Microfungi from decaying leaves of two rain forest trees in Puerto Rico

Fungal species richness and abundance were compared in leaf litter of two tree species,Guarea guidonia andManilkara bidentata, in the Luquillo Mountains of Puerto Rico. Four litter samples yielded a total of 3337 isolates, ranging from 591 to 1259 isolates/sample. The number of species/sample ranged from 134 to 228. Many uncommon litter hyphomycetes were recovered as well as coelomycetes, sterile strains, endophytes, and phytopathogens. Species-abundance distributions revealed a typical pattern of a few abundant species and a high proportion of rare species. Similarities in fungal species composition were not correlated with host species or with the site. Replicate samples examined by the moist chamber technique yielded a total of 24 species among the four litter samples. The particle filtration method indicated that leaves ofG. guidonia were more species-rich, while moist chambers indicated leaves ofM. bidentata were more species-rich. The moist chamber technique underestimated the number and species of viable fungi.     

Ficus seed shadows in a Bornean rain forest

Due to their copious seed production and numerous dispersers, rain forest fig trees have been assumed to produce extensive and dense seed shadows. To test this idea, patterns of seed dispersal of two species of large hemiepiphytic fig tree were measured in a Bornean rain forest. The sample included four Ficus stupenda and three F. subtecta trees with crop sizes ranging from 2,000 to 40,000 figs (400,000 to 13,000,000 seeds). Seed rain out to a distance of 60 m from each study tree was quantified using arrays of seed traps deployed in the understory. These trees showed a strongly leptokurtic pattern of dispersal, as expected, but all individuals had measurable seed rain at 60 m, ranging from 0.2 to 5.0 seeds/m². A regression of In-transformed seed rain density against distance gave a significant fit to all seven trees' dispersal patterns, indicating that the data could be fitted to the negative exponential distribution most commonly fitted to seed shadows. However, for six of seven trees, an improved fit was obtained for regressions in which distance was also In-transformed. This transformation corresponds to an inverse power distribution, indicating that for vertebrate-dispersed Ficus seeds, the tail of the seed rain distribution does not drop off as rapidly as in the exponential distribution typically associated with wind dispersed seed shadows. Over 50% of the seed crop was estimated to fall below each fig tree's crown. Up to 22% of the seed crop was dispersed beyond the crown edge, but within 60 m of the tree. Estimates of the maximum numbers of seeds which could have been transported beyond 60 m were 45% for the two largest crops of figs, but were under 24% for the trees with smaller crops. Seed traps positioned where they had an upper canopy layer above them were associated with higher probabilities of being hit by seeds, suggesting that vertebrate dispersal agents are likely to perch or travel through forest layers at the same level as the fig crown and could concentrate seeds in such areas to some degree. The probability of a safe site at 60 m from the fig tree being hit by seeds is calculated to be on the order of 0.01 per fruiting episode. Fig trees do not appear to saturate safe sites with seeds despite their large seed crops. If we in addition consider the rarity of quality establishment sites and post-dispersal factors reducing successful seedling establishment, hemiepiphytic fig trees appear to face severe obstacles to seedling recruitment.     

Photosynthetic acclimation to light in juveniles of two cloud forest tree species

The photosynthetic response of juveniles of Decussocarpus rospigliosii, an emergent primary forest species and shade tolerant in its juvenile stages and Alchornea triplinervia, a gap-colonizing species of tropical cloud forest in Venezuela was studied. Daily courses of microenvironmental variables and gas exchange under contrasting light conditions (gap and understory) were carried out in their natural environment and transplanted to different light regimes (shade and sun) in the field. The photosynthetic response and some anatomical characteristics of plants from different treatments were analyzed in the laboratory. Photosynthetic rates were low for both species, and were negative during some diurnal periods, related to the low photosynthetically active radiation levels obtained at both gap (6% of total radiation) and understory (2%). A. triplinervia shows higher rates (1.5–3.0 molm^{-2 -1}) than D. rospigliosii (0.7–1.1 molm^-2s^-1). Both species showed increased photosynthetic rates when grown in gaps. A. triplinervia did not adjust its maximum photosynthetic rates to the prevailing light conditions. In contrast, D. rospigliosii responded to increased light levels. Both species showed low light compensation points when grown under total shade. There was a partial stomatal closure generally during midday in D. rospigliosii. A. triplinervia presented lower leaf conductances, transpiration rates and lesser stomatal control. Some leaf anatomical characteristics, in both species, were affected by variations in the light regime (i.e. increased leaf thickness, leaf specific weight and stomatal density). These results suggest that both species have the ability to respond to variations in their natural light environments, therefore maintaining a favorable carbon balance during the day.     

