This story highlights a current research project at the Hubbard Brook Experimental Forest. To read more about research projects at HBEF, visit Current Research page. Check back regularly to learn about new research projects.
Long-term changes in the calcium concentration of wood fern fronds

 

  Contact Info:
  Ellen Denny
USDA Forest Service
271 Mast Road
Durham, NH 03824
phone: (603) 868-7683
email: ellen.denny@aya.yale.edu
Tom Siccama
School of Forestry and Environmental Studies
Yale University
Greeley Memorial Laboratory
370 Prospect Street
New Haven, CT 06511
phone: (203) 432-5140
email: tgs3@pantheon.yale.edu

Introduction
SINCE 1967 we have conducted isolated collections of wood fern (Dryopteris spinulosa) fronds to determine plant nutrient concentrations. Wood fern is the most abundant herbaceous species at the Hubbard Brook Experimental Forest, comprising 40 to 50% of the biomass of this stratum. (Lycopodium lucidulum, an evergreen clubmoss, makes up another 40 to 50%, but only 10% of its biomass consists of new growth each year.) Most of our early efforts at Hubbard Brook were focused on nutrient cycling through the tree species. However, occasional samples of wood fern were collected and analyzed to get a rough idea of how the herbaceous layer contributed to nutrient cycling in the ecosystem. In 1985 we started a more consistent annual collection of wood fern from an area just west of the Watershed 6 weir. The annual collection of wood fern fronds was initiated on Watershed 1 in 1996. These quick and simple collections were not part of a larger study, but were conducted simply to monitor gross long-term patterns in plant chemistry. As we discovered in the summer of 2000, it is important to maintain these types of long-term datasets to get an idea of the magnitude of annual variability.

  Wood fern  
  Wood fern Dryopteris spinulosa  

Methods of collection and analysis
Wood fern samples have been collected by walking over the entire area of interest and grabbing single fronds (no roots are included) from individual plants here and there. Thus, we have called them "grab" samples. All grab samples included in the graph below are from the lower reaches of the gauged watersheds on the south-facing slope of the Hubbard Brook valley. A single frond was taken from each fern plant to minimize disturbance to the plant.

A consistent annual collection was initiated in 1985 just to the west of W6 from the weir west and uphill to the first foot bridge on the trail and over to the east bank of Bear Brook--an area of roughly two hectares. Collection is routinely conducted during the second week of July, and the samples are replicated in the sense that 5 to 10 separate bags are collected, each including fronds representative of the whole area.

A collection on W1 began in 1996 when the watershed was prepared for detailed study by surveying in a 25 x 25 m plot system. Ferns are collected from four separate vegetation zones, although the only samples included in the graph below are from the low hardwood zone--all plots below the first rain gauge clearing. Grab samples from W1 are also taken during the second week of July, and 2 to 3 replicate bags are collected for each zone.

Each bag of grab sample is dried at 80o C, ground in a Wiley mill to pass a 2 mm screen, and ashed at 500o C. The ash is dissolved in a nitric acid solution (50 ml final volume), and analyzed on an ICP spectrometer for several elements including calcium, a plant macronutrient.

Long-term trend
Wood fern samples have been collected by walking over the entire area of interest and grabbing single fronds (no roots are included) from individual plants here and there. Thus, we have called them "grab" samples. All grab samples included in the graph below are from the lower reaches of the gauged watersheds on the south-facing slope of the Hubbard Brook valley. A single frond was taken from each fern plant to minimize disturbance to the plant.

A consistent annual collection was initiated in 1985 just to the west of W6 from the weir west and uphill to the first foot bridge on the trail and over to the east bank of Bear Brook--an area of roughly two hectares. Collection is routinely conducted during the second week of July, and the samples are replicated in the sense that 5 to 10 separate bags are collected, each including fronds representative of the whole area.

A collection on W1 began in 1996 when the watershed was prepared for detailed study by surveying in a 25 x 25 m plot system. Ferns are collected from four separate vegetation zones, although the only samples included in the graph below are from the low hardwood zone--all plots below the first rain gauge clearing. Grab samples from W1 are also taken during the second week of July, and 2 to 3 replicate bags are collected for each zone.

Each bag of grab sample is dried at 80o C, ground in a Wiley mill to pass a 2 mm screen, and ashed at 500o C. The ash is dissolved in a nitric acid solution (50 ml final volume), and analyzed on an ICP spectrometer for several elements including calcium, a plant macronutrient.

  Graph of wood fern calcium concentrations over time