RESUMO
The occurrence and combination of extreme meteorological events may lead to severe (megadisturbance) impacts on conserved forests and protected areas all over the world. Recent research has shown that megadisturbance impacts (after the events of hurricanes and prolonged drought) may be detected in subtropical forest cover using changes in spectral indices derived from satellite imagery. The objective of this study is to assess the impact of megadisturbance on forest types of the Alejandro de Humboldt National Park, Republic of Cuba in the 2001-2017 time-period. The Global Forest Cover Change (GFCC, available on the Global Forest Watch website) product was validated and indicated the prominence of megadisturbance for year 2016 (85% of the total disturbed area), largely associated with the Hurricane Matthew event. A robust estimator of the disturbed forest area, based on GFCC-stratified sampled verification sites, suggests that 11,110 ± 1,771 hectares of forest (~ 16% of the Park's total area) was affected by megadisturbance between 2001 and 2017. In 2017, about 1276 hectares of forests were impacted, presumably related to a long-lasting effect of megadisturbance due to Hurricane Matthew and prolonged droughts in previous years. Four types of tropical rainforests (especially lowland rainforest and submountainous sclerophyllous rainforest on serpentinite), that cover 43% of the National Park, accounted for about 85% of the impacts by megadisturbance. The Easternmost portion of these forests should be prioritized for conservation monitoring and possibly for forest restoration strategies. This study contributes to establishing methodological guidelines for rapid environmental assessment of remote, tropical protected areas facing the impacts of extreme meteorological events and climate change.
Assuntos
Florestas , Árvores , Secas , Silicatos de Magnésio , Floresta ÚmidaRESUMO
Recent trends in landscape dynamics were investigated in various forest ecosystems along the Tuxpan river basin (1887.5km²; 620-3640masl) in the State of Michoacan, Mexico. Landscape maps were developed from the interpretation, in GIS-ILWIS ver. 3.0, of land covers corresponding to four different dates (1976-2000), and the typology was based on origin vegetation, physiognomic development and permanence of the land-use disturbance. Maps were cross-related and calculations were derived on surfaces, percent change and mean annual transformation rate, and transition matrices were obtained so as to identify the main change processes. In order to explain the distribution of landscape-dynamics patterns, a landscape geography method was applied using relief units and potential vegetation as the bases for determining landscape systems. The study area comprises three landscape-dynamics patterns: i. fir forest in high volcanic peaks (>3100masl), highly preserved but showing a trend towards an increase in traditional agriculture and deforestation; ii. pine-oak forests in volcanic slopes and peaks (1900-3100masl) and tropical dry forest on sedimentary basement (<1700masl) showing a high deforestation and heavy use, with a trend towards abandonment of crops, expansion of shrublands/grasslands and scarce forest regeneration; and iii. pine-oak forest in low volcanic slopes (1700-2600) with the highest inherited modifications and a trend towards land-use intensification in human settlements and forest plantations.
Se estudiaron las tendencias recientes de la dinámica del paisaje en distintos ecosistemas forestales de la cuenca del río Tuxpan (1887,5km² y 620-3640msnm), en el estado de Michoacán, México. Los mapas de paisajes se obtuvieron a partir de la interpretación, en SIG-ILWIS ver. 3.0, de las coberturas del suelo en cuatro fechas (1976-2000). Para la tipología se consideró el origen, desarrollo fisonómico de la vegetación y permanencia del disturbio asociado al uso del suelo. Los mapas se cruzaron entre sí, se calcularon superficies, porcentajes de cambio e índices de transformación media anual y se elaboraron matrices de transición para identificar los principales procesos de cambio. Para explicar la distribución de la dinámica del paisaje se aplicó un método de la geografía del paisaje que utiliza las unidades del relieve y la vegetación potencial para determinar sistemas de paisajes. El área comprende 3 patrones de dinámica del paisaje: i. abetal de altas cumbres volcánicas (>3100msnm) con alta conservación, pero tendencia al incremento del cultivo tradicional y la deforestación; ii. bosques de pino-encino de cumbres y de laderas volcánicas altas (1900-3100) y selva baja caducifolia del basamento sedimentario (<1700) con alta deforestación e intensificación del uso, pero tendencia al abandono del cultivo y expansión de la vegetación secundaria; y iii. bosque de pino-encino de laderas volcánicas bajas (1700-2600) con la mayor transformación heredada y tendencia a la intensificación del uso del suelo en asentamientos humanos y plantaciones forestales.
