Geographic information system techniques were used in combination with remote sensing data to define the net commercial value of standing timber at two sites (Batouri and Bertoua) in the East province of Cameroon. Observed forest cover modifications for the two sites were assessed in relation to the commercial accessibility of the forest areas. Results showed that, in one site, half of the very high rent areas have already been logged indicating that the unlogged high rent area is scarce and the low rent or marginal forest area remains largely unlogged. However, this was not the case throughout the study area as shown by the observations at the other site. The two main species exploited were sapelli (Entandrophragma cylindricum) and Ayous Triplochiton scleroxylon.
Tag: prediction
Population dynamics of Hippophae rhamnoides shrub in response of sea-level rise and insect outbreaks
The coastal vegetation of islands is expected to be affected by future sea-level rise and other anthropogenic impacts. The biodiverse coastal vegetation on the eastern part of the Dutch Wadden Island of Ameland has experienced land subsidence caused by gas extraction since 1986. This subsidence mimics future sea-level rising through increased flooding and raising groundwater levels. We studied the effects of this relative sea-level rise and other environmental factors (i.e. insect outbreaks, temperature and precipitation) on the population dynamics (i.e. cover and age structure and annual growth) of the shrub seabuckthorn (Hippophae rhamnoides L.) in young (formed after 1950) and old (formed before 1950) dune areas over a period of 56 years (1959–2015). We found an increase in seabuckthorn cover in the young dune areas since 1959, while over time the population in the old dunes decreased due to successional replacement by other species. With the increasing age of the young dunes, we found also a decrease in sea-buckthorn after 2009. However the sharp decrease indicated that other environmental factors were also involved. The most important determinant of annual shrub growth appeared to be five outbreaks of the brown-tail moth (Euproctis chrysorrhoea L.), in the last decade. Relative sea-level rise caused more frequent flooding and reduced growth at lower elevations due to inundation or soil water saturation. This study clearly indicates that sea-buckthorn is affected by relative sea-level rise, but that other ecological events better explain its variation in growth. Although shrub distribution and growth can be monitored with robust methods, future predictions of vegetation dynamics are complicated by unpredictable extreme events caused by (a)biotic stressors such as insect outbreaks.