SIXTY-TWO YEARS OF CHANGE IN SUBTROPICAL WET FOREST STRUCTURE AND COMPOSITION AT EL VERDE, PUERTO RICO Allan P. Drew, Jeremy D. Boley, Yinghao Zhao, Mark H. Johnston and Frank H. Wadsworth SUMMARY A plot established in 1943 in a subtropical wet forest at the Luquil- Hurricane and the understory tree Psychotria berteriana proliferated. lo Experimental Forest of Puerto Rico has been assessed periodically Ingrowth of Prestoea montana has been greater than for all other spe- for changes in species and size of all trees >4cm diameter. Forest dy- cies since 1976 and was stimulated by Hugo and Georges as well as namics on a 0.72ha plot (EV-3) at 400masl at El Verde show recovery prior hurricanes, so that by 2005 it was the most abundant species. principally from hurricanes of 1928 and 1932, timber stand improve- Hurricane Hugo caused low mortality among the largest trees on the ment in 1958, and from Hurricanes Hugo and Georges in 1989 and plot. As a few species have become more dominant species evenness 1998. Damage from Hurricane Hugo only temporarily slowed above- has declined. Species richness is only slightly greater today than in ground biomass accretion of the developing forest. Stand increases 1943. Results are discussed in terms of “building” and “thinning” in basal area and biomass continue to be due principally to growth phases associated with major hurricanes. Hurricanes have stimulat- of the dominant overstory species, Dacryodes excelsa and Manilkara ed the addition of species to the forest in “building years,” but have bidentata, ingrowth of which was stimulated by Hugo. The pioneer maintained that richness in the intervening “thinning years”, lending species Cecropia schreberiana filled gaps abundantly following the credence to the “intermediate disturbance hypothesis”. urricanes are the dominant Weaver, 1989). Hurricane Santa Clara pro- age, and uprooting, however, were Hurricanes form of large scale distur- duced 220mm of heavy rainfall at El Verde San Cipriano and Hugo. bance in the Caribbean in 1956, but only “local or slight” damage, In 1943, the U.S. Forest Basin and in Puerto Rico (Walker et al., principally defoliation, over the Luquillo Service began establishing permanent plots on 1991). In the 20th century, Hurricane San Fe- Mountains (Wadsworth and Englerth, 1959). the LEF for monitoring forest and tree growth lipe had passed to the southwest of the Moun- In 1989, Hurricane Hugo passed just north- (Weaver, 1998). At El Verde, plot EV-3 was tains in 1928 and in 1931, Hurricane San Ni- east of the LEF with winds of 166km/h and established by Frank Wadsworth at 400m ele- colas passed to the north over the ocean. precipitation >200 mm over most of the LEF vation in the tabonuco forest type, the Hurricane San Cipriano (September 26, 1932) (Brennan, 1991; Scatena and Larsen, 1991). Dacryodes-Sloanea association sensu Beard passed directly over the Luquillo Mountains Hurricane Georges passed over southern (1949), and subtropical wet forest life zone and the Luquillo Experimental Forest (LEF) Puerto Rico in 1998, but significantly affected (Ewel and Whitmore, 1973). The above-aver- in northeastern Puerto Rico with winds of the LEF to the north. Most noticeable in age site was chosen in order to assess stem 200km/h and >430mm of rain (Crow, 1980; terms of defoliation, stem and branch break- growth of young trees of commercially valu- KEYWORDS / Dacryodes-Sloanea / El Verde / Hurricanes / Long Term Monitoring / Subtropical Wet Forest / Received: 02/07/2008. Modified: 11/21/2008. Accepted: 11/25/2008. Allan P. Drew. B.S. in Forestry, University of Illinois. M.Sc. in Watershed Management, University of Arizona. Ph.D. in Forest Management, Oregon State University. Professor, State University of New York, College of Environmental Sci- ence & Forestry (SUNY-ESF) USA. Address: 320 Bray Hall, 1 Forestry Drive, Syracuse, NY 13210, USA. e-mail: [email protected] Jeremy D. Boley. B.A. in Psychology, Grinnell College. M.Sc. in Forest and Natural Resources Management, SUNY-ESF, USA. Forester, U.S. Forest Service. e-mail: [email protected] Yinghao Zhao: B.S in Forestry, Huazhong Agricultural University, China. M.Sc. in Plant Sci- ence and Biotechnology, SUNY-ESF, USA. Graduated Student, e-mail: [email protected] Mark H. Johnston. B.S. in Forest Resources Management, University of Minnesota, USA. M. Sc. in Forest Science, University of Alberta, USA. Ph.D. in Forest Ecology, SUNY-ESF. Senior Research Scientist, Saskatchewan Research Council, Canada. e-mail: [email protected]. Frank H. Wadsworth. BSF in Forest Production, MF in Forest Ecology. Ph.D. in Forest Man- agement, University of Michigan. USA. Registered volunteer, USDA Forest Service, Río Piedras, Puerto Rico. e-mail: fwadsworth@ hotmail.com 34 0378-1844/09/01/034-07 $ 3.00/0 JAN 2009, VOL. 34 Nº 1 able species. In 1937, “a very light cutting in pacted the Forest 11-15 years prior to plot value (IV) was calculated as the sum of rela- order to