A Model to Assess Restoration of Abandoned Pasture in Costa Rica Based on Soil Hydrologic Features and Forest Structure

An ecological functional assessment (EFA) was used on 10 southwest Costa Rica sites representing a chronosequence of formerly pastured lands to undisturbed tropical wet forest. Ecological functional assessment is a tool designed to assess wetland functions in the United States that was adapted to upland forests. Models to indicate characteristic soil hydrologic features and soil structure and aboveground spatial structure of habitat were used to examine the degree to which selected sites within the chronosequence approach the undisturbed condition of the natural forest. An index of the functional model for the maintenance of characteristic soil hydrologic features (such as infiltration, bulk density, etc.) showed that the 20‐year‐old secondary forest was at approximately 60% of the condition of the undisturbed sites, whereas active pasture was evaluated at approximately 20% of the reference undisturbed forest; 4‐ and 10‐year‐old sites were intermediate. The spatial structure of habitat model showed that 20‐year‐old secondary forest was approximately 50% of reference forest, whereas active pasture was approximately 10% of the condition of undisturbed forest; 4‐year‐old sites were evaluated at approximately 20% and 10‐year‐old sites at approximately 60% of the reference state. Overall the functional assessment process indicated that degraded tropical wet forest sites have recovered almost 60% of their functional qualities 10 years following pasture abandonment. These results indicate that EFA can be a useful technique for monitoring restoration programs in the tropics.     

Avian Habitat Preference in Tropical Forest Restoration in Southern Costa Rica

An important question for tropical forest restoration is whether degraded lands can be actively managed to attract birds. We censused birds and measured vegetation structure at 27 stations in young (6–9‐yr old) actively and passively restored pasture and old growth forest at Las Cruces Biological Station in southern Costa Rica. During 481 10‐min point counts, we detected a high diversity—186 species—of birds using the restoration area. Surprisingly, species richness and detection frequency did not differ among habitats, and proportional similarity of bird assemblages to old growth forest did not differ between restoration treatments. Bird detection frequency was instead explained by exotic grass cover and understory stem density—vegetation structures that were not strongly impacted by active restoration. The similarity of bird assemblages in actively and passively restored forest may be attributed to differential habitat preferences within and among feeding guilds, low structural contrast between treatments, or the effect of nucleation from actively restored plots into passively restored areas. Rapid recovery of vegetation in this recently restored site is likely due to its proximity to old growth forest and the lack of barriers to effective seed dispersal. Previous restoration studies in highly binary environments (i.e., open pasture vs. tree plantation) have found strong differences in bird abundance and richness. Our data contradict this trend, and suggest that tropical restoration ecologists should carefully consider: (1) when the benefits of active restoration outweigh the cost of implementation; and (2) which avian guilds should be used to measure restoration success given differential responses to habitat structure.     

Seed Availability as a Limiting Factor in Forest Recovery Processes in Costa Rica

Abandoned pastures and secondary forests are increasingly prominent features of tropical landscapes. Forest regrowth on abandoned pastures is generally slow and virtually limited to regeneration from seeds from external sources, since agricultural activities alter site conditions. We hypothesize that seed availability is a major limiting factor in forest recovery on abandoned pastures. This hypothesis was tested by studying the seed bank, seed rain, and seed predation in a small pasture (1 ha) situated in a forest‐pasture mosaic in northwestern Costa Rica. The tree seed density in the pasture seed bank was much lower (21/m²) than the density in the seed bank of a neighboring secondary forest (402/m²). Within a period of five weeks, 23 tree seeds entered the pasture by seed rain. This number is low compared to densities found in closed forests but higher than densities reported in other studies where virtually no seeds were found beyond 20 m from the forest edge. Possibly the small size of the pasture with seed sources nearby and the small‐scale landscape mosaic enhance seed dispersal. Predation limits the seed density in pastures, with 42% of the woody species consumed by predators. The low seed density in the seed bank, and hampered recruitment combined with significant losses, pose severe restrictions to forest recovery on abandoned pastures. Moderate land use, and small sized clearings with seed sources nearby may increase the pace of recovery. Nevertheless, forest establishment may still take a considerable time. Thus, enlarging the available pool of species may be a worthwhile management strategy.     

