1,721,004 research outputs found
Black Spruce (Picea mariana) Regeneration in Post-fire Cryptogamic Mats
Get PDFPost-fire black spruce (Picea mariana Mill.) regeneration has received
considerable attention in management of the boreal forest of eastern Canada. Seedbed
quality is a key factor for seed germination and early seedling establishment. The
objective of this research was to investigate the potential role of cryptogamic seedbeds in
black spruce germination and seedling establishment. To compare lichen-dominated
seedbeds with thin and thick organic matter, in situ seeding experiments were conducted
at three sites in Terra Nova National Park, Newfoundland burned 11 (Rocky Pond, RP),
17 (Spracklin Road, SR) and 37 (Terra Nova Road, TNR) years ago. At each site, three
manipulation treatments (mat-intact, mat-mixed and mat-removed) were applied to the
seedbed with four replications in plots of 30 x 30 cm where 200 black spruce seeds were
broadcasted. To compare lichen vs. moss seedbed, the same experimental design was
extended to moss dominated seedbeds at the SR site. A laboratory germination bioassay
was conducted to test the possible chemical effects of four cryptogamic species on black
spruce germination and primary growth. Seed germination was highest in mat-intact and
mat-removal plots with thick OM at RP, mat-mixed plots with thin OM at SR and matmixed
plots with both thin and thick OM at TNR. There was significantly higher
germination and seedling establishment on moss seedbeds than lichen seedbeds. In moss
seedbeds, mat-mixed plots with thick OM had the highest germination but mat-intact
plots of both thin and thick OM had higher seedling establishment. Moss seedbeds had
higher soil moisture and lower surface temperature than lichen seedbeds. Laboratory
bioassay with lichen Cladonia cristatella Tuck. had significantly lower germination and
seedling growth than control but no difference between the control and moss treatments.
HPLC analysis of C. cristatella indicated the presence of a germination inhibiting
allelochemical, usnic acid. Lichen mat provides physical barrier to seed germination and
seedling growth in late post-fire site TNR but not in early post-fire sites. It appears that
moss dominated seedbeds facilitate black spruce regeneration by increasing seedbed
moisture retention and maintaining low surface temperature, while lichen seedbeds
inhibit seedling regeneration by their adverse physical and chemical effects. Cryptogamic
seedbed type, OM thickness, soil moisture and temperature are limiting factors in poor
black spruce seedling regeneration after fire
Litter fall and decomposition in 40-year-old red pine and white spruce plantations / by Martina A. Sangari.
Get PDFInterference of aquatic plants associated with wild rice (Zizania palustril L.)
Get PDFThe objective of this thesis was to determine the interference
potential of aquatic plants to wild rice (Zizania palustris L. )
through field and laboratory studies. Three companion papers
describe the influence of aquatic plants on growth of wild rice;
the allelopathic potential of aquatic plants and the isolation and
identification of allelochemicals from two selected plants.
The growth of wild rice in the presence cind in the absence of
different plemt species, namely Eleocbaris smallii, Scirpus acutus,
Equisetum fluviatile, Nymphaea odorata, Nupheur variegatum,
Sparganium fluctuans, ttyriophyllum verticillatum and Potamogeton
natans was studied. Number of wild rice plants and their growth
decreased in the presence of different plant species. Environmental
factors had no influence on the growth of wild rice, either in the
presence or absence of different species. It is suggested that the
adverse effects of different species on wild rice may be due to
either their early growth habit, shading the wild rice plant, or to
their allelopathic effects.
The allelopathic potential of the above mentioned plant
species was examined using lettuce and wild rice seedling
bioassays. The root length of lettuce and the total root length of
wild rice seedlings were significantly reduced by aqueous extracts
of these plant species. The lettuce seedling bioassay was more
responsive than that of wild rice. Shoot growth was less affected.
Bioassay with an aqueous extract of lake sediments associated with
these species had little inhibitory effect on growth of wild rice
seedling. The use of teurget species as a bioassay material and
further studies on phytotoxic effect of lake sediments have been
emphasized for evaluating their ecological significemce.
The phytotoxic compounds from water extracts of the rhizome
of Scirpus acutus and the shoot of Eleocbaris smallii were isolated
by ethyl acetate extraction emd identified by GC-Mass spectroscopy.
