Invasion and Recovery of Vegetation After a Volcanic Eruption in Hawaii
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Technical Report No. 10 INVASIOH AND RECOVERY OF VEGETATION AFTER A VOLCANIC ERUPTION IN HAWAII Garrett A. Smathers and Dieter Mueller-Dombois Department of Botany University of Hawaii Honolulu, Hawaii ISLAND ECOSYSTEMS IRP U. S. International Biological Program September 1972 PREFACE This report forms part of a dissertation of the first named author. The project was financed in part by the National Park Service, Department of Interior, in part by NSF Grant GB 4686 to D. Mueller-Dombois, entitled "Ecology of vegetation on new volcanic materials," and in the later phases by NSF Grant GB 23230 to the Hawaii IBP/ISLAND ECaYSTEMS Integrated Research Program, ABSTRACT A major volcanic eruption on the Island of Hawaii in December 1959 devastated on existing montane rain- and seasonal-forest covering an area of about 500 ha. The eruption resulted in a massive pahoehoe lava substrate on the crater floor of Kilauea Iki, in a new cinder cone, in an area covered with spatter and another with an extensive blanket of pumice varying along a fallout gradient from over 46 m to less than 2 cm deep. Six new habitats were recognized by kinds of substrate and remains of former vegetation. A study was made of plant invasion and recovery from the time of the disturbance till nine years thereafter. Plant records consisted primarily of periodically listing species by cover- abundance in a large number of quadrats along a transect system that crossed the crater floor and extended about 3 km along the fallout gradient. The atmospheric environment was studied concurrently by records of rainfall, lateral rain- and steam-interception and desiccating power. The substrates were examined for their soil moisture properties, temperatures, mineralogical properties and available plant nutrients. It was found that plants moved onto the crater floor within the first year. They progressed concentrically towards the crater center in correlation with a substrate-heat gradient that cooled progressively from the margin inward. Plant invasion on the cinder cone was delayed by 2 to 3 years, because of prolonged volcanic heating from below. X fast invasion took place on the spatter habitat where a surviving rain forest was nearby and where tree snags provided additional moisture locally at their base by intercepting wind-driven rains. Establishment - ii - at snag bases were also noted on the pumice, and generally, plant invasion occurred by aggregation of plants in favorable microhabitats which included crevices and tree molds. On the pumice, invasion progressed at a relatively uniform rate in spite of differences in substrate depth and atmospheric environment. The increase in plant cover was much faster on the habitats with vegetation remains than on those without. On the latter, the plant cover was still insignificant in year 9 after the eruption, in spite of a near total spread of plants across these habitats. The sequence of life form establishment on substrates without vegetation remnants was clearly algae first, then mosses and ferns, then lichens, then native woody seed plants and finally exotic woody and herbaceous seed plants. On the substrates with former vegetation remains, exotic seed plants participated in the invasion process from the beginning. This was related to the availability of microhabitats with water relations favorable for plants with normal root systems and probably higher water requirements than the native sclerophyllous woody plants, A remarkable recovery occurred among Metrosideros polynorpha trees that were buried up to and over 2.5 m deep under punice. Several native shrubs resprouted after their entire shoot system had been buried. The best herbaceous survivors were those with underground storage organs, which included both native and exotic species. The invad5-g exotics did in no way interfere with the establishment of the native pioneer plants. Initial stages of succession were observed whereby native woody plants began to replace exotic woody I - plants. Among herbaceous plants, exotic species were far more numerous, because there are only very few native species in this group. succession, in part caused by competitive replacement, was noted among the exotic herbaceous plants. Thus, there appears to be no threat of native plants to be replaced by exotics on these new volcanic substrates. The native forms are better adapted to these harsh environments. But exotic complementary life forms are expected to remain in association with the native vegetation because of a lack of life forms among the native species to fill the available niches. TABLE OF CONTENTS Page PREFACE ............................... i ABSTRACT .............................. ii LIST OF TABLES ........................... %x LIST OF ILLUSTRATIONS ........................ x INTRODUCTION ............................ 1 ANALYSIS OF PREVIOUS STUDIES .................... 3 StudiesinHawaii ....................... 3 Studies in other volcanic areas ................ 10 THE STUDY AREA ........................... 18 Geology ............................ 18 The December 1959 eruption ................... 20 Climate ............................ 21 The original vegetation .................... 23 The new volcanic habitats ................... 24 Habitat 1. Massive lava with joint cracks (56 ha) ....... 25 Habitat 2 . Cinder cone (19 ha) ................ 29 Habitat 3 . Spatter area with tree snags (6 ha) ........ 29 Habitat 4 . Pumice area with tree snags (31 ha) ........ 30 Habitat 5. Pumice area with surviving trees (125 ha) ..... 31 Habitat 6. Thin fallout area (263 ha) ............. 31 METHODS ............................... 32 Vegetationsampling ...................... 32 Environmental measurements ................... 34 Climate .......................... 34 Substrate ......................... 35 vi Page PLANT INVASION PATTERNS ....................... 37 Kilauea Iki lava lake (habitat 1) ............... 37 Progress of invasion ................... 37 Community formation .................... 41 Densification of colonization ............... 43 The cinder cone (habitat 2) .................. 49 Arrival pattern in comparison to habitat 1 ........ 49 Number and kinds of species in comparison to habitat 1 . 50 Quantitative spread of species .............. 51 Spatter area with tree snags (habitat 3) ............ 54 Progress of invasion ................... 55 Floristic pattern in comparison to habitats land 2 .... 58 Succession ........................ 59 Pumice area with tree snags (habitat 4) ............ 61 Arrival pattern in comparison to habitats 1. 2 and 3 ... 62 Quantitative spread of species in comparison to habitat 2 . 65 Pumice area with surviving trees (habitat 5) .......... 65 Thin fallout area. upper Kau Desert (habitat 6) ........ 68 RECOVERY OF VEGETATION ....................... 69 Surviving species ....................... 69 Plant cover development .................... 76 Habitat 3 ......................... 78 Habitat 4 ......................... 80 Habitat 5 ......................... 84 Habitat 6 ......................... 90 ENVIRONMENTALCONDITIONS ...................... 97 vii Page Theclimatic gradient ...................... 97 Temperature and relative humidity ............. 97 Desiccating power. insolation and rainfall ......... 99 Mean rainfall and dry periods ............... 101 Substrate differences ...................... 104 Substrate temperature ...................104 Substrate moisture ..................... 107 Plant nutrients in soil and rain water ........... 109 Mineralogical properties .................. 112 DISCUSSION ..............................118 Factors related to directional invasion and recovery ...... 119 Substrate-heat gradient .................. 119 Nearness of seed source ..................121 Snag-density gradient ...................122 Ash-depth gradient .....................124 Factors related to differences in invasion rate .........128 Substrate cooling. disseminule supply and life form .... 129 Availability of microhabitats ............... 131 Climaticgradient ..................... 135 Probable reasons for observed life form establishment sequences . 136 Factors influencing plant survival ............... 142 Depth and nature of pyroclastic deposit .......... 142 Size of plant .......................142 Vegetative regrowth capacity ................ 143 Primary community formation ...................144 Plant aggregation ..................... 144 viii Page Complementation and competition .............. 146 Relationship between native and exotic invaders ........ 147 ACKNOWLEDGMENTS ........................... 149 LITERATURE C ITED APPEND IX 1. Species frequency (%) of invaders during years following eruption in habitat 1 .............. 156 2. Species frequency (%) of invaders during years following eruption in habitat 2 (cinder cone) ....... 158 3. Species frequency (%) of invaders during years following eruption in habitat 3 (spatter area with snags) ...... 160 4. Species frequency (%) of invaders during years following eruption in habitat 4 (pumice area with snags) ....... 164 5. Species frequency (%) of invaders during years following eruption in habitat 5 (pumice area with survivingtrees) ................... 166 6. Species frequency (%) of invaders during years following eruption in habitat 6 (thin fallout area, Upper Kau Desert) .................. 168 7. Explanation of symbols used on life form diagrams (FIG. 8, 10, 11, 16) ............... 170 ix LIST OF TABLES TABLE Page 1 Progression of plant life from crater floor edge towards center in habitat