Composición florística, estructura y biomasa de los bosques de pino-encino en la reserva Santa Rosa, Tisey, Estelí, Nicaragua / Floristic composition, structure and biomass of pine-oak forests in the reserve Santa Rosa, Tisey, Estelí, Nicaragua

ResumenLos bosques de Pino-Encino se distribuyen desde el centro de México hasta el norte de Nicaragua y representan un ecosistema de importancia para la conservación en Mesoamérica. En Nicaragua, diferentes áreas protegidas fueron creadas para la preservación de este ecosistema tal como la reserva natural Tisey-Estanzuela, pero son considerados susceptibles a la degradación debido a la deforestación y la agricultura, así como presentarse en un nicho ecológico estrecho (700 a 1 500 msnm). En este trabajo, estudiamos la estructura y composición florística en un gradiente de altitud en un bosque mixto de PinusQuercus de tierras altas en Estelí, en el norte de Nicaragua. Un inventario de vegetación en 15 parcelas rectangulares (0.1 ha 20X50 m) fue llevado a cabo para identificar patrones de densidad de árboles, diversidad de especies y almacenamiento de carbono. En cada parcela todos los fustes con diámetro mayor o igual a 2.5 cm fueron identificados a especie y medidos (diámetro a la altura del pecho y altura total). Un total de 1 081 individuos de 24 especies (17 familias y 21 géneros) fueron registrados, siendo Q. sapotifolia, P. maximinoi, C. vicentina, M. coriacea y S. gladulosum las especies más abundantes representando 92 % de los individuos. Tres asociaciones vegetales fueron definidas basadas en la abundancia y dominancia de Q. sapotifolia, P. maximinoi y las otras especies, dos de estas asociaciones fueron dominadas por Pinus (Bosque de Pino y Bosques de Pino-encino) a altitudes entre 1 300 a 1 400 msnm, mientras la tercera asociación por encinos y otras especies (Cletha vicentina, Myrsine coriaceae, Sapium glandulosum) fue encontrada principalmente a altitudes mayores de 1 400 msnm. La composición y diversidad de especies fue influenciada significativamente por la dominancia de Pinus, mostrando una correlación negativa entre la dominancia y la riqueza de especies de árboles latifoliados diferentes de Quercus spp. Sin embargo, la asociación dominada por Pinus presentó un volumen y biomasa de fustes mayor comparado con las otras asociaciones. Los resultados de este estudio sugieren que los bosques dominados por doseles de encinos o pino-encino presentan la diversidad más alta, mientras bosques dominados por Pinus presentan menor diversidad arbórea por mayor biomasa aérea y almacenamiento de carbono. Por tal razón, se sugiere que estrategias de pagos por servicios ambientales como secuestro de carbono o conservación de la biodiversidad tomen en cuenta las diferencias de las asociaciones encontradas.

AbstractThe pine-oak forest is distributed from Central Mexico to the North of Nicaragua and represent an important ecosystem for conservation in Mesoamerica. In Nicaragua, several protected areas were established for the preservation of this ecosystem, such as the natural reserve Tisey-Estanzuela; however, this forest is considered susceptible to degradation, due to increasing deforestation and agricultural activities, besides being a narrow ecological niche (700 to 1 500 masl). We studied the floristic composition, forest structure and biomass along an altitude gradient dominated by Pinus-Quercus in forest stands on the highlands of Esteli, Northern Nicaragua. A vegetation survey on 15 plots (0.1 ha = 20x50 m) was carried out to identify patterns of tree density and diversity, and carbon stocks. In each plot, all the woody stems with diameter greater or equal to 2.5 cm were identified to species and the diameter at breast height and total height were measured. A total amount of 1 081 individuals of 24 species (17 families and 21 genera) were registered, being Q. sapotifolia, P. maximinoi, C. vicentina, M. coriacea and S. gladulosum the most abundant species representing 92 % of the individuals. Three forest associations were defined based on the abundance and dominance of Q. sapotifolia, P. maximinoi and the other species, two of those associations were dominated by Pinus (pine forest and pine-oak forest) at altitudes between 1 300 to 1 400 masl, while the third association, dominated by oak and other species (Cletha vicentina, Myrsine coriaceae and Sapium glandulosum), was found mainly at altitudes higher than 1 400 masl. Tree composition and species richness was influenced significantly by the dominance of Pinus, showing a negative correlation between the dominance and species richness of broadleaved trees other than Quercus spp. with the dominance of Pinus spp. (P < 0.001). However, the association dominated by Pinus, presented higher stem volume and biomass compared with other associations. The results from this study suggest that stands with both, an oak- or oak-pine-dominated canopy, presented the highest diversity, while Pinus dominated stands presented lower tree diversity, but higher aerial biomass and carbon storage. For this reason, we suggest that the strategies for ecosystem service payments as carbon sequestration or biodiversity conservation, must take into account differences in the type of forest associations found in this work.