The ethyl acetate organic fraction of water extract of Scirpus
rhizomes contained lactic, succinic, fumaric, 2-hydroxy succinic,
2-phenyl lactic, m-hydroxy benzoic, p-hydroxy benzoic,
protocatechuic, dehydroêüaietic and ferulic acids; p-hydroxy benzyl
alcohol, p-hydroxy phenyl ethanol and a dye, catechin. The organic
fraction of the extract of Eleocbaris shoots contained 4-methoxy
phenol, benzofuran, benzene acetic acid, l-hydroxy-5-methyl
acetophenone and 1,3,4-dimethoxy phenyl ethanone. The growth
inhibiting properties of some of these compounds under field
conditions are discussed
Riparian habitat and vegetation recovery of headwater streams after clearcut harvesting
Get PDFIn this thesis I examined two important aspects of clearcut harvesting along small headwater streams and their riparian zones. The objectives of the study were: 1) to investigate the impacts of clearcut harvesting on the morphological features of headwater systems and the pattern of recovery of those impacts over time, and 2) to explore the response of headwater riparian understory vegetation to clearcut harvesting over time
Floristic structure, composition and depth of edge influence at buffer and wildfire edges along small boreal streams
Get PDFWithin the boreal forest of northwestern Ontario clearcutting and fire are the most common edge-creating disturbances. Along streams, wild fire consumes the majority of trees to the edge of riparian zones. However, forest management relies on the retention of 30 to 70 m treed buffer reserves beside streams following harvesting. Fundamental knowledge regarding how buffer and fire edges compare near shoreline forests is lacking. The development of sustainable forest management strategies that emulate natural disturbances relies upon such information. The objective of this thesis was to examine and compare the edge influences on overstory structure, near ground microclimate and understory species composition at buffer and wild fire edges adjacent to small streams in northwestern Ontario
Soil respiration following alternative site preparation treatments in a boreal mixedwood forest
Get PDFThe effects of experimental site preparation on CO2 evolution and on planted black spruce
{Picea mariana (Mill.) B.S.P.) seedling growth were studied one year after the site preparation
treatment, during the 1994 growing season (June-October) and again in May and June of 1995
on a boreal mixedwood site. Treatments included: uncut forest, cut forest without site
preparation, cut and mixed where organic matter to a depth of 20 cm was mixed with mineral
soil, and cut and screefed where the top organic layer was removed. Carbon dioxide evolution
was determined once a month in the field by infra-red gas analyzer (IRGA) and by the soda-lime
trap technique. Soil temperature and moisture contents were measured once a month during the
1994 growing season and for two months in 1995. Concentrations of organic matter, PO43-p
and NH4+-N were also determined after treatment. Interactions of temperature, moisture and
organic matter on CO2 evolution were studied under controlled laboratory conditions.
Carbon dioxide evolution from the cut treatment plots was not significantly different from
that of the uncut plots. Carbon dioxide evolution from the cut and mixed plots was significantly
higher than from the cut and screefed plots. Evolution of CO2 varied seasonally. The IRGA
proved to be a better method for determining CO2 evolution than the soda-lime technique due
to its convenience and efficacy. Highly significant relationships among CO2 evolution, soil
organic content, soil P and moisture contents were found. It was concluded that site preparation
treatments had a significant effect on CO2 evolution by modifying the organic matter and
moisture contents of the soils. Height of planted black spruce seedlings, however, did not vary
significantly during the first two years after the treatments
Roadside floristic patterns and revegetation by using native plants in Terra Nova National Park, Newfoundland, Canada
Get PDFThis thesis reports on a study of roadside floristic patterns and revegetation
(cultural methods) of newly constructed roadsides by using native plants along Trans
Canada Highway (TCH) in Terra Nova National Park (TNNP), Newfoundland.
Recognizing the need for developing natural and self-sustained roadside
vegetation cover to mitigate road effects, the first chapter of this thesis examines two
aspects of the roadside floristic patterns: a) the nature of plant community composition
across the roadside habitats with respect to microtopographic features, substrate
properties and maintenance disturbances and b) the nature of above and below ground
architectural characteristics and biomass allocation patterns of selected dominant plants
across roadside microhabitats. The combined knowledge about floristic patterns and
autecological attributes of roadside plants should help in selecting desirable native plants
for roadside revegetation in order to mitigate road effects. The vegetation survey and soil
sampling were conducted across the right-of-way along 10-15 years old section of the
Trans Canada Highway (TCH) in Terra Nova National Park (TNNP), Newfoundland.
