Changes in landscape patterns and associated forest succession on the western slope of the Rocky Mountains, Colorado
Using repeat photography, we conducted a qualitative and quantitative analysis of changes in forest cover on the western slope of the Rocky Mountains in Colorado. For the quantitative analysis, both images in a pair were classified using remote sensing and geographic information system (GIS) technologies. Comparisons were made using three landscape metrics: total relative cover, mean relative patch size, and number of patches per major vegetation type. We noted several important changes in the pattern of the landscape and the structure of the forests. The relative area covered by interspersed, nonforested rangelands has decreased significantly, and the total forest cover across these landscapes has increased. Statistical analyses (ANOVA) of other landscape characteristics (patch number and patch size distribution) did not detect changes. However, nonstatistical observation of the trends in these data revealed that in many cases, there has been important, observable change in the configuration of the landscape at many of these locations. Furthermore, our field data show that 96% of the sampled forests have a conifer component in the overstory, understory, or both.
Quaking aspen (Populus tremuloides Michx.) at treeline: a century of change in the San Juan Mountains, Colorado, USA
During a repeat photography study quaking aspen (Populus tremuloides Michx.) was observed invading conifer stands at treeline in the San Juan Mountains of south‐western Colorado. Aspen tree core samples were collected from nine plots ranging in elevation from 3192 to 3547 m, and estimated dates of establishment of aspen were grouped into 10‐year intervals for analysis. Estimated periods of establishment were compared with century‐long climate data records to derive any correlations with aspen invasion. Other disturbance agents, such as fire and livestock grazing were also considered. Quantitative analysis of climate variables suggests that decreased mean spring precipitation and increased mean summer maximum temperature provide optimal conditions for aspen establishment. Episodes of invasion were non‐synchronous, but all occurred after 1900, and are likely from seed germination, considered unusual in aspen. Different climate variables explain stand initiation from seed and subsequent peak establishment from vegetative reproduction. Long‐term climate records indicate a general warming since the beginning of the 20th century and explain the continued invasion and persistence of aspen at treeline, resulting from asexual reproduction. Short‐term climate records identify anomalously cool, moist years that explain rarely observed sexual reproduction in aspen.
Targeting oral anticoagulation
Clinical Pharmacology & Therapeutics (2000) 68, 4–5; doi: 10.1067/mcp.2000.108197