Dry Forest Species Research Articles

Why the Yungas Tody-Tyrant (Hemitriccus spodiops) Is a Snethlagea, and Why It Matters

Recognition of biogeographical patterns depends on accurate knowledge of phylogenetic relationships. In tropical South America, where species richness is very high, but knowledge of relationships is rudimentary, numerous biogeographic patterns await discovery. Work to date has focused mostly on patterns in lowland Amazonia (see Haffer 1993 and references therein), although a few other patterns have been identified, such as the circum-Amazonian pattern (Remsen et al. 1991), Andean leapfrog pattern (Remsen 1984), and a variety of patterns associated with dry forest species (Willis 1992). With few exceptions (e.g. Cracraft and Prum 1988, Hackett 1993), pattern recognition has not been based on explicit phylogenies, but has made use of uncontroversial monophyletic taxa, such as single polytypic species, obvious species pairs, or allospecies groups. As knowledge of distributions and systematics of South American birds improves, we can expect new patterns to appear and old ones to be revised. Here, I present evidence from external morphology and voice that Hemitriccus spodiops (Yungas Tody-Tyrant) and lowland Amazonian H. minor (Snethlage's Tody-Tyrant) are sister taxa, and that both species equally and exclusively meet criteria for membership in the subgenus Snethlagea. This contradicts earlier views of relationships of H. spodiops and suggests a novel biogeographic link between the Amazonian lowlands and adjacent Andean foothills that is supported by several other presumed sister-species pairs. Hemitriccus spodiops is a tiny flycatcher endemic to Bolivia, known only from the lower montane moist forests (yungas) of the eastern slope of the Andes between 800 and 1,600 m. Published data on its natural history are limited to two brief species accounts (Remsen et al. 1982, Parker et al. 1991), and its taxonomic history also is relatively brief and straightforward. After its original description as Euscarthmus spodiops (Berlepsch 1901), it has been placed in a sequence of genera (Euscarthmornis, Idioptilon, and finally Hemitriccus; see Lanyon 1988b). These nomenclatural changes, however, apply to tody-tyrants in general and do not reflect any change in thinking about the position of spodiops within this group. Three authors have addressed the phylogenetic relationships of H. spodiops within the tody-tyrants. In

Phenology and flowering periodicity of Neotropical dry forest species: evidence from herbarium collections

ABSTRACTTo examine the potential contribution of herbarium material to the description and analysis of tropical tree phenology, flowering times and geographical distribution were graphed for 1673 flowering collections from 18 species native to Neotropical dry forests and phenological differences between species were analysed. These include the timing and duration of flowering as well as morphological differences such as flowering on leafless twigsvsflowering on shoots bearing old or new foliage. Species-specific flowering periods of herbarium collections are similar to those observed in phenological field studies, but are often longer because of the larger geographical and temporal sampling range. Conspecific collections of different geographical origin show distinct differences in flowering periodicity, which are correlated with differences in the timing and intensity of the dry season. Interspecific differences in the timing of phenology relative to the dry season indicate differences in the control of phenology by seasonal drought. Herbaria thus represent a large potential source of phenological information which can either supplement and extend phenological field studies or provide phenological information for dry forest species not studied in the field but well represented in herbarium collections.

Soil seed banks in dry Afromontane forests of Ethiopia

Abstract. The soil seed bank was investigated in four dry Afromontane forests of Ethiopia. At least 167 plant species were identified in the 0–9 cm soil layer with total densities ranging between 12 300 and 24 000 seeds/m2. Herbs were represented with the largest numbers of species and seeds in the seed bank, while the contribution of tree species was generally low. The overall vertical distribution of seeds was similar at all sites with the highest densities occurring in the upper three cm of soil and gradually decreasing densities with increasing depth. Relatively high densities also occurred in the litter layer. There were large differences in depth distribution between species, suggesting differences in seed longevity. A large number of species in dry Afromontane forests evidently store quantities of seeds in the soil and this is in contrast to the situation in most tropical rain forests, dry lowland forests and savannas, where both the number of seeds and the number of species are relatively small. It is possible that the strongly seasonal and unpredictable climate of this region may have selected for high levels of dormancy, and that herb regeneration is associated with small scale disturbance. The fact that most of the dominant tree species do not accumulate seeds in the soil suggests that their regeneration from seed would be unlikely if mature individuals disappeared. Most tree species have relatively large seeds and poor long‐distance dispersal; this implies that restoration of Afromontane forests after destruction would be difficult. Since there is a diverse seed bank of the ground flora, this component of the vegetation would have a better chance of reestablishing. However, because most cleared forest land is used for agricultural crop production, it is probable that the seed bank will be depleted in only a few years. Therefore, the future of the Afromontane forest flora seems to depend on the successful conservation of the few fragments of remaining natural forest.

