For the high-elevation Engelmann spruce - subalpine fir (ESSF) biogeoclimatic zone of southwestern British Columbia, there is little empirical data on the long-term dynamics of subalpine spruce-fir stands. A lack of a long-term perspective on the growth and development of stands in the ESSF zone hinders both ecological research and silvicultural planning in the ESSF forest. A broadly-focussed pilot study on long-term Engelmann spruce-subalpine fir stand dynamics in the ESSF zone was designed to begin to address this deficiency. This study used two methodological approaches to gain insights into long-term stand dynamics: 1) a retrospective approach to examine historical patterns of: i) postfire conifer regeneration, ii) post-establishment stand structure development, and; iii) basal area production and accumulation in ESSF spruce-fir forests, and; 2) A chronosequence approach to examine overall stand basal area development over a 575-year chronosequence, which is not amenable to detailed retrospective examination. In order to reconstruct the patterns of postfire regeneration and subsequent stand development, measurements of tree age, diameter, radial increment, and height were collected in 8 mesic, 45- to 110-year-old fire-origin stands of Engelmann spruce (Picea engelmannii Parry. ex Engel.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) in the ESSFwm and ESSFdc2 biogeoclimatic subzones of the North Cascades mountains. The results of the stand reconstruction were also used to aid in the interpretation of the chronosequence, which was based on basal area and age data from both the retrospective study sites, and the published literature. Based on the graphical analysis and discussion of the data collected in this pilot study, the following features of long-term stand development were noted in subalpine Engelmann spruce-subalpine fir stands: 1) Postfire conifer re-establishment on these burned ESSF sites was slow and erratic; the re-establishment period was 30 to 50 or more years in duration; 2) There appeared to be no consistent or predictable postfire patterns of conifer establishment on the various sites, either over time, or on a site-to site basis; 3) During postfire regeneration and immature stand development, there appeared to be no consistent differences between Engelmann spruce and subalpine fir, either in terms of i) postfire regeneration establishment, or ii) height development; 4) Fire-origin spruce-fir stands in the ESSF zone rapidly develop a complex stand structure, possibly due to the gradual and prolonged patterns of regeneration ingress on these sites; 5) Trees which have initial advantages in height or other competitive advantages over other trees on the site during the establishment phase tend to retain dominant crown positions in the stand at much later stages of development; 6) The relationship of periodic basal area increment (b.a.i.) to initial basal area stocking in immature spruce-fir stands suggests that stand increment is optimized above a critical stand density; 7) The initial basal area level necessary to optimize b.a.i. appears to increase with stand age; and 8) Apparent trends from a 575-year chronosequence of Engelmann spruce-subalpine fir stand development suggests that stand basal area tends to peak, on average, between the ages of 70 and 150 years of age. Subsequently, basal area tends to gradually decline and eventually stabilize between the ages of 300 to 400 years of age. Based on these results, preliminary recommendations were proposed for the long-term silvicultural management of ESSF spruce-fir forest types. Also, the research priorities necessary for building on the results of this pilot study were identified. / Forestry, Faculty of / Graduate

A major contributor to global warming is the increasing amount of carbon dioxide in the atmosphere. Land use management may be a means to countering global warming by increasing the carbon sink potential. Terrestrial carbon budgets were prepared for forested (Douglas-fir), agricultural (hay), and urban sites in Abbotsford, B.C. The results indicate that the greatest amount of carbon is stored in the forested sites, followed by the hay sites, with the lowest amount in the urban sites. To maximize carbon in storage the use of trees either as forests or in pockets within the landscape is the best option. To simulate and to expand the utility of these carbon budgets, the study used the CENTURY model. The results of the simulations indicate that forests are a major carbon sink as was found earlier. Carbon storage under hay is at a relative steady state, except during the cultivation years when it becomes a carbon source. Lawn in an urban setting is a carbon source. The results of the simulations suggest that management can be used to increase the carbon sink. It also indicates that soils are a major carbon pool representing 20% of the forest, 90% of the hay, and 95% of the lawn budgets. For the general public and decision-makers to become more aware of the impact of changing land use on carbon storage, at the lot, local, or regional levels, they require a userfriendly decision-making tool. A derivative of the CENTURY model, CLU (for CENTURY Land Use), was developed. It was designed to be user-friendly and at the same time maintain the integrity of the parent model. It allows the user to input site-specific data and obtain site related output carbon data on a component basis, which can be used to assess how a potential change in land use or management may affect the amount of carbon in storage. The model should be suitable as a research tool and for planning and educational purposes. / Science, Faculty of / Resources, Environment and Sustainability (IRES), Institute for / Graduate

