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Big Trees (big + tree)
Selected AbstractsWhat controls woodland regeneration after elephants have killed the big trees?JOURNAL OF APPLIED ECOLOGY, Issue 1 2009Stein R. Moe Summary 1Top-down regulation of ecosystems by large herbivores is a topic of active debate between scientists and managers, and a prime example is the interaction between elephants Loxodonta africana and trees in African savannas. A common assumption among wildlife managers is that a local reduction in elephant numbers will ultimately allow woodland to self-restore to a desired former state. Such regeneration is, however, dependent on the survival of seedlings of impacted tree species. We conducted a field experiment to investigate seedling predation in the elephant-transformed Chobe riparian woodland of northern Botswana. 2We planted seedling gardens in (i) complete exclosures that excluded all herbivores except small rodents and invertebrates, (ii) semi-permeable exclosures that excluded ungulates but included primates, lagomorphs, all rodents, gallinaceous birds, etc, and (iii) completely open plots. Seedlings were of two tree species decreasing in the area (Faidherbia albida and Garcinia livingstonei) and two that are increasing (Combretum mossambicense and Croton megalobotrys). 3After 9 months, seedling survival ranged from >75% for all species in the complete exclosure to <20% for Faidherbia albida in the open plots. Survival of all seedlings except C. megalobotrys declined precipitously in open plots during the dry season when invertebrates are largely dormant but when impalas Aepyceros melampus (locally abundant ungulates) increase the browse components of their diets. 4Seedling survival in the open plots was negatively related to local impala density but unrelated to that of any other browser. 5Synthesis and applications. Our findings relate to the current debate about managing elephants to restore southern African savanna landscapes to desired historical states. Various seedling predators, including the ubiquitous impala Aepyceros melampus, regulate the regeneration of trees from seedlings, and our experiments support the hypothesis that tall closed-canopy woodlands originate during episodic windows of opportunity for seedling survival. To artificially recreate such a window would require the decimation of seedling predators as well as elephants, which is impractical at the landscape scale. [source] Seed Dynamics in Relation to Gaps in a Tropical Montane Rainforest of Hainan Island, South China: (II) Seed BankJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 5 2008Run-Guo Zang Abstract Spatial and temporal patterns of seed bank dynamics in relation to gaps in an old growth tropical montane rainforest of Hainan Island, South China, were studied over two consecutive years. From June 2001 to June 2003, soil seed bank sampling blocks were taken near each of the four sides of each seed trap and immediately put into a nursery for observation of seedling emergence dynamics in four seasons (each experiment in each season). The abundances of seedlings that emerged from seed banks showed the trend of vine functional group (VFG) > shrub functional group (SFG) > tree functional group (TFG) > herb functional group (HFG), but the trend in species richness of seedlings that emerged from the soil seed banks was TFG > VFG > SFG > HFG. The abundances of seedlings that emerged from seed banks in the three gap zones showed no significant differences, but significant differences did exist for the species richness. The time of sampling or seasons of experiments had significant influences on both the species richness and seedling abundances. The seedling emergence processes of each experiment all revealed the unimodal patterns. Few emergences occurred 1 year after each experiment. Compared with those under closed canopies, the recruitment rates from seed to seedlings and from seedlings to saplings in gaps were higher, but the mortality rates from saplings to big trees were also higher in the gaps. [source] Cone abortion in Pinus halepensis: the role of pollen quantity, tree size and cone locationOIKOS, Issue 1 2002Shirrinka Goubitz This study describes the seasonal patterns of seed and cone abortion in natural Pinus halepensis trees and assesses the effects of pollen quantity, tree size and cone location on seed and cone abortion. The cone-set ratio was similar to the expected value, based on literature on woody perennials. The seed-ovule ratio, however, was almost twice as high as its expected value. The investment in protective cone elements was high and did not vary with the seed-ovule ratio of a cone. Pollination factors influenced cone abortion, as indicated by the high abortion rate at the