A DATA SET a series of observations collected by the same methodology. Each data set should have documentation sufficient for someone unfamiliar with the research to replicate the study. Data sets may be broken into subsets (data files) that are discrete in space and time, in that order. The documentation for a data set should include all spatial and temporal subdivisions of the data.

DATA SET IDENTIFIER: Litter decomposition of the tabonuco forest before hurricane Hugo

PROJECT TITLE: LTER
LTER core area: Organic Matter Accumulation, Disturbance Patterns
LEF research area : Soil organic matter formation

DATA SET FILES (SUBSETS):
(1) Tree species composition before Hugo: ( decotab1.txt)
(2) Annual decay rate of leaf litter before Hugo ( decotab2.txt)

RESEARCH LOCATION:
This study was conducted in the Luquillo Experimental Forest (LEF) at the El Verde Field Station (18°20'N, 65°49'W) in Puerto Rico. The research area was located in lower montane rain forest (Odum and Pigeon, 1970, Ewel and Whitmore, 1973), where the mature forest is typically dominated by tabonuco trees (Dacryodes excelsa Vahl.). Elevation of the tabonuco forest ranges between 300-600 m. Mean monthly temperature varies from 20.8-24.4°C with a mean annual precipitation of 3456 mm (Brown et al., 1983). Although there is no obvious dry season in the area, a period of reduced rainfall occurs between January and April. Soils were dominated by Zarzal series that are deep Oxisols of volcanic origin (Huffaker, 1995).

INVESTIGATORS:
PRINCIPAL INVESTIGATOR: Xiaoming Zou
OTHER RESEARCHERS:
CONTACT PERSON & PHONE: Telephone: (809) 767-0334; Fax: (809) 758-0815; Internet: x_zou@upr1.upr.clu.edu

PROJECT DESCRIPTION:
SOURCE OF FUNDING (SPONSOR) : NSF-LTER

ABSTRACT:
Understanding the long-term impact of deforestation on ecosystem structure and function of tropical forests may aid in designing future conservation programs to preserve biodiversity and sustain ecosystem productivity. We examined forest structure, tree species composition, litterfall rate, and leaf litter decomposition in a mid-successional forest (MSF) and an adjacent mature tabonuco forest (MTF) in the Luquillo Experimental Forest of Puerto Rico. Whereas the MTF site received limited human disturbance, the MSF site had been cleared for timber production by the beginning of this century and was abandoned after hurricanes struck the Luquillo Mountains in the 1920s and 1930s. We found that the MSF was dominated by successional tree species 50 yrs after secondary succession, and did not differ in tree basal area and litterfall rate from the MTF. Leaf decomposition rate in the MSF was higher than in the MTF, but this difference was small. Our results show that deforestation has long-term (>50 years) influence on tree species composition and that leaf decomposition processes in secondary forest is relatively faster than recovery of tree species composition.

METHODS:
Forest structure and species composition

A 1 ha plot (100 x 100 m) was randomly established in each of the MSF and MTF in 1980. Within each plot, twenty circular subplots (113 m2) were randomly located. All trees ò0.1 m in DBH (diameter at breath height) in each subplot were identified and the DBHs were recorded.

Litterfall and ground litter biomass

Twenty 1 m2 baskets lined with 1 mm2 mesh fiberglass screen were randomly placed in each 1 ha plot at 1 m above ground. Litterfall was collected biweekly for 1 yr between November 1980 and October 1981. All litter samples were separated into leaves, flowers, fruit, wood, and miscellaneous materials (mostly bark), oven-dried at 70øC for 72 hrs, and weighed. Ground litter was collected from 0.25 m2 subplots in both the dry season (March, 40 subplots) and the wet season (September, 20 subplots) randomly located in each of the 1 ha plots. Each sample was separated into wood and miscellaneous categories, oven-dried at 70øC for 72 hrs, and weighed.