No description available.

In California's northern Sierra Nevada mountains, the fire-dependent processes of forest ecosystems have been interrupted and altered by human land use and fire suppression. U.S. Forest Service policy directs land managers to plan for a future that includes multiple use and the restoration of resilient ecosystems. Planning decisions are to be informed by an analysis of the range of variability of ecological processes at multiple scales. Current climate trends in the northern Sierra are of increasing temperatures, increased precipitation, and earlier snowmelt, as well as changes to the frequency and duration of drought. These climate changes have and continue to influence fire frequency, extent, and severity. For this thesis, project partners and I adapted the Rocky Mountain Landscape Simulator (RMLands), a spatially explicit, stochastic, landscape disturbance and succession model, for use in the Sierra Nevada. RMLands was used to simulate wildfires and vegetation dynamics on a portion of the Tahoe National Forest in California, first under historical climate settings and then under alternative climate trajectories based on the Representative Concentration Pathway RCP8.5 projections. I then quantified the historical and the future ranges of variability in the disturbance regime, seral stage distribution, and patch configuration, and compared these to the current landscape. My results suggest more frequent and extensive high severity fire, as well as higher canopy closure, than most other studies of mixed conifer Sierran forests. However, the results typically agree qualitatively with other research, and some differences may be due to differences in study design. Under warmer and drier future climate scenarios, the total area burned, and the proportion burned at high severity, increased. Due to fire's effects on vegetation, the current landscape departs from either historical or future conditions by several statistical measures. Based on these findings, I recommend that managers implement aggressive restoration efforts, utilize mitigation measures where the consequences of changing fire regimes are socially unacceptable, and carefully balance the needs of different ecosystems and of the resident communities. My study can be used to inform goals and specific strategies in restoration planning and help project planners think about impacts at the landscape scale.

Quaking aspen (Populus tremuloides) is the most widely distributed tree in North America (Lindroth and St Clair 2013), and a keystone species in our western montane forests (Worrall et al. 2015). Aspen has become a model organism for studies of genetics and physiology in woody plants (Bradshaw et al. 2000, Taylor 2002). Aspen is also economicallyimportant (Worrall et al. 2015) – wood is harvested for various uses, its scenic beauty helps sustain the tourism economy in many areas, and it has recently been studied as a possible source of biofuel (Sannigrahi et al. 2010). Aspen is also a species of conservation concern, due to recent large-scale deterioration and decline of many aspen forests in the last two decades (Worrall et al. 2013). Several causal factors have been identified: fire suppression (Calder et al. 2011, Smith et al. 2011), increased ungulate herbivory (Kay and Bartos 2000), disease (Marchetti et al. 2011), and climate change (Worrall et al. 2013). My thesis focuses on two different biotic stressors of aspen: a fungal pathogen and ungulate herbivory. Understanding the relationship between aspen and their biotic stressors adds to our knowledge of aspen ecology and helps manage the increasing risk of decline in our aspen forests. Chapter 1 is a study of the relationship between aspen and a necrotrophic fungal pathogen (Drepanopeziza sp.) during a major disease outbreak in 2015. I quantified the relationship between Drepanopeziza infection severity and aspen leaf functional traits, including morphological, chemical and phenological traits. I found that severe Drepanopeziza infection was associated with low concentrations of a key class of herbivore defense compounds (phenolic glycosides), and strongly associated with early budbreak and leaf-out in aspen stands. The association between infection and early budbreak was likely caused by unusually rainy conditions in May of 2015, which may have exposed leaf tissue to wet conditions that favor thedispersal of Drepanopeziza spores. Chapter 2 is an experiment designed to determine whether the mode and timing of herbivory can influence aspen's defensive response. I specifically asked whether removing leaves, twigs and meristems together and removing leaves alone had unique effects on aspen sucker growth, survival, and phytochemistry. Additionally, I applied these simulated herbivory treatments to suckers on different dates to see whether early- or late-summer herbivory had greater effects on suckers. I found strong mode and timing effects on growth and survival, but not foliar chemistry.