end of the pollination period. Furthermore, abortive cones had lower pollination rates and lower pollen loads than well developed cones. Effects of resource availability were assessed as effects of tree size and cone position on twigs. Small trees aborted more cones than big trees and cone abortion was higher in apical cones than in basal cones. Abortion in P. halepensis is selective, mediated by both pollen quantity and resource availability. The relative importance of pollen and resources is suggested to be flexible, probably varying between trees and years. The high seed-ovule ratio of P. halepensis is the result of high pollination rate and selective abortion. The selective abortion might be due to the high allocation to protective cone elements relative to the allocation to seeds. [source] Effects of habitat fragmentation and disturbance on howler monkeys: a reviewAMERICAN JOURNAL OF PRIMATOLOGY, Issue 1 2010Víctor Arroyo-Rodríguez Abstract We examined the literature on the effects of habitat fragmentation and disturbance on howler monkeys (genus Alouatta) to (1) identify different threats that may affect howlers in fragmented landscapes; (2) review specific predictions developed in fragmentation theory and (3) identify the empirical evidence supporting these predictions. Although howlers are known for their ability to persist in both conserved and disturbed conditions, we found evidence that they are negatively affected by high levels of habitat loss, fragmentation and degradation. Patch size appears to be the main factor constraining populations in fragmented habitats, probably because patch size is positively related to food availability, and negatively related to anthropogenic pressures, physiological stress and parasite loads. Patch isolation is not a strong predictor of either patch occupancy or population size in howlers, a result that may be related to the ability of howlers to move among forest patches. Thus, we propose that it is probable that habitat loss has larger consistent negative effects on howler populations than habitat fragmentation per se. In general, food availability decreases with patch size, not only due to habitat loss, but also because the density of big trees, plant species richness and howlers' home range size are lower in smaller patches, where howlers' population densities are commonly higher. However, it is unclear which vegetation attributes have the biggest influence on howler populations. Similarly, our knowledge is still limited concerning the effects of postfragmentation threats (e.g. hunting and logging) on howlers living in forest patches, and how several endogenous threats (e.g. genetic diversity, physiological stress, and parasitism) affect the distribution, population structure and persistence of howlers. More long-term studies with comparable methods are necessary to quantify some of the patterns discussed in this review, and determine through meta-analyses whether there are significant inter-specific differences in species' responses to habitat loss and fragmentation. Am. J. Primatol. 72:1,16, 2010. © 2009 Wiley-Liss, Inc. [source] Differences in diet and activity pattern between two groups of Alouatta palliata associated with the availability of big trees and fruit of top food taxaAMERICAN JOURNAL OF PRIMATOLOGY, Issue 8 2009Jacob C. Dunn Abstract The threat that forest fragmentation and habitat loss presents for several Alouatta taxa requires us to determine the key elements that may promote the persistence of howler monkeys in forest fragments and to evaluate how changes in the availability of these elements may affect their future conservation prospects. In this study we analyzed the relationship between the availability of both big trees of top food taxa (BTTFT) (diameter at breast height>60) and fruit of top food taxa (FrTFT) in the home ranges of two groups of Alouatta palliata mexicana occupying different forest fragments in Los Tuxtlas, Mexico, and their diet and activity pattern. Both study groups preferred big trees for feeding and the group with lower availability of BTTFT in their home range fed from more, smaller food sources. Furthermore, both study groups also increased the number of food sources when their consumption of fruit decreased, and the group with lower availability of FrTFT in their home range fed from more food sources. The increase in the number of food sources used under such conditions, in turn, set up a process of higher foraging effort and lower rest. In summary, our results support other studies that suggest that the availability of big trees and fruit may be two important elements influencing the persistence of howler monkeys in forest fragments. Am. J. Primatol. 71:654,662, 2009. © 2009 Wiley-Liss, Inc. [source] | ||||||||||