Leaf traits and photosynthetic parameters of saplings and adult trees of co-existing species in a temperate broad-leaved forest

In Central European forestry the establishment of broad-leaved mixed forests is attaining increasing importance, but little information exists about gas exchange characteristics of some of the tree species involved, which are less abundant today. In an old-growth forest in Central Germany (Hainich, Thuringia), (i) I compared morphological and chemical leaf traits that are indicative of leaf gas exchange characteristics among eight co-existing species, and (ii) analysed photosynthetic parameters of saplings and adult trees (lower and upper canopy level) in four of these species (Acer pseudoplatanus L., Carpinus betulus L., Fraxinus excelsior L. and Tilia platyphyllos Scop.).Leaves from the upper canopy in the eight species studied varied significantly in their specific leaf area (12.9–19.4 m² kg⁻¹), stomatal density (125–313 stomata mm⁻²), leaf nitrogen concentration (95–157 mmol N m⁻²) and δ¹³C content (–27.81 to –25.85‰). F. excelsior and C. betulus were largely contrasting species, which suggests that the species, which were studied in more detail, include the widest difference in leaf gas exchange among the co-existing species. The saplings of the four selected species exhibited shade acclimated leaves with net photosynthesis rates at saturating irradiance (A_max) between 5.0 and 6.4 μmol m⁻² s⁻¹. In adult trees A_max of fully sunlit leaves was more variable and ranged from 10.5 (C. betulus) to 16.3 μmol m⁻² s⁻¹ (F. excelsior). However, less negative δ¹³C values in F. excelsior sun leaves point to a strong limitation in gas exchange. In the lower canopy of adult trees A_max of F. excelsior (12.0 μmol m⁻² s⁻¹) was also greater than that of A. pseudoplatanus, C. betulus and T. platyphyllos (5.0–5.6 μmol m⁻² s⁻¹). This can be explained by the small leaf area and the absence of shade leaves in mature F. excelsior trees. Thus, a considerable variation in leaf traits and gas exchange was found among the co-existing tree species. The results suggest that species-specific characteristics increase the spatial heterogeneity of canopy gas exchange and should be taken into account in the interpretation and prediction of gas flux from mixed stands.In der Forstwirtschaft Mitteleuropas gewinnt die Begründung von Laubmischwäldern zunehmend an Bedeutung, aber über Eigenschaften im Gasaustausch einiger beteiligter Baumarten, die heute nicht so häufig sind, ist wenig bekannt. In einem Altbestand in Mitteldeutschland (Hainich, Thüringen) habe ich (i) morphologische und chemische Eigenschaften von Sonnenblättern, die Hinweise auf Charakteristika im Blattgaswechsel geben, an acht koexistierenden Baumarten untersucht, und (ii) Photosyntheseparameter von juvenilen und adulten Bäumen (unteres und oberes Kronenniveau) von vier dieser Arten (Acer pseudoplatanus L., Carpinus betulus L., Fraxinus excelsior L. and Tilia platyphyllos Scop.) erhoben.Blätter aus dem oberen Kronenraum der acht untersuchten Arten variierten signifikant in der spezifischen Blattfläche (12.9–19.4 m² kg⁻¹), der Stomatadichte (125–313 Stomata mm⁻²), dem Blattstickstoffgehalt (95–157 mmol N m⁻²) und den δ¹³C-Werten (–27.81 bis –25.85‰). In diesem Kollektiv zeigten F. excelsior und C. betulus groβe Unterschiede, was darauf hindeutet, dass die Arten, die genauer untersucht wurden, die Spannweite an Gaswechseleigenschaften unter den koexistierenden Baumarten umfassen. Die Jungpflanzen der vier ausgewählten Arten besaßen Schattenblätter, deren Netto-Photosyntheserate bei hoher Lichtintensität (A_max) zwischen 5.0 and 6.4 μmol m⁻² s⁻¹ variierte. An Sonnenblättern von Altbäumen war A_max variabler und lag zwischen 10.5 (C. betulus) und 16.3 μmol m⁻² s⁻¹ (F. excelsior). Allerdings weisen hohe δ¹³C-Werte in Sonnenblättern von F. excelsior auf eine starke Limitierung des Gasaustauschs hin. Auch in der unteren Krone der Altbäume war A_max von F. excelsior (12.0 μmol m⁻² s⁻¹) höher als A_max von A. pseudoplatanus, C. betulus und T. platyphyllos (5.0–5.6 μmol m⁻² s⁻¹). Dies kann durch die geringe Blattfläche und die Abwesenheit von Schattenblättern in der Krone adulter Bäume von F. excelsior erklärt werden. Zwischen den koexistierenden Baumarten wurde somit in Bezug auf Blatteigenschaften und Photosyntheseparameter eine erhebliche Variation festgestellt. Die Ergebnisse legen nahe, dass artspezifische Eigenschaften die räumliche Heterogenität des Gaswechsels im Kronenraum erhöhen und bei der Interpretation und Vorhersage von Gasflüssen über Mischbeständen berücksichtigt werden sollten.     

