Donald R. Drake

Relationships among the seed rain, seed bank and vegetation of a Hawaiian forest

. Hawaiian ecosystems are prone to invasion by alien plant species. I compared the seed rain, seed bank, and vegetation of a native Hawaiian forest to examine the potential role that seed ecology plays in allowing alien species to invade native forest. Absolute cover of seed plants in the forest was 126 %, annual seed rain was 5 713 seeds m-2 yr-1, and the mean density of seedlings emerging from the seed bank averaged across four seasons was 1 020/m2. The endemic tree Metrosideros polymorpha was the most abundant species in the vegetation, seed rain and winter seed bank. Overall, native seed plants comprised 95 % of the relative cover in the vegetation and 99 % of the seeds in the seed rain, but alien species comprised 67 % of the seeds in the seed bank. Alien species tended to form persistent seed banks while native species formed transient or pseudo-persistent seed banks. Dominance of the seed bank by alien species with persistent seed banks suggests that aliens are favorably placed to increase in abundance in the vegetation if the forest is disturbed.

Are introduced rats (Rattus rattus) both seed predators and dispersers in Hawaii

Invasive rodents are among the most ubiquitous and problematic species introduced to islands; more than 80% of the world’s island groups have been invaded. Introduced rats (black rat, Rattus rattus; Norway rat, R. norvegicus; Pacific rat, R. exulans) are well known as seed predators but are often overlooked as potential seed dispersers despite their common habit of transporting fruits and seeds prior to consumption. The relative likelihood of seed predation and dispersal by the black rat, which is the most common rat in Hawaiian forest, was tested with field and laboratory experiments. In the field, fruits of eight native and four non-native common woody plant species were arranged individually on the forest floor in four treatments that excluded vertebrates of different sizes. Eleven species had a portion (3–100%) of their fruits removed from vertebrate-accessible treatments, and automated cameras photographed only black rats removing fruit. In the laboratory, black rats were offered fruits of all 12 species to assess consumption and seed fate. Seeds of two species (non-native Clidemia hirta and native Kadua affinis) passed intact through the digestive tracts of rats. Most of the remaining larger-seeded species had their seeds chewed and destroyed, but for several of these, some partly damaged or undamaged seeds survived rat exposure. The combined field and laboratory findings indicate that many interactions between black rats and seeds of native and non-native plants may result in dispersal. Rats are likely to be affecting plant communities through both seed predation and dispersal.

Potential contributions of the seed rain and seed bank to regeneration of native forest under plantation pine in New Zealand

The seed rain, seed bank, and vegetatio n were studied in a Pinus radiata plantation destined for restoration to native forest, in order to gain in - formation on the vegetation dynamics and potential future vegetation composition of this forest. A total of 1812 ± 245 seeds m-2from 34 species fell in the seed rain between October 1996 and May 1997 . The seed bank had a density of 8841 ± 1157 seeds m 2 , and contained at least 45 species. Alien species con- tributed 2% of the seedlings and saplings, 6% of th e adults, 9% of the seed rain, and 30% of the see d bank, and accounted for 28 of the 69 species identi- fied in this study. As long as disturbance to the for- est is minimal, native species can be expected t o dominate regeneration. However, only 30 species o f seed plants were present as seedlings, saplings, o r adults, and several late-successional native specie s have become locally extinct . The seed rain is a po- tential source of recruits for these species (12 of the 34 species found in the seed rain were not presen t in the vegetation), but some species will need to be actively reintroduced if the forest is to be returne d to its pre-human condition .

Fate of a wet montane forest during soil ageing in Hawaii

KANEHIRO KITAYAMA*, EDWARD A.G. SCHUURt, DONALD R. DRAKE: and DIETER MUELLER-DOMBOIS? *The Japanese Forestry and Forest Products Research Institute, PO Box 16, Tsukuba Norin Kenkyu Danchi, Ibaraki 305, Japan, tEcosystem Sciences Division, University of California at Berkeley, Berkeley, California 94720, USA, tSchool of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand, and ?Department of Botany, University of Hawaii, 3190 Maile Way no. 101, Honolulu, Hawaii 96822, USA

Influence of vegetation structure on spatial patterns of seed deposition by birds

