For the 2007 Report Card new challenges include forest health and the importance of fire mitigation and disease in this region, energy development impacts on Rockies' communities and infrastructure, water use in the Rockies and the growing need for agriculture to urban water transfers, and trends in new communities, including "new urbanism". Edited by Walter E. Hecox (CC professor of economics), Matthew K. Reuer, and Christopher B. Jackson (CC class of 2006).
Long term and large-scale ecological studies often require intensive sampling and replication. However, the inevitable impacts resulting from intensive researcher activity are often considered negligible and largely ignored in data analysis and interpretation of ecological data. This thesis study examines the impact of researcher trampling activity on the density and diversity of understory fern and woody seedling communities in a northern temperate forest research plot in Northern Wisconsin. I established thirty 1X1 m plots in heavily trampled, moderately trampled, and untrampled locations on and near the Wabikon Lake Forest Dynamics Plot. Fern and woody seedlings were identified to species, and fern species richness and Shannon’s diversity scores for woody seedlings analyzed for each plot and across trampling treatments. Fern and woody seedling diversity varied significantly with trampling intensity (ferns: Chi 2 = 9.772, df = 2, p = 0.008; woody seedlings: Chi 2 = 10.546, df = 2, p = 0.005). Decreases in fern density occurred between control and moderately trampled (MW = 269.000, WW = 734.000, p = 0.006) and between control and heavily trampled locations (MW = 283.500, WW = 784.500, p = 0.012), however moderately and heavily disturbed locations did not vary significantly in fern density (MW = 405.500, WW = 870.500, p = 0.485). Overall seedling density showed no significant variation between trampling treatments, however individual species assessments of Acer saccharum and Fraxinus americana seedlings indicate a significant decrease between trampling treatments for both species. Fraxinus americana seedling density decreased significantly control and moderately trampled (MW = 306.000, WW = 771.000, p = 0.031) and control and heavily trampled plots (MW = 317.500, WW = 782.500, p = 0.047), with no significant decrease between moderately and heavily trampled plots (MW = 436.000, WW = 901.000, p = 0.832). Conversely, Acer saccharum seedlings did not decrease significantly between control and moderately trampled plots (MW = 440.500, WW = 905.500, p = .874), but decreased significantly between control and heavily trampled (MW = 310.000, WW = 775.000, p = 0.008) and between moderately and heavily trampled locations (MW = 322.500, WW = 787.500, p = 0.013). Significant reductions in density and diversity of understory communities suggest that researcher activity can significantly alter a study ecosystem. This has both ecological and ethical implications, as researcher-induced alterations to understory composition may bias ecologists’ understanding of ecosystem dynamics and ecosystem response to environmental change.
The tree line is a climatic boundary, however its ability to respond to changing climate seems to be constrained by the spatial distribution of trees at the leading edge; compared to abrupt or krummholz tree lines, diffuse tree lines are moving upslope much more readily in response to recent anthropogenic warming. Here we report on the micrometeorological processes that result from the diffuse leading edge of a moving tree line on Pikes Peak, Colorado, USA, and on the impacts these processes have on tree temperatures. We focus on the layering and movement of air in the lower 10m of the atmosphere including the height of the displacement of the zero velocity plane. Our experimental design consisted of 300m upslope transects through the tree line into the alpine tundra where we measured: (1) height of the zero plane displacement using handheld anemometers, (2) temperature of 10cm tall seedlings, 3-5m tall trees, and tundra grasses using an IR camera, (3) temperature and relative humidity at 2.5cm an 2m using Kestrel hand held weather stations, (4) the vertical atmospheric profiles using 10m towers equipped with 8 anemometers at 5 different elevations, (5) vertical movement of air using a bubble-blowing machine. Our results show that (1) the zero plane height decreased exponentially with increasing elevation (R2=0.432, N=57, p<0.0005) from approximately 25cm within the tree line to 2.5cm in the tundra above. The spatial variability of the zero plane height also decreased with elevation. (2) The temperature of small seedlings was (3) closely coupled to the ground vegetation (paired t-test t= 2.213, df=10, p=0.051),but seedlings were on average 3.88°C warmer than trees (paired t-test t= 5.808, df=10, p<0.0005), and trees were 6.1°C colder that the tundra (paired t-test t= 6.617, df=10, p<0.0005). (3) Compared to the air at 2m, the air layer at 2cm had higher temperature (+2.5°C, paired t-test t= 7.205, df=19, p<0.0005), and higher relative humidity higher (+29%, paired t-test t= 9.657, df=19, p<0.0005). (4) The vertical wind profile had a simple and smooth slow down to the zero plane at 2.5cm in the alpine tundra. However the profile was complex in all locations where trees were present: It showed an initial slow down to a very low speed at 3-4m, increase in velocity at 2m, and final slow down to the zero plane at 25cm. Qualitative and quantitative analysis of bubble movement (5) showed that the upper boundary layer was turbulent.
Forest ecosystems in the Colorado Front Range have evolved to thrive in the unique climatic conditions of the region and natural disturbance regimes that existed prior to European settlement. Knowledge of how forests were structured in the past and the factors that affect their establishment and growth is essential to their management. Part of Notable Lectures & Performances series, Colorado College. Recorded January 25, 2007.