Growth responses to arbuscular mycorrhizae by rain forest seedlings vary with light intensity and tree species

Light intensity and root colonization by arbuscular mycorrhizal (AM) fungi are considered important factors affecting the performance of rain forest plants, yet few studies have examined how these two factors interact. Whether AM colonization promoted growth or caused shifts in biomass allocation in seedlings of four species of Australian rain forest tree (Flindersia brayleana, Acmena resa, Cryptocarya mackinnoniana and Cryptocarya angulata), grown in a glasshouse under light conditions that mimicked the shaded understory (3% PAR) and small light gaps (10% PAR), was examined. Seedlings were grown in sterilized field soil and either inoculated with AM fungi or provided sterile inoculum. Four major findings emerged. First, in all species, seedlings grown in small gap light intensities were larger than seedlings grown in understory light intensities. Second, when seedling biomass was included as a covariate, variation in light intensity was associated with significant shifts in biomass allocation. In all species, leaf area ratio was lower at 10% PAR than at 3% PAR, while root-to-shoot ratio showed the opposite pattern in one of the four species (C. mackinonniana). Third, although percentage root length colonized by AM fungi was greater at 10% PAR than 3% PAR in all species, this difference could be accounted for by variation in seedling size in all species except C. angulata. Fourth, growth and biomass allocation responses to AM colonization varied with light intensity and plant species. AM colonization promoted growth in both light regimes only in F. brayleana, while it had no effect on growth in C. mackinnoniana and C. angulata in either light regime and promoted growth only under high light in A. resa. AM colonization had no effect on leaf area ratio or root-to-shoot ratio in any of the species, and significantly altered specific root length in only one of the four species (C. mackinnoniana). These findings suggest that rain forest seedlings are highly variable in their growth responses to AM colonization and that some of this variability is related to the light intensity of the environment. Given that seedlings may spend many years in the shaded understory, these differences among species could have important effects on long-term seedling performance and seedling community dynamics.     

Fine root biomass under light gap openings in an Amazon rain forest

Summary Belowground processes in light gap openings are poorly understood, particularly in tropical forests. Fine roots in three zones of light gap openings and adjacent intact forest were regularly measured in buried bags and surface litter envelopes for 2 years. Fine root biomass does not vary significantly within gaps for either buried bags or for surface litter envelopes. When entire gaps are compared without regard for within gap zones, root growth into both surface litter and buried bags is significantly different between gaps, with highest rates of fine root biomass accumulation in the smallest gap. These results suggest that the aboveground within-gap zones do not result in a congruent pattern of below-ground zonation. Gap size, decomposition of the fallen tree, and pre-gap fine root growth rates should be considered to determine fine root growth patterns following the formation of light gap openings.     

