The effect of PCT on the abundance of herbaceous species Kerienne La France and Mark Roberts September 9, 2008 T. Mamashita Forest Ecology Lab Faculty of Forestry and Environmental Management, University of New Brunswick
Introduction & Methodology Impact on crop trees well documented, but what about other ecosystem components? The effect of PCT on herbaceous species is not fully understood Herbaceous layer includes all vascular plants < 1 m in height Majority of plant species diversity Nutrient cycling and energy flow T. Mamashita
Introduction Plant survival, growth and germination may be influenced by the following: Stand-level characteristics: Light availability Growing space Fine-scale disturbance features: Slash Substrates Microtopography All of these environmental features can be directly affected by thinning activities
Introduction Objectives 1) Compare species abundance and environmental features between PCT stands and unthinned controls over time. 2) Identify relationships between plant species abundance and possible causal factors (ie: environmental variables).
Methodology Study Area South-East New Brunswick moist soils, soft-wood dominated Clear-cut, naturally regenerating stands Sites were selected using GIS records (where available). Age range 16-42 years. GIS Map J.D. Irving Ltd.
Methodology Stand-level features: Sampled in six 5.64 m fixed radius plots per stand: volume of CWD (perpendicular distance method) tree height and DBH tree density tree species 300 m 200 m
Methodology Study Design Sampling area 6 ha 4 parallel transects 50 1m 2 quadrats 300 m Vegetation & environmental variables measured within each quadrat 200 m
Methodology Vegetation & Environmental Variables: Percent cover for each species Percent cover & number of regenerating seedlings Canopy cover HW & SW (available light) Ground disturbance percent cover & depth of tracks Slash (HW & SW ) <0.5 cm 0.5-7 7 cm > 7 cm Substrates mineral soil humus HW & SW litter A. Witkowski
Results Stand-level Environmental Variables: Significant Treatment*Age interactions: Total Stem Density Stump Density Other significant differences: Snag Density (decreased in PCT) Stems/ha 0 2000 4000 6000 8000 10000 12000 Total Stem Density PCT unthinned 10 15 20 25 30 35 40 45 Stand age (yrs)
Results Stand-level Environmental Variables PCA : 2.5 2 1.5 stump dens height PCT unthinned Axis 2 (EV=0.1485) 1 0.5 0 hw dens cwdvol stump ht shrub dens snag dens snag ht -0.5-1 sw dens -1.5-2 -1-0.5 0 0.5 1 1.5 2 2.5 Axis 1 (EV=0.2025)
Results Quadrat-level Environmental Variables: Significant Treatment effects on: Slash Several variables showed a sig. change over time: Slash height (decreased) Softwood canopy cover (increased) SW litter (increased) % Cover % Cover 0 2 4 6 8 10 0 20 40 60 80 Slash PCT unthinned 10 15 20 25 30 35 40 45 SW Canopy Cover 10 15 20 25 30 35 40 45 Stand age (yrs)
Results Quadrat-level Environmental Variables PCA : 1.2 1 0.8 0.6 slashht slash/cwd Axis 2 (EV=0.0941) 0.4 0.2 0-0.2 hwcover hwlitter conepcs swlitter swcover -0.4-0.6-0.8 PCT unthinned -1-2 -1.5-1 -0.5 0 0.5 1 1.5 Axis 1 (EV=0.1570)
Results Species Diversity: Shannon s Diversity Sig. treatment*age interaction: Shannon s Diversity No sig. difference between PCT & Control stands for: Simpson s Diversity Species Richness Evenness Diversity Index 1.0 1.5 2.0 2.5 3.0 PCT unthinned 10 15 20 25 30 35 40 45 Stand age (yrs)
Results V. angustifolium Individual Species Cover: Several species showed a sig. decrease over time: Vaccinium angustifolium Vaccinium myrtilloides Kalmia angustifolia Viburnum nudum PCT had a sig. effect on several species: Aralia nudicaulis Maianthemum canadense Trientalis borealis Clintonia borealis % Cover % Cover 0 2 4 6 8 0.0 0.5 1.0 1.5 2.0 2.5 3.0 PCT unthinned 10 15 20 25 30 35 40 45 M. canadense 10 15 20 25 30 35 40 45 Stand age (yrs)
Results Quadrat-level Environmental/Vegetation CCA: 4 3 2 1 a) Samples PCT unthinned slash/cwd slashht swcover Axis 2 (EV=0.0562) 0-1 -2-3 -4 hwleaves hwcover -5-6 -3-2 -1 0 1 2 3 4 5 Axis 1 (EV=0.1163)
Results Quadrat-level Environmental/Vegetation CCA: 0.6 0.4 b) Species slash/cwd picrub Axis 2 (EV=0.0562) 0.2 0-0.2 gaupro rhocan slashht gauhis swcover nemmuc gaybac picmar vacmyr osmcin kalang corcan coptri vacang abibal vibnud pteaqu dalrep acerub tribor -0.4 aranud -0.6 maican hwleaves hwcover -0.8-0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1 Axis 1 (EV=0.1163)
Conclusions & Recommendations PCT sites initially have lower stem density & fewer snags PCT sites have more slash, although slash height was similar in both treatments Managers may consider avoiding large slash piles that may inhibit germination
Conclusions PCT increases cover for some species (ecologically sig.?) Changes in overall herbaceous species composition are attributed to stand age rather than treatment. Increasing canopy cover over time seems to be the driving factor in overall species composition. The effects of PCT do not exceed the natural range of variability
Conclusions Additional patterns in species composition may be clearer by analysing species by groups: Growth Form (trees, shrubs, forbs, ferns, etc.) Raunkaier s Life Forms (Ph, Ch, Cr, etc) Reproductive Mechanism (veg( vs. seed)
Acknowledgments Advisory Committee: Supervisor: Mark Roberts Graham Forbes Charles Bourque T. Mamashita NSERC J.D. Irving Ltd. Fundy Model Forest Network Sustainable Forest Management Network Special thanks to the grad students and summer assistants in the Forest Ecology, Wildlife Ecology & Bryophyte Labs!