The Multi-response Permutation Procedure (MRPP) confirmed the zonation of plant
community across the right-of-way by distinguishing four plant communities occurring
on four roadside microhabitats, such as shoulder, side slope, ditch and hack slope. The
Canonical Correspondence Analysis (CCA) showed that the composition of roadside
plant communities in different microhabitats was related to soil moisture content, bulk
density, organic, matter depth and pH
Plant community assembly 15-37 years after clearcutting, clearcutting plus prescribed burning, and wildfire in jack pine (Pinus banksiana Lamb.) forest of Central Canada
Get PDFStudy area: Northwestern Ontario.It has been suggested that clearcutting be followed by prescribed burning as a means of
reconciling effects of clearcutting and wildfire on plant communities. To address the
effectiveness of clearcutting followed by prescribed burning (PB), I assessed understorey
communities in northwestern Ontario using fifty 10 ? 10 m plots, located in 15-37 year old jack
pine (Pinus banksiana Lamb.) stands established after clearcutting, PB, and wildfire. My findings
are presented in two chapters, first I examined structural and compositional differences in plant
communities originating from the three disturbance types, and secondly I examined the
relationship of species' traits to disturbance type. In Chapter 1, I hypothesized that understorey
communities established after PB would resemble those established after wildfire more closely
than those established after clearcutting alone. However, I found that all three disturbance
types had similar understorey species richness and diversity, while species composition within
PB sites differed significantly from clearcut and wildfire sites. Compositional differences
associated with PB were comparable to those found after successive short-interval wildfires.
Indicator species of PB sites were mostly ruderai and disturbance tolerant species; suggesting
that PB created a compound effect on plant communities. Since application of prescribed
burning after clearcutting does not involve a novel disturbance, compositional differences may
be related to the short-interval between clearcutting and PB. In Chapter 2, I hypothesized that
compositional differences between communities originating from PB correspond to the
interaction of short-interval disturbance with species' life history and regeneration traits. I
analyzed traits related to post-disturbance regeneration to quantify relationships with
disturbance type. For trait analysis I used the abundance-weighted analyses RLQ, Fourth-Corner
Analysis, calculation of functional diversity indices (functional richness, evenness, and
dispersion), and community weighted means. I found no significant relationship between the
suite of traits and disturbance type. However I found significant relationships between PB and
species' traits such as Raunkiaer's lifeform, seed banking, wind dispersal, deciduous foliage,
rosettes and alien status. My hypothesis was supported by the prevalence of seed banking and
wind dispersal in the PB sites, both of which are known to increase with short-interval
disturbances. From these results I conclude that application of PB following clearcutting causes
compositional differences that result from disturbance-mediated plant trait selection by short-interval
disturbances
Small-scale disturbance and vegetation dynamics in trembling aspen dominated forests in northeastern Ontario
Get PDFThe scientific understanding of boreal forest stand development and vegetation
dynamics has been well documented with respect to stand-initiating disturbances;
however, the role of subtler disturbance events has received less attention. Two scenarios
that warrant the study of small-scale disturbance in the boreal forest of Ontario include i)
forest management practices and changing climatic factors that range in spatial scale
from local to global are predicted to skew age class distribution of forests towards
mature, oldgrowth stages of development, and ii) during these stages of forest
development, small-scale disturbance is hypothesized to be the major disturbance
mechanism to influence vegetation dynamics. Many principles and methods of the
research that has been conducted on vegetation dynamics and small-scale disturbance in
deciduous temperate and tropical forests can be applied to the boreal forest as a study
system. This thesis attempts to understand vegetation dynamics during intermediate
stages of boreal forest development, with an emphasis on the role of small-scale
disturbance.
The thesis is presented in four chapters that, i) develop the rationale for studying
small-scale disturbances in boreal forests, ii) characterize the extent of small-scale
disturbance in trembling aspen forests, and ii) quantify the effect of small-scale
disturbance on understorey plant communities. Analyses varied considerably among
chapters. Multivariate ordination techniques and average basal area change
measurements were used to assess stand and species dynamics of 217 forests stands
sampled across northeastern Ontario. Relationships between small-scale disturbance with
time since stand initiation (60 - 120 years) of ten trembling aspen were assessed using linear models. Juvenile tree recruitment patterns and community changes (woody and
herbaceous plant species) in gaps and understorey environments of five trembling aspen
stands were assessed using general linear models and various multivariate methods.
Consistent patterns in boreal forest stand development include early dominance of
shade intolerant species such as Populus tremuloides and Pinus banksiana, followed by
increasing basal area of shade tolerant conifer species such as balsam fir, black spruce,
and white cedar. Important declines, between 80 and 100 years since stand initiation, in
the basal area of species that dominate the initial post-disturbance cohort point towards
the occurrence of small-scale disturbance (i.e. mortality of mature canopy trees). The
occurrence of such disturbance warrants the investigation of i) how important small-scale
disturbance actually is, and ii) the effect that it has on the vegetation dynamics of
understorey plant communities.