Allometric models for estimating the phytomass of a secondary Atlantic Forest area of southeastern Brazil / Modelos alométricos para estimativa de fitomassa de Floresta Atlântica secundária no sudeste do Brasil

The purpose of this study was to develop and validate equations to estimate the aboveground phytomass of a 30 years old plot of Atlantic Forest. In two plots of 100 m², a total of 82 trees were cut down at ground level. For each tree, height and diameter were measured. Leaves and woody material were separated in order to determine their fresh weights in field conditions. Samples of each fraction were oven dried at 80 ºC to constant weight to determine their dry weight. Tree data were divided into two random samples. One sample was used for the development of the regression equations, and the other for validation. The models were developed using single linear regression analysis, where the dependent variable was the dry mass, and the independent variables were height (h), diameter (d) and d²h. The validation was carried out using Pearson correlation coefficient, paired t-Student test and standard error of estimation. The best equations to estimate aboveground phytomass were: lnDW = -3.068+2.522lnd (r² = 0.91; s y/x = 0.67) and lnDW = -3.676+0.951ln d²h (r² = 0.94; s y/x = 0.56).

O objetivo deste estudo foi desenvolver e validar modelos preditores para a fitomassa epigéa de uma área de Floresta Atlântica secundária. Em duas parcelas de 100m², 82 árvores foram cortadas, ao nível do solo, e anotadas suas medidas de altura e diâmetro. As folhas foram separadas dos ramos para determinação do massa fresca da porção foliar e lenhosa. Amostras de cada fração foram secas em estufa a 80 ºC, até massa constante, para determinação do massa seca. As árvores foram distribuídas em duas amostras aleatórias, sendo uma utilizada para o desenvolvimento das equações de regressão, e a outra para validá-las. Os modelos foram desenvolvidos através da análise de regressão linear simples, tendo como variável dependente a massa seca (DW) e, como variáveis independentes a altura (h), o diâmetro (d) e o quadrado do diâmetro multiplicado pela altura (d²h). A validação foi analisada através da comparação entre os valores obtidos em campo e os estimados pelas equações, através da análise de correlação intraclasse de Pearson e teste t-Sudent pareado. As melhores equações para estimar o massa seca das árvores foram: lnDW = -3,068+2,522lnd (r² = 0,91; s y/x = 0,67) e lnDW = -3,676+0,951ln d²h (r² = 0,94; s y/x = 0,56).

Wood specific gravity of trees and forest types in the southern Peruvian Amazon

Estimates of terrestrial biomass depend critically on reliable information about the specific gravity of the wood of forest trees. The study reported on here was carried out in the southern Peruvian Amazon and involved collection of wood samples from trees (70 spp.) in intact forest stands. Results demonstrate the high degree of variability in specific gravity (ovendry weight/green volume) in trees at single locations. Three forest types (swamp, high terrace forest with alluvial soil, and sandy-soil forest) had values close to the average reported for tropical forest woods (.69). Two early successional forest types, which make up as much as 12% of the total vegetated area in this part of the Amazon, had values significantly lower (.40). An increase in specific gravity with increasing age of the tree, which has been reported in some spe cies of tropical-forest woods, is seen in a positive relationship between specific gravity and di ameter for a species prevalent in one plot. Increases in specific gravity with tree and forest age may be significant in estimating changes in carbon stores over time.

Estimativas de biomassa em ecossistemas terrestres dependem de informações confiáveis sobre a densidade da madeira das árvores. Neste estudo, realizado no sul da Amazônia peruana, foram coletadas amostras de madeira de árvores (70 spp.) em florestas intactas. Os resultados demonstram a grande variabilidade na densidade específica (peso seco / volume fresco) entre as árvores de um único sítio. Três tipos de floresta (baixio de terraço alto, floresta sobre terraço aluvial alto argiloso, e floresta de terra firme sobre solo arenoso) tiveram valores de densidade específica próximos à média reportada para madeiras de floresta tropical (0,69). Duas florestas em fase sucessional, que constituem até 12% da área vegetada nesta parte da Amazônia, tiveram valores significativamente menores (média de 0,40). Um incremento da densidade específica com a idade da árvore, reportada anteriormente para algumas espécies de árvores de floresta tropical, foi também encontrado para uma espécie avaliada neste estudo, com uma relação positiva entre sua densidade específica e seu diâmetro. Os aumentos de densidade específica com a idade, tanto das espécies como das florestas, podem ser importantes para estimativas de mudanças temporais nos estoques de carbono.