Heidi Asbjornsen Associate Professor of Natural Resources, COLSA, travels to Costa Rica

Experiential Student Learning and Collaborative Research: Understanding Tropical Ecosystem Response to Climate Change from Leaves to Landscapes. During January 2012, I traveled to Costa Rica to visit potential field sites for a future UNH J-term course in Tropical Ecology and to collect preliminary data for a new research project linked to the course. Both of these initiatives are in collaboration with Dr. Michael Palace, a research scientist at UNH’s Earth Systems Research Center. Together, we visited three sites in Costa Rica, each having very different climates and vegetation: Curu Wildlife Refuge, a tropical dry deciduous forest receiving only about 1,500mm rain annually; La Selva Biological Station, a lowland tropical rainforest that receives over 4,000 m of rain annually, and Monteverde Reserve, a tropical montane cloud forest that is immersed in fog for much of the year

Scaling from single-point sap velocity measurements to stand transpiration in a multi-species deciduous forest: uncertainty sources, stand structure effect, and future scenarios impacts

ABSTRACT A major challenge in studies estimating stand water use in mixed-species forests is how to effectively scale data from individual trees to the stand. This is the case for forest ecosystems in the northeastern USA where differences in water use among species and across different size classes have not been extensively studied, despite their relevance for a wide range of ecosystem services. Our objectives were to assess the importance of different sources of variability ontranspiration upscaling and explore the potential impacts of future shifts in species composition on forest water budget. We measured sap velocity in five tree species (Fagus grandiflora, Acer rubrum, A. saccharum, Betula alleghaniensis, B. papyrifera) in a mature and young stand in NH (USA). Our results showed that the greatest potential source of error was radial variability and that tree size was more important than species in determining sap velocity. Total sapwood area was demonstrated to exert a strong controlling influence on transpiration, varying depending on tree size and species. We conclude that the effect of potential species shifts on transpirationwill depend on the sap velocity, determined mainly by radial variation and tree size, but also on the sapwood area distribution in the stand

Scaling from single-point sap velocity measurements to stand transpiration in a multi-species deciduous forest: uncertainty sources, stand structure effect, and future scenarios impacts

ABSTRACT A major challenge in studies estimating stand water use in mixed-species forests is how to effectively scale data from individual trees to the stand. This is the case for forest ecosystems in the northeastern USA where differences in water use among species and across different size classes have not been extensively studied, despite their relevance for a wide range of ecosystem services. Our objectives were to assess the importance of different sources of variability ontranspiration upscaling and explore the potential impacts of future shifts in species composition on forest water budget. We measured sap velocity in five tree species (Fagus grandiflora, Acer rubrum, A. saccharum, Betula alleghaniensis, B. papyrifera) in a mature and young stand in NH (USA). Our results showed that the greatest potential source of error was radial variability and that tree size was more important than species in determining sap velocity. Total sapwood area was demonstrated to exert a strong controlling influence on transpiration, varying depending on tree size and species. We conclude that the effect of potential species shifts on transpirationwill depend on the sap velocity, determined mainly by radial variation and tree size, but also on the sapwood area distribution in the stand

Correcting tree-ring δ13C time series for tree-size effects in eight temperate tree species

Stable carbon isotope ratios (δ13C) in tree rings have been widely used to study changes in intrinsic water-use efficiency (iWUE), sometimes with limited consideration of how C-isotope discrimination is affected by tree height and canopy position. Our goals were to quantify the relationships between tree size or tree microenvironment and wood δ13C for eight functionally diverse temperate tree species in northern New England, and to better understand the physical and physiological mechanisms underlying these differences. We collected short increment cores in closed-canopy stands and analyzed δ13C in the most recent 5 years of growth. We also sampled saplings in both shaded and sun-exposed environments. In closed-canopy stands, we found strong tree-size effects on δ13C, with 3.7 – 7.2‰ of difference explained by linear regression vs. height (0.11 – 0.28‰ m-1), which in some cases is substantially stronger than the effect reported in previous studies. However, open-grown saplings were often isotopically more similar to large codominant trees than to shade-grown saplings, indicating that light exposure contributes more to the physiological and isotopic differences between small and large trees than does height. We found that in closed-canopy forests, δ13C correlations with DBH were nonlinear but also strong, allowing a straightforward procedure to correct tree- or stand-scale δ13C-based iWUE chronologies for changing tree size. We demonstrate how to use such data to correct and interpret multi-decadal composite isotope chronologies in both shade-regenerated and open-grown tree cohorts, and we highlight the importance of understanding site history when interpreting δ13C time series