minimize the impact on the water- establishment. tive dominance (basal area), relative frequen- shed” was conducted by the Forest Service of cy (over 18 sub-plots, each 20×20m), and rel- the area where the plot was subsequently sited Methods ative density on a scale of 0 to 300. (no records kept) and a timber-stand improve- Diversity was assessed us- ment treatment was applied in 1958 (F. Wads- Site and species ing the Shannon-Weiner diversity index worth, cited by Odum, 1970; Crow, 1980) (Shannon and Weaver, 1949) H= -Σpilogepi, which removed 146 stems, 109 from the Plot EV-3 at El Verde is where pi is the proportion of trees in species 4-8cm diameter class, 26 from the 8-16cm 0.72ha in size, rectangular (60×120m) with a i. Overall evenness of species abundances class and 11 trees that were >16cm. Sloanea northwest aspect and is situated on a ridge on was expressed by Pielou’s J (Pielou, 1966; berteriana, Dacryodes excelsa and Manilkara the south side of the Río Soñadora in the Lu- Peet, 1974) where J= H/Hmax. Hmax is the bidentata were among the most common spe- quillo Experimental Forest, a long-term eco- maximum possible value of H for the ob- cies removed. The plot has been monitored at logical research site. The plot is ~0.5km from served number of species which would occur 1 to 12 year intervals from establishment the site of the earlier irradiation studies and with all pi equal. through 2005, making it one of the longest the 16ha Forest Dynamics plot. Between 1975 Stand biomass was deter- continuously monitored forest growth plots in and 2003 the mean annual precipitation at El mined using equations developed by Weaver the neotropics. Frequent hurricane activity in Verde Field Station was 3536mm and the and Gillespie (1992) for tabonuco forest on the area allowed for long-term assessment of mean annual temperature, 24.0°C. The mini- the LEF. Total aboveground dry weight (Y, species change and forest growth dynamics in mum monthly precipitation usually occurs in leaves + wood) in kg per tree, independent of response to catastrophic disturbance. January, averaging ~232mm. Soils on EV-3 species, was estimated using tree dbh (D) in The University of Puerto are derived from marine deposited volcanic cm as the sole predictor. For D<5cm, Y= Rico’s El Verde Field Station was the general “sandstones” (Scatena, 1989) and are mostly 0.3210D1.3925, and for D>5cm, Y= 4.7306- location for U.S. Atomic Energy Commission acid clays of low cation exchange capacity 2.8566D+0.5832D2. studies on effects of gamma irradiation on (Soil Survey Staff, 1995). Aboveground woody dry tropical forests (Odum, 1970) between 1963 Seven “indicator” species weight (Y) in kg per tree was similarly esti- and 1967, and has since served as the site for (sensu Crow, 1980) cover a wide range of mated using tree dbh (D) in cm as the sole numerous field studies in tropical ecology ecologic functional niches within the tabonu- predictor. In this case, for D<5cm, Y= (Reagan and Waide, 1996). The 16ha plot of co forest. These species (Cecropia schreberi- 0.2634D1.4539, and for D>5cm, Y= tabonuco forest at El Verde, the Luquillo For- ana L., Croton poecilanthus Urb., Dacryodes 5.7266-3.0469D+0.5659D2. est Dynamics Plot (LFDP) established in 1990 excelsa Vahl, Manilkara bidentata (A. DC.) The dry weights of indi- ~0.5km from EV-3, is currently being moni- Chev., Prestoea montana (R. Graham) Nich- vidual stems were summed using both equa- tored for woody species recovery from hurri- ols, Schefflera morototoni (Aubl.) Maguire, tions to yield the total aboveground and canes (Thompson et al., 2004) and provides a Steyerm. & Frodin, Sloanea berteriana aboveground woody biomass for the stand ex- nearby large scale example of changing forest Choisy), have been dominant on EV-3 since clusive of palms. Crow’s (1980) biomass fig- dynamics to which EV-3 has been compared measurements began or have well known suc- ures, based on equations of Ovington and Ol- for the years following Hurricane Hugo. Al- cessional roles and are highlighted in the on- son (1970), were recalculated using Weaver though it is only a single plot, the long-term going plot dynamics. and Gillespie’s (1992) improved equations and growth record provided by EV-3 is an invalu- presented for the plot from its inception. able supplement to the more recently estab- Plot assessment Palm stand biomass was lished LFDP and provides information on the determined using the linear regression equa- local forest that predates the larger 16ha plot. Since the assessment by tion developed by Frangi and Lugo (1985). EV-3 has also served as the site for intensive Tom Crow in 1976 (Crow, 1980), EV-3 was Total aboveground dry weight (Y) in kg per studies of variation in oxisol soil series and assessed by Mark Johnston in 1988 (Johnston, palm was estimated using stem height (X) in vegetation according to topographic position 1990), Salvador Alemañy in 1993, by Ying- m as the sole predictor, as Y= 7.7X+4.5.