Amey S. Bailey

Hydrometeorological database for Hubbard Brook Experimental Forest: 1955-2000

The 3,160-ha Hubbard Brook Experimental Forest (HBEF) in New Hampshire has been a prime area of research on forest and stream ecosystems since its establishment by the USDA Forest Service in 1955. Streamflow and precipitation have been measured continuously on the HBEF, and long-term datasets exist for air and soil temperature, snow cover, soil frost, solar radiation, windspeed and direction, and humidity. This information has provided the basis for hundreds of publications by Forest Service and cooperating scientists on numerous aspects of forest hydrology research as part of the ongoing Hubbard Brook Ecosystem Study. This report updates the tables, methods, watershed descriptions, and other pertinent data in ?Thirty Years of Hydrometeorological Data at the Hubbard Brook Experimental Forest, New Hampshire? (General Technical Report NE-141).

A tale of two springs: using recent climate anomalies to characterize the sensitivity of temperate forest phenology to climate change

By the end of this century, mean annual temperatures in the Northeastern United States are expected to warm by 3–5 °C, which will have significant impacts on the structure and function of temperate forests in this region. To improve understanding of these impacts, we exploited two recent climate anomalies to explore how the springtime phenology of Northeastern temperate deciduous forests will respond to future climate warming. Specifically, springtime temperatures in 2010 and 2012 were the warmest on record in the Northeastern United States, with temperatures that were roughly equivalent to the lower end of warming scenarios that are projected for this region decades from now. Climate conditions in these two years therefore provide a unique empirical basis, that complements model-based studies, for improving understanding of how northeastern temperate forest phenology will change in the future. To perform our investigation, we analyzed near surface air temperatures from the United States Historical Climatology Network, time series of satellite-derived vegetation indices from NASA’s Moderate Resolution Imaging Spectroradiometer, and in situ phenological observations. Our study region encompassed the northern third of the eastern temperate forest ecoregion, extending from Pennsylvania to Canada. Springtime temperatures in 2010 and 2012 were nearly 3 °C warmer than long-term average temperatures from 1971–2000 over the region, leading to median anomalies of more than 100 growing degree days. In response, satellite and ground observations show that leaf emergence occurred up to two weeks earlier than normal, but with significant sensitivity to the specific timing of thermal forcing. These results are important for two reasons. First, they provide an empirical demonstration of the sensitivity of springtime phenology in northeastern temperate forests to future climate change that supports and complements modelbased predictions. Second, our results show that subtle differences in the character of thermal

Decreased water flowing from a forest amended with calcium silicate

Acid deposition during the 20th century caused widespread depletion of available soil calcium (Ca) throughout much of the industrialized world. To better understand how forest ecosystems respond to changes in a component of acidification stress, an 11.8-ha watershed was amended with wollastonite, a calcium silicate mineral, to restore available soil Ca to preindustrial levels through natural weathering. An unexpected outcome of the Ca amendment was a change in watershed hydrology; annual evapotranspiration increased by 25%, 18%, and 19%, respectively, for the 3 y following treatment before returning to pretreatment levels. During this period, the watershed retained Ca from the wollastonite, indicating a watershed-scale fertilization effect on transpiration. That response is unique in being a measured manipulation of watershed runoff attributable to fertilization, a response of similar magnitude to effects of deforestation. Our results suggest that past and future changes in available soil Ca concentrations have important and previously unrecognized implications for the water cycle.

Downsizing a long-term precipitation network: Using a quantitative approach to inform difficult decisions

The design of a precipitation monitoring network must balance the demand for accurate estimates with the resources needed to build and maintain the network. If there are changes in the objectives of the monitoring or the availability of resources, network designs should be adjusted. At the Hubbard Brook Experimental Forest in New Hampshire, USA, precipitation has been monitored with a network established in 1955 that has grown to 23 gauges distributed across nine small catchments. This high sampling intensity allowed us to simulate reduced sampling schemes and thereby evaluate the effect of decommissioning gauges on the quality of precipitation estimates. We considered all possible scenarios of sampling intensity for the catchments on the south-facing slope (2047 combinations) and the north-facing slope (4095 combinations), from the current scenario with 11 or 12 gauges to only 1 gauge remaining. Gauge scenarios differed by as much as 6.0% from the best estimate (based on all the gauges), depending on the catchment, but 95% of the scenarios gave estimates within 2% of the long-term average annual precipitation. The insensitivity of precipitation estimates and the catchment fluxes that depend on them under many reduced monitoring scenarios allowed us to base our reduction decision on other factors such as technician safety, the time required for monitoring, and co-location with other hydrometeorological measurements (snow, air temperature). At Hubbard Brook, precipitation gauges could be reduced from 23 to 10 with a change of <2% in the long-term precipitation estimates. The decision-making approach illustrated in this case study is applicable to the redesign of monitoring networks when reduction of effort seems warranted.

Reply to Smith and Shortle: Lacking evidence of hydraulic efficiency changes

After calcium silicate amendment to an entire watershed at the Hubbard Brook Experimental Forest, evapotranspiration (ET) increased by ∼20% for 2 y, broadly attributed to a fertilization of tree physiology (1). We suggested that the increase in ET most likely arose from enhanced transpiration due to increased stomatal conductance (gs) associated with increased photosynthesis. Smith and Shortle (2) point out that enhanced xylem conductivity due to increased soil water ionic strength could help account for increased stomatal conductance because of the role calcium plays in the construction and efficiency of xylem water transport. We accept that this may be a relevant mechanism due to the importance of the entire hydraulic architecture of a tree to stomatal function (3). However, although we agree that enhanced xylem conductivity could have contributed to the enhanced ET response after calcium silicate amendment, we have no evidence that this mechanism was active during the enhancement. Our data were consistent with increased photosynthetic capacity [a major control on stomatal conductance (4)], which led to a general stimulation of primary production (tree and leaf biomass) during and after the enhanced ET (1). Thus, the available information leads us to conclude that increased gs was related to increased photosynthesis.