Understanding edge effects in different remnants of natural vegetation is crucial for the management of many fragmented landscapes. We compared edges of different wooded habitats in a fragmented ...tropical rainforest in Los Tuxtlas, Veracruz, Mexico. Selected habitats in a pasture matrix included four forest fragments (>50 ha), four linear forest remnants along streams (riparian forest), and eight isolated remnant forest trees (four fenced and four without fences). Edge habitats were defined in terms of microclimate, vegetation structure, and floristic composition. In forest-pasture sites, significant edge effects were detected for some variables, but depth of influence varied. Compared to the other habitats, riparian sites and isolated trees without fences exhibited distinct edge conditions. Isolated trees fenced for 54 months, however, exhibited some microenvironmental conditions similar to those of forest interior. In total, 244 woody plant species were recorded in the sampled area (<1 ha), and these represented 56% of woody species reported for Los Tuxtlas reserve. Only two species, Acalypha diversifolia and Siparuna andina, occurred in the interior, edge, and pasture of all studied landscape units. Twelve species occurred in all edges and pastures (e.g., Acacia mayana, Tabernaemontana arborea, Cupania glabra, Stemmadenia donnell-smithii). Twenty-six species were found exclusively at edges, whereas 44 species were recorded only in interiors. Fenced, isolated trees can provide a suitable habitat for the establishment of several primary-forest trees (e.g., Nectandra spp.). Many primary-forest species were found in the fragmented habitats we studied, suggesting that these species are not lost in fragmented landscapes and that plant diversity loss is probably proceeding slowly. Collectively, riparian strips and isolated trees in a pasture matrix could effectively function as a focus for rainforest regeneration. Riparian strips and trees, therefore, need to be incorporated into landscape designs for maintaining and enhancing ecological diversity.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
(1) Micro-environmental conditions, vegetation structure and tree mortality in five forest edges ten months to twelve years old were studied in the tropical premontane wet forest of Panama. (2) Along ...transects from clearings to the interior of the forest, the greatest change in temperature and relative humidity occurred between 2.5 and 15 m into the forest. The forest canopy was most open at the clearing-forest border. At the most recently cleared site, this open canopy extended farther into the forest edge than at sites where clearing took place earlier. (3) Density and basal area of trees (< 10 cm diameter at 1.3 m high) were twice as great at the forest edges compared with the interior of forests at the sites where the boundaries were created five to twelve years previously. (4) Floristic composition was unchanged along transects from the forest boundaries to the interior of forests and light-demanding species were not more abundant at forest edges compared with the forest interior. (5) The edge: interior ratio of trees that died after the edges were created was 14:1. (6) Beyond 15-25 m into the forest, neither environmental conditions nor the forest structure and tree mortality were influenced by proximity to the forest boundary. Between 0 and 15 m, however, vegetation structure changed with both distance from the forest boundary and time elapsed since clearing. This study indicates the ecological significance of edge vegetation as a buffer protecting forest vegetation from conditions in adjacent clearings.
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BFBNIB, INZLJ, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK, ZRSKP
The density and floristic composition of the soil seed bank was assessed in six cloud forest fragments with different levels of human disturbance in central Veracruz, Mexico. A total of 8416 seeds ...germinated in 60 soil samples, at 5-cm depth, corresponding to 107 species, 85 genera, and 48 families. Significant differences were found among study sites in seed densities with values ranging from 873 to 3632/m2. Tree species contributed 20 percent of the total soil seed bank in four sites and herbs accounted for the majority of the species in each site. Among tree species, Trema micrantha displayed the highest seed density, accounting for 84 percent of the germinated seeds. In general, the tree species composition of the soil seed bank did not closely reflect the composition of the tree community. Results suggest that disturbance produced by human activities (trail use, selective cutting of trees, livestock) may influence the size and composition of the soil seed bank in forest fragments. Sites where human activity has been reduced showed the highest proportion of dormant seeds. /// La densidad composición florística del banco de semillas del suelo se determinó en seis fragmentos de bosque de niebla con distinto nivel de alteración humana, en Veracruz, México. Un total de 8416 semillas germinaron en 60 muestras de suelo, correspondientes a 107 especies, 85 géneros y 48 familias. Se encontraron diferencias significativas entre los sitios de estudio, con valores desde 873 a 3632 semillas/m2. La mayoría de las especies fueron hierbas y en cuatro de los sitios las especies arbóreas contribuyeron un 20 por ciento al total de semillas del banco del suelo. Entre las especies arbóreas, Trema micrantha (L.) Blume (Ulmaceae) presentó la mayor densidad de semillas (84% de las semillas germinadas). En general, la composición de especies arbóreas en el banco del suelo no reflejó la composición de la comunidad de árboles en cada sitio. Los resultados sugieren que la alteración causada por actividad humana (uso de senderos, tala selectiva y pastoreo) puede influir en el tamaño y composición del banco de semillas del suelo en fragmentos de bosque. Los sitios donde la actividad humana es reducida tienen la mayor proporción de semillas latentes.