The aim of this dissertation was to improve our understanding of the mechanisms underlying biodiversity ecosystem functioning (BEF) relationships and the provisioning of ecosystem functions in temperate forest soils. I studied the role of tree diversity on soil microbial properties, standard litter decomposition, abiotic soil properties, and soil surface temperature. All studies took place in the Kreinitz tree diversity experiment in Central Germany which was established in 2005. It spans a tree diversity gradient from 1 to 6 different commonly cultivated tree species. My experiments included measurements within the whole diversity gradient in November 2017 and a high-resolution time series on monocultures and five-species mixtures in 2017 and 2018. In addition, I utilized tree inventory data about tree mortality, height, diameter and biomass. Chapter I aimed to assess general BEF relationships in soil. Chapter II followed a spatio-temporal framework explaining BEF relationships in forest soils via the spatial and temporal stability of biotic and abiotic properties, based on concepts like species asynchrony and complementarity. Chapter III utilized the perturbation of the extreme summer drought of 2018. It focused on biodiversity-resistance relationships and assessed how tree species richness and identity affected tree mortality rates in the experiment. All three studies showed that tree species identity and community composition are essential in shaping BEF relationships in temperate forest soils and are pivotal for the stable provisioning of ecosystem functions. The influence of tree species identity and community composition could be related to changes in abiotic soil properties and microclimatic conditions (i.e. soil surface temperature). I found evidence that spatio-temporal dynamics are indeed crucial determinants in BEF relationships in forest ecosystems. Overall, my thesis indicated how climate change and other global change factors will likely influence the provisioning and stability of soil ecosystem functions in forest via their intense pressure on tree community composition and the perturbation of spatiotemporal patterns. Overall, this dissertation advanced our mechanistic understanding of BEF relationships in temperate forest soils. While it underlined the dangers of global change for the provisioning of ecosystem functions, it also offered vantage points to prepare our forests for a changing future.

Although deforestation remains widespread in the tropics, many places are now experiencing significant forest recovery, offering an optimistic outlook for natural ecosystem recovery and carbon sequestration. Natural forest regeneration is a key component of global ecosystem restoration scenarios. Regenerated forests, however, may not persist so a more nuanced understanding of the drivers of forest persistence in the tropics is critical to ensure the success reforestation efforts and carbon sequestration targets. Furthermore, the maintenance of native forests, including young second-growth ones, is essential for the continuous provision of a myriad of ecosystem services that we, as a society, rely on. More specifically, native forests play a crucial role in watershed protection and forest cover loss via changes in land use can lead to deterioration of water quality. Ensuring a sufficient and adequate supply of water for humans and ecosystems is a pressing environmental challenge and land use decisions can severely degrade stream water quality and compromise water supply. This dissertation focusses on two pressing current issues, the dynamics of tropical forest regeneration and the effects of land use on water resources. First, I use a long-term series of detailed land cover data to study forest cover trajectories and persistence of regenerated forest in the Brazilian Atlantic Forest (AF), a restoration hotspot. Secondly, I use 20 years of stream water quality data combined with land cover information to investigate the effects of land cover composition on water resources in the state of São Paulo, Brazil. In Chapter 1, I investigate forest cover trajectories in 3,014 municipalities and quantify the carbon sequestration potential of forest regeneration in the AF. I found that deforestation reversals were the prevalent trend in the region (38%) but concomittant reforestation reversals (13%) suggest that these short-term increases in native forest cover do not necessarily translate into persistent trends, which limited carbon sequestration from reforestation to less than one third of its potential. In Chapter 2, I quantify forest regeneration in the AF and study its persistence. I mapped over 4.47 Mha of native forest regeneration in the region between 1985 and 2019, of which, two thirds persisted until 2019 (3.1 Mha). The relatively low persistence of second-growth forests suggests a rapid turnover of regrowing forests under certain conditions. In Chapter 3, I combine stream water quality data with detailed and land cover information to investigate the effects of landscape composition on the quality of water resources in the state of São Paulo, Brazil. I found that human dominated watersheds had lower overall water quality when compared to conserved ones, with urban cover showing the most detrimental impacts on water quality, while forest cover was associated with a better overall water quality across the studied watersheds. Finally, in Chapter 4, I examine temporal changes in water quality and their association with land use and sewage treatment also in the state of São Paulo. I show that a large proportion of stream water samples failed to meet legal thresholds for at least one water quality metric and that urbanization and agricultural activity led to deterioration of water quality over time, while sewage treatment infrastructure was an important factor in improving water quality. Overall, my dissertation underscores the importance of developing policies that promote second-growth forest persistence to ensure the success of future restoration efforts. It also highlights the need to need to plan and manage landscapes to improve water quality and reduce the growing costs of water treatment, including restoring native forest cover, which is a cost-effective intervention to sustain adequate water quality.