Leaf decomposition

A total of 140 litterbags were constructed among which 70 litterbags were filled with fresh leaves collected from the MSF and 70 from the MTF (Blair et al., 1990). These fresh leaves represented the tree species composition in natural litterfall in April at both sites. The species composition of litterfall was determined using leaffall in the 1-m2 randomly placed baskets in each plot. Fresh leaves were collected for each forest within 24 hours of senescence in May and sorted by species. Leaves of the 13 most common species from each forest, representing 82-91% of the total fresh leaf mass, were placed in 1-mm2 mesh fiberglass screen bags (0.2 by 0.25 m) in proportion to their biomass in litterfall (Table 1). Leaves of the remaining 25 species were put in a miscellaneous category and randomly selected to obtain a total of 10-g fresh leaf material (4.6 g mean oven-dry mass) in each bag.
For each leaf type, 35 litterbags were placed equally in 5 randomly selected subsites in the 1 ha plots where leaves were collected. In order to separate the effects of leaf chemistry on leaf decomposition from those of biotic and abiotic environmental conditions between the two forests, the other 35 litterbags for both leaf types were together placed in a 10 x 10 m plot in the MTF at five randomly selected locations. The 1 ha plots covered an area with heterogeneous geographical locations including ridges and valleys, whereas the 0.01 ha plot was located on a ridge top and upper slope position. One randomly selected litterbag was collected after 0, 7, 14, 28, 60, 120, and 300 days in the field at each site from each plot. There were 2 (leaf types) x 2 (incubation sites) x 5 (replicates) x 7 (collections) = 140 litterbags.
Small roots which had entered the litter bags were carefully removed in the laboratory. The remaining litter in each bag was oven dried at 70øC for 72 hours and weighed to determine dry mass loss. Dry litter was then ground with a Wiley mill through a 0.85 mm (20 mesh) stainless steel sieve. One gram of the ground leaf material from each litterbag was digested with H2O2 and concentrated HNO3 (Luh Huang and Schulte, 1985) before analyzing for P, K, Ca, and Mg content with an atomic absorption and emission spectrophotometer. Total C and N in leaf material were analyzed by direct combustion in a C-H-N analyzer (Carlo-Erba Model 1106).

Data analyses

Basal area, tree density, and leaffall for each species were calculated for each forest. Total litterfall rate and ground litter biomass of all species were also calculated for each forest. The analysis of variance (ANOVA) was employed to test the differences in basal area, tree density, leaffall rate, and ground litter biomass between the forests or the seasons (SAS, 1987). Leaf decay rates were calculated using a single exponential model Mt = M0e-kt, where Mt was the remaining mass of leaf materials in a litter bag at time t and M0 was its initial mass. Slope k was obtained using linear regression after taking the natural logarithms of the equation. Multivariate tests were used to examine differences in k values between the two forests and between sites (SAS, 1987). The significance level was set at à = 0.05.
Percentage of initial weight remaining was calculated using oven-dried weight. Percentage of initial element remaining in litterbags was obtained by multiplying the ratio of total element at time t (t = 0, 7, 14, 28, 60, 120, and 300 days) to that at time 0 by 100. Total element content in a litterbag was calculated as the product of element concentration and the oven- dry weight. Differences in elemental concentrations between forests and among decomposing dates were tested with ANOVA. Where significant differences were obtained by ANOVA, Bonferroni t-test (SAS Inc., 1987) was used to compare these differences in elemental concentrations. The significance levels for ANOVA and Bonferroni t-test were both set at à = 0.05. Plots of residuals vs. predicted values indicated that no variables significantly violated the homogeneity assumption, with the exception of K concentrations. A non-parametric analysis was employed by ranking K concentrations prior to performing ANOVA and Bonferroni t test.

DATA COLLECTION TIME PERIOD: November 1980 and October 1981

STARTING DATE: November 1980
PERIODICITY OF SAMPLE : biweekly
END PERIOD : October 1981

REFERENCES :
Blair, J.M., Parmelee R. W. and Beare, M. H., 1990. Decay rates, nitrogen fluxes, and decomposer communities of single- and mixed-species foliar litter. Ecology, 71: 1976-1985.

Luh Huang, C. Y. and Schulte, E. E., 1985. Digestion of plant tissue for analysis by ICP emission spectroscopy. Comm. Soil Sci. Plant Anal., 16: 943-958.

SAS Inc., 1987. SAS Guide for personal computers. 6th edition. Cary, North Carolina, USA.

Odum, H. T. and Pigeon, R. F. 1970. A tropical rain forest: A study of irradiation and ecology at El Verde, Puerto Rico. U.S. Atomic Energy Commission, National Technical Information Service, Springfield, Virginia, USA.