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Tropical montane cloud forest exhibits great heterogeneity in speciescomposition and structure over short geographic distances. In central Veracruz,Mexico, the conservation priority of seven cloud ...forest fragments was assessedby considering differences in woody plant species richness and complementarityof species among sites, forest structure, tree mortality, and timber andfirewood extraction as indicators of anthropogenic disturbance. Densities oftrees ≥5 cm dbh (360-1700 trees/ha) weredifferent among the sites, but basal area (35.3-89.3m^sup 2^/ha) did not differ among fragments. The number of dead trees rangedfrom 10-30 to 170-200 trees/ha. The fragments'species composition was different but complementary. The Morisita-Hornindex indicated low similarity between fragments. A non-parametric estimator ofspecies richness indicated that more sampling effort would be necessary tocomplete the inventory (15 additional trees and two understory shrub species).Unfortunately, most of the fragments are threatened with deforestation. The numberof cut trees was similar among sites (0-15 cut trees/0.1 ha).Sites with immediate need for conservation were close to settlements, with highnumbers of cut trees and no legal protection. The selected sites represent thevariety of situations that exist in the region. Given the high complementarityobserved between fragments, a regional conservation approach will be required topreserve the last repositories of part of the tremendous biodiversity of theonce continuous forest in this region.PUBLICATION ABSTRACT
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Fagus grandifolia var. mexicana seedling dynamics were studied in a relict forest inside the crater of a volcano where it is the only canopy tree species. The objectives of the study were (1) to ...determine changes in seedling density before and after a mast year, as well as to monitor seedling recruitment, mortality and growth rate in relation to the micro-environment, and (2) to discuss the impact of masting on seedling dynamics of the population. Before masting, seedling density was 8.8 seedlings m–2, afterwards seedling density peaked at 51.5 seedlings m–2, then decreased by 50% in 3 months and by 85% after 8 months, down to levels of before the mast year (9.9 seedlings m–2) after 16 months. Seedlings in the forest floor before the mast-seeding event showed a low relative growth rate − 0.14 mm mm–1 mo–1 against 1.27 mm mm–1 mo–1 for seedlings that emerged immediately after masting. Seed germination was high (83%) and rapid (L50 = 7 days) following masting. Seedling growth was positively correlated with soil water content but not with temperatures and relative humidity. Data suggested that seed production in mast years is important in maintaining the seedling bank, and thus the viability of relict Fagus populations. Abbreviations: PAR = Photosynthetically active radiation; RGR = Relative growth rate.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Four native tree species (Liquidambar styraciflua, Juglans pyriformis, Podocarpus matudae, and Carpinus caroliniana) were evaluated for their suitability in rehabilitating degraded areas of Mexican ...cloud forest. Plant survival and growth in height and diameter were determined in three mixed-experimental plantations with different land use histories; their performance was compared with two on-farm plantations started by landowners for forest restoration. Nearby forest fragments were controls for soil compaction. An experimental plantation with remnant trees had the highest plant survival (82%), height, basal diameter and relative growth rate. The plantation with the steepest slope had high plant survival (63%) and growth. The plantation characterized by dominance of grasses and compacted soils had the lowest survival (22%) and growth. On-farm plantations had good establishment of planted trees (5-10 species planted), and facilitated the recruitment of 9-11 woody species. Carpinus and Liquidambar appear to be suitable species for reforestation in all these areas. Podocarpus grew relatively slowly, although it performed well in two experimental sites. Juglans had high survival (76%) under the stressful conditions of the most adverse site, and therefore may be useful for rehabilitation of degraded sites. Differences among species and sites strongly suggest that species success depends on plantation site quality.PUBLICATION ABSTRACT
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