Changes in soil respiration across a chronosequence of tallgrass prairie reconstructions

Close relationships among climatic factors and soil respiration (Rs) are commonly reported. However, variation in Rs across the landscape is compounded by site-specific differences that impede the development of spatially explicit models. Among factors that influence Rs, the effect of ecosystem age is poorly documented. We hypothesized that Rs increases with grassland age and tested this hypothesis in a chronosequence of tallgrass prairie reconstructions in central Iowa, U.S.A. We also assessed changes in root biomass, root ingrowth, aboveground net primary productivity (ANPP), and the strength of soil temperature and moisture in predicting Rs. We found a significant increase in total growing season Rs with prairie age (R2 = 0.79), ranging from 714 g C m−2 in the youngest reconstruction (age 4) to 939 g C m−2 in the oldest prairie (age 12). Soil temperature was a strong predictor of intra-seasonal Rs among prairies (R2 = 0.78–0.87) but mean growing season soil temperature and moisture did not relate to total Rs. The increase in Rs with age was positively correlated with root biomass (r = 0.80) and ANPP (r = 0.87) but not with root ingrowth. Our findings suggest that growing season Rs increases with tallgrass prairie age, root biomass, and ANPP during young grassland development

Water quality benefits of perennial filter strips in row-cropped watersheds

Nonpoint source pollution is an increasingly serious problem in agricultural landscapes, especially as growing populations intensify pressures on a fixed land area for food and energy, and climate change threatens production stability. Vegetative filter strips (VFS) have been demonstrated as a practical strategy in reducing soil loss and nutrient transport from agricultural land. While restoration of native grassland on agricultural landscapes would improve environment quality, however, this practice is not feasible across large regions where local communities depend on agriculture. One alternative strategy for erosion control and water quality improvement is the incorporation of relatively small amounts of vegetative filter strips in strategic locations within agricultural landscapes

Nutrient removal by prairie filter strips in agricultural landscapes

Nitrogen (N) and phosphorus (P) from agricultural landscapes have been identified as primary sources of excess nutrients in aquatic systems. The main objective of this study was to evaluate the effectiveness of prairie filter strips (PFS) in removing nutrients from cropland runoff in 12 small watersheds in central Iowa. Four treatments with PFS of different spatial coverage and distribution (No-PFS, 10% PFS, 10% PFS with strips, and 20% PFS with strips) were arranged in a balanced incomplete block design across four blocks in 2007. A no-tillage two-year corn (Zea mays L.) –soybean (Glycine max [L.] Merr.) rotation was grown in row-cropped areas beginning in 2007. Runoff was monitored by H flumes, and runoff water samples were collected during the growing seasons to determine concentrations of nitrate-nitrogen (NO3-N), total nitrogen (TN) and total phosphorus (TP) through 2011. Overall, the presence of PFS reduced mean annual NO3-N, TN, and TP concentrations by 35%, 73%, and 82%, respectively, and reduced annual NO3-N, TN, and TP losses by 67%, 84%, and 90%, respectively. However, the amount and distribution of PFS had no significant impact on runoff and nutrient yields. The findings suggest that utilization of PFS at the footslope position of annual row crop systems provides an effective approach to reducing nutrient loss in runoff from small agricultural watersheds