Nalini M. Nadkarni

Composition and distribution of epiphytic organic matter in a neotropical cloud forest, Costa Rica

We describe the abundance (dry weight) of angiosperms and other organic matter suspended within the inner crowns of a dominant host tree species, Ocotea tonduzii (Lauraceae) in a Neotropical lower montane forest. Epiphytic organic matter (EOM), defined as vegetation and dead organic matter, was randomly sampled from inner canopy branches of ten trees in Monteverde, Costa Rica. Total EOM (grams per square decimeter of branch surface area) showed a strong positive correlation with branch circumference and a strong negative correlation with branch angle. Approximately three times more dry mass occurred on large (86-140 centimeters circumference) branches than on small (15-50 centimeters) branches, and four times more dry mass occurred on less inclined ( 300) than on more inclined (>60?) branches. The variation of EOM was much greater within trees (between branches) than among different trees. EOM was composed of approximately 60 percent dead organic matter, 20 percent live and dead roots, 10 percent angiosperms, 5 percent ferns, and 5 percent cryptogams. Sixty-five angiosperm species in 18 families, with no strongly dominant species, were found among the 75 percent of plots that supported angiosperms. Araceae, Bromeliaceae, Ericaceae, Melastomataceae, and Orchidaceae contributed about 70 percent of the angiosperm biomass. Orchidaceae and Piperaceae were the most frequently represented families and those with the most species in the study plots. The most species-rich plots (-6 species) occurred on branches >50 centimeters in circumference, but the highest density of epiphytic angiosperm seedlings occurred on smaller, presumably younger branches.

Invertebrates in canopy and ground organic matter in a neotropical montane forest, Costa Rica

In a neotropical cloud forest of Costa Rica, we compared the density and composition of macro- and mesoinvertebrates in organic matter found within the canopy to that found in the upper soil horizons on the forest floor. We used a Winkler sifting apparatus to extract invertebrates from accumulated litter and humus. The numerically dominant invertebrate groups in both canopy humus and forest floor leaf litter were mites, adult beetles, holometabolous insect larvae, ants, collembola, amphipods, and isopods. Relative abundances of these major taxa were the same in canopy and on the forest floor, indicating that canopy organic matter shares a fundamentally similar invertebrate community with forest floor. All of these groups except ants had significantly higher densities in the canopy, with a mean density 2.6 times greater on the ground than in the canopy. Ant density was similar in both microhabitats.

A Comparison of Ground and Canopy Leaf Litter Ants (Hymenoptera: Formicidae) in a Neotropical Montane Forest

The most conspicuous habitat discontinuity in forests is that between ground and canopy. These two microhabitats support strikingly distinct biotic communities. Among ants, species that nest in the ground or in leaf litter are typically in different genera from arboreal species, which nest in or on plants, the two groups exhibiting divergent morphologies which reflect their respective nesting habits (Wheeler 1910, Wilson 1959). The arboreal microhabitat is clearly three-dimensional (Richards 1983) and has inspired investigations of vertical stratification among arboreal taxa, including birds (Pearson 1971, Terborgh 1980), mammals (Harrison 1962), and flying insects (Bates 1944, Sutton et al, 1983). Arboreal ants exhibit vertical stratification, some species being restricted to high canopy, others to forest understory (Wilson 1959). The ground microhabitat is generally considered to be a twodimensional layer of soil and leaf litter, home to an ant community very distinct from the arboreal community. In many tropical forests, however, large amounts of leaf litter and other organic material accumulate in the canopy, imparting a three-dimensional structure to dead organic matter. The crown humus (Jenik 1973) consists of litter intercepted from overstory tree branches and from abscissed epiphyte tissues. Accumulations of crown humus are particularly pronounced in montane forests (Nadkarni 1984; P6cs 1976, 1980).

Structural characteristics and floristic composition of a Neotropical cloud forest, Monteverde, Costa Rica