. Fagus grandifolia var. mexicana seedling dynamics were studied in a relict forest inside the crater of a volcano where it is the only canopy tree species. The objectives of the study were (1) to ...determine changes in seedling density before and after a mast year, as well as to monitor seedling recruitment, mortality and growth rate in relation to the micro‐environment, and (2) to discuss the impact of masting on seedling dynamics of the population. Before masting, seedling density was 8.8 seedlings m–2, afterwards seedling density peaked at 51.5 seedlings m–2, then decreased by 50% in 3 months and by 85% after 8 months, down to levels of before the mast year (9.9 seedlings m–2) after 16 months. Seedlings in the forest floor before the mast‐seeding event showed a low relative growth rate – 0.14 mm mm–1 mo–1 against 1.27 mm mm–1 mo–1 for seedlings that emerged immediately after masting. Seed germination was high (83%) and rapid (L50= 7 days) following masting. Seedling growth was positively correlated with soil water content but not with temperatures and relative humidity. Data suggested that seed production in mast years is important in maintaining the seedling bank, and thus the viability of relict Fagus populations.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Using 15 shade coffee farms and two forest reserves located in central Veracruz, Mexico, we evaluated how tree vegetation structure and richness changed as a function of management type and compared ...to that remnant forest fragments. Coffee farms were classified as shade monocultures (SMs), simple polycultures (SPs), or diverse polycultures (DPs). A total of 124 sampling units representing 15.19
ha were randomly located in farms with the number of sampling units varying as a function of farm area. Twenty additional plots were sampled in two nearby cloud forest fragments. Forest vegetation structure was higher than in farms, except for mean canopy height that was similar to that in SP and DP farms. Within farms, tree density was generally higher in SM, whereas basal area and both mean and maximum height were higher in SP and DP sites. We recorded 2833 individuals representing 107 tree species ≥5
cm
dbh in coffee farms, including 24 non-native species, and 83 native species (33 primary, and 50 secondary tree species). Patterns of richness followed the expected pattern with 11
±
1.4 (S.E.) tree species in SM farms, 14
±
1.8 in SP farms, 29
±
2.3 in DP farms, and 38
±
16 in forest control sites; however, rarefaction strongly suggests that DP sites are actually richer in species than the forests studied. The proportion of native tree species in each coffee management type was consistently elevated (78%). Since the majority of species (71%) were rare and found only in one or two farms, complementarity among types of coffee management (68–77%), and coffee managements and forest (90–92%) was very high. SP and DP farms had the highest proportions of animal-dispersed species and were similar to forest. Species richness was positively correlated with tree density for DP, and to basal area for SM farms. Our results suggest that shade diversity is actively managed by coffee farmers and that all three types of coffee management studied may have an important role to play in the conservation of regional biodiversity. Considering factors such as complementarity, landscape heterogeneity, functional diversity, and the rigor of vegetation surveys may also help improve the validity, and thus the impact, of coffee certification programs designed with the goal of conserving tropical montane biodiversity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Patterns of genetic variation were examined within two endemic tree species restricted to Mexican cloud forest, Magnolia sharpii and Magnolia schiedeana. Leaf samples collected from natural ...populations were analysed using PCR RFLP of cpDNA, Inter-SSR and isozyme genetic markers, which were used to test a series of hypotheses regarding patterns of intraspecific variation within the two species. Genetic diversity estimates derived from Inter-SSR markers (mean Spop of 0.56 and 0.50 for M. sharpii and M. schiedeana respectively) are comparable to values obtained for other tree species. As predicted on the basis of its larger geographic range, the degree of population differentiation was found to be higher within M. schiedeana than M. sharpii, with 12.9% and 3.4% of total variation recorded between populations for the two species respectively using isozymes, and 26% and 11% using Inter- SSR markers. Isozyme analyses indicated negative F
values, which may be suggestive of inbreeding in populations of M. sharpii, but provided less evidence of inbreeding in M. schiedeana. On the basis of PCR RFLP analysis of cpDNA, two chloroplast types were differentiated, type A being recorded for all of the individuals of both species, with the exception of one population of M. schiedeana that was fixed for type B. These results are consistent with recent evidence suggesting that some endemic plant taxa are able to maintain relatively high diversity within populations despite the occurrence of inbreeding and genetic drift, and that species with wider geographic ranges tend to exhibit relatively high genetic differentiation among populations. Conservation strategies for these species need to take into account the significant genetic differences recorded among the populations studied.
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