The Influence of Habitat Variables on Bird Communities in Forest Remnants in Costa Rica

This study examined the effects of forest structure (tree species richness, canopy height, percent canopy cover, understory density, tree density and DBH) and avian species traits (nest type and indicator list status) on the diversity, abundance and dissimilarity of bird communities in forest remnants and reforestation areas adjacent to Costa Rican banana plantations. Bird species richness and abundance were significantly related to tree species richness, canopy height and canopy cover in multiple linear regressions, the latter two forest structure variables being the best statistical predictors. Stratification of analyses by bird species indicator categories improved fits of regressions, because correlations with environmental variables differed in sign for different guilds of birds, a result likely to hold for other avifaunas. Analysis of avifauna dissimilarities among sites demonstrated that the species composition of bird communities was highly correlated with forest structure and tree species composition. Logistic regressions indicated that birds making protected (cavity, burrow, pendant, sphere and covered) nests were 2–6 times more likely to be present in the study avifauna than birds making open (cup, saucer, platform and scrape) nests and indicators of disturbed habitats were 11 times more likely to be present than indicators of primary forest. The forest structure data used were simple and inexpensive to collect, and data on avian traits were drawn from the literature. Thus, these methods could easily be replicated at other locations and would be valuable management aids and biodiversity assessment tools for conservation planning.     

Influence of Microclimate on the Occurrence of Cyanobacteria in the Phyllosphere in a Premontane Rain Forest of Costa Rica

Abstract: The occurrence of cyanobacteria in the phyllosphere of several understory plants was investigated during a one and a half year study in a primary premontane rain forest in Costa Rica. Altogether, seven species of epiphyllous cyanobacteria were identified and are discussed here. The ecology of the two most frequent species in the understory, Scytonema javanicum and Sc. hofmannii , was studied in further detail. Within the Understory, the relative abundance of these species, as well as of epiphyllous bryophytes, was more influenced by air humidity than by light. The humidity, characterized as potential evaporation, also had influence on the pseudosuccession of the phyllosphere vegetation. While at moist sites bryophytes and both species of Scytonema appeared nearly simultaneously on 6–9-month-old leaves, at dryer sites Sc. javanicum , and especially Sc. hofmannii , appeared 6–9 months after bryophytes had established. On 13–15-month-old leaves bryophytes and Scytoriema were usually well established. On average, 20–30% of the leaf area of 2–5-year old leaves of Spathacanthus hoffmannii (Acan-thaceae, an abundant understory shrub) were covered by bryophytes, 2–3% by Sc. javanicum , and 0.1–0.2% by Sc. hofmannhi . An influence of phorophyte species on the occurrence and abundance of these two species of Scytonema could not be detected. However, Sc. hofmannii was more frequent on leaves with higher bryophyte cover, while Sc. javanicum was independent from bryophytes. A comparison of leaves from the understory and from the canopy showed that the composition and abundance of cyanobacteria species changed with height above forest floor.     

Allometric Models for Tree Volume and Total Aboveground Biomass in a Tropical Humid Forest in Costa Rica1

Allometric equations for the estimation of tree volume and aboveground biomass in a tropical humid forest were developed based on direct measurements of 19 individuals of seven tree species in Northern Costa Rica. The volume and the biomass of the stems represented about two‐thirds of the total volume and total aboveground biomass, respectively. The average stem volume varied between 4 and 11 Mg/tree and the average total aboveground biomass ranged from 4 to 10 mg/tree. The mean specific gravity of the sampled trees was 0.62 ± 0.06 (g/cm³). The average biomass expansion factor was 1.6 ± 0.2. The best‐fit equations for stem and total volume were of logarithmic form, with diameter at breast height (R²= 0.66 ? 0.81) as an independent variable. The best‐fit equations for total aboveground biomass that were based on combinations of diameter at breast height, and total and commercial height as independent variables had R² values between 0.77 and 0.87. Models recommended for estimating total aboveground biomass are based on diameter at breast height, because the simplicity of these models is advantageous. This variable is easy to measure accurately in the field and is the most common variable recorded in forest inventories. Two widely used models in literature tend to underestimate aboveground biomass in large trees. In contrast, the models developed in this study accurately estimate the total aboveground biomass in these trees.     

