Subtropical Climate Vegetated Roof Performance in Australia

In Australia, subtropical climate vegetated roofs are gaining popularity due to their numerous benefits. They can reduce stormwater runoff by up to 70%.

These roofs are designed to mimic natural ecosystems, providing a habitat for local wildlife. Vegetated roofs in Australia can support a wide range of plant species, including native grasses and trees.

A key advantage of subtropical climate vegetated roofs is their ability to insulate buildings, reducing energy consumption by up to 30%. This is especially important in Australia's subtropical regions where temperatures can fluctuate significantly.

By incorporating a subtropical climate vegetated roof, property owners can also increase the value of their buildings, with some studies showing a return on investment of up to 10%.

On a similar theme: Climate for Peach Trees

We field tested 15 plant species on a green roof in College Station, Texas. The green roof modules were 11.4 cm deep.

The testing took place on a four-storey building, providing a unique environment for the plants to thrive.

Irrigation was limited to the first few weeks after establishment, allowing us to see how the plants would adapt to the subtropical climate.

Climate data and plant growth were measured over three growing seasons, giving us a comprehensive understanding of the plants' performance.

Species survival was also monitored, helping us identify which plants were best suited for a subtropical climate vegetated roof.

For another approach, see: List of Companion Plants

Four species, Graptopetalum paraguayense, Malephora lutea, Manfreda maculosa, and Phemeranthus calycinus, were able to survive the entire growing season without any losses.

The climate in College Station, Texas, is characterized by hot summers and mild winters, with average temperatures ranging from 10.45°C in January to 29.19°C in July.

During the hottest and driest periods, Phemeranthus calycinus performed consistently, but its dormancy cycle begins in early fall, resulting in a GI of zero from November to March.

The species that experienced varying levels of mortality included Bulbine frutescens, Delosperma cooperi, Lampranthus spectabilis, Sedum kamtschaticum, Sedum mexicanum, and Nassella tenuissima.

Here's an interesting read: Type B Metal Roof Deck

In 2011, Sedum kamtschaticum achieved a maximum GI of 1452 cm, which was the highest volume of any species, and maintained dominance until August.

Here are the 30-year climate characteristics for College Station, Texas:

In 2012, Phemeranthus calycinus experienced a significant increase in precipitation, with 236.22 mm in February, which was the highest amount recorded in the 30-year period.

We tested the hardiness of several plant species, and some were more resilient than others. Four species made it through the growing season without any losses: Graptopetalum paraguayense, Malephora lutea, Manfreda maculosa, and Phemeranthus calycinus.

These four species were able to withstand the challenges of the growing season without any issues. They're great options for gardeners who want low-maintenance plants.

Six species, on the other hand, experienced varying levels of mortality: Bulbine frutescens, Delosperma cooperi, Lampranthus spectabilis, Sedum kamtschaticum, Sedum mexicanum, and Nassella tenuissima.

Unfortunately, five species had no survivors: Dichondra argentea, Stemodia lanata, Myoporum parvifolium, Sedum moranense, and Sedum tetractinum.

Table 1 provides a clear picture of the 30-year climate characteristics in College Station, Texas, compared to the monthly means from 2009-2012.

The mean temperature in January was 10.45°C, while the mean maximum temperature was 16.17°C. This is a significant difference, as the maximum temperature is usually higher than the mean temperature.

The years 2011 and 2012 saw a notable increase in mean temperature, with 2012's January mean temperature being 19.67°C, a 5.22°C increase from the long-term mean.

Here's a breakdown of the mean temperatures for each month:

The mean precipitation in January was 80.52 mm, while the mean precipitation in December was 79.50 mm.

As we delve into the results of our extensive green roof study, let's take a closer look at the plants that made the cut. Table 2 showcases the list of plants investigated for use on extensive green roofs in College Station, Texas.

The plants on this list have been carefully selected for their ability to thrive in the local climate. The International Plant Names Index (IPNI) is used for plant nomenclature, ensuring accuracy and consistency.

Here's an interesting read: List of Crop Plants Pollinated by Bees

Some of the plants on this list are native to Texas or the USA, which is a big plus for local ecosystems. According to the online USDA Plants Database, species like Manfreda maculosa and Nassella tenuissima are native to Texas.