Estudaram-se as tendências recentes da dinâmica da paisagem em distintos ecossistemas florestais da bacia do rio Tuxpan (1887,5km² e 620-3640msnm), no estado de Michoacán, México. Os mapas de paisagens se obtiveram a partir da interpretação, em SIG-ILWIS ver. 3.0, das coberturas do solo em quatro datas (1976-2000). Para a tipologia se considerou a origem, o desenvolvimento fisionômico da vegetação e a permanência do distúrbio associado ao uso do solo. Os mapas se cruzaram entre si, se calcularam superfícies, porcentagens de mudança e índices de transformação média anual; foram elaboradas matrizes de transição para identificar os principais processos de mudança. Para explicar a distribuição da dinâmica da paisagem se aplicou um método da geografia da paisagem que utiliza as unidades de relevo e a vegetação potencial para determinar sistemas de paisagens. A área compreende três padrões de dinâmica da paisagem: i. abetal de altos cumes vulcânicos (>3100msnm) com alta conservação, mas tendência ao incremento do cultivo tradicional e ao desflorestamento; ii. bosques de pinho-encino de cumes e de ladeiras vulcânicas altas (1900-3100) e selva baixa caducifólia do basamento sedimentário (<1700) com alto desflorestamento e intensificação do uso, mas tendência ao abandono do cultivo e expansão da vegetação secundária; e iii. bosque de pinho-encino de ladeiras vulcânicas baixas (1700-2600) com a maior transformação herdada e tendência à intensificação do uso do solo em assentamentos humanos e plantações florestais.
RESUMO
Se estudia el proceso de recuperación del paisaje post-fuego en pastizales subalpinos del volcán Iztaccíhuatl, 70km al SE de la cuidad de México. La información de base se obtuvo de 57 inventarios florísticos-ambientales. La edad post-fuego del 60 por ciento de los sitios se obtuvo de entrevistas de campo, y mediante tablas de correlación binaria entre la riqueza y la abundancia de especies se determinaron la edad post-fuego en el resto de los sitios y las variables de la vegetación que mejor se correlacionan con la edad del incendio: Riqueza Media de Especies y Cobertura Total Media de Lupinus montanus, Penstemon gestianoides y pastos. El análisis de correlación binaria (Casewise MD deletion) entre dichas variables fue utilizado para establecer 12 geofacies de paisaje que representan distintos estados de recuperación post-fuego. La correlación espacial -en GIS entre las geofacies y 7 unidades ambientales definidas por altitud, orientación y morfología de laderas, sirvió para reconocer 6 geofacies cosmopolitas que definen la Serie General del Paisaje post-fuego, así como 6 geofacies excepcionales que se integran a la serie general bajo condiciones ambientales específicas
Assuntos
Montana , Pastagens , Ecologia , MéxicoRESUMO
Land-cover types were analyzed for 1970, 1990 and 2000 as the bases for determining land-use systems and their influence on the resilience of tropical rain forests in the Tehuantepec Isthmus, Mexico. Deforestation (DR) and mean annual transformation rates were calculated from land-cover change data; thus, the classification of land-use change processes was determined according to their impact on resilience: a) Modification, including land-cover conservation and intensification, and b) Conversion, including disturbance and regeneration processes. Regeneration processes, from secondary vegetation under extensive use, cultivated vegetation under intensive use, and cultivated or induced vegetation under extensive use to mature or secondary vegetation, have high resilience capacity. In contrast, cattle-raising is characterized by rapid expansion, long-lasting change, and intense damages; thus, recent disturbance processes, which include the conversion to cattle-raising, provoke the downfall of the traditional agricultural system, and nullify the capacity of resilience of tropical rain forest. The land-use cover change processes reveal a) the existence of four land-use systems (forestry, extensive agriculture, extensive cattle-raising, and intensive uses) and b) a trend towards the replacement of agricultural and forestry systems by extensive cattle-raising, which was consolidated during 1990-2000 (DR of evergreen tropical rain forest = 4.6%). Only the forestry system, which is not subject to deforestation, but is affected by factors such as selective timber, extraction, firewood collection, grazing, or human-induced fire, is considered to have high resilience (2 years), compared to agriculture (2-10 years) or cattle-raising (nonresilient). It is concluded that the analysis of land-use systems is essential for understanding the implications of land-use cover dynamics on forest recovery and land degradation in tropical rain forests.