Population structure and genetic diversity in four tropical tree species in Costa Rica

Despite intensified interest in conservation of tropical forests, knowledge of the population genetics of tropical forest trees remains limited. We used random amplified polymorphic DNA (RAPD) data to evaluate trends in genetic diversity and differentiation for four tropical tree species, Alchornea latifolia, Dendropanax arboreus, Inga thibaudiana and Protium glabrum . These species occur at contrasting population densities along an elevational gradient and we use RAPD and ecological data to examine natural levels of genetic diversity of each species, trends in genetic variability with population density and structure, genetic differentiation along the elevation gradient, and the relationship between genetic diversity and such factors as seed dispersal and pollination syndrome. At the distances we examined (plot distances ranging from 0.8 to 8.6 km) there was very little genetic structuring at any distance along the gradient. All four species exhibited levels of variation expected for spatial distribution, mating system and pollinator syndrome; greater than 96% of the genetic variation occurred within plots for Inga thibaudiana, Protium glabrum and Dendropanax arboreus. Alchornea latifolia only occurred in a single plot. The results of this study contribute to a growing database of genetic diversity data that can be utilized to make predictions about the effect of disturbance and subsequent reductions in population size on genetic variation and structure in tropical tree species.     

Reproductive Ecology of Understory Species in a Tropical Montane Forest in Costa Rica1

The reproductive ecology of nine hermaphroditic understory species in a tropical montane Quercus forest was studied at two sites (2300 and 2600 m elev.) in the Cordillera de Talamanca, Costa Rica. Flower life span, studied in six species, averaged 4.4 d. This is longer than flower life spans found in the Monteverde cloud forest (2.7 d) and comparable to flower life spans found for arctic and alpine species. We studied the breeding system in five species and found no self-incompatible species. Four species proved self-compatible, and three of these showed autogamy. The main diurnal insect pollinator was the bumblebee Bombus ephippiatus. Natural fruit set was low (8-32%) in six species with few seeds per fruit, while two many-seeded species showed a high rate of fruit set (90 and 96%). The incidence of pre–dispersal seed predation was high; the percentage of seeds infested in four species ranged from 8 to 56 percent.     

哥斯达黎加外海夏季表层浮游动物种类组成及分布

根据2009年7—8月在东热带太平洋哥斯达黎加外海(4°30’—10°24’N、91°20’—100°00’W)进行茎柔鱼探捕调查期间采集的表层浮游动物资料,对其种类组成、生物量及其分布进行了分析。结果表明,调查海域,鉴定出腔肠动物8目10科17属23种;甲壳动物8目30科43属74种;毛颚动物1目1科1属4种;尾索动物3目3科5属5种;环节动物为1目3科5属6种;软体动物1目1科3属3种;其他浮游动物有头足类的幼体、鱼卵和仔稚鱼以及浮游幼虫。调查海域总生物量和丰度的平均值分别为(124.78±176.83)mg/m3和(848±1219)个/m3,生物量较大的类群主要是甲壳动物的桡足类和毛颚动物的箭虫类其中桡足类的丰度(727个/m3)为最高,其次为箭虫类(373个/m3);出现频率较高的为桡足类、箭虫类、长尾类、头足类和鱼类仔稚鱼。     

Hypocrealean (Hypocreales,Ascomycota) Fungal Diversity in Different Stages of Tropical Forest Succession in Costa Rica1

The relationship between forest succession and microfungal diversity has been poorly studied. Fungi provide important ecosystem services that may deteriorate in deforested or highly disturbed forests. To determine the possible effects of deforestation and forest succession on microfungi, species diversity of hypocrealean fungi (Ascomycota) was compared in forest stands in Eastern Costa Rica representing three stages of succession: 1–2, 25–27 yr old, and an old growth forest. Species diversity in a second‐growth forest fragment surrounded by timber plantations and second‐growth forest was also compared to that of a stand surrounded by old growth forest. The results show that the overall diversity of hypocrealean fungi was inversely proportional to the age of the forest stand, and each family showed different successional trends. Clavicipitaceae was more diverse in the old‐growth forest and was positively related to the age of the forest stand. Nectriaceae was highly diverse in the 1‐ to 2‐yr‐old stand and less diverse in the old‐growth stand. Saprobic and plant pathogenic fungal species were more diverse in the 1‐ to 2‐yr‐old stand and their diversity was inversely proportional to the age of the forest stand. The diversity of insect pathogens was positively related to the age of the forest stand. The 20‐ to 22‐yr‐old forest fragment had the lowest number of species overall. Based on the data gathered in this study, hypocrealean fungal species diversity is related to the successional stage and fragmentation of tropical forest.     