HABITOS ALIMENTARIOS DEL PECARI DE COLLAR {PECAR! TAJACU) EN UN BOSQUE TROPICAL CADUCIFOLIO DE JALISCO, MEXICO

Se determinaron los constituyentes principales y su variación en el Tiempo, de la dieta del pacari do collar [Pacari tajacu) en e! bosque tropical caducifolio de la Estación de Biología "Chamela", Jalisco, durante el período do mayo do 1992 a mayo de 1993. Para conocer la dieta de esta especie se analizaron los excrementos, clasificando los restos encontrados en: raíces, hojas-ramas, frutos y desconocido. Del análisis de 162 excretas se encontró que las componentes más abundantes fueron las raíces (47.9%) y las hojas-ramas (41.2%), luego los frutos (10.6%), el componente "desconocido" se encontró en menos del 1%, Los frutos más consumidos fueron; Opuntia excelsa, Ficus spp., Brosimum alicastrum, Sideroxylon capiri, Spondias purpurea, Vítex mollis y una leguminosa no identificada. A diferencia de otros sitios, en el área de estudio el pacari prácticamente no consume artrópodos. La proporción de cada componente en la dieta del pacari y su variación a lo largo del año, está relacionado con la variación estacional en la disponibilidad de los recursos vegetales en este bosque tropical. Consume un mayor porcentaje de hojas-ramas en la época húmeda y un mayor porcentaje de raíces durante la época seca. Los resultados de la dieta encontrados concuerdan con los obtenidos en otros bosques tropicales secos, excepto por los frutos los cuales se encontraron en menor proporción. Es recomendable evaluar el papel de esta especie como agente dispersor y depredador de algunas semillas de árboles y cactáceas.

Seed Ecology of Woody Species in a Caribbean Dry Forest

AbstractPeak flowering activity among woody species in the tropical dry forests of St. John, U.S. Virgin Islands, coincided with the brief spring rainy season but continued at moderate levels for six months, abating with the autumn rains. Fruit maturation showed a major peak in the long winter dry season and a minor crest during the summer dry season. Seeds of wind‐dispersed species disseminated mainly during the winter dry season, while animal dispersal of seeds (74% of all woody species) followed the bimodal pattern (for wet and dry seasons) described for the community as a whole. Under shadehouse conditions, most dry forest tree species germinated well (> 80%) and emerged promptly (within four weeks of planting) and synchronously (90% emergence within a four‐week interval). Nine of 29 species tested in the shadehouse manifested dormancy of at least six weeks. Seed germinability varied among tree species, and the viability of most species began to decline following six months of dry storage. Few species retained high germinability after nine months of dry storage. The species composition of soil seed banks did not correspond closely with above‐ground communities on three forested sites of varying stand age. In the youngest stand (35 years old), dominated by the weedy, arborescent legume Leucaena leucocephala, the soil seed bank was also dominated by this species, but no seeds of any other tree species were found in the soil samples. Seeds of native trees were scarcely encountered (only one indigenous species) in soil seed bank samples of three forest sites. Local seed rain from less disturbed forest may not be sufficient for prompt recovery of the dry forest community on degraded sites.

Soil and Stem Water Storage Determine Phenology and Distribution of Tropical Dry Forest Trees

Many trees of tropical dry forests flower or form new shoots soon after leaf shedding during the dry season, i.e., during a period when trees are likely to be severely water stressed. To resolve this apparent paradox, phenology and seasonal changes in tree water status was monitored during two consecutive dry seasons in >150 trees of 37 species growing at different sites in the tropical dry lowland forest of Guanascaste, Costa Rica. Tree development during the dry season varied considerably between species and between sites of different moisture availability. Leaf shedding, flowering, and shoot growth (flushing) were strongly correlated with seasonal changes in tree water status, measured by conventional and newly developed techniques. Tree water status varied with the availability of subsoil water and a variety of biotic factors such as structure and life—span of leaves, time of leaf shedding, wood density and capacity for stem water storage, and depth and density of root systems. Observed tree species differed widely in wood density (from 0.19 to 1.1. g/cm3) and stem water storage capacity (400—20% of dry mass), which was highly correlated with the degree of desiccation during drought. Only hardwood trees at dry upland sites, lacking stem water storage and access to subsoil water, desiccated strongly (stem water potential <—4 MPa) and remained inactive throughout the dry season. In all other trees elimination of transpirational water loss during leaf shedding in conjunction with utilization of residual water enabled rehydration of stem tissues and subsequent flowering or flushing during the dry season. Rate and degree of rehydration varied strongly with the availability of water stored in tree trunks or in the subsoil. Stored water buffers the impact of seasonal drought and enables flowering and flushing during the dry season. Climatic data thus not sufficient to explain tree phenology in seasonally dry tropical forests. Phenology, seasonal changes in water status, and water storage capacity of tree species are highly correlated. Tree species cluster into a number of distinct functional types ranging from deciduous hardwood trees and water—storing lightwood trees in dry upland forests to evergreen light— and softwood trees confined to moist lowland sites. Seasonal variation in tree water status thus appears to be the principal determinant of both phenology and distribution of tree species in tropical dry forests.

Use of Plant-Derived Food Resources by Ants in the Dry Tropical Lowlands of Coastal Veracruz, Mexico

This research quantified the number of ant-plant associations mediated by liquid/energy food sources and the intensity of their use by ants. Thirty ant species and 102 plant species were related in 312 associations. The Leguminosae (23 species) was the family of plants most visited by ants. Camponotus planattus was the ant using the most plant species (72) as food source. Ant-plant specificity was very low. Food resources most used by ants were nectar from reproductive structures, homopteran honeydew, floral nectar, and extrafloral nectar. Extrafloral nectaries are associated with leaves and most species in tropical dry forests flush new leaves after the onset of the annual rainy season. Both ant-extrafloral nectar and ant-homopteran associations show a significant increase after the start of the rainy season, decreasing abruptly once the dry season begins. In contrast, associations between ants and both floral nectar and other reproductive structures reach their peak during the dry season. There is a significant negative ant-floral nectar and ant-homopteran relationship at any given season; this may reflect the use of alternative (dry season/wet season) resources (floral nectar/ honeydew) with similar nutritional value.

Establishment of two dry monsoon forest tree species on a fire‐protected monsoon forest‐savanna boundary, Cobourg Peninsula, northern Australia

Abstract A numerical classification of presence‐absence data of vascular plant species on a transect across a dry monsoon foresl‐Eucalyptus savanna boundary at Cobourg Peninsula was used to define savanna, ecotone or monsoon forest communities. The boundary was protected from fire. After 4 years no Aglaia rufa seedlings had established in 24 permanent quadrats (1 × 4 m) in the savanna while three Diospyros maritima seedlings established in these savanna quadrats. The number of established A. rufa seedlings in 26 ecotone quadrats fell by 50% to one individual, the number of D. maritima seedlings increased by 43% to a total of seven individuals. After 3 months significantly more transplanted D. maritima seedlings had died in the savanna than the monsoon forest, but survival of A. rufa was high, and not significantly different, in both communities. Seedlings from both species did not have significantly greater survival in the monsoon forest compared to the savanna, 42 months after transplantation.

Monsoon Forests in Northwestern Australia I. Vegetation Classification and the Environmental Control of Tree Species

An indirect gradient analysis was performed on woody species basal area data collected from 144 monsoon forests situated throughout northewestern Australia. In order to eliminate edge effects each monsoon forest was differentiated from surrounding vegetation by inspection of sorted lists of tree species recorded from quadrats $(10 \times 20 m)$ placed on a transect that traversed each forest boundary. On each transect the monsoon forest quadrats were amalgamated to yield a single averaged sample of tree species basal area and environmental characteristics to represent each fo the 144 sampled forests. Surface soil physical and chemical characteristics were related to compositional patterns of tree species abundance data in one-, two-and three-dimensional Hybrid Multi-dimensional Scaling ordination solutions. The unidimensional ordination recovered a major environmental gradient where dry fertile soils, often on rocky slopes occur at one extreme and infertile waterlogged soils charcterize the other. Mean basal area of the fifty species with the highest importance values showed a continuously varying sequence of unimodal curves over the unidimensional ordination axis, although individual species distribution and abundance showed considerable variation on the gradient. Forest biomass, as measured by mean canopy height and mean total basal area, increased linearly over the gradient. With the exception of the dry extreme, stem density was relatively uniform across the gradient. Both the wet and dry extremes of the gradient have lower species richness per $200 m^2$ and fewer species with peaks of abundance. There appears to be a relatively sharp environmental and physiognomic discontinuity along the gradient as indicated by surface soil moisture content, and the cover of ferns and palm regeneration. This beak is consistent with a primary dichotomy of wet and dry forest formations as derived by other floristic and structural classifications of this vegetation. Of the common tree species (149), 53% of the dry forest species (125) only occurred in that community, while 29% of the wet forest species (83) were restricted to the wet forest.

Cost-Benefit Relationships in Deciduous and Evergreen Leaves of Tropical Dry Forest Species

Evidence from previous studies relates the significance of evergreeness and deciduousness to differences in leaf drought resistance and nutrient-use characteristics. Considering possible differences in leaf construction costs and lifespans in both plant types, I hypothesized that they should have contrasting strategies underlying their nitrogen-use efficiency (NUE) and water-use efficiency (WUE). Thus, leaves of six deciduous and four evergreen species were analysed to compare their construction and maintenance costs, maximum CO2 assimilation capacity (Amax) and potential (instantaneous) NUE and WUE. Leaf construction and maintenance costs were always higher in evergreen than in deciduous species. The largest Amax were recorded in some deciduous species. However, another deciduous species had Amax comparable to evergreen leaves. Therefore, a clear-cut difference between deciduous and evergreen leaves was not detected. However, NUE and WUE related to construction cost differences in the two plant groups. Indeed, NUE and WUE were largest in deciduous plants. Notwithstanding, overall carbon return per unit invested nitrogen may be increased in evergreens because leaves are photosynthetically active for longer periods. In fact, increases in the ratio between investment (construction cost) to potential payback (Amax) increase leaf life-spans (payback interval). Nevertheless, in tropical dry forests deciduous species are dominant and evergreen species are scarce. Carbon diversion to non-photosynthetic tissue (deep roots) and highest leaf cost may offset competitive capability of evergreen species. Key-words: Carbon assimilation, construction costs, deciduous, evergreen, maintenance cost, nitrogen-use efficiency, tropical dry forest, water-use efficiency

WOOD SPECIFIC GRAVITY GRADIENTS IN TROPICAL DRY AND MONTANE RAIN FOREST TREES

Pith to bark specific gravity (SG) trends were investigated in 18 tropical dry forest and six montane rain forest tree species of Costa Rica. Eleven dry forest species showed statistically significant increases in SG with distance from pith. The increases ranged from 20–80%; the greatest changes were exhibited by species which are known to occur in tropical wet as well as tropical dry forests. The other seven species showed no change in SG with distance from pith. Of the montane forest species, one showed a significant decrease of 20%, and three showed significant increases ranging from 20–40%. Two species exhibited no change in SG. Comparison of these changes with trends found in tropical wet forest and temperate forest suggests that the increase in SG with size is most common in tropical wet forest, least common in temperate forest, and intermediate in tropical dry and montane forests.

Contribution of Nontrees to Species Richness of a Tropical Rain Forest

Contribution of Nontrees to Species Richness of a Tropical Rain Forest

Leafcutting Ant Diet Selection: The Role of Nutrients, Water, and Secondary Chemistry

The relationship of plant secondary chemistry, water content, and nutrient content to the palatability of leaves to the leafcutting ant Atta cephalotes was determined in a study of individuals from 50 woody plant species in tropical dry forest of Costa Rica. The study took place during the yearly period of maximum leaf harvest, in the early rainy season. The palatability of plants was determined by presenting leaf disks to ants on active foraging trails of three ant colonies. The distribution of several classes of polar secondary compounds in leaf samples was determined using chemical spot tests, and that of ant—deterrent nonpolar compounds using laboratory bioassays of plant nonpolar extracts. Nitrogen, energy, and water availability in leaves were assessed using quantitative analyses. Plants of high relative palatability generally lacked deterrent nonpolar extracts but did contain hydrolyzable tannins; the opposite was true for plants of low palatability. Little or no relationship was found to exist between plant palatability and measures of leaf nitrogen, energy content, and moisture content, or the presence of alkaloids and condensed tannins in leaves. No statistically significant interactions among leaf characteristics were found. The number of leaf disks harvested by ant colonies decreased during the study period. This decrease was unrelated to nutrient and moisture availability in leaves, but may be related to changes in secondary chemistry over the course of the season. Although plants were not equally palatable to all colonies tested, there was no evidence that colony—to—colony differences in plant preferences were related to the plant characteristic studied. Overall, the results suggest that plant secondary chemistry is the best predictor of plant species utilization by leafcutting ants.

The Flammability and Energy Content of Some Important Plant Species and Fuel Components in the Forests of Southeastern Tasmania

Energy content and rate of flame front movement in various plant species and fuel components from the forests of southeastern Tasmania exhibited a range in values, and responses. Eucalypt dry forest species and fuel components showed the highest energy content and the greatest tendency to propagate fire whereas species from wet sclerophyll and gully habitats and Casuarina dry forest communities propagated fire less readily. Species from dry habitats have, in general, low ash contents, high energy levels, high volatile oil contents and low moisture contents. Wet habitat species have high percentages of moisture and ash. General support is given to the hypothesis that natural selection has favoured flammable characteristics in fire-dependent plant communities.

Flower Defenses Against Nectar-Pilferage by Ants

ro determine palatability, floral nectars from 25, and floral tissue extracts from 17, plant species of wet and dry forests of Costa Rica were offered to foraging ants in pairwise tests with sugar solutions. Nectars from all 25, and floral tissues from 10, species were analyzed chemically to ascertain the presence of potentially attractive and deterrent substances. In general, floral nectars are palatable to ants, whereas floral tissues showed highly variable palatability. We observed ants foraging in flowers of only 10 species of plants. Defense from nectar thievery by chewing insects seems most often to involve varying degrees of chemical and morphological modification of floral parts, rather than by the production of deterrent compounds in the nectar itself. FLOWERS THAT OFFER NECTAR as a primary reward to pollinators are common in the tropics. Nectar is generally nutritious and energy-rich, and pollination and seed set regularly occur as a result of the nectargathering activities by a wide array of animals, including many hymenoptera. Ants, however, are only rarely considered reliable pollinators (Kerner von Marilaun 1878, Proctor and Yeo 1972, Hickman 1974, Faegri and van der Pijl 1979), even though they are extremely abundant in a wide variety of habitats and are notorious for their skill in locating even small amounts of sugar. It is surprising that observations in the tropics reveal ants foraging for nectar in flowers only occasionally (van der Pijl

Comparative Phenological Studies of Treelet and Shrub Species in Tropical Wet and Dry Forests in the Lowlands of Costa Rica

SUMMARY (1) During 1970-73, marked individuals of 154 treelet and shrub species at a Wet forest site and 95 species at a Dry forest site in Costa Rica were observed regularly at 4- to 6-week intervals for changes in leafing, flowering and fruiting. (2) All the shrubs in the Wet forest were evergreen. New leaves were produced continually throughout the year by half the species, although this behaviour was more pronounced in species of secondary forest (87%0). For the community as a whole, leaf production was equable throughout the year. (3) About half of the treelets and shrubs in the Dry forest were deciduous. Hill forest treelets and shrubs produced most leaves at the beginning of the wet season, Riparian forest treelets and shrubs had a peak in leaf production near the end of the wet season, and leafing of species of secondary forest was continuous throughout the wet season. Most treelets and shrubs were bare or dormant during the dry season. Leaf loss was greatest during February. (4) There were no consistent peaks of flowering for treelet and shrub species in the Wet forest, but flowering levels tended to be greatest in the first half of each year. (4) Continuous flowering was rare among Wet forest treelets and shrubs, being characteristic of only a few species of secondary forest. Most Wet forest treelets and shrubs (64%) had several flowering episodes each year, with the episodes separated by 3-5-month intervals. Species with only a single brief synchronous flowering period were rare. (6) By contrast, flowering amongst Dry forest treelets and shrubs showed a pronounced seasonal pattern. The Hill forest treelet and shrub community had a sharp peak of flowering at the beginning of the wet season, while, in contrast, the Riparian forest treelet and shrub community had its major flowering at the end of the wet season. Most Dry forest species flowered synchronously once or twice each year. (7) There was a weak tendency for maximum fruiting of Wet forest shrubs in the second half of each year. A short period of fruit maturation (4 months) was shown by most Wet forest treelets and shrubs, although one species had a fruit maturation time of 27 months. Ten species of Wet forest treelets and shrubs flowered at least once during the study, but failed to produce fruit.