Abstract The bird‐disseminated species in the seed rain and the soil seed bank were sampled on Mana Island, New Zealand, to assess the importance of communally roosting starlings (Sturnus vulgaris) as seed dispersers. Density and species composition of dispersed seeds were compared between forested sites and grassland, representing potential perch sites and non‐perch sites, respectively, to determine the influence of vegetation structure on deposition patterns of bird‐dispersed seeds. Mean density of bird‐dispersed seeds falling in forest was 3742 ±914 seeds m‐2 compared with 7.7 ± 1.0 seeds m‐2 in grassland. This enormous disparity was reflected in the seed bank, with mean densities of 86 852 ± 16 579 and 883 ± 189 seeds m‐2 for forest and grassland sites, respectively. Species richness in forest ranged from 3 to 23 species 0.25 m‐2 for the seed rain, and from 1 to 19 species 0.002 m‐2 for the seed bank. Relative abundance of most species differed between the seed rain and seed bank. The seed rain was do...

Invasive rodents on islands: integrating historical and contemporary ecology

The colonization of islands by humans dramaticallytransformed environments, initiating extinctions,extirpations, and a complex array of ecosystemchanges (e.g. Kirch 1997; Grayson 2001; Anderson2008; Athens et al. 2002; McConkey and Drake2002; Steadman 2006; Kennett et al. 2006).Researchers in historical ecology have describedthese human-induced transformations as conse-quences of forest clearing, fire, and the introductionand establishment of a portmanteau biota (Crosby2004). Rodents (especially the rats Rattus exulans, R.rattus, and R. norvegicus) may have been the mostwidely introduced vertebrates to accompany humansin our history of global dispersal. Indeed, one couldargue that rats (Rattus spp.) are the original invasive‘‘species’’—from the colonization of the PacificIslands to the global expansion of Europeans. Eco-logical, palaeoecological, and archaeological studieshave documented the direct and indirect impacts ofrodents on native plants and animals, and implicatedthem in transforming many island environments (e.g.Atkinson 1985; Diamond 1985; Athens et al. 2002;Steadman 2006; Towns et al. 2006; Hunt 2007; Joneset al. 2008). However, in some cases, effectsattributed to rodents are based on circumstantialevidence, and a better understanding of the roleplayed by rodents awaits integration of historical andcontemporary ecology. Today, the integration ofthese fields has become increasingly important,because invasions and threats of extinction continue,and because ecological restoration of islands fre-quently depends on understanding rodent ecology inorder to predict the consequences of their removal(Towns and Broome 2003; Caut et al. 2007).Based on the dramatic ecological impactsobserved in contemporary field studies, ecologistshave typically adopted a default hypothesis thatinvasive rats must have had strong impacts in the past(see critical review by Towns et al. 2006). In contrast,archaeologists and palaeoecologists have, untilrecently, viewed human-induced impacts on islandecosystems largely as consequences of forest clearingand fire. Focusing on such direct human activities,these researchers have been reluctant to attributemajor impacts to the direct or indirect effects of rats.For us this contrast came into focus when StephenAthens (Athens et al. 2002; see Athens 2008)reported findings from his integrated palaeoecologi-cal and archaeological research on the Ewa Plain ofOahu, Hawaiian Islands. Athens, an archaeologist,showed with a detailed palaeoenvironmental andarchaeological record that rats (R. exulans) intro-duced by Polynesians to the Hawaiian Islands some1,000 years ago likely had a catastrophic impact on

Husking stations provide evidence of seed predation by introduced rodents in Tongan rain forests

Abstract The islands of Tonga, in Western Polynesia, lacked rodents prior to human colonization. During the past 3000 years, people have introduced three species of rats ( Rattus ). Seed predation by rodents structures plant communities in many parts of the world. Therefore, there is the potential for rats to have a significant impact on the regeneration of plant communities in Tonga. We found 53 husking stations—sheltered sites used by rats to strip inedible protective structures (husks) from the seeds they eat—on eight islands in Tonga. The stations contained 13,555 empty husks from at least 18 plant species, but only 165 viable seeds and seedlings. These husking stations provide evidence of seed predation by rats. Determining the extent to which seed predation threatens plant regeneration will be important for conservation of native forest remnants.

