This study examined the affects of desiccation during and after cold storage on the physiology, growth, and marketability of bare-root Acer platanoides (Norway maple), Crataegus phaenopyrum (Washington hawthorn) and Prunus x yedoensis (Yoshino cherry). Histological examination of Acer and Crataegus stems was also conducted. Maple and cherry trees were transplanted into pine bark-filled containers and subjected to mist or non-mist treatments. Xylem water potential increased (became less negative) for misted maple and cherry trees. Water potential increased for non-misted maple and decreased for non-misted cherry trees. Maple and hawthorn seedlings were subjected to cold storage durations of 2, 4, 6, 8, 10, and 12 weeks and storage treatments: whole plant covered, shoots exposed, roots exposed and whole plant exposed. Shoot (Ψ_s) and root (Ψ_r) water potentials for all treatments and both species decreased during storage. For maple, (Ψ_s) and (Ψ_r) of the exposed shoot treatment were the same as the whole plant covered treatment. In contrast, hawthorn (Ψ_s) and (Ψ_r) of the exposed shoot treatment were lower (more negative) than for the whole plant covered treatment. Root hydraulic conductivity was the same for both species and decreased with increased storage duration and for treatments with exposed roots. For the root covered treatments, maple root growth potential (RGP) increased while hawthorn RGP decreased with increased cold storage duration. RGP for both species remained low throughout storage for treatments exposing roots. Days to bud break for Acer and Crataegus seedlings decreased with increased storage time for the whole plant covered treatments but increased for both species when stored with exposed roots. Maple marketability, percent of trees with ≤ 10% shoot dieback, for root covered treatments was high for most storage durations. Hawthorn marketability was generally low except for the whole plant covered treatment during the first six weeks of storage. There was a high positive correlation between RGP and marketability for both maple and hawthorn. Histological examination revealed that Acer stems had a highly suberized periderm, and a uniform cuticle with few disruptions. Periderm suberization of Crataegus stems was variable and extensive peridermal cracking was evident. Cuticle wax decreased with increasing distance from the stem apex for both species. Collectively, results indicated that hawthorn stems had more pathways for water loss than maple shoots. While protection of roots of all bare-root stock is important, desiccation sensitive species such as Washington hawthorn require both root and shoot protection during storage and at transplanting to minimize water loss. / Ph. D.

This study examined the existing, or potential, risk of invasion by street trees into an urban forested park (Breithaupt Park, a 32.5 hectare semi-forested park, and its surrounding residential neighbourhood in the City of Kitchener.). The primary research question is: What are the spatial distribution and dispersal patterns of street trees and park trees in urban areas? For street populations, height, crown spread, diameter at breast height (DBH), tree condition, trunk condition and foliage transparency were measured. Qualitative tree health indicators were used to gauge the condition of the street tree population only. For trees in Breithaupt Park, a point-quarter sampling method combined with a line-plot sampling method was used. There were 33 identified (and several unidentified) species of street trees and 24 identified species of forest trees. Acer platanoides was the most abundant street tree species, while Acer saccharum was the most abundant forest tree species. 52% of the street tree population and 9% of the forest tree population were exotic species; however, the exotics were mainly species not originating from the nearby streets (i.e. Rhamnus cathartica). Despite the well-established population of exotic invasive species such as Acer platanoides on the streets, spatial assessment of the nearby forested park revealed that relatively few exotic species had actually established there. Acer platanoides composed 1.9% of all trees, 3.2% of all saplings and 2.7% of all seedlings in the forest sample. The four possible sources of Acer platanoides seeds were trees planted on the street, trees planted in backyards, the leaf drop site in the parking lot of Breithaupt Park (only in the fall) and trees potentially planted directly in the forest. Explanations for the lack of invasion by Acer platanoides (in particular) include: 1) houses located between Acer platanoides street trees and Breithaupt Park functioning as a barrier to seed dispersal; 2) the highway traversing the northeast corner of the park; 3) the short length of time since Acer platanoides street trees reached their age of maturity to produce enough viable seeds to invade the forest and the lag time in the establishment phase; 4) unique park characteristics; and 5) opposing predominant wind directions. While Acer platanoides may be more invasive under different circumstances, it was concluded that Acer platanoides is not currently invading the park at a considerable rate but may be tending towards a future invasion. The main recommendations are: 1) to not cut down the Acer platanoides currently growing as street trees as they do not pose a high risk of invasion (though this is specific to the current study); 2) to manage the forest for invasive species and remove and restore the ecology of the forest as necessary; 3) to remove Acer platanoides currently growing in the forest; and 4) to replace dead street trees with non-invasive, hardy native trees instead of the historical planting of Acer platanoides and other exotics, in case the risk of invasion changes because of climate or urban design changes.

This study examined the existing, or potential, risk of invasion by street trees into an urban forested park (Breithaupt Park, a 32.5 hectare semi-forested park, and its surrounding residential neighbourhood in the City of Kitchener.). The primary research question is: What are the spatial distribution and dispersal patterns of street trees and park trees in urban areas? For street populations, height, crown spread, diameter at breast height (DBH), tree condition, trunk condition and foliage transparency were measured. Qualitative tree health indicators were used to gauge the condition of the street tree population only. For trees in Breithaupt Park, a point-quarter sampling method combined with a line-plot sampling method was used. There were 33 identified (and several unidentified) species of street trees and 24 identified species of forest trees. Acer platanoides was the most abundant street tree species, while Acer saccharum was the most abundant forest tree species. 52% of the street tree population and 9% of the forest tree population were exotic species; however, the exotics were mainly species not originating from the nearby streets (i.e. Rhamnus cathartica). Despite the well-established population of exotic invasive species such as Acer platanoides on the streets, spatial assessment of the nearby forested park revealed that relatively few exotic species had actually established there. Acer platanoides composed 1.9% of all trees, 3.2% of all saplings and 2.7% of all seedlings in the forest sample. The four possible sources of Acer platanoides seeds were trees planted on the street, trees planted in backyards, the leaf drop site in the parking lot of Breithaupt Park (only in the fall) and trees potentially planted directly in the forest. Explanations for the lack of invasion by Acer platanoides (in particular) include: 1) houses located between Acer platanoides street trees and Breithaupt Park functioning as a barrier to seed dispersal; 2) the highway traversing the northeast corner of the park; 3) the short length of time since Acer platanoides street trees reached their age of maturity to produce enough viable seeds to invade the forest and the lag time in the establishment phase; 4) unique park characteristics; and 5) opposing predominant wind directions. While Acer platanoides may be more invasive under different circumstances, it was concluded that Acer platanoides is not currently invading the park at a considerable rate but may be tending towards a future invasion. The main recommendations are: 1) to not cut down the Acer platanoides currently growing as street trees as they do not pose a high risk of invasion (though this is specific to the current study); 2) to manage the forest for invasive species and remove and restore the ecology of the forest as necessary; 3) to remove Acer platanoides currently growing in the forest; and 4) to replace dead street trees with non-invasive, hardy native trees instead of the historical planting of Acer platanoides and other exotics, in case the risk of invasion changes because of climate or urban design changes.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal