Tropical Deciduous Forest In Mexico Research Articles

Sheep and goat browsing a tropical deciduous forest during the rainy season: why does similar plant species consumption result in different nutrient intake?

During the rainy season, the tropical deciduous forest (TDF) supposedly represents an abundance of biomass for sheep and goats. Nevertheless, quantitative estimations of feed intake during the rainy season are lacking. This study investigated the feeding behaviour of sheep and goats in a TDF in Mexico and quantified their nutrient intake during the rainy season. Plant species (PS) consumed, size and weight of bites, and nutritional quality were determined by continuous bite monitoring through direct observation. Adult ewes (n = 3) and goats (n = 3) were observed in their grazing circuits (4 h/day) for 12 days during the rainy season. Sheep and goats consumed 61 PS and performed a similar median number of bites (1751 vs 2053 bites/day, respectively; P > 0.05). Although they shared 52.5% of the PS consumed, only seven PS contributed most of the dry matter intake (DMI) for sheep (96.7%) or goats (90.5%). Sheep consumed more grass than goats (79.8% vs 48.3% of their DMI, respectively), whereas goats ate more shrubs than sheep (30.0% vs 7.6% of their DMI, respectively). The diet ingested by goats included more polyphenols (P < 0.05) and a higher frequency of larger and heavier bites than sheep (P < 0.05). Sheep reached 61.3% and 57.7% of their metabolisable energy and crude protein maintenance requirements. Similarly, goats covered 63.3% of their metabolisable energy and 108.2% of crude protein requirement. Although the main ration of sheep and goats was composed of similar PS, their different feeding behaviour resulted in different macronutrient consumption.

Seed reserve translocation and early seedling growth of eight tree species in a tropical deciduous forest in Mexico

Seed reserves play an essential role during germination and seedling establishment and are particularly important for species that grow in seasonal ecosystems with a short growing season. In this study, we examined (a) how and when the seedlings change their dependence from seed resources to external resources, (b) the lipid, nitrogen, and non-structural carbohydrate reserve translocation from seeds to seedlings over time, and (c) whether reserve translocation may be correlated to cotyledon and leaf lifespan of seedlings for eight tree species in a tropical deciduous forest in north-western Mexico. Our results showed that the cotyledon lifespan was not related to the cotyledon type (photosynthetic or reserve) and that the cotyledon biomass did not decrease significantly until germination. In six of the eight studied species, biomass allocation to the leaves was favored; lipids were the first reserve exhausted before the first leaves were totally expanded in seven of the eight study species. Species with the highest N concentration had expanded leaves and lost their cotyledons faster than species with a low N concentration. Our results suggest that tropical deciduous forest species employ different strategies to survive the dry season and re-sprout in the next growing season mediated by seed reserve concentrations, translocation patterns and subsequent biomass allocation.

Effects of burial and storage on germination and seed reserves of 18 tree species in a tropical deciduous forest in Mexico

The changes in germination and seed reserve composition that occur while seeds are stored in the laboratory or buried in the soil are important for understanding the potential and ecological longevity of seeds as well as seed-bank dynamics. Both germination and seed-bank dynamics depend on water availability. We studied 18 tree species, including those with permeable or impermeable seeds, from a tropical deciduous forest in Mexico. We measured seed germination in a growth chamber after (1) dispersal, (2) laboratory storage, (3) seed burial at two field sites and directly in the field, and (4) two rainy seasons. Lipids, nitrogen, and nonstructural carbohydrates were quantified after dispersal and after laboratory or field storage. Sixteen species were viable after three periods of laboratory storage (~3 years). Eleven species were viable after two burial periods in the field (~2 years). Nitrogen concentration decreased after storage and burial in 11 species. Species lipid concentration had a negative relationship with species water content at dispersal and after one burial period, whereas nonstructural carbohydrates showed the opposite trend. Potential and ecological longevities were similar in impermeable seeds. Most of the species studied can form persistent seed banks consisting mainly of species with impermeable seeds that can remain in the soil without degrading their viability. Germination in the field is staggered following natural precipitation pulses as a strategy to stagger seedling recruitment, which may insure against unfavorable conditions.