Studies in Neotropical paleobotany. XII. A palynoflorafrom the Pliocene Rio Banano Formation of Costa Rica and the Neogenevegetation of Mesoamerica

An assemblage of 17 identified and four unknown pollen and sporetypes is reported from the Pliocene Rio Banano Formation of southeasternCosta Rica. The most abundant are monolete fern spores, Palmae, cf.Antrophyum, Symphonia, Pelliceria,Lacmella (previously unreported in the fossil record),Alchornea, and Sabicea. These arrange into twopaleocommunities-mangroves and lowland tropical rain forest. Annual precipitation is estimated at near the present ～3500 mm, butless seasonal, and the MAT (mean annual temperature) at ～27°C. No pollen taxa representing distinctly arid or high-altitude vegetationwas being blown or washed into the coastal depositional basin, and nopollen grains were recovered of northern temperate elements that arepresent in Neogene floras to the north in Guatemala and southeasternMexico. These data are consistent with those from 12 other Miocene andPliocene palynofloras from northern Latin America, indicating the lateappearance of dry habitats and moderate paleoelevations and aprogressive southward introduction of northern temperate elements withlate Cenozoic cooling.     

Tree community diversity of lowland swamp forest in Northeast Costa Rica, and changes associated with controlled selective logging

In the Atlantic lowlands of Northeast Costa Rica, logging occurs in tracts of poorly drained wet forest ('swamp forest'), yet little is known about factors affecting swamp forest diversity or the potential for biodiversity retention during harvest. This paper quantitatively describes the species composition and diversity of the swamp forest habitat, and reports the immediate impact of controlled, selective logging on tree community diversity. Pentaclethra macroloba (Leguminosae), Carapa nicaraguensis (Meliaceae) and Pterocarpus officinalis (Leguminosae) accounted for >70% of the primary swamp forest basal area. Nevertheless, 225 species from 53 families with individuals 10cm dbh were encountered in 16.4 ha; most species had very low abundances. Gamma diversity is a component of overall swamp forest diversity. Extraction of 49.2m3ha–1 (5.5 trees ha–1) of timber from a 4ha plot reduced species richness by 14, supporting assertions that random mortality during logging can affect the distribution of rare species. However, tree community diversity as measured by rarefaction was not greatly affected by selective logging. Total post-logging stem recruitment over a 3-year period was greater in logged plots than in undisturbed plots; the recruitment of the ruderal species Ochroma lagopus (Bombacaceae) was the most clearly affected by logging. Any localized dominance by this species will be limited in space and time in a carefully managed forest. The results suggest that controlled selective logging can be consistent with biodiversity conservation, and complement protected areas in Northeast Costa Rica.     

The occurrence of Frankia in tropical forest soils of Costa Rica

Infective and effective Frankia were shown to occur in five diverse tropical forest soils of Costa Rica. Results of a plant infection assay indicated that Frankia is a common component of the soil biota in low and high elevation, primary and secondary forest soils. This is the first report of Frankia in lowland tropical rainforests of the Americas. These results suggest either a nonsymbiotic population of soil Frankia, the presence of unknown actinorhizal host species, or an ability of Frankia to be dispersed over long distances.     

Ecology of Foliicolous Lichens at the “Botarrama” Trail (Costa Rica), a Neotropical Rain Forest. I. Species Composition and its Ecogeographical Implications1

A total of 217 species of typically foliicolous lichens were found at the “Botarrama” trail, a premontane rain forest in the Braulio Carrillo National Park, Costa Rica. The species composition confirmed the classification of this study sice as transitional between lowland wet and montane rain forest. In terms of species tichness, the foliicolous lichen flora was dominated by the families Gomphillaceae (Calenia, Echinoplaca, Gyalideopsis, and Tricharia), Trichotheliaceae (Porina and Tricbothelium), and Pilocarpaceae (Byssoloma and Fellhanera). The most frequent species were Porina mirabilis (including its supposed anamorph Phyllophiale alba), Gyalectidium filicinum, Porina rufula, and Strigula platypoda. A large proportion of the species was rare. Frequency distributions based on area cover corresponded well to general community models by closely fitting a log-normal approximation. Half of the species had narrow ecological amplitudes while more than 70 percent exhibited a wide geographical distribution, thus making che study site representative of a Neotropical rain forest. The use of foliicolous lichens as indicators of altitudinal zonation is discussed.     