Ewel, J. J., and Whitmore, J. L., 1973. The ecological life zones of Puerto Rico and the U. S. Virgin Islands. U.S.D.A. Forest Service Research Paper ITF-18, 71 pp.

Brown, S., Lugo, A., Silander S. and Liegel, L., 1983. Research history and opportunities in the Luquillo Experimental Forest. USDA Forest Service General Technical Report SO-44, 128 pp.

Huffaker, L., 1995. Soil survey of the Caribbean National Forest and Luquillo Experimental Forest. USDA Forest Service, Washington D.C. (in press).

CROSS-REFERENCES (other data sets related to this one): LTERDBAS #93: Litter decomposition in tabonuco forest before Hugo; LTERDBAS #94: Litterfall of the tabonuco forest before Hurricane Hugo; LTERDBAS #95: Litterfall along topographic gradients at lower Bisley; LTERDBAS #111: Litterfall in tabonuco (subtropical wet) forest in the Luquillo Experimental Forest, Puerto Rico (MRCE Litterfall data); LTERDBAS #115: Short-term disappearance of foliar litter of three tree species native to rain forest of Puerto Rico

SAMPLE LOCATION: ITES, Soil Laboratory

STORAGE SITES ITES, Data Manager's File DM-002 , Drawer #1

KEYWORDS:
forest recovery, leaf decomposition, secondary forest, tabonuco forest

PUBLICATIONS:
CITATION:

Zou, X., C. Zucca, R. B. Waide, and W. H. McDowell. 1995. Long-term influence of deforestation on tree species composition and litter dynamics of a tropical rain forest in Puerto Rico. Forest Ecology and Management 78:147-157. (Abstract)

DISSEMINATION:
*UNRESTRICTED

CHECKLIST:

* Documentation for Data Set
* Documentation for Data Files
Documentation for Variables

FILING MEDIA
On-line data Data entered by investigator

DATE OF LAST REVIEW : May 5, 1997

DATE OF LAST ENTRY : October 1981

STAGE OF DATA SET MANAGEMENT (dates) :
RECEIVED: October 10, 1996
CATALOGUED: May 5, 1997
ON-LINE: May 6, 1997
REVIEWED BY RESEARCHER: May 5, 1997

FILING MEDIA:
NAME OF DOCUMENTATION FILE : LEFDS196.FM*

NAME OF DATA FILE : decotab1.txt, decotab2.txt

NAME OF ON - LINE CATALOG : LEFDSET RECORD # : 96

DOCUMENT TYPE : magnetic media - paper

PRIORITY TO BE ENTERED : N/A

DESCRIPTION OF DATA SET FORMAT (MAGNETIC MEDIA):

DATA FILE NAME :(1) Tree species composition before Hugo

Columns		Type of datum		Name of Variable		Abbreviation(s)
1		alphanumeric		Scientific name		Species
2		real		wt. fresh leaves by  species in litterbags in mid-successional forest		MSF
3		real		wt. fresh leaves by  species in litterbags in  a mature tabonuco forest		MTF

Observations

FILE NAME (IF MAGNETIC MEDIA): decotab1.txt)

PREVIOUS VERSIONS OF DATA : none

SUMMARY STATISTICS : 

DATA FILE NAME : 2) Leaf litter in the tabonuco forest

Columns		Type of datum		Name of Variable		Abbreviation(s)
1		alphanumeric		Leaf type		none
2		alphanumeric		Location (MTF, MSF)		Incubation site
3		real		Decomposition coefficient		k
4		real		r square		r2
5		percent		% mass loss per year		% mass loss yr-

Observations
Locations: MSF = mid-successional forest
MTF = mature tabonuco forest

Note from the investigator: For more information and/or raw data contact Xiaoming Zou at Tel. 787-767-0350 or e-mail: xzou@lternet.edu

FILE NAME (IF MAGNETIC MEDIA):
(2) Annual decay rate of leaf litter before Hugo ( decotab2.txt)

PREVIOUS VERSIONS OF DATA :

SUMMARY STATISTICS : 

ON-LINE FILES NAME
Documentation File: lefds196.fm*
Data Files: decotab#.txt, decotab#.wq1, # = 1,2