Oral graduate thesis defense (September 14, 2011, Guelph, Ontario).
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The document summarizes the key findings of a thesis examining the long-term effects of drainage on plant community structure and function in boreal peatlands. It found that (1) bog plant composition was somewhat resistant to drainage, while fen understory response varied depending on tree response; and (2) drainage increased tree/shrub biomass and productivity at poor fen sites, but did not significantly change understory biomass at treed sites. The study provides insights into vegetation-hydrology feedbacks under climate change and implications for long-term carbon storage in northern peatlands.
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Similar to Oral graduate thesis defense (September 14, 2011, Guelph, Ontario). (10)
Oral graduate thesis defense (September 14, 2011, Guelph, Ontario).
- 1. THE EFFECT OF LONG-TERM DRAINAGE ON PLANT COMMUNITY STRUCTURE AND FUNCTION IN BOREAL CONTINENTAL PEATLANDS An M.Sc. Thesis presentation by Courtney A. Miller
- 2. Overview 1. Introduction to boreal peatlands 2. Chapter 1: Drainage and plant community structure 3. Chapter 2: Drainage and plant community function 4. Conclusions
- 3. What is a Peatland? Yu, et al., 2010
- 4. Boreal Peatland Types BOG FEN 1. Rich Fen Sphagnum and Black Spruce dominated 2. Poor fen – have Sphagnum spp.
- 5. Why Does Peat Accumulate? • Input > Output Input Output • Decomposition limited by cold, wet soil conditions • Strong plant controls on decomposition
- 6. Boreal Peatlands and Climate Change IPCC, 2007
- 7. Why Does Peat Accumulate? • Input > Output Input Output • Decomposition limited by cold, wet soil conditions • Strong plant controls on decomposition
- 8. How to Predict Climate Change Impacts to Peatlands • Methods: – Microcosm – Short term field based – Modelling • Succession?
- 10. Road-Impacted Drainage Site #1 Dry Wet Dry Site #2 Wet Dry Wet
- 12. Study sites • CFS and ALFS ditched site • McLennan poor fen • Road-impacted sites – 2 bogs (RB1 and RB2) – 1 open poor fen (ROF) – 1 moderate-rich treed fen (RMF) – 1 poor treed fen (RPF)
- 13. General Objectives Ch1: Quantify the impact of long- term drainage on boreal peatland species composition Ch2: Quantify the impact of long- term drainage on boreal peatland aboveground biomass and productivity
- 14. CH1: Community Level Hypotheses H1: root zone depth tree cover H2: light availability change in understory species composition H3: Because of differences in hydrology, change in understory species composition will be larger in fens than in bogs.
- 15. Plant Group Predictions Tree Shrub Feather Moss Sphagnum
- 16. Hummock Hollow
- 17. Field Measurements Wet side Dry side Treatment Plot Control Plot
- 18. Statistical Methods Ex. 1 • Nonmetric Multi- Dimensional Scaling Axis 2 (NMDS) – Multi-response permutation procedure (MRPP) Axis 1 Ex. 2 • Sørensen Axis 2 quantitative similarity index Axis 1
- 19. H1: root zone depth tree cover RB2 RB1 RPF ROF NP RMF McLennan -6000 -4000 -2000 0 2000 4000 6000 Change in total plot basal area (m2/100 m)
- 20. H1: root zone depth tree cover RB2 * RB1 RPF* ROF RMF McLennan * -25 -15 -5 5 15 25 Average change in % canopy cover * Denote significant differences (α=0.05)
- 21. H2/3: Fen understory plant species composition will change more than bog sites with drainage Fens Bogs 1.5 1 0.5 0 T Statistic -0.5 0 0.2 0.4 0.6 0.8 1 -1 -1.5 -2 r = 0.92010 -2.5 p = 0.0080 -3 -3.5 SI
- 22. RMF Ordination Control Hummock Control Hollow Treatment Hummock Treatment Hollow final stress = 5.66838, n = 12 with 23 taxa