Leaf age and the timing of leaf abscission in two tropical dry forest trees

We used experimental defoliations to examine the effect of leaf age on the timing of leaf shedding in two tropical dry forest trees. Trees of the deciduous Bombacopsis quinata (bombacaceae, a.k.a. Pachira quinata) and the brevi-deciduous Astronium graveolens (anacardiaceae) were manually defoliated for three times during the rainy season. All trees started to produce a new crown of leaves 2 weeks after defoliation, and continued expanding leaves throughout the rainy season. At the transition to the dry season, the experimental groups consisted of trees with known differences in maximum leaf age. Defoliations resulted in declines in stem growth but did not affect the mineral content or water relations of the leaves subsequently produced. There was no effect of leaf age on the timing of leaf abscission in B. quinata. In A. graveolens, the initiation of leaf shedding followed in rank order, the maximum leaf age of the four treatments, but there was substantial coherence among treatments in the major period of leaf abscission such that trees completed leaf shedding at the same time. In the two species, leaf water potential (Ψ_L) and stomatal conducantce (g _S) declined with the onset of the dry season, reaching minimum values of –0.9 MPa in P. quinata and <–2.0 MPa in A. graveolens. Within each species, leaves of different age exhibited similar Ψ_L and g _S at the onset of drought, and then decreased at a similar rate as the dry season progressed. Overall, our study suggests that the environmental factors were more important than leaf age in controlling the timing of leaf shedding.     

Croton campanulatus (Euphorbiaceae s.s.), a new species from the Brazilian Atlantic rain forest

Croton campanulatus, a new species from southeastern Brazil in the states of Minas Gerais and Rio de Janeiro, is here described and illustrated. Morphological data indicate that this species belongs to Croton section Cleodora based on its arborescent habit, pistillate flowers with imbricate sepals, reduced petals, and multifid styles that are fused at the base.     

Differences in light energy utilisation and dissipation between dipterocarp rain forest tree seedlings

 The light environment within tropical rain forests varies considerably both spatially and temporally, and photon flux density (PFD) is considered to be an important factor determining the growth and survival of rain forest tree seedlings. In this paper we examine the ability of four ecologically contrasting dipterocarps (Dryobalanops lanceolata, Shorea leprosula, Hopea nervosa and Vatica oblongifolia) to utilise and dissipate light energy when grown in different light environments in lowland dipterocarp rain forest in the Danum Valley Conservation Area, Sabah, East Malaysia. Specifically we report (i) photosynthetic light response curves and associated fluorescence characteristics, including quantum yield (ΦPSII) and non-photochemical quenching (qN) and (ii) the extent to which photoinhibition occurs when plants grown in either high or low light are exposed to short bursts of high PFD. When grown in low light (artificial or forest shade) all four species had low light saturated rates of photosynthesis which were achieved at low PFDs. In addition, values of ΦPSII and qN were similar over a range of measurement PFDs. D. lanceolata and S. leprosula were also grown at high PFD and showed marked differences in their responses. S. leprosula demonstrated an ability to increase its rate of photosynthesis and there was a small increase in capacity to dissipate excess light energy non-photochemically at high PFDs. Partitioning of this qN into its fast, photo-protective (qE) and slow, photoinhibitory (qI) components indicated that there was an increase in qE quenching. In contrast, although D. lanceolata survived in the high light environment, greater rates of photosynthesis were not observed and the plants showed a greater capacity to dissipate energy non-photochemically. Partitioning of qN revealed that the majority of this increase was attributable to the slower relaxing phases. Received: 10 February 1996 / Accepted: 14 June 1996     

On the density-dependence of seed predation in<Emphasis Type="Italic"> Dipteryx micrantha</Emphasis>, a bat-dispersed rain forest tree

We studied the effect of seed density on seed predation by following the fate of bat-dispersed Dipteryx micrantha (Leguminosae) seeds deposited under bat feeding roosts. The study was conducted in Cocha Cashu biological station, Amazonian Peru, during the fruiting period of Dipteryx. Predation of Dipteryx seeds in the area is mainly by large to medium-sized rodents. Seed deposits beneath bat feeding roosts were monitored for a 13-week period in an 18-ha study area. A total of 210 seed deposits were found, and on average, seed predators encountered 22% of them during any one week. About one-third of the seed deposits escaped predation, and those deposits that had relatively few seeds were more likely to go unnoticed by rodents than were deposits with many seeds. The mean seed destruction rate was 8% per week; deposits with many seeds tended to lose a smaller proportion of their seeds to seed predators than did deposits with few seeds. Regression tests for the weekly data showed that, at the beginning of the observation period, seed predation was not density-dependent. Later, when the total seed crop beneath roosts was high, the number of seeds predated per deposit was positively density-dependent, while the proportion of seeds predated was negatively density-dependent, indicating predator satiation. Seed deposits that had been visited by seed predators once had a higher probability of being revisited the week after, especially if they contained many seeds when first encountered. This indicates that the foraging behavior of rodents may be affected by their remembering the location of seed-rich patches.     

