Landscape Ecological Vegetation Map of Sint Eustatius (Lesser Antilles) Carmabi – Imares Knaw
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Landscape ecological vegetation map of Sint Eustatius Eustatius Landscape ecological vegetation map of Sint Landscape ecological vegetation map of Sint Eustatius (Lesser Antilles) carmabi – imares knaw J.A. de Freitas, A.C. Rojer, B.S.J. Nijhof & A.O. Debrot 9 789069 846798 landscape ecological vegetation map of sint eustatius landscape ecological vegetation map of sint eustatius i sint-eustatius.indd 1 2/4/2014 8:58:09 AM ii j.a. de freitas, a.c. rojer, b.s.j. nijhof and a.o. debrot sint-eustatius.indd 2 2/4/2014 8:58:09 AM landscape ecological vegetation map of sint eustatius (lesser antilles) J.A. De Freitas, A.C. Rojer, B.S.J. Nijhof and A.O. Debrot Amsterdam, 2014 Caribbean Research and Management of Biodiversity Curaçao Royal Netherlands Academy of Arts and Sciences, the Netherlands Institute for Marine Resources and Ecosystem Studies, the Netherlands landscape ecological vegetation map of sint eustatius iii sint-eustatius.indd 3 2/4/2014 8:58:09 AM © 2014 Royal Netherlands Academy of Arts and Sciences Some rights reserved. Usage and distribution of this work is defined in the Creative Commons License, Attribution 3.0 Netherlands. To view a copy of this licence, visit: http://www.creativecommons.org/licenses/by/3.0/nl/ Royal Netherlands Academy of Arts and Sciences PO Box 19121, NL-1000 GC Amsterdam T +31 (0)20 551 0700 F +31 (0)20 620 4941 [email protected] www.knaw.nl Caribbean Research and Management of Biodiversity Foundation (CARMABI Foundation) PO Box 2090, Willemstad, Curaçao, Netherlands Antilles E [email protected] www.carmabi.org Institute for Marine Resources and Ecosystem Studies www.wageningenur.nl/en/imares isbn 978-90-6984-679-8 Photographs cover: John de Freitas The paper in this publication meets the requirements of ∞ iso-norm 9706 (1994) for permanence. iv j.a. de freitas, a.c. rojer, b.s.j. nijhof and a.o. debrot sint-eustatius.indd 4 2/4/2014 8:58:09 AM acknowledgments This publication was completed as part of the Wageningen University BO research program (BO-11-011.05-004) and has been financed by the Ministry of Economic Affairs, Agriculture and Innovation (el&i) under project number 4308202004. A special word of thanks goes to the principal financiers of the project: the Kabinet voor Nederlands-Antilliaanse Zaken (project nr. 108.755) and Dutch Ministry of Economic Affairs, Agriculture and Innovation for funds with which to finish this project. The printing costs of this publication were covered through a grant from the Prins Bernhard Cultuurfonds Caribisch Gebied. We would like to thank the Meteorological Department of Curaçao (Stenny Rosalia, Fred Capello) for the provi- sion of data on hurricanes that passed close to St. Eustatius since 1956. Roy Huggins of gis4c and David Haberkorn (Agricultural University of Wageningen) provided help with the finalization of the vegetation map in Arcgis. We thank Paul Hoetjes for con- structive criticism on an earlier draft, Hannah Madden of stenapa for her help revis- iting several of the vegetation types of St. Eustatius, Gershon Lopes for information on Cactoblastis and Frank Axelrod for help with new plant names. The Central Bureau of Statistics of Curaçao provided general statistics on St. Eustatius. The printing of this publication has been possible through a grant from the Prins Bernhard Cultuurfonds Caribisch Gebied. landscape ecological vegetation map of sint eustatius v sint-eustatius.indd 5 2/4/2014 8:58:09 AM vi j.a. de freitas, a.c. rojer, b.s.j. nijhof and a.o. debrot sint-eustatius.indd 6 2/4/2014 8:58:09 AM contents Acknowledgments v Abstract 8 Introduction 10 The Island of Sint Eustatius 12 Geography 12 Climatic data 13 Geology and geomorphology 14 Soil- and landtypes of the geological formations 18 Flora and vegetation 21 Human influence on flora and vegetation 23 Methods 25 Photo-interpretation and fieldwork 25 Data collection 25 Data processing 26 Final map compilation 27 Results 28 Vegetation types 28 Description of the final legend units 39 Discussion and Conclusions 43 Anthropogenic effects 43 Comparison of the vegetation types in the present study with those of Stoffers (1956) 45 Main land type 47 Comparison of the vegetation map of Stoffers (1956) with that of the present study 48 Overall assessment and recommendations 52 References 54 Synoptic table of the vegetation types of St. Eustatius 60 Appendices 1. Monthly and annual average meteorological parameters for St. Eustatius 59 2. Hurricanes passing within 222 km from St. Eustatius (1956-1999) 60 3. New plant species names according to Axelrod (2011) 61 4. Synoptic table of the vegetation types of St. Eustatius 62 landscape ecological vegetation map of sint eustatius vii sint-eustatius.indd 7 2/4/2014 8:58:09 AM abstract A semi-detailed landscape-based vegetation map (scale: 1: 37,500) based on field data from 