Climatic changes have induced striking altitudinal and latitudinal vegetation shifts throughout history. These shifts will almost certainly recur in the future; threatening other flora and fauna, and influencing climate feedback loops. Changes in the spatial distribution of vegetation are most conspicuous at physiognomically distinct ecotones, particularly between the subalpine forest and alpine tundra. Traditionally, ecological research has linked abiotic variables with the position of this ecotone (e.g., cold temperatures inhibit tree survival at high elevations). Thus, the prevailing assumption states that this ecotone is in equilibrium or quasi-equilibrium with the surrounding physical environment and that any dynamic shifts express direct linkages with the physical environment. This dissertation employs a landscape ecology approach to examine the abiotic and biotic ecological mechanisms most important in controlling tree establishment at this ecotone. The study site is on the western slopes of Mount Rainier, which was severely burned by a slash fire in 1930. Therefore, a crucial underlying assumption is that the ecological mechanisms controlling tree establishment are similar at disturbed and undisturbed sites. I exploited the use of 1970 CORONA satellite imagery and 2003 aerial photography to map 33 years of changes in arboreal vegetation. I created detailed maps of abiotic variables from a LIDAR-based DEM and biotic variables from classified remotely sensed data. I linked tree establishment patterns with abiotic and biotic variables in a GIS, and analyzed the correlations with standard logistic regression and logistic regression in the hierarchical partitioning framework at multiple spatial resolutions. A biotic factor (proximity to previously existing trees) was found to exert a strong influence on tree establishment patterns; equaling and in most cases exceeding the significance of the abiotic factors. The abiotic setting was more important at restricted spatial extents near the extreme upper limits of the ecotone and when analyzing coarse resolution data, but even in these cases proximity to existing trees remained significant. The strong overall influence of proximity to existing trees on patterns of tree establishment is unequivocal. If the underlying assumption of this dissertation is true, it challenges the long-held ecological assumption that vegetation in mountainous terrain is in equilibrium with and most strongly influenced by the surrounding physical environment.

RESUMÉ Tato práce se zabývá vlivem teplotních poměrů na intra-anuální růst smrku ztepitélo (Picea Abies (L.) Karsten) na alpínské hranici lesa v Krkonoších ve vegetačních sezónách 2011 a 2012. Monitoring probíhal na dvou lokalitách na jižním svahu Luční hory. První lokalita se nacházela v nadmořské výšce 1310 m n. m., přibližně na horní hranici zapojeného lesa, druhá pak v nadmořské výšce 1450 m n. m., ve stromových skupinkách nad horní hranicí lesa. Mezi lokalitami byl pozorován poměrně vysoký vertikální teplotní gradient jak u teplot vzduchu (1,2 - 1,7 řC), tak u teplot půdy v hloubce 10 cm (0,8 - 1,2 řC). Teplotní rozdíl mezi lokalitami se pak projevil v nižším pozorovaném přírůstu na výše položené lokalitě. Pozorované počátky kambiální aktivity se pohybovaly od 26. 4. do 21. 5. Začátek kambiální aktivity je ovlivněn množstvím sněhové pokrývky akumulované na lokalitách v průběhu zimy a s tím souvisejícím datem jejího odtátí, teplotami půdy a teplotami v přízemní vrstvě atmosféry. Délka kambiální aktivity se pohybovala mezi 55 - 77 dny, přičemž její délka byla nižší na výše položené lokalitě. Diferenciace buněk nastala bezprostředně po počátku kambiální aktivity a trvala od 111 do 132 dní. V porovnání sledovaných růstových sezón vyšla lépe růstová sezóna 2012, ve které byl průměrný přírůst stromů vyšší na...

This study analyzes the structure and biophysical correlates of density of two whitebark pine (Pinus albicaulis) populations in the northern Rocky Mountains. Whitebark pine is a keystone species and an important component of treeline ecosystem dynamics; however, subalpine populations have declined nearly rangewide in recent decades. Though declines in subalpine forests have been well documented in the literature, few studies have assessed population structure and habitat requirements at treeline. Various disturbances have combined to impact whitebark pine populations across its range, but the primary threat at treeline sites in the northern Rocky Mountains is white pine blister rust, caused by the exotic fungal pathogen Cronartium ribicola. In this study, I aim to: 1) assess population structure and regeneration within two geographically different treelines experiencing contrasting levels of infection, and 2) examine associations among several biophysical variables and whitebark pine density to better understand treeline habitat variability and regeneration patterns. I used density-diameter curves and non-parametric Kruskal-Wallis tests to compare population structure between sites, and developed generalized linear mixed models to assess correlations between whitebark pine density and biophysical site variables. The results demonstrate that despite very different ecosystems and blister rust infection rates, our two study sites have similar population structure. Our model results highlight marked differences between populations in terms of biophysical correlates of density. While correlations are similar within site, seedlings and saplings have stronger correlations with biophysical variables than established trees. / Master of Science

No description available.