Soil aggregates in a tropical deciduous forest: effects on C and N dynamics, and microbial communities as determined by t-RFLPs

The aim of this study was to analyze C and N dynamics, as well as, soil bacterial community structure within soil micro- and macro-aggregates in a tropical deciduous forest in Mexico. We measured, for three landscape positions and three seasons of the year: total, microbial and available forms of C and N; potential C and N mineralization; and soil bacterial communities by using t-RFLPs. The highest total C concentrations were found in the north-slopes and in the dry season (DS) samples. In general, micro-aggregates had higher concentrations than macro-aggregates of available C and N forms, and microbial C. Similarly, micro-aggregates had the highest potential C mineralization and net N mineralization. We detected 149 different OTUs (operational taxonomic units) from which 50% was shared by the two aggregate size fractions, 25% was exclusive to micro-aggregates and the 25% left was found only in macro-aggregates. Top-hills were richer in OTUs than north and south-slopes. The Unweighted Pair Group Method with Arithmetic mean (UPGMA) analysis indicated clear differences in community composition between the two aggregate size-fractions in relation to the presence of OTUs. These results suggest that the main difference between micro- and macro-aggregates is due to the community structure within each soil fraction and this difference could affect soil nutrients dynamics.

Effects of forest‐pasture edge on C, N and P associated with Caesalpinia eriostachys, a dominant tree species in a tropical deciduous forest in Mexico

AbstractForest fragmentation in tropical ecosystems can alter nutrient cycling in diverse ways. We have analysed the effects of the forest‐pasture edge on nutrient soil dynamics in a tropical deciduous forest (TDF) in Mexico. In two remnant forest fragments, both larger than 10 ha, litterfall, litter and soil samples associated to the tree Caesalpinia eriostachys were collected at five distances from the pasture edge into the inner forest (10 m in the pasture and 0–10, 30–40, 70–80 and 100–110 m towards the forest interior). We measured the concentrations of carbon (C), nitrogen (N) and phosphorus (P) in litterfall, surface litter and soil, and soil microbial C (Cmic) and microbial N (Nmic). Soil nutrient concentrations and Cmic and Nmic were lower in the pasture soils than in the forest soil samples. Total C and N pools, and Cmic and Nmic in the pasture were lower than in the forest. In contrast, net N immobilization and the increase in Nmic from rain to dry season increased from the edge to the inner forest. Soil P concentration was lower in the pasture and at the first distance class in the forest margin (0–10 m) than in the sites located further into the forest, while litter P concentration had the inverse pattern. Litterfall P was also reduced near the edge and increased towards the forest interior. As a consequence, litterfall C:P and N:P ratios decreased from the edge to the inner forest. These results suggest that the forest–pasture edge disrupts P dynamics within the first 10 m in the forest. Thus, plants' use of nutrients and productivity could be altered in the edge of fragmented forests.

Multi-species fruit and seed removal in a tropical deciduous forest in Mexico

We determined patterns of post-dispersal fruit and seed removal for 11 common native plants, as well as sunflower seeds ( Helianthus annuus L.), within a tropical deciduous forest in Jalisco, Mexico. Removal values were high in Delonyx regia (Bojer) Raf. (90%), Crescentia alata Kunth. (87%), H. annus (81%), Pithecellobium dulces (Roxb.) Benth (81%), Albizia occidentalis Brandegee (80%), Coccoloba barbadensis Jacq. (80%), Recchia mexicana DC. (80%), Caesalpinia pulcherrima (L.) Sw. (79%), Enterolobium cyclocarpum (Jacq.) Griseb. (73%), moderate in Guazuma ulmifolia Lam. (42%) and Celtis iguanaeus Sarg. (44%), and low in Amphipterygium adstringens (Schlechtend.) Schiede ex Standl. (17%). Low removal rates (29%) in experimental patches open only to arthropods suggest that arthropods have a minor role in removing fruits and seeds of these species. Removal values were high in experimental patches open to all potential agents (77%) and semipermeable patches open to forest-dwelling rodents (76%), suggesting that the latter group, the most abundant terrestrial mammal in this forest, was an important agent for removing the fruits and seeds of study plants. Removal values were higher in experimental patches located in tropical deciduous forest than in tropical semideciduous forest, as well as higher in high density (patches of 30 fruits or seeds) than in low density (patches of five fruits or seeds) experimental patches for most study plants. Mice appear to selectively remove and hoard fruits and seeds according to their energy and nutritional content and the presence of secondary metabolites, and from from high-density food patches and preferred habitats. Nonindependent effects of species, habitat, and density suggest that a complex interplay of factors determines fruit and seed removal for the plants examined from the Chamela tropical forest.