Effects of dung and seed size on secondary dispersal,seed predation,and seedling establishment of rain forest trees

Seeds dispersed by tropical, arboreal mammals are usually deposited singly and without dung or in clumps of fecal material. After dispersal through defecation by mammals, most seeds are secondarily dispersed by dung beetles or consumed by rodents. These post-dispersal, plant-animal interactions are likely to interact themselves, as seeds buried by dung beetles are less likely to be found by rodents than unburied seeds. In a series of three experiments with seeds of 15 species in central Amazonia (Brazil), we determined (1) how presence and amount of dung associated with seeds influences long-term seed fate and seedling establishment, (2) how deeply dung beetles bury seeds and how burial depth affects seedling establishment, and (3) how seed size affects the interaction between seeds, dung beetles, and rodents. Our overall goal was to understand how post-dispersal plant-animal interactions determine the link between primary seed dispersal and seedling establishment. On average, 43% of seeds surrounded by dung were buried by dung beetles, compared to 0% of seeds not surrounded by dung (n=2,156). Seeds in dung, however, tended to be more prone than bare seeds to predation by rodents. Of seeds in dung, probability of burial was negatively related to seed size and positively related to amount of dung. Burial of seeds decreased the probability of seed predation by rodents three-fold, and increased the probability of seedling establishment two-fold. Mean burial depth was 4 cm (0.5–20 cm) and was not related to seed size, contrary to previous studies. Probability of seedling establishment was negatively correlated with burial depth and not related to seed size at 5 or 10 cm depths. These results illustrate a complex web of interactions among dung beetles, rodents, and dispersed seeds. These interactions affect the probability of seedling establishment and are themselves strongly tied to how seeds are deposited by primary dispersers. More generally, our results emphasize the importance of looking beyond a single type of plant-animal interaction (e.g., seed dispersal or seed predation) to incorporate potential effects of interacting interactions.     

High-throughput DNA extraction from forest trees

It is difficult to extract pure high-quality DNA from trees, which may not be amenable to advances in extraction methods suitable for other plants. A new commercial high-throughput DNA extraction system, using a silica binding matrix for purification and a multisample mixer mill for tissue disruption, was evaluated for its suitability withEucalyptus spp.,Pinus spp., andAraucaria cunninghamii (hoop pine). DNA suitable for a range of molecular biology applications was successfully extracted from all genera. The method was highly reliable when tested in more than 500 preparations and could be adapted to different tree species with relatively minor modifications.     

Pollination and phenology of flowers in the canopy of two contrasting rain forest types in Amazonia,Colombia

The main objective of this investigation was to study the pollination characteristics of two types of Amazonian rain forest at plant community level. Seasonally inundated forest was compared with upland (tierra firme) forest. The study focused on plant species in the canopy. The pollination spectra show that in both forests most canopy trees and lianas are pollinated by small bees, large bees, butterflies or by small, relatively unspecialized insects. In the upland forest small bees are the most important pollinators (32% of all species of trees and lianas are pollinated by them), whereas large bees are predominant in the floodplain (22%). Other pollinators, like hummingbirds, bats, moths, and beetles are less common (>10%), but always somewhat more important in the flood plain than in the upland forest. Bees are the most common pollinators of epiphytes. In the flood plain forest, flies are also important as epiphyte pollinators (19%), whereas in the upland forest hummingbirds pollinate more epiphytes. The phenological patterns are quite similar in both the upland and the flood plain. We found a peak in flowering in the transition period between the wet and the dry season. Flowering activity was lowest during the wet season. Differentiation in sexual systems was correlated with life form. Dioecy and monoecy were found mostly among tree species. Most species of all life forms though were hermaphroditic. No difference with respect to the relative importance of sexual systems was found between the two forest types.     