Density, Distribution, and Attributes of Tree Cavities in an Old-Growth Tropical Rain Forest

Tree cavities are a critical resource for many animals, especially as nesting sites for birds. Patterns of cavity distribution in temperate forests are well studied, yet little is known of cavities in tropical forests, despite a hypothesized decrease in cavity availability with decreasing latitude. We studied cavity density and distribution in a wet lowland tropical forest in Costa Rica and compared our results with estimates from forests around the world. Cavities at our site were common, occurred frequently in living trees, and were often formed by damage or decay rather than by woodpeckers. Most cavities had small openings, and woodpecker-created cavities were nonrandomly oriented. Contrary to prediction, cavity density appears to increase from the poles to the tropics. We suggest potential mechanisms to explain these patterns.     

The soil C pool in different agroecosystems derived from the dry tropical forest of Guanacaste, Costa Rica

Inventories of soil C pools are still lacking from tropical sites. Our objective was to assess total C and N concentrations in the different mineral soil fractions down to 50 cm depth in relation to selected physical and chemical properties of 5 ecosystems at La Flor Sustainable Center in Guanacaste, Costa Rica. The ecosystems studied were a derived savanna with scattered trees, a gallery forest, an abandoned Mango indigofera L. plantation, a Citrus sp. plantation, and a Saccharum officinarum L. (sugarcane) plantation. Significant differences were found for the main fixed factor ecosystem for all variables analyzed (ANOVA). The TSC concentration was significantly higher in the sugarcane plantation compared to the rest of land use systems. The TSC concentration decreased significantly with increase in depth in all ecosystems and ranged from 20.3–38.3 to 4.3–20.9 g kg⁻¹ in the 0–10 and 40–50 cm depth, respectively. In all cases, the clay + silt fraction (<50 μm) contained the highest C concentration. N concentration (0–10 cm depth) at La Flor ranged from 0.32 to 0.19%, and decreased in the order sugarcane > Curatella savanna > Mango and Citrus plantations > gallery forest. A principal component analysis (PCA) performed with all variables studied showed that the ordination of land uses (ecosystems) in the factorial plane defined by the first two axes was significant (Monte Carlo permutation test, P < 0.0001). The highest TSC pool down to 50 cm depth was obtained in the sugarcane plantation (160 Mg C ha⁻¹) while less C was found in the rest of ecosystems, i.e. from 66 (gallery forest) to 80 Mg C ha⁻¹ (Curatella savanna). The TSC concentration obtained in the sugarcane plot is likely the result of the incorporation of surface residues into the soil that would have otherwise been lost through burning, which is the current practice in the region. Further studies on C stabilization in the clay fraction are thus needed to test the hypothesis of soil C enrichment due to residue management. Finally, trade-offs are to be considered for both preservation of the fragile dTf and the productivity of derived land uses that increases soil C at the same time.     

Species Richness,Spatial Variation,and Abundance of the Soil Seed Bank of a Secondary Tropical Rain Forest1

Despite the importance of the soil seed bank in tropical forest regeneration, little is known about spatial variability in species composition and abundance of seeds stored in the soil. To develop sampling methods for comparative studies, we examined species richness, spatial variation, and abundance of germinants from the soil seed bank in a 16 year old secondary, tropical wet forest at La Selva Biological Station, Costa Rica. Surface soil (10 cm deep, 4.7 cm diameter) was collected at the intersection points of a gridded 1 ha plot (10 × 10-m grid, 121 samples) and in a nested 100 m² subplot (2 × 2-m grid, 36 samples). The 1 ha plot had a density of 4535 seeds/m² with 34 species observed. Based on a series of 100 randomized species accumulation curves, a Michaelis-Menten fit predicted a mean species richness of 36.3 species; the number of observed species was close to the predicted asymptote. A nonparametric, first-order jackknife species richness estimator predicted a species richness of 37.0 species. Eighty-five and 95 percent of the observed species richness is contained, on average, within 41 and 74 pooled samples, respectively. Within the 100 m² nested subplot, a density of 5476 seeds/m² was observed, comprising 26 species with an estimated species richness (Michaelis-Menten fit) of 29.1 species. The jackknife species richness estimator predicted a species richness of 36.7 species. For species richness and abundance of both plots, spatial autocorrelation statistics (Moran's I) were not significantly different from zero at lag distances from 2 to 100 m, indicating a random distribution at these spatial scales. For this site, accurate estimates of species composition depend upon the number of samples collected as well as the spatial distribution of sampling effort. Many small samples distributed over a large area provide greater accuracy and precision for estimating species richness of the soil seed bank.