Seasonal variation in trehalose contents of roots and nodules of leguminous trees in a tropical deciduous forest in Mexico

Seasonal variations of trehalose contents in roots and root-nodules of five legumes in a tropical deciduous forest in Jalisco, México, were determined. The tree species were: Lonchocarpus eriocarinalis and Erythrina lanata (sub-family Papilionoideae) and Piptadenia constricta, Albizia occidentalis and Lysiloma microphylum (sub-family Mimosoideae). Trehalose accumulation in nodules and roots varied seasonally and among species. For example, the Papilionoid-species retained nodules longer than those in the Mimosoideae (5 and 4 months, respectively), and accumulated the highest amounts of trehalose (average values of 178 vs. 2.88 mg g −1 nodule (d. wt), respectively). Generally, maximum trehalose contents in nodules and roots were observed in November, at the beginning of the dry season.

Comparison of population structures and ecology of a congeneric pair of common and rare neotropical tree species

We compared the general ecology and population profiles of Jatropha standleyi and J. chamelensis, two ecologically similar, dioecious forest trees in order to illuminate why they differ in range size, an important measure of relative commonness and rarity. Jatropha standleyi is widespread throughout the tropical deciduous forest in Mexico and the endangered J. chamelensis is restricted to a small region on the Pacific coast of Mexico. Using data collected over the same time period from a site central to the distributions of both species, we found significant differences in population size distributions and seedling mortality, but no discernible differences in seedling or adult growth rates, local abundance or local distribution. The observed difference in relative rarity could be explained by a number of hypotheses depending on whether the populations are at a stable equilibrium or not. The high ratio of pre-reproductive individuals may indicate a growing, rather than stable, population for J. chamelensis. Jatropha standleyi is more widespread and has a significantly lower ratio of pre-reproductive to mature individuals. Alternatively, both populations may be at equilibrium with J. chamelensis restricted to its limited range by large-scale environmental constraints or niche differences not elucidated in this study. In either case however, the greater and less variable seed output of the J. standleyi population will also mean a greater number of rare long-distance dispersal events and a better chance of establishing a persistent remote population for J. standleyi than for J. chamelensis. The dioecy to be found in both these species would exacerbate the limiting effects of low seed production on the ability of a species to ‘travel’ successfully. A more extensive field investigation of mortality and factors contributing to mortality in sub-canopy and pre-reproductive individuals would allow more light to be shed on relative population processes in these species.

Dietary Value of Fruits and Seeds to Spiny Pocket Mice (Liomys pictus) in a Tropical Deciduous Forest in Mexico