1999 has been available as an update of Stoffers’ 1956 map of the Lesser Antillean island of St. Eustatius, Netherlands Caribbean, but up to now was never finalized or published. In this report we complete the documentation of that map to provide new insights into vegetation change over a period of more than 40 years, and a quantitative reference point for future studies on landscape-related vegetation development for the island. ‘The principal lower sections (below 400 m) of the 21 km2 island of St. Eustatius possess a tropical savannah climate according to the Köppen (1931) classification system. The higher parts are characterized by a tropical monsoon climate. The docu- mented flora of the island amounts to 505 species. Color aerial photographs (1: 8,000) taken in 1991 and field data from 1999 were used to produce the map. A total of 84 vegetation sample plots were analysed using a stratified random sampling design and twinspan cluster analysis. Four main and 16 sub-landscape types were distinguished based on geology, geomorphology and dif- ferent mixes and expressions of the component vegetation types. The five principal landscape types are in descending order of importance: H1, H2, M4, M9 and C, and covered some 67 % of the (semi-)natural habitat of the island. H1 and H2 are the Pisonia-Justicia hills and Pisonia-Bothriochloa hills and are limited to the area of The Mountains. Analysis of the sampling data resulted in the distinction of 13 (semi-)nat- ural vegetation types. The three principal vegetation types were, the Pisonia-Justicia type, Pisonia-Ayenia type and Bothriochloa-Bouteloua type which together accounted for 38 % of total (semi-)natural vegetation cover. The following well-developed veg- etation types of St. Eustatius represent primary climax communities: Types 1, 2, 3, 5 and 7, all found in and around the Quill in the southwestern part of the island. A comparison of the vegetation types in the present study with those of stoffers (1956) showed that only one vegetation type closely resembles one in stoffers’ study. Major changes have taken place in certain types of the natural vegetation of the island in the intervening five decades. The majority of the central sections of the island around Oranjestad the so-named ‘Cultuurvlakte’, amounting to approximately 25 % of the surface of the island, have suf- fered intensive disturbance due to past agriculture, livestock husbandry and invasive spe- cies and were not mapped. Only a small remnant portion of the semi-natural lowlands vegetation (present in L1 and L2) was left in the coastal areas of Billy’s Gut. Nevertheless, this area is heavily affected by grazing and the invasive vine Antigonon leptopus. A comparison with the 1950s vegetation map by Stoffers shows that the rarest and most valuable elfin woodland vegetation of the rim of the Quill crater had been largely 8 j.a. de freitas, a.c. rojer, b.s.j. nijhof and a.o. debrot sint-eustatius.indd 8 2/4/2014 8:58:09 AM lost and that the areas he described as ‘Montane thickets’ (Type 2) had declined and been degraded. We speculate that these losses may be most directly attributable to the impact of recent hurricanes and/or grazing by introduced livestock. On the lower slopes of the Quill, several areas mapped by Stoffers as farmland had been aban- doned and have evidently regenerated into mixed deciduous and evergreen thorny woodlands. The vegetation of the Mountains area showed some recovery since the 1950s. There were more evergreen bushes, and less Acacia and Leucaena than stoffers described. The vegetation Stoffers described for the lowlands had more Acacia than we found but the invasive Antigonon has since dramatically increased as a ubiquitous and often dominant species. The former importance of Opuntia prickly pear cacti in disturbed vegetations has dramatically declined since the 1950s. We ascribe this to the likely effect of the invasive parasitic insect Cactoblastis cactorum. In the 1980s and 1990s many Opuntia cacti were seen affected by this insect. Our field data show that all wilderness areas of St. Eustatius remained heavily affected by grazers. This reduces the resilience of natural vegetations and interferes with natural succession by imparting heavy losses to hardwood seedlings and sap- lings (see e.g. melendez-ackerman et al. 2008), by reducing plant biomass (which increases exposure to wind and sun), and by favoring hardy invasive plant species. In Curaçao, large scale reduction in densities of feral grazers in the Christoffelpark since 1993 has led to rapid recovery of several rare plant species and vegetation types. The problem of feral livestock remains severe. Therefore the number one priority for terrestrial conservation in St. Eustatius will be to reduce feral grazer densities and impacts in key wilderness areas. landscape ecological vegetation map of sint eustatius 9 sint-eustatius.indd 9 2/4/2014 8:58:09 AM introduction The Dutch Caribbean volcanic island of St.