- 23. Site Microform SI RMF Hollow 0.319 Hummock 0.383 RB1 Hollow 0.538 Hummock 0.619 RB2 Hollow 0.624 Hummock 0.737
- 24. Shrub Response to Drainage RB2 RB1 RPF ROF RMF McLennan -40 -30 -20 -10 0 10 20 30 40 Average change in shrub cover (%)
- 25. Feather Moss Response to Drainage RB2 RB1 RPF ROF NP RMF NP McLennan -70 -50 -30 -10 10 30 50 70 Average change in feather moss cover (%)
- 26. Sphagnum Response to Drainage RB2 RB1 RPF ROF NP RMF McLennan -60 -40 -20 0 20 40 60 Average change in Sphagnum cover (%)
- 27. Hummock vs. Hollow Sphagnum Response to Drainage Hummock Hollow RB2 RB1 RPF ROF NP RMF McLennan -60 -40 -20 0 20 40 60 Average change in Sphagnum cover (%)
- 28. SI T Change in r = 0.8274 r = -0.6245 Water Table p = 0.0471 p = 0.1850 Change in r = -0.7887 r = -0.7986 Canopy Closure p = 0.0623 p = 0.0567
- 29. SI T Change in r = 0.8274 r = -0.6245 Water Table p = 0.0471 p = 0.1850 Change in r = -0.7887 r = -0.7986 Canopy Closure p = 0.0623 p = 0.0567 Fens Bogs 1 2 0.8 1 T Statistic 0.6 0 SI -1 0.4 -2 0.2 -3 0 -4 -5 15 35 -5 15 Change in % canopy cover Change in % canopy cover
- 30. Chapter 1 Summary • Bog species composition somewhat resistant to drainage (hummocks > hollows). • Fen understory response to drainage was variable, and may have depended on the magnitude of tree response
- 31. Objectives 1. Quantify the impact of long- term drainage on boreal peatland species composition 2. Quantify the impact of long- term drainage on boreal peatland aboveground biomass and productivity
- 32. Productivity and Biomass – H4: root zone depth tree/shrub aboveground productivity or biomass – H5: Understory biomass and productivity would in fens, but would not change in bogs
- 33. Biomass Methods • Understory vascular • Shrub • Sedge • Forb
- 34. Productivity Methods • RMF and McLennan • Dendrochronology • Understory ANPP • Sedge, Forb • Shrub • Cranked wires
- 35. Effect of Drainage on Tree Biomass RB2* RB1* RPF* ROF NP RMF McLennan* -2000 -1500 -1000 -500 0 500 1000 1500 2000 Change in tree biomass (g C/m2)
- 36. Effect of Drainage on Shrub Biomass RB2 RB1 RPF ROF* RMF McLennan -400 -300 -200 -100 0 100 200 300 400 Average change in shrub biomass (g C/m2)
- 37. Effect of Drainage on ANPP - McLennan Tree Shrub Sedge Forb Moss 400 350 ANPP (g C/m2/yr) 300 250 200 150 100 50 0 Control Treatment
- 38. Effect of Drainage on ANPP - RMF Tree Shrub Sedge Forb Moss 400 350 ANPP (g C/m2/yr) 300 250 200 150 100 50 0 Control Treatment
- 39. Chapter 2 Summary • Increase in tree/shrub biomass at all poor fen sites • No significant differences in total understory aboveground biomass at any treed site • Tree NPP responded strongly to drainage at McLennan; moss NPP increased somewhat at the RMF site
- 40. Study Limitations • Drainage ≠ Drought – Pulse vs. Press disturbance • Wasn’t able to explicitly test a drainage x microform interaction • Response of roots?
- 41. Broader Implications • Are there vegetation – water table feedbacks that increase the magnitude of drying? • Will an increase in trees/shrubs translate into increased long-term C storage?
- 43. ET ET Drainage Drought
- 44. Broader Implications • Are there vegetation – water table feedbacks that increase the magnitude of drying? • Will an increase in trees/shrubs translate into increased long-term C storage?
- 45. Photo credit: Alberta Wildfire Info
Editor's Notes
- Welcome committee members, colleagues and peers.Thank you all for taking the time to come to my thesis defenseThe effects of long term drainage on peatland plant community structure as well as biomass and productivity.