Results from chapter two clearly show that small-scale disturbances are an
important and conspicuous element of forest stand development when trembling aspen
are the dominant tree species. The most important factors that lead to tree mortality
include infection by wood decay pathogens and wind. The increasing number of gap
makers per gap, and number of gap maker decay classes per gap with time suggests that
gap expansion, resulting from punctuated disturbance events is an important mechanism
of gap formation. Snapped gap makers, followed by standing dead and uprooted gap
makers were the most important structural attributes of gaps, and their relative
importance remained similar with time.
Despite the importance of small-scale disturbance during 95-120 years since stand
initiation, juvenile tree recruitment patterns and plant community response to gap environments of different sizes and ages was negligible. There was no detectable
difference in stem density and growth of all important juvenile tree species (including
Abies balsamea, P. tremuloides, Picea mariana, Picea glauca, and Betula papyrifera)
when compared among gap environments and the closed canopy understorey condition.
Similarly, understorey plant communities showed no difference when compared among
different gap types. High across-stand variability in community composition limited the
ability to detect consistent compositional trends with respect to gap size and age.
However, regardless of gap type, slight increases in species richness and abundance were
detected for understorey woody species of heights between 2 and 5 m.
The effect of small-scale canopy tree mortality on understorey plant communities
in trembling aspen dominated forests is minimal. This is in contrast to predictions that
were made based on expectations from the role of small-scale disturbance dynamics in
temperate and tropical forests. Based on the results of this thesis, future studies of boreal
forest development and understorey vegetation dynamics should consider i) the
establishment mechanisms of shade tolerant conifer species such as A. balsamea during
early stages of forest development, ii) minimal gap sizes that facilitate growth of shade
intolerant tree species that are taller than two metres, and iii) appropriately replicate
different understorey community types
Functional niche differentiation in co-occurring congeneric plants
Get PDFNiche differentiation is argued as one of the mechanisms explaining species coexistence. Despite their sessile nature, similar resource needs and traits to acquire and utilize resources closely related plant species coexist. I hypothesized that i) spatial distribution of congeneric species would be similar because they are closely related with similar traits and resource needs and ii) each species will perform different biological functions (growth vs. reproduction) optimally at different points along a resource gradient and thereby differentiate their functional niche to ensure coexistence by complementary resource use. I collected data on two congeneric wild blueberry species, Vaccinium angustifolium and V. myrtilloides on occurrence from 13,500 20 x 20 cm quadrates, their growth and reproductive response to light and microhabitat parameters from 360 1 x 1 m quadrates along 90 30 m transects from 5 regions of NW Ontario. I also grew these two species in a common garden experiment (CGE) under a shade gradient to test their response to light in competition-free environment. A chi-square test confirmed that V. angustifolium and V. myrtilloides are co-occurring species. Variance partitioning analysis revealed that light is the most important microsite variable. Frequency of occurrence showed their abundance gradually increase from low to high light with high niche overlaps. Regression model fitting of cover (indicating growth) and berry yield (indicating reproduction) along the light gradient provided species functional response curves. By rescaling the response curves I obtained comparable functional fitness/performance curves, which showed that for both species optimum performance for growth and reproduction peaked at different light levels in natural habitats and in CGE. But their niche overlaps between growth and reproduction functions were markedly lower in natural habitats than in CGE meaning that these congeneric species differentiate their niche preferences for growth and reproduction. Both species showed conspicuous shift of functional niche in natural habitats from the CGE. Higher growth of one species was often corresponded with lower growth of the other suggesting a complimentary use of finite growing space. These results suggest that neighbouring plants may reduce their competitive stress by adjusting their biological functions through functional niche differentiation. To my knowledge this is the first study providing clear quantitative evidence of functional niche differentiation in two closely related coexisting plants. One of the mechanisms by which clonal understory woody plants avoid competition for light is through differentiating ‘physical space niches’ by foraging small resource patches by clonal extension. The results of my study reveal another mechanism of species co-existence, which has evolutionary significance. I show how two congeneric clonal species occupying the same physical niche space can avoid competition by differentiating their functional niche. Further discovery of functional niche differentiation in multiple coexisting species along multiple resource gradients (such as soil nutrients, soil moisture) will make a significant contribution to refining community assembly rules
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