Spiny pocket mice (Liomys pictus) were maintained on monospecific diets of fruits and seeds of twelve plant species from a tropical deciduous forest in Mexico. Average consumption rates over 5-day trials were determined and classified as high, moderate or low. The products of plant species providing the most valuable food to spiny pocket mice were shown to contain high crude protein or lipid contents. The least valuable dietary components contained glucosides and alkaloids possibly deterrent to spiny mice, however, some of these fruits or seeds were moderately consumed. It is concluded that nutritional value or presence of toxic compounds in fruits and seeds might affect dietary choices of spiny pocket mice. Individuos del ratón espinoso de abazones Liomys pictus fueron alimentados con dietas monoespec¡ficas de frutos y semillas de 12 especies de plantas de una selva tropical decidua en México. El consumo promedio durante cinco días del experimento fue mayor (> 0.25 g semilla/g ratón) para las semillas de Pithecellobium dulces, Delonyx regia, Albizia occidentalis y Enterolobium cyclocarpum (Leguminosae) y de girasol Helianthus annuus (Compositae), moderado (0.10–0.20 g semilla/g ratón) para los frutos de Guazuma ulmifolia (Sterculaceae) y Coccoloba barbadensis (Polygonaceae) y las semillas de Crescentia alata (Bignoniaceae) y Recchia mexicana (Simaroubaceae) y, menor (< 0.10 g semilla/g ratón) para las semillas de Caesalpinia pulcherrima (Leguminosae) y frutos de Celtis iguanaeus (Ulmaceae) y Amphypterygium adstringens (Julianaceae). Los valores dietéticos (promedio de la variación de la masa corporal/promedio de consumo de frutos y semillas) indicaron que H. annuus, E. cyclocarpum, A. occidentalis y D. regia fueron las especies con mejores rendimientos y mostraron contenidos altos en proteína ó lípidos crudos. Por su parte, C. iguanaeus, A. adstringens y C. pulcherrima fueron las especies con rendimientos más bajos y mostraron contenidos de glucósidos y/o alcaloides, posiblemente tóxicos para L. pictus. Sin embargo, algunos frutos y semillas fueron consumidos a£n mostrando contenidos de alcaloides. El contenido nutricional y la presencia de compuestos tóxicos pueden determinar la selección de frutos y semillas del ratón espinoso de abazones en condici ones naturales.

The relationship between solar radiation interception and soil water content in a tropical deciduous forest in Mexico

Spatial and temporal patterns of potential solar radiation interception (SRI) were estimated in a tropical deciduous forest ecosystem in the West of Mexico using a Geographic Information System modeling approach. The study area was a small catchment (16 ha) divided into three altitudinal segments: top, middle and bottom. Both amount and pattern of SRI were strongly influenced by aspect. It increased with slope inclination. Catchment relief affected SRI distribution throughout the year: the highest values were on the gently sloping top segments and south-facing bottom locations, and the lowest values were in the steep north-facing bottom locations. With the onset of the rainy season soil water content (SWC) was affected by soil characteristics, but SRI was still more important than these during the rainy season. Consequently, north-facing bottom locations had less SRI but greater SWCs for longer periods. In contrast, the top and middle locations with high SRI had smaller SWCs. Vegetation structure was also affected by SWC: the north-facing bottom locations had greater tree density and, greater tree diameter at breast height and greater leaf area than the top and middle levels.

Coppice shoot and foliar crown growth after disturbance of a tropical deciduous forest in Mexico

The number of coppice shoots, length of the longest shoot, and foliar crown area were measured on woody species in a recently disturbed tropical deciduous forest near Chamela, Jalisco, Mexico. Coppice growth after slashing was measured on 582 individuals representing 80 species. Growth of 454 individuals of 65 species was measured during August for two years following the April–May burns in the slashed plots. Post-burn growth of 207 woody individuals of 33 species was measured in the adjacent pasture that was slashed 11 years earlier and burned three times before the measurements were made. After an initial slash fire, coppice shoot length and foliar crown areas were similar in abundant and rare woody species. Vines had significantly longer shoots and larger crown areas than trees or shrubs. Leguminous shrubs and trees that were multi-trunked before slashing had significantly longer shoots and larger crown areas than non-legumes or single-trunked individuals. After slashing, evergreen trees had significantly larger crown areas than deciduous trees with high- or low-density wood or water-storage trees, but after burning water-storage trees had the longest shoots and largest crown areas. Coppicing between slashing and burning did not reduce growth of those individuals that survived burning compared to individuals of the same species that coppiced only after burning. In the adjacent pasture 11 years after the initial burn, rare species had significantly longer shoots and larger crown areas than abundant species. Growth of trees and shrubs was similar, but leguminous trees and shrubs had significantly longer shoots than non-legumes.