- I’d like to start by…
- Wetland that has accumulated >40 cm of peat. Can be treed or openPeat is partially decayed organic matterBORAL ca. 87% of the world’s peatlands (3.4 million SQUARE KM) 1.1 million km2 of peatlands occupies the boreal and subarctic regions of CanadaIn continental Western Canada (i.e., Alberta, Saskatchewan, and Manitoba), peatlands cover about 1/5th of of the land-base
- Bogs and fensare characterized by their hydrology. Bogs are Ombrotrophic and fens are minerotrophic. Bogs always have sphagnum and have black spruce canopies in continental western CanadaFens are variable in their vegetation. This is why they can be further classified as rich and poor fens. Like bogs, poor fens have Sphagnum, but may or may not be treed with Bl. Sp. OR Tamarack. Rich fens have are highly variable in their plant community composition and can sometimes be biodiversity hot spots.. Poor fens are acidic, minerotrophic and Sphagnum moss dominated, while rich fens can be alkaline, basic to neutral and typically are dominated by true moss species
- Peat accumulates when the rate of inputs (i.e. productivity) exceed the rate of outputs. Outputs could be from leaching, or disturbance fro wildfire. But the major contributing factor to why we have peat in boreal peatlands is the cold wet soil conditions. HOWEVER
- Climate models predict an increase in temperature in the boreal region, which will increase ET and lead to dryingboreal peat accumulation may no longer be constrainted due to cold wet soils. Which could increase decomposition rates and release of C into the atmosphere. Currently, the amount of c in peat is equal to the c in the atmosphere.
- BUT THERE ARE VERY STRONG PLANT CONTROLS ON DECOMPOSITION THAT ARE NOT INCLUDED IN MODELS. SPHAGNUM IN BOTH POOR FENS AND BOGS.recalcitrantRELATIVELY FAST PRODUCTIVITY HIGH INPUT AND LOW OUTPUT.HOW DO WE PREDICT THE POTENTIAL EFFECTS OF CLIMATE CHANGE ON PEATLANDS?
- Dynamic vegetation model (DVM), there are very few for peat.BUT none of these consider succession
- Alfs and CFS ditched peatlands for forestry in 1980sProvides opportunity to use these drainages sites as a surrogate for the drainage associated with climate change
- Thealberta landscape is a mosaic of logging, oil and gas roads, some of which transect peatlands.A few studies have looked at the road impacts on the tree community in peatlands, but do not use a control plot.
- First, bogs may be more resistant to drainage than fens. A bog has little to no lateral flow under pristine conditions. Furthermore, bog species are adapted to low nutrient availability and are typically drier than fens. An increase in nutrient turnover times has been observed with drainage due to increases in tree biomass (Laiho, et al., 2003), which may not have an effect of bog species composition.
- Focused on plant groups that would most impact the quality of the peat. There are three types of feather moss in the boreal associated with uplandsIncrease in feather moss because of increased canopy closure and it is photo inhibited.A decrease in sphagnum cover because of increased canopy closure and decreased soil moisture. So I expected FM to out compete Sphagnum.HOWEVER not all sphagnum are equal. Some sphagnum are more dessication tolerant than other species,
- There is hummocks or hollow sphagnumHummock sphagnum is more desiccation tolerant than hollow sphagna, but it is also grows more densely than hollows, which increases water retention and the capillary rise from the water table. This helps hummocks stay moist even when they are further from the water table. However, sphagnum is generally found in open canopied sites. So while I expected an increase in hummock sphagnum, I also expected a decrease in total sphagnum cover due to increased tree canopy closure.
- To address these hypothesis …Control verification through transectMoss and tree cover. I chose to only do moss and tree cover because mosses most reflect hydrologic regimes of a site and treeQuadrates to asses the species number determined through species area curvesCanopy photos to get an estimate of percent canopy cover at each quadrate
- NMDS uses Species composition data to interatively generate a matrix of dissimilaity values between quadrates and this is plotted in ordination space.NMDS is robust with data that containts a large propotion of zeros and is tehrefore suited to non-notrmal data sets, which are commonly found in ecology.The test statistic (T) is a measure of distance between groups; a strongly negative T value indicates a strong separation between groups.Sorensen is different than other similarity indexes (i.e. simpson’s) because uses species abundances to estimate similarity between samples.Values close to 1 are considered most similar, while values close to 0 are most dissimilar.
- Right means an increase with drainage. This was calculated as the sum of the basal area of all trees in each plot based on the basal diameter measurements and the assumption that each tree was roughly circular.
- Right means increase in canopy cover with drainage
- The bogs are reasonably close to one another, but the fens are much more variable. Noticed something about the ordinations though.
- Note: axis two separates hollows from one another but not hummocks
- Hummocks are more resistant to drainage than hollows.I couldn’t test this in the other sites, as they were less patterned.
- Right means increaseIncrease at the bog and road impacted poor fen sitesDecrease at the McLennan site – light availabili
- Right means increasePredicted an increaseBogs decreasePoor treed fens increased
- Right means increaseThe poor fen treed sites decreased in total sphagnum, which bothexperiend an increase in canopy cover and feather mossFM decreased at the bog sites, and sphagnum didn’t really change, so what replaced fm – lichen. or the canopy closure was insuffient
- Right means increaseDecrease in hollow sphagnum at the RPF site.The McLennan site had a decrease in total sphagnum, and did not have much hollow sphagnum in the control plot – instead wet portions were true mosse.Wasn’t significant change at the ROF, RB2 or RB1 siteAbsent from the RMF site.
