Design and Implementation of a Simple Litter Catch-Basket System for Soil Studies
Peer Reviewed Papers
Eric C. Brevik* and Henry W. Mimms The accumulation of litter is an important source of organic matter in forest soils. This makes it important to be able to accurately and reliably measure litter fall during soil genesis studies in forested areas. This study reports on results obtained using litter collecting baskets built from inexpensive materials easily obtainable in local retail stores. The litter collecting baskets met all primary objectives established for them during the course of the study and collected litter amounts consistent with amounts expected in southeastern U.S. forest environments. Problems encountered were minor and can be easily and inexpensively addressed with regular monitoring and maintenance of the collection baskets.
L
itter fall and accumulation, which includes both leaf and twig material, is an important source of soil organic matter in forest soils (Finkl and Restrepo-Coupe, 2007; Schaetzl and Anderson, 2005; Buol et al., 1997). Litter accumulation on the soil surface provides a food source to soil organisms (Moore et al., 2006; Anderson, 1975), supplies organic matter and plant nutrients to the underlying mineral horizons (Moore et al., 2006; Meier et al., 2005; Madeira and Ribeiro, 1995), moderates soil temperature fluctuations and evaporation rates (Burdt et al., 2005; Schaetzl and Anderson, 2005), and influences germination and establishment of plants (Brearley et al., 2003; Vellend et al., 2000). Because litter influences many soil properties and processes, the study of litter is of interest to soil scientists. This study was undertaken to develop a reliable way to collect and analyze litter additions to forest soils that were part of a study on soil formation being undertaken in southern Georgia, USA.
• The pit bottom, which is the deepest part of the excavation (Fig. 1), has a bowl shape, and is characterized by a mix of slash pines (Pinus caribaea Morelet) and deciduous trees including sweetgum (Liquidambar styraciflua L.) and blackgum (Nyssa biflora Walter), with a lack of underbrush or grass (Fig. 2a). • The sparsely vegetated area, which is on a shelf or terrace within the pit that rises above the pit bottom, includes vegetative growth that is limited primarily to a few stunted slash and longleaf (Pinus palustris Mill.) pines and a sparse lichen cover, including “deer moss” [Cladina evansii (Abbayes) Hale & W.L. Culb.] on the ground surface (Fig. 2b). The land in the pit slopes slightly toward the grassy area and steeply toward
Materials and Methods The study was conducted in an abandoned sand borrow pit located immediately east of Interstate Highway 75 about 16 km (10 miles) north of the Florida border at 30.7220 N latitude, 83.2560 W longitude. This is about 8 km (5 miles) south of the city of Valdosta, Georgia. The borrow pit offered a number of different vegetative settings for the testing of the litter collectors. These settings included the following:
Eric C. Brevik, Dep. of Natural Sciences and Agriculture and Technical Studies, Dickinson State University, Dickinson, ND 58601; Henry W. Mimms, Dep. of Physics, Astronomy, and Geosciences, Valdosta State University, Valdosta, GA 31698-0055 (
[email protected]). *Corresponding author (Eric.Brevik@ dickinsonstate.edu). doi:10.2136/sh12-01-0003 Published in Soil Horizons (2012). © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.
Fig. 1. A detailed topographic map of the study area in southern Georgia, USA. Elevation values shown are meters above sea level with a contour interval of 0.5 m. Shown are the pit bottom (A), the sparsely vegetated area (B), the grassy area C), and the control (D). Topographic map from Dixon-Coppage et al. (2005).