Disturbance and Seasonal Dynamics of Mycorrhizae in a Tropical Deciduous Forest in Mexico1

ABSTRACTMycorrhizal fungi were sampled in a deciduous tropical forest on the Pacific coast of Mexico during different seasons and in natural treefall gaps and pastures. All 12 plant species sampled in the forest were arbuscular mycorrhizal. The percent root infection and spore production were closely related to the phenology of the plants. Most tree species and all herbaceous species had the highest infection in the summer rainy season, but two species, Opuntia excelsa and Jacquinia pungens, had highest infection in the dry season. Unusually high rainfall during the dry season was associated with increased infection but not increased spore production. Spore density was low for all species at all sample times, except at the beginning of the July 1993 rainy season in, when we observed up to 28 spores/g soil.The percent cover of shrubs or herbs did not increase in gaps after two years, and we observed no colonizing seedlings. No plant species with cover higher than 2.7 percent occurred exclusively in gaps or forest. The percent mycorrhizal infection did not differ significantly between gaps and forest. Spore counts were as high in the gaps as in the forest in two of the three gaps but lower in the third gap. The lack of significant response of plants in these gaps after two years differed from the rapid response in tropical rainforests. It is likely related to the small size of the gaps and to light infiltration to the forest floor. Pastures were dominated by two species of exotic grasses and one species of mycorrhizal fungus, whereas forests had 15 fungal species. The slow regrowth of vegetation in gaps was not limited by mycorrhizal fungi, since they were still abundant after the treefalls, but recovery in pastures could be affected by low fungal diversity and dominance of grasses.

Responses to light changes in tropical deciduous woody seedlings with contrasting growth rates.

We evaluated the responses in growth, biomass allocation, photosynthesis and stomatal conductance, to changes in light in woody seedlings from the tropical deciduous forest in Mexico, which shows a highly seasonal rain pattern. We studied ten species, which differed by 30-fold in relative growth rate (RGR). We analyzed plant growth in two contrasting light levels during 52 days and two transfers: from high to low (HL) and from low to high (LH) light intensity, and the respective controls in high (HH) and low (LL) light for another 52 days. The photosynthetic capacity (A max) and stomatal conductance were measured at the day of the transfer between light conditions and at the end of the experiment. Species with high RGR showed the largest changes in RGR in response to contrasting light conditions (HH/LL ratio), and species with low RGR showed low responses. The fast-growing species were the most plastic, followed by species with intermediate growth rates, with the slow-growing species being the least plastic. Fast-growing species achieved higher maximum photosynthetic capacities (A max) and stomatal conductance and higher response to light than slow-growing species. Species with high RGR showed a low RGR HH/LH ratio, suggesting a large response of L plants when transfered to H. The RGR of the species were associated with species specific leaf area and with the response in the leaf area, net assimilation rate and leaf weight ratio, suggesting the importance of the leaf area produced and the leaf characteristics rather than root:shoot ratio in determining RGR. Considering that seed germination is expected at the beginning of the rainy period, seedlings of most of the species will experience high-light conditions during its early growth. There are large annual variations in the time required for canopy closure (35-75 days). The influence of these variations may have different effect on the species studied. Species with intermediate growth rate and intermediate response to light changes were less affected by light reduction than fast-growing species. The intermediate-RGR species Caesalpiniaeriostachys is the most abundant and widely distributed species, perhaps this could be in part due to its ability to acclimate to both light increases and decreases. The fast-growing species studied here can be found in open sites in the forest and in areas cleared for pasture growth. These fast-growing species eventually reach the canopy, although this may require several canopy openings during their lives, which implies juvenile shade tolerance. In the tropical deciduous forest juvenile pioneer trees also benefit from the temporary high light available caused by the dry period during the rainy season. The slow-growing species Celaenodendronmexicanum forms small patches of monospecific forest; the adult trees are not completely deciduous, and they retain their old leaves for a long time period before shedding. Thus seedlings of this species may receive lower levels of light, in agreement with its shade tolerance and its lower response to light increases.