The minimum cold hardiness of these plants is also worth noting. For example, Bulbine frutescens and Graptopetalum paraguayense can handle temperatures as low as -6.7°C, making them great options for our climate.

Here's a breakdown of the plants by life-form:

By understanding the characteristics of these plants, we can make informed decisions about which ones to use in our green roof designs.

Fig. 3 shows a graph comparing the monthly growth indices (GI) of different species with maximum and minimum air temperatures and precipitation events. The graph highlights the unique growth patterns of each species.

S. kamtschaticum dominated the growth chart, achieving a maximum GI of 1452 cm in July. This was a record-breaking volume that outpaced all other species.

P. calycinus performed consistently well throughout the hottest and driest periods, but its dormancy cycle began in early fall, causing its GI to drop to zero from November 2009 to March 2010 and October 2010.

The GI for B. frutescens peaked at 1507 cm in April 2010, but plant growth began to decline after temperatures consistently rose above 37.0 °C and dry conditions persisted.

The graph also shows the rapid decline of S. moranense modules, which reached a peak GI of 1468 cm in June and were dead after 150 days.

Fig 4 shows a comparison of species monthly GI means with maximum and minimum air temperatures and precipitation events. This graph is a visual representation of the data collected in the 2010 study.

Four species, G. paraguayense, P. calycinus, M. maculosa, and M. lutea, survived the experiment without any losses. These species were among the healthiest, with mean health ratings of 4.0 or higher.

The healthiest species included M. lutea, M. maculosa, and P. calycinus, with mean health ratings of 4.0, indicating they were in excellent condition. L. spectabilis had a mean rating of 3.7, suggesting it was also relatively healthy.

Several species suffered some mortality, including B. frutescens, N. tenuissima, L. spectabilis, and S. mexicanum. These species did not fare as well as the ones that survived without losses.

The graph in Fig 4 provides a clear picture of the relationship between species health and environmental factors.

The researchers started with over 100 species of plants, narrowing it down to 15 native and exotic shallow-rooted species that exhibit good resistance to drought and heat stress.

These species were chosen based on their ability to thrive in shallow substrates, such as the 8.9 cm green roof substrate used in this study.

The researchers looked to succulents and subshrubs as alternatives to forbs and grasses, which typically require more than 12.7 cm of substrate to thrive.

Plant installations were conducted in three monoculture replicate trays for each of the 15 species, with nine 5-cm-deep nursery-grown plant plugs spaced 20.32 cm apart.

The researchers also investigated denser plant spacing to increase shading on the growth media and retain soil moisture, with some species spaced as closely as 10 cm apart.

In the third plant study, 14 species were planted in a completely randomized arrangement, with plants spaced 5-10 cm apart to achieve a vegetative cover of mixed species.

Irrigation was applied only during the first several weeks of establishment, and only when natural rainfall subsided to a point where irrigation was determined as beneficial for the establishment of plants.

Plants were watered at a rate of 5.3 mm depth of water per module with a sprinkling can once every 7–10 days if there was no rain.

For the April 2009 installations, plants were watered 14 times between April and August and no supplemental irrigation was applied after 24 August 2009.

The 2010 plant installations were watered by hand on 14 and 29 March, indicating a more limited watering schedule compared to the previous year.

Suggestion: List of Honey Plants

In Brisbane, green roofs can be a great way to reduce stormwater runoff, with some studies showing that they can decrease it by up to 50%.

The City of Brisbane has implemented a green roof policy that requires new buildings to have a minimum of 20% green roof coverage.

Green roofs in Brisbane can also help to reduce urban heat island effects by up to 2°C, as seen in a study on a local office building.

The average rainfall in Brisbane is around 1,200 mm per year, which is a significant amount of water that can be managed through green roof water balance monitoring.

A study on a green roof in Brisbane found that the roof's water storage capacity was around 100 mm, which is roughly 8% of the average annual rainfall.

Regular inspections of green roofs in Brisbane are crucial to ensure they are functioning correctly and not causing any damage to the building or surrounding infrastructure.

