studied, with the exception of typical green roof plants, which could experience damage on green roofs and walls with public access or when installed near roadways or by the ocean.  Two studies were conducted comparing salt tolerance of five Sedum species, two Allium species and a mixture of turf grasses when exposed to six levels of salinity applied either as foliar spray or as liquid applications to the soil.  A third study compared salt tolerance when plants were placed at three distances from a major highway.  Response variables measured included survival, a health score from 0 to 5, and a growth index. Allium cernuum, A. senscens and S. ellecombianum were relatively tolerant of both saline spray and soil inundation at high saline concentrations in terms of survival, mean health scores, percentage of healthy plants and growth index.  Sedum reflexum was much less tolerant of saline spray at higher salinity concentrations and soil inundation regardless of salinity levels.  Distance from the road had no effect on plant survival rates but plants farthest from the road had higher mean health scores and a greater percentage of healthy plants than plants closer to the highway.

Complete results are published in:
Whittinghill, L.J. and D. B. Rowe.  2011.  Salt tolerance of common green roof and green wall plants. Urban Ecosystems 14(4):783-794.

snow-covered platforms with a greenhouse and highway in the background.
Plants were placed at various distances from Interstate 96 to measure the effect of salt spray from the highway on plant health

A hand with a green glove pouring salt water into plant containers
Measured quantities of salt solution were applied to the substrate to simulate salt water runoff

Establishment of a Native Prairie on the Molecular Plant Sciences Building

A study to evaluate establishment, survival, and changes in plant community over time was initiated on the Molecular Plant Sciences Building on October 8, 2011.  Four grasses and 13 herbaceous perennials native to Michigan were installed at substrate depths of 10 cm (4 in) and 20 cm (8 in).  Species being used in the study include the grasses Eragrostis spectabilis (Purple Love Grass), Koeleria macrantha (June grass), Schizachyrium scoparius (Little Bluestem), and Sporobolus heterolepis (Prairie Dropseed): and the herbaceous perennials Allium cernuum (Nodding wild onion), Anemone virginiana (Thimbleweed), Asclepias tuberosa (Butterfly Weed), Aster laevis (Smooth Aster), Aster oolentangiensis (Prairie Heart Leaved Aster), Campanula rotundifolia (Harebell), Coreopsis lanceolata (Sand Coreopsis, Lanceleaf Coreopsis), Echinacea purpurea (Purple Coneflower), Geum triflorum (Praire Smoke), Liatris aspera (Rough Blazing Star), Monarda fistulosa (Bee Balm), Penstemon hirsutus (Penstemon), and Tradescantia ohiensis (Spiderwort).  Up to 45 plugs of each species (Wildtype Nursery, Mason, MI) were planted on 20 cm centers. 

Survival rates were recorded during June 2012.  Most species experienced greater survival when grown in 20 cm relative to those at 10 cm.  Eragrostis spectabilis, Schizachyrium scoparium, and Sporobolus heterolepis experienced survival rates of 38%, 44%, 62%, and 23%, 55%, 87% at depths of 10 and 20 cm, respectively.  Koeleria likely requires irrigation at a depth of 10 cm, but may be able to depend on natural rainfall if grown in 20 cm.  Of the herbaceous perennials, all plants of Allium cernuum, Anemone virginiana, Echinacea purpurea, Penstemon hirsutus, and Tradescantia ohiensis survived the first summer at 20 cm.  Plant species composition will likely change over time as individual plants reseed themselves and compete for water and space.  The study is currently in progress and will continue for several years.

A green roof with tall 2 to 3 foot foliage; some purple flowers are seen also
Molecular Plant Sciences Bldg (July 2012)

two men servicing a green roof; mostly green with purple and yellow flowers
Molecular Plant Sciences Bldg (June 2013)

flowering plants growing on platforms; yellow, pink and purple in color
Native species (Year 1)

Plants on platforms; looking dry; tallest in the center.
10 cm depth; no irrigation (Year 2)

Three platforms, yellow flowering on the left, purple on the right, mostly green in the center.
Sedum dominating by year 3
(10 cm depth; no irrigation)

A metal frame with perpendicular intersecting wires.
A point frame transect is used to measure plant competition over time

Several platforms; one in the foreground has a point frame installed.
Point frame placed over platform

Close up of a point frame with a needle for measurements.
At each of the 100 intersection points, leaf area index is measured by recording all species that come in contact with a vertical needle at three canopy levels.

Platform plants; primarily green with white and pink flowering.
Encroachment of one species on another as they begin to compete for space

Several varieties of sedum mixed; mostly green with some red.
Sedum album, Sedum ‘Angelina’, and sedum spurium

several roof plots divided into thirds
Test plots located in the shade

a roof plot; green, pink and red in color with grey substrate.
Plot (July 2005)

a plot with a point frame; mostly green in color
Plot (July 2006) with point frame transect to recorded species coverage

A grassy plant surrounded in snow
Carex flacca (December 2005)

a dead grassy plant; close up imageCarex flacca (August 2007) survived winter temperatures, but after three years could not survive summer droughts when grown in 12 cm depth.

A brown barn with red doors and a green roof
Barn located on the Old Mission Peninsula, Grand Traverse County, MI

Planted area; sparse near concrete.
Damage to plants form use of de-icing salts

A wand-like sprayer watering plants; a person's feet can be seen behind plants
Measured quantities of salt were applied to leaves with a sprayer to simulate salt spray conditions in a controlled experiment

close up on a flat of plants
Effects of slat on various Allium, sedum, and turfgrass species

snow covered plants; slightly exposed
Salt spray and salt inundation experiments during the winter