Nutrient Availability and growth Rate of 34 Woody Species from a Tropical Deciduous Forest in Mexico

To test the predicted relationship between growth rate and biomass allocation in relation to nutrient availability, seedlings of 34 woody species from the tropical deciduous forest in Mexico were grown under two contrasting nutrient conditions. Dry biomass, relative growth rate (RGR), root/shoot ratio (R/S), specific leaf area (SLA), leaf area ratio (LAR), leaf weight ratio (LWR), root weight ratio (RWR), net assimilation rate (NAR) and the nitrogen and carbon leaf percentage were determined following an initial and final harvest. In all the parameters evaluated, the trend followed by the species under low nutrient conditions was similar to the trend attained in high nutrient conditions but with different magnitude. The species with the largest seed biomass was Thevetia ovata (3808.6 mg). Lagrezia monosperma had the smallest seeds (0.13 mg) and the highest RGR in the high nutrient treatment. However, the relationship between RGR and seed biomass among the 34 species studied was weak (r = -0.50 in low and -0.62 in high nutrients). Higher biomass allocation to roots was shown under low nutrient condition but the relationship between RGR and root/shoot ratio was non-significant. Species variation in RGR to both the nutrient treatments employed is followed by species variations in LAR (r = 0.50) more than changes in NAR (r = 0.20). Changes in LAR are explained by LWR (r = 0.62) and SLA (r = 0.70). Under low and high nutrients, the RGR was highly correlated with SLA (r = 0.67 and 0.60), suggesting the importance of both the total leaf area produced and the leaf morphological characteristics in determining the RGR. A general characteristic of the distribution of the species' responses in RGR to both nutrient treatments was the existence of a continuum, for all of the parameters studied. This suggests differences in the species' resource utilization and tolerance, which are reflected in different plastic capacities.

Influence of mineral nutrient availability on growth of tree seedlings from the tropical deciduous forest

The effects of different nutrient availabilities on growth and biomass partitioning in seedlings from the tropical deciduous forest in Mexico were compared. The tree species studied were Heliocarpus pallidus, a species associated with disturbed parts of the forest, and Caesalpinia eriotachys, Jacquinia pungens and Recchia mexicana, species from mature, undisturbed habitats. The tropical deciduous tree seedlings were grown in pure silica sand for 50 days inside growth chambers under four nutrient regimes; 5, 20, 100 and 200% Long Ashton nutrient solutions. Data showed contrasting responses among species to different nutrient availabilities. Except Jacquinia pungens, all species had increased growth and productivity as nutrient level increased from 5 to 100%; however, no significant differences in these parameters were detected between 100 and 200% in all species. Compared with mature forest species, pioneer species showed higher variations in biomass production, relative growth rate and net assimilation rate. In contrast to mature forest species, root/ shoot ratios in Heliocarpus pallidus were greater and thus showed higher biomass allocation to roots when nutrient supply was limited. This response suggests higher phenotypic plasticity in pioneer species. Species from mature parts of the forest (Caesalpinia eriostachys, Recchia mexicana) showed less dependency on nutrient supply than pioneer species. These responses appear to support observations from studies with temperate plants investigating growth responses to soil fertility.

Discovery of the larger grain borer in a tropical deciduous forest in Mexico

AbstractWe report on the first records of natural host plant utilization by Prostephanus truncatus. Spondias purpurea (‘ciruelo’) and Bursera fagaroides (‘cuajiote amarillo’) branches cut down by Oncideres albomarginata chamela were colonized by P. truncatus in the tropical deciduous forest of the Pacific Coast of México. An average of 328 P. truncatus individuals were captured in pheromone traps and 48 adults in direct samplings of S. purpurea twigs. Five host tree records collected previously are mentioned, all were recorded in the dry season. Strong preferences for cacahuazintle maize were detected by P. truncatus from S. purpurea twigs under laboratory conditions. All beetles had moved to the grain in 19 days. No P. truncatus were observed in either maize fields or rural storage houses of the region, only Sitophilus zeamais was detected, while the pheromone traps in the forest were capturing P. truncatus. Populations of P. truncatus are considered to be utilizing the natural vegetation as possible dissemination points for colonizing neighboring agricultural fields as food sources to which they were suited by chance.