Recovery of species richness and conservation of native Atlantic forest trees in the cacao plantations of southern Bahia in Brazil

The Atlantic forests of southern Bahia in Brazil present great species richness and a high degree of endemism. A large part of these native forests were transformed into cacao plantations in an agroforestry system known locally as cabrucas, where native trees were culled and cacao was planted under the shade of remaining trees. The present study analyzed the influence of time of implantation (age) and time of abandonment of management practices on tree species diversity of cabruca plantations to evaluate the capacity for conservation and recovery of species richness of native Atlantic Forest trees in cabrucas. Phytosociological surveys were conducted in five cabrucas with different conditions of age and state of abandonment. All trees, including hemiepiphytes and excluding the cacao plants, with a minimum stem diameter of 10 cm at breast height, were surveyed within a 3-ha sampling area in each plantation. A total of 2514 individual trees belonging to 293 species and 52 families were recorded in the five cabrucas. The Shannon diversity index varied from 3.31 to 4.22 among the cabrucas and was positively correlated with the time of abandonment (r = 0.97). The new cabrucas showed the highest values of estimated total richness (Chao) and the highest proportion of late successional species than the old ones. All areas preserved a very high proportion of native forest species while the three old cabrucas showed a higher proportion of exotic species than the two new ones. Thus the exotic species seem to replace more of the native species in the long run because of management practices and local preferences. The cabrucas presented also a high capacity for the regeneration of tree species richness after abandonment. Simple alterations in management practices could improve the recruitment of late successional species in these areas. Economic incentives may be necessary for the farmers to adopt management practices to retain native species which bring no economic returns.     

Predation by vertebrates and invertebrates on the seeds of five canopy tree species of an Amazonian forest

We studied the pre-germination loss of seeds to invertebrate and vertebrate seed predators of 5 species of Amazonian trees (Astrocaryum macrocalyx—Palmae; Bertholletia excelsa—Lecithydaceae; Calatola venezuelana—Icacinaceae; Dipteryx micrantha—Leguminosae (Papilionoidae); Hymenaea courbaril-Leguminosae (Caesalpinoidae)). These five species were selected from a large tree flora on several criteria. All possess large (3–10 cm) well-protected seeds that might plausibly be attractive to mammalian seed predators. The reproductive biology of three of the species, or close congeners, had been studied elsewhere in the Neotropics (Astrocaryum, Dipteryx, Hymenaea); one is important to the economy of southeastern Peru (Bertholletia); and one, despite large and apparently edible seeds, appeared to suffer no pre-germination loss to predators (Calatola). We conducted the research in mature forests in the Manu National Park of southeastern Peru where mammal densities are unperturbed by human activities. Densities of adult trees of the five species in our area range from very high (>30 per ha: Astrocaryum) to very low (1 per ha: Hymenaea).Loss of seeds to all causes, and to mammalian seed predators in particular, was determined for seeds placed in 2-square meter mammal exclosures and in open controls located at 10 m (near) and 50 m (far) from a large mature individual of the target species (with minor variations in the design for Astrocaryum and Calatola). The exclosures were of two types: impermeable—designed to exclude all mammals, but not invertebrate seed predators, and semipermeable—designed to admit small (<500 g), but not large mammals. Experimental and control plots were stocked with apparently viable seeds during the dry-wet transition period (October–November) and scored one year later.A significant distance effect (higher predation near vs far from a large conspecific adult) was found in only one of the species (Astrocaryum), the only one to be attacked with high frequency by invertebrate seed predators. The absence of any detectable distance effect attributable to mammals suggests that mammals, over the course of a year, thoroughly search the forest floor for seeds. Invertebrates may thus be responsible for most pre-germination distance (density) effects. With respect to the treatments, we found three qualitatively distinct results: seeds of three species (Astrocaryum, Bertholletia, Dipteryx) were significantly protected by the impermeable, but not semipermeable exclosures, implicating small mammals in seed loss; the seeds of one species (Hymenaea) were significantly protected by exclosures of both types, implicating large mammals; and the seeds of one species (Calatola) exhibited 100% survival, whether or not protected by exclosures.The importance of large mammals as seed predators is generally underestimated in these experiments because semipermeable exclosures may serve as foraging reserves for small mammals. Finally, we noted no relationship between the intensity of mammalian seed predation (as suggested by the survival of unprotected seeds) and the abundance of adults of the five species in the environment. The diversity of results obtained for the five species reveals that large-seeded tropical trees may display a wide range of demographic patterns, and points to the likely importance of post-germination bottlenecks in the population biology of many species, even those that may experience severe pre-germination seed loss.     

