United States Department of A Summary of 20 Years Agriculture Forest Service of Forest Monitoring in Cinnamon Bay Watershed, International Institute St. John, U.S. Virgin Islands of Tropical Forestry General Technical Peter L. Weaver Report IITF–34 Author Peter L. Weaver, Research Forester, U.S. Department of Agriculture, Forest Service, International Institute of Tropical Forestry, Jardín Botánico Sur, 1201 Calle Ceiba, San Juan, PR 00926-1119. Cover photos Top right: The island’s attractive scenery prompted President Eisenhower to authorize the establishment of the Virgin Islands National Park as a sanctuary of natural beauty in 1956. Left: A hiker looks up at large Ceiba trees (Ceiba pentandra) at an interpretative stop on one of the many hiking trails scattered throughout Virgin Islands National Park. Bottom right: Picturesque Cruz Bay Harbor with government house situated on a narrow peninsula. All photos in report by Peter L. Weaver. October 2006 International Institute of Tropical Forestry Jardín Botánico Sur 1201 Calle Ceiba San Juan, PR 00926-1119 A Summary of 20 Years of Forest Monitoring in Cinnamon Bay Watershed, St. John, U.S. Virgin Islands Peter L. Weaver Abstract St. John, and probably the Cnnamon Bay watershed, has a hstory of human use datng to 1700 B.C. The most notable mpacts, however, occurred from 1730 to 1780 when sugar cane and cotton producton peaked on the sland. As agrculture was abandoned, the sland regenerated n secondary forest, and n 1956, the Vrgn Islands Natonal Park was created. From 1983 to 2003, the staff of the Internatonal Insttute of Trop cal Forestry montored 16 plots, stratfied by elevaton and topography, n the Cnnamon Bay watershed. The perod ncluded Hurrcanes Hugo n 1989 and Marlyn n 1995 and a severe drought n 1994-95. In all years, plot talles showed that from 55 to 60 percent of the stems were n heght classes between 4 and 8 m, and 75 percent of the stems were n dameter at breast heght (1.4 m above the ground; d.b.h.) classes between 4 and 10 cm. Stem densty was greatest on the summt, followed by rdges, then slopes, and lowest n valleys. After 20 years, 65 percent of the orgnal stems survved, wth an average d.b.h. growth rate of 0.07 cm year-1. Tree speces abundances vared by topography and elevaton wthn the watershed. In 1983, total aboveground bomass on all plots combned averaged 138.7 t ha-1; by 2003, t had declned by nearly 7 percent. In 1983, bomass was greatest on the summt, ntermedate on slopes and valleys, and least on rdges; by 2003, the quanttes for all stes had converged except on the summt plot. In 1992, total aboveground productvty was estmated at 10.64 t ha-1 year -1. Standng herbvory for leaves was 4.5 percent, and the herbvory rate was 4.6 percent per year. The standng crop of ltter was 9.33 t ha-1. Hurrcanes had a major mpact on forest structure and speces composton. The trees mpacted (snapped, uprooted, or standng dead) by Hurrcane Hugo totaled 210 ha-1 after 10 months and 288 ha-1 after 19 months. The proporton of mpacted stems dffered by elevaton, topography, aspect, and slope. Tree speces wth ≥ 20 ndvduals showed a dfference n the proporton of mpacted stems, rangng from as low as 0.6 percent for Pimenta racemosa (Mll.) J.W. Moore to as hgh as 22.8 percent for Nectandra coriaceae (Sw.) Grseb. In concluson, the structure, speces composton, and forest dynamcs wthn the Cnnamon Bay watershed vary n tme and space, and short-term observatons characterze only a fragment of the watershed’s contnuously changng vegetatonal hstory. Montorng of forest structure and dynamcs should contnue. Keywords: Bomass; dry forest; montorng; St. John, U.S. Vrgn Islands; tree speces. Contents Page Abstract ....................................................................................................................................i List of Figures ....................................................................................................................... iv List of Tables ......................................................................................................................... v Introduction .......................................................................................................................... 1 Historical Perspective ......................................................................................................... 1 Setting: St. John and Cinnamon Bay .............................................................................. 5 Geology ................................................................................................................................. 5 Physiography and Soils ......................................................................................................... 5 Climate .................................................................................................................................. 5 Hydrology ............................................................................................................................. 6 Vegetation ............................................................................................................................. 7 Terrestrial Research Initiative ............................................................................................... 9 Methods at Cinnamon Bay .............................................................................................. 10 Results at Cinnamon Bay ................................................................................................. 11 Forest Structure .................................................................................................................. 11 Number of stems ........................................................................................................... 11 Height classes ................................................................................................................ 14 D.b.h. classes ................................................................................................................. 14 Crown classes ................................................................................................................ 14 Forest Dynamics ................................................................................................................ 14 D.b.h. increment ............................................................................................................ 14 Biomass increment ....................................................................................................... 14 Species composition ...................................................................................................... 16 Discussion ............................................................................................................................ 18 Climate ................................................................................................................................ 18 Forest Structure .................................................................................................................. 18 Forest Dynamics ................................................................................................................ 21 Species Composition .......................................................................................................... 21 Conclusions ......................................................................................................................... 24 Acknowledgments .............................................................................................................. 25 Endnotes .............................................................................................................................. 25 Literature Cited ................................................................................................................. 25 Appendix A—Chronology of major events (exploration, settlement, forest exploitation, forest recovery, terrestrial research, and tourism) in the history of St. John, U.S. Virgin Islands, with emphasis on the Cinnamon Bay watershed ..................... 29 Appendix B—Stem density by species and year on 16 plots totaling 0.8 ha in the Cinnamon Bay watershed, St. John, U.S. Virgin Islands ........................................................ 32 continued iii List of Figures Figure 1—Locaton of places mentoned n text. ................................................................. 4 Figure 2—Clmatc dagram for the Cnnamon Bay watershed based on 30-year normals for Cathernberg, 1971 to 2000 (N 18°20', W 64°45'). ........................................... 6 Figure 3—Vegetaton types on St. John (Woodbury and Weaver 1987). ............................ 7 Figure 4—Total number of stems on all plots combned n the Cnnamon Bay watershed: green bars = survvng stems from the ntal tally n 1983; yellow bars = cumulatve ngrowth; brown bars = cumulatve mortalty of ngrowth; blue bars = total stems n partcular year. Survvng stems are equal to total stems at first measurement n 1983. Ingrowth begns n 1988, and mortalty of ngrowth starts n 1993. ..................... 11 Figure 5—Total number of stems by crown classes on all plots combned from 1983 to 2003. ....................................................................................................................... 14 Figure 6—Abundance of stems by speces on all plots combned n 1983 and 2003. ...... 24 v List of Tables Table 1—Forest montorng plots on St. John ...................................................................