Nature-based solutions (NBS) are promising strategies for protecting vulnerable coasts in the context of climate change, utilizing the coastal protection capabilities of natural ecosystems for engineering applications. The ability of coastal marsh vegetation to attenuate wave energy and prevent coastal erosion has been acknowledged for decades, however, consideration for their use in coastal protection strategies is presently limited, particularly in Canada due to a lack of engineering guidelines and limited available research considering region-specific variables. Physical modelling presents a useful tool for investigating the coastal protection function provided by marsh vegetation in a controlled, repeatable environment, which can ultimately inform the design of nature-based coastal protection strategies. To date, such studies have investigated the influence of plant biophysical parameters (stem flexibility, width, and height) and hydrodynamic conditions (wave height, wave period, and plant submergence) on wave attenuation. These studies have used either live vegetation, requiring full-scale wave testing, or surrogate vegetation, which allows simplified testing at either full- or reduced-scale. Overall, live vegetation studies have been limited in the variety of saltmarsh plants considered, with few studies considering plant species native to the Canadian coastline. Several physical modelling studies have been performed using surrogate plants, however, methods of surrogate development for flexible vegetation or reduced-scale testing are not yet well developed. This thesis aims to address knowledge gaps pertaining to the use of marsh vegetation in coastal protection strategies, particularly through the development of experimental methods with both live and surrogate plants. A full-scale flume study with live vegetation was performed to develop fundamental knowledge of wave-vegetation interactions for Spartina alterniflora and Spartina patens, two salt marsh species native to Canada’s Atlantic coast. S. alterniflora was observed to demonstrate a resistance strategy in response to hydrodynamic forcing, versus the avoidance strategy of S. patens, supporting complementary functioning of the two species if utilized together in coastal protection schemes. Observations of plant properties and stem bending from live plant tests were subsequently applied in the development of a small-scale flume study, which examined wave attenuation associated with a downscaled S. alterniflora meadow in the configuration of a “living dyke” structure. Wave damping induced by surrogate vegetation was observed to be minimal for the tested wave conditions (0.073 m < Hm0 < 0.225 m, 2.0 < Tp < 3.2 s, 1:4 scale) and beach slope (1V:20H), with wave height evolution dominated by wave shoaling and breaking. Several methods were considered for modelling the S. alterniflora meadow at reduced scale, and results demonstrated a sensitivity to surrogate diameter but not flexibility. The development of robust experimental methods for investigating the performance of nature-based coastal infrastructure is essential for the establishment of appropriate design conditions. The scale series approach of this thesis supports such methodological advancements and is expected to make preliminary contributions to design guidance on coastal marsh-based NBS and provide critical direction for future studies.

Wildland fire, which includes both planned (prescribed fire) and unplanned (wildfire) fires, is an important component of many ecosystems. Prescribed burning (controlled burning) is used as an effective tool in managing a variety of ecosystems in the United States to reduce accumulation of hazardous fuels, manage wildlife habitats, mimic natural fire occurrence, manage traditional native foods, and provide other ecological and societal benefits. During wildland fires, both live and dead (biomass) plants undergo a two-step thermal degradation process (pyrolysis and combustion) when exposed to high temperatures. Pyrolysis is the thermal decomposition of organic material, which does not require the presence of oxygen. Pyrolysis products may later react with oxygen at high temperatures, and form flames in the presence of an ignition source. In order to improve prescribed fire application, accomplish desired fire effects, and limit potential runaway fires, an improved understanding of the fundamental processes related to the pyrolysis and ignition of heterogeneous fuel beds of live and dead plants is needed.In this research, fast pyrolysis of 14 plant species native to the forests of the southern United States has been studied using a flat-flame burner (FFB) apparatus. The results of fast pyrolysis experiments were then compared to the results of slow pyrolysis experiments. The plant species were selected, which represent a range of common plants in the region where the prescribed burning has been performed. The fast pyrolysis experiments were performed on both live and dead (biomass) plants using three heating modes: (1) convection-only, where the FFB apparatus was operated at a high heating rate of 180 °C s-1 (convective heat flux of 100 kW m-2) and a maximum fuel surface temperature of 750 °C; (2) radiation-only, where the plants were pyrolyzed under a moderate heating rate of 4 °C s-1 (radiative heat flux of 50 kW m-2), and (3) a combination of radiation and convection, where the plants were exposed to both convective and radiative heat transfer mechanisms. During the experiments, pyrolysis products were collected and analyzed using a gas chromatograph equipped with a mass spectrometer (GC-MS) for the analysis of tars and a gas chromatograph equipped with a thermal conductivity detector (GC-TCD) for the analysis of light gases.The results showed that pyrolysis temperature, heating rate, and fuel type, have significant impacts on the yields and the compositions of pyrolysis products. These experiments were part of a large project to determine heat release rates and model reactions that occur during slow and fast pyrolysis of live and dead vegetation. Understanding the reactions that occur during pyrolysis then can be used to develop more accurate models, improve the prediction of the conditions of prescribed burning, and improve the prediction of fire propagation.

Prescribed (i.e., controlled) burning is a common practice used in many vegetation types in the world to accomplish a wide range of land management objectives including wildfire risk reduction, wildlife habitat improvement, forest regeneration, and land clearing. To properly apply controlled fire and reduce unwanted fire behavior, an improved understanding of fundamental processes related to combustion of live and dead vegetation is needed. Since the combustion process starts with pyrolysis, there is a need for more data and better models of pyrolysis of live and dead fuels. In this study, slow pyrolysis experiments were carried out in a pyrolyzer apparatus and a Thermogravimetric analyzer (TGA) under oxygen free environment in three groups of experiments. In the first group, the effects of temperature (400–800 °C), a slow heating rate (H.R.) (5–30 °C min−1), and carrier gas flow rate (50–350 ml min−1) on yields of tar and light gas obtained from pyrolysis of dead longleaf pine litter in the pyrolyzer apparatus were investigated to find the optimum condition which results in the maximum tar yield. In the second group of experiments, 14 plant species (live and dead) native to forests in the southern United States, were heated in the pyrolyzer apparatus at the optimum condition. A gas chromatograph equipped with a mass spectrometer (GC–MS) and a gas chromatograph equipped with a thermal conductivity detector (GC-TCD) were used to study the speciation of tar and light gases, respectively. In the third group of experiments, the slow pyrolysis experiments for all plant species (live and dead) were carried out in the TGA at 5 different heating rates ranged from 10 to 30 ℃ min-1 to study the kinetics of pyrolysis. The results showed that the highest tar yield was obtained at a temperature of 500 °C, heating rate of 30 °C min−1, and sweep gas flow rate of 100 ml min−1. In addition, the tar composition is dominated by oxygenated aromatic compounds consisting mainly of phenols. The light gas analysis showed that CO and CO2 were the dominant light gas species for all plant samples on a dry wt% basis, followed by CH4 and H2. The kinetics of pyrolysis was studied using one model-free method and three model-fitting methods. First, the model-free method of Kissinger-Akahira-Sunose (KAS) was used to calculate the rates of pyrolysis as a function of the extent of conversion. The results showed that different plant species had different rates at different conversions. Then, three model fitting methods were used to find the kinetic parameters to potentially provide a single rate for each plant species. The results showed that the simple one-step model did not fit the one-peak pyrolysis data as well as the distributed activation energy model (DAEM) model. The multiple-reaction DAEM model provided very good fits to the experimental data where multiple peaks were observed, even at different heating rates.