Herbivore Pressure on Two Types of Tropical Forests

The herbivore pressure on the understory of two types of Costa Rican forest was measured and compared during the dry season. Leaves were collected from plants, classified as old and new and categorized according to the amount of herbivore damage present. There was no significant difference between the number of new leaves being produced in the understory of each forest. There was a significant difference in the number of individual plants producing new leaves in each forest-a large number of riparian plants produced a small number of new leaves, and a small number of the dry forest plants produced a large number of new leaves. Old leaves from the riparian forest had sustained significantly less damage than old dry forest leaves. Old leaves from both forests showed significantly more damage than young leaves. These results are discussed in terms of two strategies. Because of year-long predation by insects, it was reasoned that the riparian forest species should spend more energy producing insect-resistant leaves; dry forest species should spend less energy producing insect-resistant foliage because they lose their leaves annually. THE GUANACASTE LOWLANDS of Costa Rica are characterized by high average temperature, low rainfall and an extended dry season from November to April. The vegetation is described as tropical dry forest (Holdridge 1964). During the dry season almost all canopy and understory trees drop their leaves, but riparian forests remain much greener. The riparian plants are not forced into deciduousness by the drought, and the leaves are probably longer-lived than those of the dry forest. Riparian forests also have a higher insect density than do the dry forests during the dry season, because the streambeds provide a refuge for insects escaping from the drought (Janzen and Schoener 1968; Janzen 1973a,b). As a consequence herbivore pressure could be very intense in the riparian forest during the dry season. I reasoned that since dry forest plants have leaves with a shorter half-life, they might be less likely than riparian forest plants to evolve leaves rich with substances rendering them more highly resistant to herbivores. If this strategy is operating, then leaves from riparian forests should show significantly less damage per unit time than leaves from dry forests. Two hypotheses were advanced. First, old leaves from the dry forest should show significantly more damage than leaves from the riparian forest. Second, young leaves from both forests should show comparable degrees of damage, since there is some evidence that it takes time for toxic compounds to build up in the leaves (Feeny 1970). This paper reports on the testing of these two hypotheses.

Passive sonar processing for noise with unknown covariance structure

The piedmont dry forest of northwestern Argentina has been under intensive and unplanned forest logging focused on 12 tree species, without any attempts having been made to ensure their regeneration or long-term conservation. In this study, we assessed the conservation status of these timber species in the piedmont dry forest of northwestern Argentina and compared our results with the IUCN assessment. We considered an inadequate conservation status if the species: (1) occurred in less than 50 % of the sampled plots, (2) had a density of large trees (more than 40 cm DBH) lower than one in. ha−1, or (3) had a density of saplings (more than 30 cm in height and less than 9.9 cm in DBH) lower than 30 in. ha−1. Our results showed an inadequate conservation status for eight of the 12 studied timber tree species. Additionally, only seven species were previously assessed and categorized on the IUCN Red List, with our categorization agreeing with only four of them. The data provided in this work can serve as a baseline to monitor the population trends of these species; information can also help to prioritize conservation efforts, which is essential considering the high number of tree species that have potential extinction risk in the short-term.

Composition of Certain Native Dry Forests: Mokuleia, Oahu, T.H.

The richness in tree species of Hawaiian dry forests has attracted the attention of many botanists. Rock (1913) thought it possible to collect more species in dry forests in single day than in a week or two in the rainforests. Selling (1948) stated: More than half of the many species of trees in these islands belong to this dry He thought, however, that dry forests had mostly disappeared from Oahu, Kauai, Molokai, and West Maui, and that only scattered remnants remained elsewhere. The recent studies of Hosaka (1937) and Egler (1939, 1942, 1947) tended to support this view. Nevertheless, scattered references to botanical bananzas in remote areas of Oahu exist in the literature. Thus Judd (1931) reported: An interesting mine of 42 different species of Hawaiian trees was discovered in small gulch in Makua Valley, on Oahu. His mention of Mehamehame (Drypetes phyllanthoides (Rock) Sherff) and Kalamona (Cassia gaudichaudii Hook. & Arn.) trees leaves little doubt that he was dealing with dry forest. In the spring and summer of 1950 the writer accompanied Miss Amy Greenwell, of Captain Cook, Hawaii, and Mr. Otto Degener, of Waialua, Oahu, on several plant-collecting excursions in the Mokuleia region of Oahu, during which many forests rich in reputedly rare, dryland tree species were discovered. The purpose of this paper is to describe certain of these seasonal forests and to mention certain features of the autecology of the more noteworthy species, for it is my opinion that, in addition to the intrinsic interest of these plants, they may have considerable potential importance in the management of Hawaiian watersheds.