Monospecific Dominance of a Tropical Deciduous Forest in Mexico

Monospecific Dominance of a Tropical Deciduous Forest in Mexico

Growth responses of tropical deciduous tree seedlings to contrasting light conditions

The growth responses of seedlings of Amphipterygium adstringens, Caesalpinia eriostachys, and C. platyloba, species associated with undisturbed parts of the tropical deciduous forest in Mexico, and Apoplanesia paniculata and Heliocarpus pallidus, two gap-requiring pioneer species, were determined under contrasting light conditions in a growth chamber experiment. The high (400 μmol m−2 s−1) and low (80 μmol m−2 s−1) light treatments correspond to the light available in a medium size gap and underneath the vegetation canopy in the deciduous forest during the rainy season, respectively. Following four destructive harvests the biomass production, relative growth rate, root/shoot ratio, specific leaf area, net assimilation rate, leaf area ratio and light dependency were determined for all species. In the high light treatment all species achieved higher relative growth rates and net assimilation rates than when growing at low light intensity. However, the two pioneer species showed the highest light dependency and were the species more affected by the low light treatment in biomass production. The two Caesalpinia species showed similar growth responses, but C. platyloba was the most shade tolerant species. Plastic adjustments in terms of the specific leaf area were more evident in the two pioneer species.

Effect of vesicular-arbuscular mycorrhizae on seedling growth of four tree species from the tropical deciduous forest in Mexico

The influence of vesicular-arbuscular mycorrhizae on the growth of seedlings of Caesalpinia eriostachys, Cordia alliodora, Ipomoea wolcottiana and Pithecellobium mangense was investigated in a greenhouse experiment conducted at the Biological Station of Chamela on the Pacific coast of Mexico. Dry biomass production, relative growth rate, root/shoot ratio and mycorrhizal dependency were quantified for 75-day-old seedlings. With the exception of the pioneer species I. wolcottiana, mycorrhizal infection resulted in increases in biomass production, relative growth rate and leaf area. The root/shoot ratios attained for the species, however, did not show a consistent trend with infection. Nevertheless, all species had root/shoot ratios below 1 with infection and only one, Cordia alliodora, had a ratio greater than 1 without infection. The two late successional species from the mature part of the forest, Caesalpinia eriostachys and P. mangense, showed a larger mycorrhizal dependency than the two associated with disturbed environments.

Litterfall patterns in a tropical deciduous forest in Mexico over a five-year period

ABSTRACTContinuous litterfall measurements were made from 1977 to 1982, at two sites with contrasting topography in a mature tropical deciduous forest in Chamela, Jalisco, on the Pacific Coast of Mexico (19° 30′ N, 105° 03′ W). The climate is strongly seasonal with the annual rainfall (x = 748 mm) concentrated in six months (June to November) and a mean annual temperature of 24.9°C. Results of the five-year study show that at the Valley Site (slope &lt;5°) the mean annual litterfall was 6.58 ±0.15 (SE) Mg ha−1 y−1 composed of 73.3% leaves, 17.1% woody material, 5.6% reproductive remains and 4.0% finely fragmented debris. At the Hill Site (slope 20°–40°) mean annual litterfall was 3.95 ± 0.16 Mg ha−1 y−1, consisting of 68.8% leaves, 17.0% woody material, 9.4% reproductive remains and 4.7% fragmented debris. At the Valley Site the year-to-year variation in total litterfall was not significant. In contrast, at the Hill Site it fluctuated markedly from year to year. Litter production exhibited a pronounced seasonally: at the Hill Site total litterfall peaked near the onset of the dry season; at the Valley Site it occurred two months later, apparently as a result of differences in soil moisture availability between the study sites.