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

PROJECT TITLE: Litterfall and Decomposition

PROJECT DESCRIPTION: 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 examine forest structure, tree species composition, litterfall (fine and coarse) due to Hurricane Hugo and subsequent fine annual litterfall inputs, litterfall rate, and leaf litter decomposition.

History of litterfall and decomposition studies at the Luquillo Experimental Forest (LEF)

The Minority Research Centers of Excellence (MRCE) experiment was designed originally to determine whether forest productivity was limited by nutrient availability, genetic constraints or climatic variables along a steep environmental gradient in the Luquillo Mountains of Puerto Rico. Comparisons were made between dwarf forest at 500 m elev. and tabonuco forest from 300-400 m elev. There were two main experiments in the original design: 1) forest fertilization (complete versus none); 2) transplant experiments using common gardens at high and low elevation, with and without wind protection at high elevation. In addition, phenology of leaves was studied in the dwarf forest to determine the longevity of leaves in the canopy. The occurrence of Hurricane Hugo in September 1989, just as the forest plot fertilization experiments were to begin, neccesitated the addition of a hurricane debris-removal treatment as a second type of control in the lower elevation tabonuco forest. The hurricane also changed the nature of the study into one of looking at changes in forest composition and the recovery of forest productivity in response to fertilization and hurricane debris-removal. Seedling, sapling, herbaceous plant, and fern responses, as well as measurements of light availability and canopy closure were added to the originally planned measurements of tree diameter growth, leaf litter production, and fine root production and turnover. Another hurricane in 1998 (Hurricane Georges) presented an opportunity to look at the effects of removing only the woody debris (in new plots) versus removing all hurricane debris.

Funding for continued studies of the MRCE plots ended in 1998, but they were of such great value as a long-term experiment that they were incorporated into the LTER program.

LTER CORE AREAS: (Annotate all that apply)

Matter Accumulation

Disturbance Patterns

LEF LTER 1 RESEARCH TOPIC: (Annotate all that apply)

Soil organic matter formation

We define a data file as a component of a data set. A data set can have only one data file or more. Basically, different data files have different data structures or format.
DATA SET FILES (SUBSETS):

Data File No.	Data File Identifier	On-Line Filename	Starting Date	Periodicity of sample	End Period
1	Tree species composition before Hugo	decotab1.txt	November 1980	biweekly	October 1981
2	Annual decay rate of leaf litter before Hugo	decotab2.txt	November 1980	biweekly	October 1981

RESEARCH LOCATION:

INVESTIGATORS:

PRINCIPAL INVESTIGATORS E-MAIL address

Xiaoming Zou

x_zou@upr1.upr.clu.edu

OTHER RESEARCHERS E-MAIL address

CONTACT PERSONS E-MAIL address Phone Number (Include area code)

Xiaoming Zou

x_zou@upr1.upr.clu.edu

(787) 764-0000. Ext.

SOURCE OF FUNDING (SPONSOR): NSF-LTER

DATA SET ABSTRACT: 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.

DATA SET 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.

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

INVESTIGATOR'S ASSIGNED KEYWORDS: forest recovery, leaf decomposition, secondary forest, tabonuco forest

LEF LTER OFFICIAL KEYWORDS (See table): EL VERDE, TABONUCO, DECOMPOSITION, LITTER FALL, HURRICANE, SECOND FOREST, TREES, PEER REVIEWED JOURNAL

PUBLICATIONS:

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

REASONS TO RESTRICT DATA IN THIS DATA SET BEYOND ITS TWO YEAR POLICY PERIOD*:

*WILL HAVE TO BE APPROVED BY LTER PRINCIPAL INVESTIGATORS: J. ZIMMERMAN, A. LUGO , D.J. LODGE

SITES DESCRIPTIONS: 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).

Geographical positional system (GPS) Coordinates for each location:

location	latitude	longitude
MSF = mid-successional forest
MTF = mature tabonuco forest

VARIABLES (ATTRIBUTES):

FILE NAME OR #ABOVE (all in which the variable appears)	1	1	1	2
ABBREVIATION (as it appears on the data file)	SPECIES	MSF(g)	MTF(g)	LEAF_TYPE
NAME OF VARIABLE	Scientific name	Weight of a mid-successional forest fresh leaves	Weight of a mature tabonuco forest fresh leaves	Leaf type
DEFINITION OF VARIABLE	Tree species composition of fresh leaf materials by species in litterbags that represent natural litterfall in forest	Weight of fresh leaves by  species in litterbags in a mid-successional forest	Weight of fresh leaves by  species in litterbags in a mature tabonuco forest	Type of forest where leaf materials where collected
UNIT	N/A	g	g	N/A
PRECISION	N/A	±0.01	±0.01	N/A
RANGE OR LIST OF VALUES	Guarea guidonia Manilkara bidentata Dacryodes excelsa Homalium racemosum Philodendron gigandeum Coccoloba diversifolia Schefflera morototoni Sapium laurocerasus Cecropia schreberiana Marcgravia rectiflora Chionanthus domingensis Miconia tetrandra Sloanea berteriana Buchenavia tetraphylla Schlegelia brachyantha Alchornea latifolia Casearia arborea Ormosia krugii Byrsonima spicata Ocotea leucoxylon Other species			MSF = mid-successional forest in Puerto Rico MTF = mature tabonuco forests in Puerto Rico
DATA TYPE	alphabetic	decimal	decimal	alphanumeric
MISSING DATA CODES	none	none	none	none

VARIABLES:

FILE NAME OR #ABOVE (all in which the variable appears)	2	2	2	2
ABBREVIATION (as it appears on the data file)	INCUBATION_SITE	K	R2	MASS_LOSS(%_PER_YR)
NAME OF VARIABLE	Location	Decomposition coefficient	r square	% mass loss per year
DEFINITION OF VARIABLE	Site where litterbag was placed for decomposition	Annual decay rates k (-SE<k<SE) calculated from a simple negative exponential model Mt = Mo(e-kt) (where Mt = remaining at year t; Mo = initial mass) for leaf materials		Average percentage of annual mass loss for leaf litter
UNIT	N/A	N/A	N/A
PRECISION	N/A	varies	±0.01
RANGE OR LIST OF VALUES	MTFx = litterbags were incubated at five random locations within a 0.01 ha plot, MSF, MTF = litterbags were incubated at five random locations incubated within a 1 ha plot
DATA TYPE	alphanumeric	decimal	decimal	percent
MISSING DATA CODES	none	none	none	none

COMPUTATIONAL METHODS:

VARIABLE NAME	FORMULA OR DESCRIPTION

FOR DATA MANAGER USE ONLY

DATE OF LAST REVIEW: May 5, 2005
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

Rev. date of this form: 13 March 2002