Green Roofs for Urban Biodiversity: Latornell Symposium. Gavin Miller TRCA Flora Biologist November 2010

Transcription

1 Green Roofs for Urban Biodiversity: Latornell Symposium Gavin Miller TRCA Flora Biologist November 2010

2 Green Roof Research to Date Hydrology storm water quantity attenuation storm water quality improvement Energy conservation insulation evapotranspirative cooling Urban agriculture & open space

3 How can a green roof support biodiversity? Target suitable species & communities Site conditions (extensive green roof) Analogous ecosystems in nature Two roofs looked at: York & Kortright Flora (and fauna) Recommendations

4 Typical Conditions Shallow substrate (about 15 cm) Heat, wind, dryness (York irrigated) Nutrient leaching More similarity to primary succession Fairly low vegetation cover Tough conditions favour more unusual conservative species in long term

5 Analogue ecosystem - Alvar Flat limestone pavement with thin soil closest analogue to most extensive green roofs. Globally significant habitat.

6 Analogue ecosystem Sand Barren Dry, exposed sites with minimal organic matter

7 Analogue ecosystem Mineral Fen Constant mineral-rich calcareous ground-water seepage; fairly low nutrient status. May be associated with old gravel pits. Similar to irrigated green roof.

8 York University Green Roof

9 York University Green Roof Built in 2001 study in Substrate volcanic pumice from BC Some compost, peat, sand, clay 14 cm depth Two main sections each with own seed mix Smaller sections Regular irrigation.

10 Roof sections Ornamental flower seed mix Grass seed mix Smaller sections quickly surveyed: mostly flower mix, one unseeded Mostly non-native species (showy semiwild flowers and fescue grasses) Seed mixes skewed results

11 Results York University study 91 species of vascular plant in species in % native / 63% exotic Flower roof 62 species in 2005 (29% native) Grass roof 62 species in 2005 (42% native) One small unseeded section 36 spp. (50% native) High moss & liverwort cover (30-40%); discontinuous vascular plant cover

12 Vegetation Cover York U Roof

13 Floristic Quality Biodiversity still fairly low Untested but fairly consistent slight increase from 2004 to 2005 Coefficient of conservatism (0-10 scale) Roof as a whole 2.8 Flower roof mean Grass roof mean High quality prairie mean >4

14 Seed mix still dominant after 4 yrs

15 A closer look Some sensitive species were found Mostly colonized spontaneously 7 species of TRCA regional concern; 8 with CC of 5 or more Most of these spontaneous; 2 in seed mix Familiar invasive species in area (e.g. thistle, buckthorn) did not colonize well!

16 York University Roof - Asters

17 York University Roof - Orchids

18 the birds and the bees

19 Fauna bird and bee observations Six species of birds observed Birds seemed to favour adjacent ground habitats 21 species of bees in 2004 and 27 in 2005 on a few York University sites including green roof Green roof appears to support similar bee diversity as on-ground old-field.

20 Limitations to York U study Very short time frame (2 seasons) New green roof cannot be justly compared with high quality prairie Study wasn t able to compare green roof with comparable surface habitat Green roof is small only one in vicinity, so no cumulative effects Roof was seeded with non-native seed mix!

21 Archetype Sustainable House Kortright Centre

22 Kortright Green Roof A new roof, no pre-existing seed mix Allowed for experimentation with native species Small area, but open to public viewing and interpretation Deliberately chose alvar species Combination of salvaged plants from Kawarthas and nursery-propagated.

23 At time of planting - April 2009

24 Kortright Roof some species Nodding wild onion (Allium cernuum) Wild chives (Allium schoenoprasum) Prairie smoke (Geum triflorum) Columbine (Aquilegia canadensis) Hairy beard-tongue (Penstemon hirsutus) Prickly-pear (Opuntia humifusa) 1 plant Prairie ragwort (Packera paupercula) Bristle-stalked sedge (Carex eburnea).

25 About a month later

26 A year later August 2010

27 Good showings a year later by Chives Nodding wild onion False pennyroyal Prairie ragwort Prairie smoke Columbine Bristle-stalked sedge Some of these species are sensitive.

28

29

30 Limitations & Opportunities - Kortright Qualitative no actual study Small size Need to track performance of individual species. Easily accessible Clean slate Nearby comparisons Earthrangers.

31 Sedums or native plants? Sedum roof, Earthrangers Alvar roof, Kortright

32 The potential 20% of the City of Toronto surface is roof tops 16% of Don watershed (2002) is natural cover (forest, wetland, meadow) Therefore green roofs are essential for improving health of urban watershed.

33 Aid to existing or target natural cover

34 Role of TRCA re. Green Roofs Support programs like City of Toronto s Standard setting for hydrological performance and native biodiversity TRCA has interest due to storm water mitigation and natural heritage TRCA has hydrological and biological expertise for restoration design.

35 Recommendations Reduce fertilizer substrate can contribute to phosphate loading seed mix ensure native and document sourcing don t just use sedum could rely more on what seeds naturally target certain suitable flora of conservation concern for recovery decisions about target community, substrate depth, irrigation, etc.

36 Next steps long-term monitoring of different roofs substrate types, depths, irrigation native versus sedum plantings versus spontaneous include invertebrates 5 7 year minimum to get clear monitoring signal.

37