The theme of last summer’s Seeley Conference, floriculture’s environmental footprint, included a discussion on how sustainable peat is as a soil amendment. The discussion stemmed from part of a presentation highlighting the new Sustainable Sites Initiative created by the American Society of Landscape Architects, the Lady Bird Johnson Wildflower Center and the United States Botanical Garden.
The three organizations are teaming on the Sustainable Sites Initiative (SITES) to create voluntary national guidelines and performance benchmarks for sustainable land design, construction and maintenance practices. But two recommended requirements of the initiative–using peat-free planting media and avoiding sphagnum peat as a soil conditioner–sparked a debate at the Seeley Conference.
To further explain the requirements, as well as the reasons SITES drafted them, Greenhouse Grower tasked the SITES with sharing some perspective. We also asked Mark Elzinga, president of Elzinga & Hoeksema Greenhouses, to share his reaction to the requirements regarding peat and the role peat plays in his greenhouse operation. Both SITES, represented by Steve Windhager, and Elzinga participated in the 2010 Seeley Conference discussion.
To read Elzinga’s essay, “A Case For Canadian Peat Moss,. Below is SITES’ case against Canadian Peat Moss.
The use of sphagnum peat as a soil amendment was considered by the technical committees of the Sustainable Sites Initiative (SITES) in the development of the “Guidelines and Performance Benchmarks 2009,” available as a free download at www.sustainablesites.org/report. Reference to peat occurs specifically in Prerequisite 7.2 (restore soils disturbed during construction) and credits 5.9 (support sustainable practices in plant production) and 7.3 (restore soils disturbed by previous development).
Based on this technical committee work, the Sustainable Sites Initiative does not consider the use of sphagnum peat to be sustainable, as it is non-renewable within a 50-year time span.
Why Peat Is Not Sustainable
While the rates of annual accumulation of peat in Canada on an annual basis do exceed the volume extracted for horticultural purposes, this does not make this harvest sustainable. Peat accumulates at a rate of 0.5 to 1 millimeters annually, and thus an area cannot recover from harvesting within a sustainable time frame. Even the Canadian Sphagnum Peat Moss Association concedes that in regard to peatland restoration, “the full natural capital of the pristine bog [will not return] within any normative human timeline measurement.”
Peatlands are critical sinks for carbon and its extraction increases greenhouse gas emissions, covering only 3 percent of the world’s surface area but providing for 30 percent of all carbon stored in the soil. While extraction of peat for horticultural purposes currently only represents a small portion of total greenhouse gas emissions, harvesting peat does contribute to climate change.
One researcher has pointed out that because carbon dioxide (CO2) emissions from harvested, cutover peatlands are approximately three times greater than the emissions from natural sites, the loss of only 5 percent of Canadian peatlands–whether for horticultural extraction or some other cause–will result in Canadian peatlands being converted from a net carbon sink to a net source of CO2.
In addition, rising temperatures associated with global warming could significantly impact Canadian peatlands and trigger a feedback loop that would greatly increase peatland degradation and greenhouse gas emissions from them.
Abandoned, cutover peatlands rarely return to functional peatland ecosystems post-extraction because the physical and hydrological conditions required for sphagnum re-establishment have been eliminated in most cases. These degraded, cutover peatlands then become long-term, persistent sources of CO2 emissions. Thus, restoration of cutover peatlands is preferred to their abandonment, and it is possible to return a degraded peatland from a CO2 source to a carbon sink within three to five years–although a six- to 10-year time frame may also apply.
Continuing advances in extraction and restoration techniques may further reduce greenhouse gas emissions associated with horticultural extraction and facilitate more rapid and robust restoration. However, intact, non-degraded peatlands sequester carbon at a greater rate than restored peatlands and disturbance associated with peat extraction irrevocably alters peatland ecology despite restoration.
In addition, negative consequences associated with peatland restoration, such as increases in phosphorus leaching from the rewetting of peat surfaces, are possible. And restoration will not regenerate peat stores at a rate that would permit sustainable extraction.
Therefore, while restoration of cutover peatlands is far preferable to their abandonment, there are significant environmental costs associated with cutover peatlands irrespective of restoration.
Climate Change Implications
Finally, climate change associated with greenhouse gas emissions is expected to bring hotter, drier conditions. By lowering existing groundwater levels, climate change can upset the delicate balance in peatland ecology between carbon sequestration and greenhouse gas emission, transforming many peatlands from net carbon sinks into net sources of CO2.
Canadian peatlands in the subarctic and boreal wetland regions, such as the Hudson Bay Lowlands, the Mackenzie River Valley region and the northern parts of Alberta and Manitoba, are most likely to be affected.
Researchers have calculated that climate change will impact 60 percent of the total area of Canadian peatlands and 51 percent of the organic carbon sequestered. In addition, greenhouse gas emissions from peatlands triggered by climate change could create a feedback loop that could raise temperatures still further and accelerate peatland degradation.
While additional research needs to be done to evaluate climate change’s impact on peatlands and carbon fluxes globally, the carbon sink-source relationship for Canadian peatlands is more likely to become a more significant contribution to climate change with continued harvesting.
Peat Moss Alternatives
Compliance with SITES credits that preclude the use of sphagnum peat moss is practical and achievable because alternatives do exist to the use of peat moss for soil restoration and as a medium for horticultural plant production. Compost, which the Soils Technical Subcommittee has judged to be a superior source of organic matter for soil restoration than peat moss, is widely, though not universally available, and typically at a much closer distance to a development site than a Canadian peatland.
Alternatives to peat moss as a plant-growing medium, such as coir fiber and dust, wood fiber and bark, biosolids, bracken and compost, are available if not as extensively used.
It should also be noted that the efficacy of particular peat moss alternatives is relative to the use (i.e. plant propagation versus horticultural production) and to specific plants, and that the use of peat moss alternatives is in a learning phase as horticulturists become more familiar with them and understand the techniques and requirements needed to obtain best results. However, encouraging change and innovation that reasonably raises the bar for existing practices is consistent with SITES principles.
It is also important to note SITES is a voluntary set of guidelines for landscape sustainability aimed at market transformation and that certification is possible without achieving credits 5.9 or 7.3. SITES is striving to ensure that the built landscape is part of the solution for our global environmental problems, and we believe avoiding the use of peat is an important part of achieving this goal.
About the author: Multiple people associated with the Sustainable Sites Initiative (SITES), including Steve Windhager, director of the Lady Bird Johnson Wildflower Center and SITES, produced this essay. SITES can be contacted at firstname.lastname@example.org.