European beech (Fagus sylvatica) is a drought-sensitive species that likely will retreat from its xeric distribution edges in the course of climate warming. Physiological measurements indicate that the species may not only be sensitive to soil water deficits, but also to high temperatures and elevated atmospheric vapor pressure deficits (vpd). Through microclimatological measurements in the stand interior across near-natural beech forest–oak forest ecotones, we searched for microclimatic tipping points in the contact zone with the aim to define the thermic and hydrometeorological limits of beech more precisely. In three transects in the foothills of the Romanian western Carpathians, we measured in mid-summer 2019 air temperature, relative air humidity, and vpd at 2 m height in the stand interior across the ecotone from pure oak to pure beech forests, and compared the readings to the microclimate in forest gaps. Mean daytime temperature (T) and vpd were by 2 K and 2 hPa, respectively, higher in the oak forests than the beech forests; the extremes differed even more. Especially in the second half of the day, the oak forests heated up and were more xeric than the beech forests. Part of the differences is explained by the elevation difference between oak and beech forests (200–300 m), but species differences in canopy structure, leaf area, and canopy transmissivity enhance the microclimatic contrast. Our T and vpd data point to thresholds at about 30 °C and 25 hPa as maxima tolerated by beech in the lowermost shade canopy for extended periods. In conclusion, the rather sharp stand microclimatic gradient demonstrated here for the xeric distribution limit of beech may well be the decisive factor that hinders the spread of beech into the warmer oak forests.
In the humid tropics of Latin America, considerable proportions of agro-scapes are covered with degraded pastures that were taken over by dense weedy shrub canopies hampering further forest succession. While tree seeds are still constantly dispersed by bats and birds, these often do not reach the soil but got stuck in the dense shrubby vegetation. While manual up-rooting of weedy shrubs or tree replantation is too expensive, we tested if burrowing pigs or trampling cattle can enhance proportions of bare soils for fallow restoration. These hypotheses were tested in on-farm experiments at Igarapé-Açu, northeastern Pará. Soil-opening effects of ten pigs (40 days + nights) and ten oxen (40 overnight stays), respectively, were tested against manual clearing and control on three plots per treatment, respectively. Ground cover percentages of bare soil, weedy shrubs, grasses, and tree species were visually determined in 40 plots/treatment before and directly after treatments, and half a year later (n = 480 samples). Both animal treatments could not really match manual clearing (62%) but pigs reached above 36% bare ground cover, while cattle just 20%. As pigs are almost omnipresent on Amazonian smallholdings and even give a modest economic refund, the use of pigs is recommended to smallholders who want to break up the lush weed layers for the benefit of forest restoration.
9 February 2021 in Neotropical Biology and Conservation
The northern coast of Honduras is potentially covered with tropical rainforests, reaching from the Caribbean Sea up to the cloud forests of the Pico Bonito summits. Therefore, it was blessed with the mega-diverse avifauna of the Central American humid neotropics. Although local bird species have been generally well documented, there are hardly any updates on the biodiversity of northern Honduras. Thus, this study contributes to our knowledge of the natural shift of bird life, following up the Cangrejal River with its different slight land use intensification in the region. Standardized bird records along the valley are analyzed, reaching from the beaches of La Ceiba up to the managed rainforests of El Toncontíns in the lower montane rainforests. Nine points were checked over the course of at least 6 days, taking point counts between 16 March and 20 June 2005. A NMDS of the joined nine point-lists elucidates four main groups, namely the beach/city ecosystems, open habitats along the river banks, slightly cleared forests (park landscape), and a mature rainforest. In total, 115 bird species, from 102 genera and 44 families, were found in 2005. As methods are limited, results can represent merely a prodromus of bird composition of neotropical valleys of the Central American isthmus. However, avi-diversity is affected by forest degradation and increasing land-use changes. Since deforestation is still soaring in the region, bird species composition should be monitored, as it will be as dynamic as land use changes in the region.