Potential implications of management practices on boreal mixedwood ecosystems in the boreal forest of western Canada

Transcription

1 Potential implications of management practices on boreal mixedwood ecosystems in the boreal forest of western Canada Phil Comeau and Mike Bokalo University of Alberta Edmonton, Alberta Canada

2 Boreal forest in Alberta

3 Forest Composition (upland productive forest) Productive upland forest comprises about 40-50% of the landscape (wetlands, peatlands and peatland forests make up 50-60%) About 45% of upland forest is Mixedwood (Aspen + Spruce) Estimate (for Central Mixedwood Natural Subregion in Alberta) (My estimate) Mixedwo od 45% Pine 5% Aspen 35% Spruce 15%

4 Post-disturbance (fire, clearcut) succession upland mesic sites in western boreal forest tendency for aspen to dominate regeneration on mixedwood sites

5 Post-disturbance (fire, clearcut) successional trends upland mesic sites in western boreal forest general 200 year trend Aspen Mixedwood - Spruce From Macdonald et al 2010

6 Why mixedwoods Important component of the natural landscape which develops after fire Biodiversity (supported by stand and landscape level mix) Productivity (and C sequestration) potentially higher in mixtures (MacPherson et al. 2001) Increased resilience Large pure spruce stands high risk for fire Black-throated Green Warbler Dendroica virens

7 Aspen is a nurse crop for young white spruce: - Reduces frost injury - Reduces grass competition, - Aspen litter beneficial to long-term productivity

8 Root collar diameter (cm) DIFN Aspen does compete with white spruce Aspen basal area (m 2.ha -1 ) BWBS SBS SBPS IDF p-bwbs p-sbs p-sbps p-idf Spruce rcd (cm) age 19/20 (WESBOGY LTS - 4 Installations) Figure 1. Scatter plot showing the relationship between understory light (difn) and aspen basal area (BAA). Lines illustrate regression models fit for each zone and for all data. Regression models are described in table 2. Light levels decline with increase in aspen stocking (Comeau et al. 2006) Aspen density (sph) Spruce growth declines with increase in aspen stocking (Bokalo and Comeau unpubl.) Hare damage higher under aspen Physical damage ( leader whipping ) of spruce by aspen (see MacIsaac Poster)

9 Challenges and issues in management of boreal white spruce and mixedwood stands Management tends to reduce mean stand age in a management unit reducing areas in mid- or late successional stages. We can successfully regenerate spruce plantations How can we avoid eliminating older successional stages (esp. Conifer dominated mixedwoods)? Mixtures require selective treatments that can be expensive It is less costly to regenerate pure aspen and pure spruce stands (we know how to grow spruce in spruce plantations and how to grow aspen; this has been a focus for 3 decades!) Access in the boreal region is poor, expensive, and local labour force small (and we compete with oil and gas for forestry labour)

10 Mixedwood Managemention -Some Options A. CC, plant spruce and tend o Preharvest aspen control o Spot, Band, Patch, or Broadcast herbicide treatments, or thinning B. Regenerate (planting or natural) and leave for extended rotation o With or without commercial thinning (understory protection)

11 A. CC, plant spruce and tend Plant and treat to create bands or patches Banded and patchy treatmentsshow good spruce growth response linearity unnattractive Striping, banding, patches Aerial herbicide treatments potentially very cost-effective ($250/ha in 2012$) GPS and spatial data might enable planning of planting to match treated ground.

12 A. CC, plant spruce and tend Precommercial thin aspen (age 4-10) Thinning is expensive ($600/ha+) and sites must be accessible

13 Spruce rcd (age 20) (cm) Spruce growth increased by precommercial thinning to reduce aspen density WESBOGY Long Term Study Effects of aspen on spruce diameter at age 20 (WESBOGY LTS - 4 agencies x 2 installations) Natural (unthinned) Aspen # (tph) Bokalo and Comeau (unpubl). See Poster!

14 Performance survey Sw density (s Future Stand composition predicted based on densities at age 14 (based on model projections from MGM2008) %Conifer (by volume) at Age 90 AwSI=20 SwSI=18 (size data from WESBOGY DMI) note scales are categorical C: red, CD: green, DC: blue, D: lt blue 1000 C CD DC %-100% 80%-90% 70%-80% 60%-70% 50%-60% 40%-50% D %-40% 20%-30% 10%-20% 100 0%-10% Perform ance survey Aw density (sph) Stadt, Bokalo, and Comeau. Unpubl.

15 A. CC, plant spruce and tend Spot treatments for mixedwood stands Tend 1-2 m around low to moderate density of planted spruce (chemical site prep, herbicide or manual/motor manual) Retain aspen surrounding each spruce Provides frost protection, good stem form, reduces aspen resprouts Cost? >$300/ha for 400 spots (backpack), >$400/ha for motormanual Need good acccess for work crews See Pitt et al. 2010

16 B. Manage extended rotation with CT to remove aspen, and clearcut for final harvest ( Understory Protection ) Remove overstory aspen at ages 60 to 80 while leaving advance regeneration of white spruce let spruce grow to merch sizes (40-80 years) Underplant stands at age 40 to provide advance regeneration where needed Advantage: height of advance spruce regeneration provides it with a growth advantage; no need for site preparation or vegetation control (Comeau et al. 2010)

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18 Forecasts of potential outcomes Mixedwood Growth Model (MGM) (Bokalo et al. 2013; Deterministic, individual tree, distance independent Aspen SI50=20, Spruce SI50=20 (mesic sites, Central Mixedwood Natural Subregion) NPV 5% discount rate, $50/m3 aspen, $75/m3 spruce

19 Yield implications of 7 selected crop plans Crop Plan Cost ($ CDN) MAI Spruce (m3/ha/y) MAI Aspen (m3/ha/y) MAI total (m3/ha/y) NPV 1. CC, aspen natural (70 yr rotation) 2. CC, plant Sw, herbicide (90 y rotation) CC, plant Sw, thin aspen to 1500 sph (90 y rotation) Spot treatment 400 spruce/ha (90 y) CC, plant Sw, spray patches (40%) (90 y) CC, plant Sw, harvest aspen at 70, spruce at CC, spruce natural, harvest aspen at 70, spruce at Based on Mixedwood Growth Model (Bokalo et al. 2013) simulations Spot Treatment = Phil s guess (cannott be simulated directly) NPV $25/m3 aspen, $40/m3 spruce, 5% discount rate

20 Structural and Biodiversity Implications Scenario 2 Spruce (90 y rotation)

21 Structural and Biodiversity Implications Scenario 3 PCT (90 year rotation)

22 Structural and Biodiversity Implications Scenario 6 Understory Protection 120 year rotation

23 Gray and Hamann 2011 Climate change contraction of mixedwood forest Will mixedwood stands be more resilient than spruce stands? ---Perhaps.

24 Summary Sustainable forest management (sustaining ecological, economic and social values) requires us to maintain a large component of the region as mixedwood forests and not monocultures Maintaining the mixtures in the landscape requires thought and planning Sustainable and Ecosystem Based Management for: Biodiversity/Habitat, Recreation, High value conifer, Aspen for chips and pulp and other uses, Bioenergy, Institutional barriers and attitudes need to continue to change to embrace mixedwood silviculture Several options available, need to apply a mix Extended rotation, multiple entry approach that utilizes succession (commercial thinning, understory protection) is very promising and economically the best option (but requires planning at the forest level to maintain forest composition) Climate Change implications?

25 Thank-you