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UBC Theses and Dissertations

Spatial patterns of stand structure in Pinus ponderosa dominated forests within the Blacks Mountain Experimental Forest, California, USA, in 1930s and contemporary conditions Nepal, Sushil


Spatial patterns of forest overstory prior to timber harvest activities associated with Euro-American settlement can serve as helpful forest reference conditions. Yet, such historical reference patterns can be challenging to quantify due to a lack of appropriate spatially explicit field data and the limitations of dendrochronological techniques. As a result, many studies have investigated contemporary spatial patterns of tree density and tree size, but few have successfully described changes in spatial patterns. In this dissertation, I first used overstory census data collected in 1934, over an area of ~4,000 ha, to characterize forest overstory reference conditions for Blacks Mountain Experimental Forest (BMEF), California, USA. Specifically, I quantified the 1934 spatial patterns of stand density index by seven vigor classes for Ponderosa pine/Jeffrey pine and white fir and incense-cedar. The forest reference conditions for BMEF consisted of clusters of open forests dominated by high vigor ponderosa pine trees associated with soil moisture and elevation gradients. Second, I used both 1934 and 2018 regeneration data from BMEF to compare the stocking between reference and contemporary conditions. The stocking of the reference conditions was dominated by ponderosa pine seedlings and was associated with available water capacity at 150 cm and overstory basal area (m2 ha-1). Third, I utilized 2016 Light Detection and Ranging data and overstory ground truth data to compare among stands that received thinning treatments, prescribed burn treatments, and a combination of thinning with prescribed burn treatments. I then compared above-ground biomass (Mg ha-1) between contemporary (2016) and reference (1934 census data) conditions. Spatial patterns in above-ground biomass were more heterogeneous in reference conditions than in contemporary conditions. However, in contemporary conditions, prescribed burns combined with thinning were better able to emulate the spatial patterns of reference conditions than thinning treatments alone. The findings of this dissertation can be utilized by managers: a) as a reference point against which they can evaluate the success of restoration treatments, b) to understand the relationships between regeneration and environmental factors, which shape the overall stand structure, and c) to identify contemporary stands at-risk of insect, disease, and fire that may benefit from restoration treatments.

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