A phytosociological analysis of woody species in forest communities of a part of Kumaun Himalaya

This paper reports on a detailed phytosociological analysis of forests in the NW catchment of the Gola River in Kumaun Himalaya, 29°19–29°27N and 79°32–79°42E. Fourteen sites and 56 stands at elevations ranging from 1200 to 2523 m and covering the following five forest types were investigated: Pinus roxburghii, mixed, Quercus leucotrichophora, Q. lanuginosa, and Q. floribunda. The basal cover of the forests differed according to slope position and aspect. The three oak forests had more basal cover than the other two, and Q. lanuginosa had the most. The performance of individual tree and shrub species and the number of saplings and seedlings differed according to slope position and aspect. The mixed forest had the greatest tree diversity, and among the others diversity increased with increasing basal cover. The diversity of trees, saplings, and herb layer was greatest on aspects with intermediate temperature and moisture conditions; whereas that of shrubs and seedlings increased towards the cooler (and wetter) and warmer (and drier) exposures. There was a positive relation between the diversity of shrubs plus seedlings and trees plus saplings in P. roxburghii and mixed forests; whereas this relationship was inverse in the three oak forests. In general, the dominance-diversity curves for the tree layer followed a geometric series conforming to the niche pre-emption situation in communities of low diversity. Among the forests, the regeneration was best in Q. lanuginosa and worst in Q. leucotrichophora.Nomenclature follows: Osmaston (1926).Finacial support from the Council of Scientific and Industrial Research, New Delhi and the Indian Space Research Organisation, Banglore is gratefully acknowledged.     

Photosynthetic plasticity of two rain forest shrubs across natural gap transects

Summary Photosynthetic plasticity of two congeneric shrub species growing under natural field conditions was compared along transects spanning two canopy gaps in a Costa Rican rain forest. Piper arieianum is a shadetolerant species common in successional and mature forests, whereas P. sancti-felicis is a pioneer species abundant in abandoned clearings and large gaps. Twenty potted cuttings of each species were placed at regular intervals along two east-west transects crossing a small branch-fall gap and a large tree-fall gap. Along the transects, the percent of full sun photon flux density varied from less than 2% to 45%. After six months of growth under these conditions, leaves were monitored for incident photon flux density, photographic measures of light availability, photosynthetic capacity (A_max), leaf nitrogen content, leaf chlorophyll content, and specific leaf mass. Although both species demonstrated considerable plasticity in A_max across gap transects, P. sancti-felicis leaves had a superior capacity to track closely variation in light availability, particularly in the larger gap. For regressions of A_max on measures of light availability, P. sancti-felicis consistently showed a 3.5 to 5-fold higher coefficient of determination (R²) and a 3 to 4-fold higher slope than P. arieianum. In both species leaf nitrogen content per leaf area increased significantly with light availability, although P. sancti-felicis, again, showed a much stronger relationship between these variables. Across the transects, mean chlorophyll content per unit leaf area did not differ significantly between the species, whereas mean chlorophyll content per unit leaf dry mass was 3-times greater in leaves of P. sancti-felicis. Piper arieianum exhibited highly significant increases in chlorophyll a:b ratio with increased light availability, whereas P. sancti-felicis lacked significant variation in this trait across a gradient of light availability. Mean specific leaf mass did not vary significantly between species across the gap transects. The nature of the light acclimatory response differs quantitatively and qualitatively between these species. An important constraint on light acclimation of the shade-tolerant P. arieianum is its inability to increase photosynthetic nitrogen-use efficiency under conditions of high light availability. The lack of plasticity in chlorophyll a:b ratios does not restrict light acclimation of A_max in P. sancti-felicis. Leaves of P. arieianum exhibited symptoms of chronic photoinhibition in exposed microsites within the large gap. Species differences in the capacity to finely adjust A_max across a wide range of light conditions may be attributed to their maximum growth potential. Light acclimation in species with low maximum growth potential may be constrained at the cellular level by rates of protein and chlorophyll synthesis and at the whole-plant level by low maximum rates of uptake and supply of nutrients and water. For P. arieianum, restriction of photosynthetic plasticity is likely to limit competitive abilities of plants in high-light conditions of large gaps and clearings, whereas observed habitat restrictions for P. sancti-felicis do not appear to depend upon the highly-developed capacity for adjustment of A_max observed in this species.