The Monteverde Cloud Forest Reserve protects a variety of primary montane forest communities on volcanic parent materials. We describe the structure and composition of the forest to provide background information for epiphyte and nutrient cycling studies and for comparison with other tropical montane forests. In a 4-ha study plot in leeward cloud forest, density of stems (2062 individuals ha- for stems >2 cm dbh, 555 individuals ha- for stems >10 cm dbh) and stem basal area (73.8 m2 ha- for stems >2 cm, 62.0 m2 ha- for stems >10 cm dbh) were high relative to other montane forests. Stems in a subset of the plot (c. 1/3 of the area) were identified and assigned to 47 families, 83 genera and 114 species, which is rich compared with other montane forests. Large stems had a higher spatial variability of structural and floristic characteristics than small stems. RESUMEN. Caracteristicas estructurales y composici6n floristica de un bosque nuboso neotropical en Monteverde, Costa Rica. La Reserva del Bosque Nuboso de Monteverde proteje una variedad de ambitos naturales de bosques primarios montaniosos sobre suelos volcanicos. Describimos los bosques como fondo para el estudio de plantas epifiticas y ciclos de nutrientes y como comparaci6n a otros estudios de la estructura y floristica de bosques tropicales montaniosos. Las medidas de la densidad de los arboles >2 cm dbh (2062 individuos ha-) y de la area basal (73.8 m2 ha-) fueron altas en relaci6n a otros bosques montafiosos. La especie de cada arbol fue 1/3 area determinada; tallos pertenecientes a 47 familias, 83 generos, y 114 especies fueron coleccionados, lo cual supera la diversidad de otros bosques montaniosos. La variebilidad de las caracteristicas estructurales y floristicas en varias escales espaciales es discutida en el contexto de la area investigada por clases distintas de tamanio de tallos.

Vesicular-arbuscular mycorrhizae of epiphytic and terrestrial Piperaceae under field and greenhouse conditions

We examined the roots of 27 epiphytic and terrestrial species of Piperaceae collected in primary and secondary habitats in Monteverde, Costa Rica. Terrestrial roots of only two of the nine Peperomia species, two of eight Piper species, and of Pothomorphe umbellatum contained internal vesicles and/or arbuscules. We did not find internal vesicles and/or arbuscules in 3024 cm of fine roots of epiphytic Piperaceae, even though 15% of these root segments had associated external typical glomalean hyphae. Glomus and Acaulospora spores, and Gigaspora auxiliary cells occurred in both canopy and terrestrial habitats. After inoculation of a low nutrient substrate, the facultatively epiphytic Peperomia costaricensis averaged 23% mycorrhizal root length. Relatively high atmospheric inputs of dissolved inorganic nutrients that alleviate the requirement for mycorrhizae, and heterogeneity of mycorrhiza inocula in the canopy may explain the absence of mycorrhizae from epiphytic Piperaceae. We suggest that the Piperaceae comprises predominantly facultatively mycotrophic species, and that facultative mycotrophism facilitates their radiation to the canopy.

Seasonal patterns of nutrient deposition in a Quercus douglasii woodland in central California

The monthly deposition of total nitrogen, phosphorus, potassium, calcium and magnesium via canopy throughfall, and various components of the litterfall was measured for 31 months under mature Quercus douglasii and in the bulk precipitation in the surrounding open grassland. Seasonal patterns of nutrient concentration in leaf litter, throughfall, and precipitation were also measured. Total annual subcanopy deposition exceeded open precipitation deposition by approximately 45–60x for nitrogen, 5–15x for phosphorus, 30–35x for potassium, 25–35x for calcium, and 5–10x for magnesium. Total annual subcanopy deposition was low in comparison to other oak woodland sites reported in the literature. Throughfall and leaf litter were the primary sources of nutrients and thus determined the seasonal peaks of nutrient deposition. The first autumn rains and leaf fall were associated with one peak in nutrient deposition, and throughfall during early spring leaf emergence was associated with a second peak in potassium, magnesium and phosphorus. Non-leaf plant litter (excluding acorns) provided approximately 15–35% of most nutrients, with twigs and bark depositing over 12% of the annual calcium flux in 1987–1988, and flower litter depositing over 8% of the annual nitrogen flux in 1986–1987. Acorns had high concentrations of phosphorus and nitrogen and during the mast season of 1987–1988 they contained a large proportion of the total subcanopy annual flux of these elements. With acorns excluded, total annual nutrient deposition was similar between years, but timing of nutrient deposition differed. Late summer leaf fall associated with drought, variation in precipitation, and variation in deposition of non-leaf parts were associated with seasonal differences in nutrient deposition between years.

A comparison of mineral uptake and translocation by above-ground and below-ground root systems ofSalix syringiana

Nutrient uptake and translocation by above-ground adventitious roots and below-ground roots of woodySalix syringiana saplings were studied with gamma spectrometry. Each of four radionuclides (75Se,138Cs,54Mn, and65Zn) administered to adventitious and belowground roots were detected in stems and leaves within one month. Nuclides tended to be immobilized in the leaves and branches closest to the adventitious roots that absorbed them, while nuclides absorbed from below-ground sources were distributed more evenly throughout the plant. The capacity of adventitious roots to acquire nutrients from above-ground sources suggests they function as a potential ‘auxiliary’ pathway of nutrient uptake and might enhance plant nutrient status where below-ground root uptake it hindered by adverse soil conditions.