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Fig. 2. The four areas used in this study: (a) pit bottom, (b) sparsely vegetated area showing areas of open soil between stunted trees (top right), (c) grassy area, and (d) the control area (bottom right) in southern Georgia, USA. the pit bottom from the sparsely vegetated area (Fig. 1), meaning overland flow is away from the sparsely vegetated area in all directions. • The grassy area has a mix of trees similar to that found in the pit bottom, but includes a thick cover of grass (Andropogon spp.) (Fig. 2c). • The control area immediately surrounding the pit is characterized by a mature stand of primarily deciduous trees including live oaks (Quercus virginiana Mill.), water oaks (Quercus nigra L.), and magnolias (Magnolia spp.) (Fig. 2d). Some underbrush is present in the control area, but it is not overly dense. Water frequently collects in the pit bottom and the grassy area, which are both located in depressions (Fig. 1 and 3). The primary objectives the litter collectors needed to achieve included: (i) reliable collection and retention of litter samples, (ii) drainage of rainwater from the collectors, (iii) keeping litter samples above standing water in areas of the study site that peri-
odically collected rainwater, and (iv) separating litter samples from the soil surface and previously fallen litter. These objectives are in line with those of Elder and Cairns (1982) and Megonigal et al. (1997) when they designed litter catch-baskets for their own studies. To achieve this, plastic buckets 0.59 m long, 0.43 m wide, and about 0.5 m deep were selected as the catch baskets. These were easily and inexpensively obtainable at a local store, provided separation from the soil and previously fallen litter, and represented a reasonably large catch-basin area of 0.2537 m2. Custom-made 0.25 m2 litter catchers are commonly used for litter studies (Megonigal et al., 1997; Shure and Gottschalk, 1985; Shure and Phillips, 1987). The deep nature of the buckets was intended to prevent sample loss due to wind or washover during rainfall. To allow drainage of rainwater from the collectors, several 3-mm holes were drilled in the bottoms and sides of the collectors. To keep the samples above standing water, the buckets were mounted on 1.2-m-long metal fence posts that were driven about 0.3 m into the ground (Fig. 4). The final result was a set of collectors that functioned similar to those of Elder and Cairns (1982), Shure and Gottschalk (1985), Shure and Phillips (1987), and
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Megonigal et al. (1997), although constructed of different materials. All collectors, even those not in areas that collected standing water, were mounted on the fence posts to maintain uniformity among sites. One of the distinct advantages to this particular catchbasket design was the low cost. The baskets were purchased and assembled in 2002. At that time the plastic buckets cost about $3.00 each, and the fence posts cost about $2.50 each, with three posts used per basket, giving a total cost of about $10.50 per basket. A roll of wire was also purchased to attach the baskets to the fence posts. Sixteen catch-baskets were assembled for this study at a total cost of about $170. During the testing phase litter was collected monthly and stored refrigerated in labeled 3.8-L (1-gallon) zipper-seal plastic bags until the samples could be analyzed. Litter samples were dried for a 24-h period in an oven set at 70°C to drive off water and weighed on a digital scale that recorded weight to the hundredth of a gram. The amount of litter was then standardized to dry litter additions over a 1-m2 area for each catch-basket.
Fig. 3. Percentage of time from February 2002 to May 2004 that the water table was at or above a given level at each of the areas in and around the pit in southern Georgia, USA. Note that both the pit bottom and grassy area had standing water approximately 30% of the time during this 2-yr period. The sparsely vegetated area and the control area never experience standing water during this time span. Water level data from Dixon-Coppage et al. (2005).
Results and Discussion Although the parts for the baskets were originally purchased in 2002, the litter baskets were not tested until 2006, thus the 2006 and 2007 dates in Table 1. It was expected that the sparsely vegetated area would have a much lower total than the other areas based on the lack of litter cover on the soil surface and the relative lack of tree growth (Fig. 5). It was also expected that the pit bottom, grassy area, and control area would have similar levels of litter additions, again based on litter cover on the soil surface and similar densities of tree growth. These expectations were born out in the data collected from the litter baskets. The values obtained for leaf litter amounts in the pit bottom, grassy area, and control area were also within the ranges (200–2000 g m−2 yr−1) expected for southeastern forests, while the sparsely vegetated area was well below the expected range of litter accumulation for a southeastern U.S. forest (Baker et al., 2001) (Table 2). The baskets were also successful in keeping rainwater drained from the litter samples, keepFig. 