Green roofs in Brisbane are required to have a minimum of 100 mm of water storage capacity to meet the city's stormwater management requirements.

Related reading: Solar Water Heating

Maintenance was a crucial aspect of the experiment, with irrigation being applied only when necessary.

Irrigation was done by hand watering at a rate of 5.3 mm depth of water per module with a sprinkling can once every 7-10 days if there was no rain.

The frequency of watering varied depending on the year, with plants receiving supplemental watering at different times.

In the April 2009 installations, plants were watered 14 times between April and August, and no supplemental irrigation was applied after August 24, 2009.

The 2010 plant installations were watered by hand on two specific days, March 14 and 29.

Supplemental watering was applied to the 2011 plantings on eight different occasions, including February 18, 25, and March 5, 16, 25, 27, April 10, and August 1.

By paying close attention to irrigation needs, the researchers were able to conserve water and promote healthy plant growth.

Hand watering was the preferred method of irrigation, allowing for more control over the amount of water applied to each module.

For another approach, see: Water Garden

Plant measurements are crucial for understanding plant growth and health. Monthly plant growth measurements, known as the growth index (GI), were taken for several species, including D. cooperi, S. kamtschaticum, and P. calycinus.

The GI is a measurement of the volumetric plant canopy area and porosity of each plant's canopy. It's calculated by multiplying the height of the plant canopy by the two-dimensional area of the plant canopy and the estimated percentage of live growth occupying the area.

Photographs were taken once a month for 2011 plant installations, and a plant health rating was calculated at the end of 1 year of growth. The visual inspection resulted in plant health ratings based on a scale of 1 to 5, where 1 represents severe decline and 5 represents healthy and evidence of reproduction.

Weeds were removed from the trays to prevent competition for resources, and dead plants were left in place to be included in the analyses. The mean canopy height was also measured, in addition to the idealized sphere method used by Schroll et al. (2009).

Monthly growth means and standard errors of species cover were analysed statistically to determine growth rates and survival. Species differences in plant health ratings and GI analyses were analysed using analysis of variance (ANOVA).

For your interest: Bilco Type S Roof Hatch

Some plant species can thrive on shallow unirrigated green roofs in humid subtropical climates. Four species, including G. paraguayense and P. calycinus, survived without losses in a study.

The climate in south-central Texas was consistently drier and warmer than normal during the study period, which highlights the need for longer-term research on these species under different conditions. This research would help expand knowledge of establishment requirements for these species.

It's possible that some species may perform better with irrigation or deeper substrates, as seen with the six species that had varied performance.

As we've discussed the importance of effective communication, it's clear that active listening is a crucial aspect of successful discussions.

The article highlighted that active listening involves maintaining eye contact, nodding, and summarizing what the other person has said. This helps to build trust and ensures that everyone is on the same page.

In a workplace setting, active listening can prevent misunderstandings and improve collaboration among team members. For instance, a study found that employees who felt heard and understood were more likely to be engaged and motivated.

Curious to learn more? Check out: Active Design

Effective communication is not just about speaking, but also about being aware of nonverbal cues. The article mentioned that body language, such as crossing arms or legs, can convey a negative message and hinder the discussion.

In personal relationships, being aware of nonverbal cues can help to avoid misunderstandings and improve conflict resolution. For example, making eye contact and using open body language can help to diffuse tension and create a more constructive conversation.

Ultimately, effective communication is key to successful discussions, and being aware of the strategies and techniques outlined in this article can help individuals to become better communicators.

The study suggests that irrigation limited to the first few weeks after planting may be an effective approach for green roofs in challenging climatic conditions.

In the southern USA, where the study took place, the climate was consistently drier and warmer than normal, which highlights the importance of further research on these species under a wider range of conditions.

The results show that four out of 15 species planted in 11.4-cm-deep modular green roof trays survived without losses, indicating that there may be several plant species suitable for shallow unirrigated green roofs in humid subtropical climates.

Some species, like G. paraguayense and M. lutea, demonstrated resilience and survived without losses, while others, such as D. argentea and S. lanata, had no survivors.

This suggests that the species with varied performance may benefit from additional support, such as irrigation or deeper substrates, to improve their chances of survival.