- So my original goal was to not only characterize changes in spp between treatment and control plots, but to understand how drainage influenced resources (light, moisture, etc.) important to community structure. And while I wasn’t able to test the importance of these resources directly, here is evidence that changes in light were more important than changes in WT associated with drainage……
- So my original goal was to not only characterize changes in spp between treatment and control plots, but to understand how drainage influenced resources (light, moisture, etc.) important to community structure. And while I wasn’t able to test the importance of these resources directly, here is evidence that changes in light were more important than changes in WT associated with drainage……
- H4 trees in treed peatlands and shrubs in open sites as they woudlnt be light limited but the tree canopy.H5: species in bogs are already adapted to lower water table positions, and nutrient limitations.
- Tree cookies – basal diameter for biomass, and analyzed cookies using WinDendro to estimate annual productivityQuadrates: Aboveground biomass – sedge, forb, or shrub.
- 1) they were forested, allowing me to examine changes in both tree and understory productivity, 2) because I expected community structure and long-term biomass accumulation to change in fens moreso than in bogs, I wanted to focus on fens, and 3) the McLennan and RMF sites represent two fen types (McLennan=poor fen; RMF=moderate rich fen). Aboveground biomass – sedge, forb, or shrubNPP was estimated using the biomass data. Sedge and forb species die every winter, so I assumed this annual NPP was equivalent ot the aboveground biomass estimate. Estimates of shrub NPP were defined as terminal growth only (leaves, flowers, new twigs), as radial stem growth is difficult to obtain, especially in dwarf shrubsTo determine moss NPP I used a the cranked wire estimate. Where a small wire is inserted into the moss surface and throughout the season you measure the vertical growth of the moss up the wire.
- AXIS! Asterisks denote sig. differences. At alpha level of 0.05In the poor fen sites and the younger of the two bog sites, there was an increase in tree biomass. These are the same sites that had significant increases in canopy closure, this is not necessarily surprising. At the RB1 site, there was a significant difference, but, it is likely due to stand age -stand age old site biomass peaked earlier so road construction may not have affected tree biomass
- AxisAsterisks denote sign. Differences.Error bars are 1 standard errorof the meanStatistical Increase shrub biomass ONLY at the ROF site, which is the only untreed site.
- axisSignificant vascular understory reduction in biomassIncreasein tree, decrease in moss
- No significant change in understory vascular productivityNo change in tree, increase in moss --- due to increase in hummock moss productivity
- Understory Ecosystem function may not have changed with drainage
- Drainage is an event that occurs at a discrete event in time, or a pulse disturbance. Drounghtress gradual pressure on the ecosystem. Is this land use change relevant for making predictions about future climate yes, it’s the best thing we have. Hummocks have higher peat accumulations, but hollows epxerienced species shifts, for example, in thebog sites, there was increase shrub cover in hollows as a result of drainage, but not at hummocks.No sig. difference may not actually be representative of what’s going on
- This comes at the cost of moss. But the finns have found that this translates into an increase in long-term C storageSo what does this mean for peatlands? The response of the entire ecosystem to drainage, depends on the response of the trees to drainage!
- A stand volume increase of 10 m3ha–corresponded with a drop of 1 cm in water table
- A stand volume increase of 10 m3ha–corresponded with a drop of 1 cm in water table. DID YOU FIND ANY EVIDENCE OF THIS IN YOUR RESULTS????IT WOULD BE INTERESTING TO GO BACK AND QUANTIFY THE ET AT THESE SITES, AND WE’RE WORKING WITH HYDROLOGISTS ON THIS
- Increase trees and shrubs, increase ligning,keepdecomposiiton levels relatively low, low radiative forcing.
- Already there is an increase in frequency and intensity in wildfire from the 1960’sDecrease in WT position will already make peat more vulnerable to deep burning which would release more C into the atmosphere. Additionally increases in Tree and shrub associated with the decrease in wt increases the fuels available for fires, which would increase spread rate and intensity of fires. Making our Canadian peatlands a positive radiative forcing. We collected some dataImpact of drainage and total C cycling, i.e. including losses from fire, is a huge uncertainty in the boreal landscape but by using these drainage sites, we can begin to understand the potential impact of CC on peatlands.