4. A completed catch-basket installed and ready for litter collection in ing the samples above standing water in the portions of southern Georgia, USA. the study area that were subject to ponding (Fig. 6), and keeping litter samples separate from the soil surface and previously fallen litter. In these respects, the catch-basket design inally set up in 2002. Some of the baskets that were originally was deemed to be successful. set up in 2002 had to be changed out before the 2006–2007 litter collection study because they had become brittle and weak due The field test also highlighted some challenges with this design. to UV rays from the sun. This was primarily an issue in the Although the baskets were not used until 2006 due to lack of sparsely vegetated area where there was little canopy cover to personnel and time to collect the litter samples, they were origshield the baskets from direct sunlight. Another issue was large
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Table 1. Results from one year of litter collection with catchbaskets in southern Georgia, USA. Litter collected
Date
Natural area
Pit bottom
Grassy area
Sparsely vegetated area
——————— g m−2 ——————— May 2006
22.37
19.00
11.40
0.00
June 2006
61.38
30.60
45.60
3.36
July 2006
46.26
24.55
21.96
1.50
August 2006
16.40
32.72
43.04
4.23
6.60
25.80
11.95
0.00
October 2006
49.63
129.16
92.32
2.36
November 2006
23.61
46.42
37.30
7.72
December 2006
40.17
90.56
47.59
9.56
9.16
2.28
4.28
0.00
February 2007
85.57
19.15
38.60
0.00
March 2007
54.77
9.01
23.81
0.00
April 2007
31.12
12.49
27.22
2.90
Average
37.25
36.81
33.76
2.64
447.04
441.74
405.07
31.63
September 2006
January 2007
Annual total
Fig. 5. (Top) Litter collection buckets in the sparsely vegetated area and (bottom) the pit bottom after one month’s worth of litter collection in southern Georgia, USA. Note the much lighter litter load in the bucket in the sparsely vegetated area. This was characteristic of the sparsely vegetated area’s litter accumulation compared to the other three areas studied.
Table 2. Comparison of average annual litter accumulation rates during this study to rates from other studies in the southeastern United States. Study Litter collected Location Sparsely vegetated area (this study)
g m−2 yr−1 31.63
Southern Georgia, USA
Megonigal et al. (1997)
138–561
Barataria Basin, Louisiana, USA
Megonigal et al. (1997)
314–767
Savannah River, South Carolina, USA
Megonigal et al. (1997)
316–598
Verret Basin, Louisiana, USA
Grassy area (this study)
405.07
Southern Georgia, USA
Pit bottom (this study)
441.74
Southern Georgia, USA
Natural area (this study)
447.04
Southern Georgia, USA
Elder and Cairns (1982)
483.4
Apalachicola River flood plain, northwest Florida, USA
Shure and Phillips (1987)
534
Nantahala National Forest, North Carolina, USA
Shure and Gottschalk (1985)
571–667
Lower Three Runs Creek floodplain, South Carolina, USA
Megonigal et al. (1997)
581–776
Upper Three Runs, South Carolina, USA
Megonigal et al. (1997)
625–972
Meyers Branch, South Carolina, USA
Megonigal et al. (1997)
672–855
Pearl River, Louisiana, USA
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limbs dropped by surrounding trees that were able to break the baskets; one of the 16 baskets had to be replaced between 2002 and 2006 for this reason. Both of these issues were seen as relatively minor because the baskets were easily and inexpensively replaced, but they could have led to the loss of at least a month of data had they occurred during the 2006–2007 sampling period. A few spare baskets ready to be mounted on the fence posts were always kept in the laboratory storage room to allow replacement as needed. Finally, some of the litter fell onto the edge of the basket such that it was balanced on the rim, partially in and partially out of the basket, which could make it difficult to determine exactly how much of the litter should be counted as being caught by the basket.
Conclusions Litter accumulation is an important way that organic matter is added to forest soils, which makes the measurement of litter fall important for soil genesis studies in forested regions. The inexpensive, easy to assemble litter collecting baskets presented in this study successfully collected litter in expected proportions in the four areas studied. They also collected litter in amounts expected for a forested region in the southeastern United States and met the other desired objectives of the study. Problems encountered with the collectors were relatively minor and were easily and inexpensively addressed with reasonable checks and maintenance.
Acknowledgments This research was conducted when E.C. Brevik was a faculty member and H.W. Mimms a student in the Department of Physics, Astronomy, and Geosciences, Valdosta State University, Valdosta, GA. This research was supported by a Valdosta State University faculty research grant. Trade names or commercial products are given solely for the purpose of providing information on the exact equipment used in this study, and do not imply recommendation or endorsement by Dickinson State University or Valdosta State University.
References
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