Seed dispersal by Pacific Pigeons (Ducula pacifica) in Tonga, Western Polynesia

Abstract Owing to extensive prehistoric extinctions of large frugivores, Pacific Pigeons (Ducula pacifica) are thought to be one of the most important seed dispersers of large-seeded plants in Tonga, yet little is known about their interactions with their food plants. We reviewed their known food plants and recorded defaecations, regurgitations, and movement patterns of this species over 11 months in Tonga. The fruit of at least 38 native plant species and the leaf buds of one species are eaten by Pacific Pigeons in Tonga. Most defaecations and all regurgitations contained a single seed of a single species. Pigeons usually regurgitated seeds larger than 20 mm in diameter whereas smaller seeds were typically defaecated. On the basis of observed movement patterns in Tonga and retention times for Ducula, most seeds are probably dispersed away from fruiting trees (85% of regurgitated seeds, 99% of defaecated seeds), but within 50 m of the crown. Distances of more than 100 km are theoretically possible for defaecated seeds, although pigeon behaviour is likely to limit this maximum. Results from this study suggest Pacific Pigeons are excellent seed dispersers in Tonga.

Environment, disturbance history and rain forest composition across the islands of Tonga, Western Polynesia

Abstract Questions: How do forest types differ in their distinctiveness among islands in relation to environmental and anthropogenic disturbance gradients? Are biogeographic factors also involved? Location: Tonga, ca. 170 oceanic islands totalling 700 km2 spread across 8° of latitude in Western Polynesia. Method: Relative basal area was analysed for 134 species of woody plants in 187 plots. We used clustering, indirect gradient analysis, and indicator species analysis to identify continuous and discontinuous variation in species composition across geographical, environmental and disturbance gradients. Partial DCA related environmental to compositional gradients for each major forest type after accounting for locality. CCA and partial CCA partitioned observed compositional variation into components explained by environment/disturbance, locality and covariation between them. Results: Differences among forest types are related to environment and degree of anthropogenic disturbance. After accounting for inter-island differences, compositional variation (1) in coastal forest types is related to substrate, steepness and proximity to coast; (2) in early-successional, lowland rain forest to proximity to the coast, steepness and cultivation disturbance; (3) in late-successional, lowland forest types to elevation. For coastal/littoral forests, most of the compositional variation (71%) is explained by disturbance and environmental variables that do not covary with island while for both early and late-successional forests there is a higher degree of compositional variation reflecting covariation between disturbance/environment and island. Conclusions: There are regional similarities, across islands, among littoral/coastal forest types dominated by widespread seawater-dispersed species. The early-successional species that dominate secondary forests are distributed broadly across islands and environmental gradients, consistent with the gradient-in-time model of succession. Among-island differences in early-successional forest may reflect differences in land-use practices rather than environmental differences or biogeographical history. In late-successional forests, variation in composition among islands can be partly explained by differences among islands and hypothesized tight links between species and environment. Disentangling the effects of anthropogenic disturbance history versus biogeographic history on late-successional forest in this region awaits further study. Abbreviations: GA = Group averaging; MRPP = Multi-response Permutation Procedure; NMS = Non-metric Multidimensional Scaling; pCCA = Partial CCA. Nomenclature: Smith (1979, 1981, 1985, 1988, 1991); for species not treated by Smith: Yuncker (1959), Whistler (1991), Wagner et al. (1999).

Post‐dispersal seed predation on eleven large‐seeded species from the New Zealand flora: A preliminary study in secondary forest

Abstract Seed predation trials were conducted for 11 large‐seeded species native to New Zealand in secondary forest. The species used were: Alectryon excelsus, Beilschmiedia tawa, Coprosma grandifolia, Corynocarpus laevigatus, Hedycarya arborea, Myoporum laetum, Nestegis cunninghamii, Prumnopitys ferruginea, Prumnopitys taxifolia, Rhopalostylis sapida, and Ripogonum scandens. Seed removal was monitored for 15 days for 160 seeds of each species, placed in piles of 5 seeds in each of 4 treatments at each of 8 sites in the Karori Wildlife Sanctuary, Wellington, in 1998. Removal of depulped seeds from treatments to which all species had access ranged from 3.8% to 23.8%, with a mean of 9.8%. No seeds were removed from the treatment that excluded all vertebrates. Presence of flesh on the seeds significantly increased seed removal rates in the three species tested with and without flesh. No relationship was found between seed removal and seed size, seed mass, or the proportion of the seed mass that was contribut...