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Ecological restoration has the potential to provide a multitude of benefits, such as conserving biodiversity and supporting natural-resources dependent livelihoods. Tropical dry forests (TDFs) occur in densely populated human-modified landscapes in the tropics and are susceptible to degradation, making them an important biome to restore when degraded. TDFs are also socio-ecological systems, where local people rely on the forest for subsistence and livelihoods and effectively manage them for desire outcomes. People’s reliance on TDFs necessitates restoration projects to take into account more than biophysical and abiotic considerations when they are designed. In this decade of restoration, while there is the much-needed impetus to restore degraded land, to achieve enduring and just outcomes at large spatial scales, restoration projects need to more intentionally address local considerations, such as traditional land tenure systems and livelihood strategies, and goals such as socio-economic development. At the same time, to guide restoration efforts and realistically forecast the consequences of these efforts in the future, there is a need for rapid and accurate assessment tools to quantify the impact of restoration on biodiversity and people at several time steps. In Chapter 1, I use India, a country with high biophysical potential for restoration, as a case study to demonstrate a people-centric approach for identifying restoration opportunities. I find that there is a large overlap between areas of high biophysical restoration potential and high poverty, indicating potential and need to pursue restoration in a manner that addresses both ecological and social goals. In Chapter 2, I study a commonly adopted livelihood strategy, seasonal migration, in forest-dependent communities in India. I find that households in more agricultural and prosperous districts experience lower rates of migration but are more sensitive to climatic variability than households in poorer districts. In Chapter 3, I examine the impact of ecological restoration of a tropical dry forest in central India (CI). I find no significant difference in the cumulative number of bird species detected, but a significant difference in bird communities across the sites. In the lower frequencies dominated by birds and insects, I find that restored sites were positively associated with acoustic space occupancy in comparison to unrestored and low Lantana density (LLD) sites. In Chapter 4, I study the combined socio-ecological outcomes of restoration in the same sites in CI. I find that in the absence of alternative, people rely on Lantana camara, an invasive shrub, for subsistence and livelihoods, in the form of firewood and farm boundaries. I do not find any significant effect of restoration or LLD on people’s perception of ease of forest use, except for the distances covered for grazing, an important indicator of restoration success in this landscape. Finally, I also find that restoration is not associated with any significant changes in soundscapes in the higher frequency ranges dominated by insects and bats. Taken together, my chapters contribute to a greater understanding of the potential for restoration to meet social and ecological goals, the vulnerability of the livelihoods of people living on forest-fringes of TDFs to climate variability and expected and unexpected socio-ecological outcomes of restoration.

No description available.