The effect of human disturbance on tree species composition and demographic structure in Kalinzu Forest Reserve,Uganda

Tree abundance and species composition in the mechanically logged, intensively pitsawn and minimally disturbed areas of Kalinzu Forest Reserve were determined. The spatial and diameter size‐class distribution of ten selected tree species representing pioneer, secondary colonizer, understorey, canopy, dominant and endangered species were also assessed. The species were: Musanga leo‐errerae, Trema orientalis, Funtumia africana, Strombosia scheffleri, Oxyansus speciosus, Parinari excelsa, Tabernaemontana holstii, Newtonia buchananii, Lovoa swynnertonii and Entandrophragma angolense. The mean stem density of all trees ≥0.5 m in height was 2809.1 per hectare and 150 species were enumerated in the three forest areas. Most individuals (47.73%) and species (75.0%) were recorded in the minimally disturbed and least in the mechanically logged areas. Of the selected species, F. africana was the most abundant (n = 789) and widely distributed in each of the areas. Entandrophragma angolense was the least abundant (n = 63) and most of its individuals (74.6%) were recorded in the minimally disturbed area. Funtumia africana and S. scheffleri (subcanopy), O. speciosus and T. holstii (understorey), N. buchananii (canopy) and P. excelsa (an upper canopy and a climax species of this forest reserve) had an inverse J‐shaped diameter size‐class structure while pioneer species (M. leo‐errerae and T. orientalis) had a bell‐shaped size‐class structure.     

Recovery of late-seral vascular plants in a chronosequence of post-clearcut forest stands in coastal Nova Scotia,Canada

We investigated the impacts of clearcutting on the ground vegetation of remnant late-successional coastal Acadian forests in southwestern Nova Scotia. Vegetation was sampled in 750 1-m² quadrats established in 16 stands belonging to different recovery periods since clearcutting (3–54 years) and 9 late-successional forests (100–165 years) with no signs of significant human disturbance. Our objectives were to: i) describe the changes in species richness, diversity, and abundance of ground vegetation after clearcutting; ii) examine the responses of residual species (i.e., late-successional flora) to clearcutting; and iii) determine whether any forest species were restricted to or dependent upon the late-successional stages of stand development for maximal frequency and/or abundance. Although clearcutting had no immediate impact on overall alpha richness or diversity, the richness and diversity of residual plants declined after canopy removal and showed no evidence of recovery over 54 years of secondary succession. Consequently, compositional differences between secondary and late-seral stands persisted for many decades after clearcutting. Several understory herbs (e.g., Coptis trifolia (L.) , Oxalis montana (L.), Monotropa uniflora (L.)) were restricted to or attained their highest frequency and abundance in late-seral forests. These results suggest that the preservation of remnant old stands may be necessary for the maintenance of some residual plants in highly disturbed and fragmented forest landscapes in eastern Canada.     

Tree fruiting phenology in Kalinzu Forest, Uganda

The spatial and temporal variations in species composition and abundance of trees that fruited in mechanically logged, intensively pit‐sawn and essentially undisturbed forest areas in Kalinzu Forest (0°17′S, 0°30′S and 30°00′, 30°07′E) were assessed. The duration and frequency of fruiting episodes of selected pioneer, understorey and canopy tree species were also determined. These phenology aspects were monitored for 18 months (between February 1997 and July 1998) in 99 plots, each 20 m × 20 m in size. Eighty species consisting of 1489 trees fruited during the study. Most of the species were recorded in the undisturbed forest area and least in the mechanically logged areas. Monthly number of individuals and species that fruited in each forest condition were significantly related to monthly rainfall. Two pioneer species (Musanga leo‐errerae and Trema orientalis), one sub‐canopy (Funtumia africana) and canopy (Parinari excelsa) species had extended fruiting phases (>5 months). Two understorey species (Oxyancius speciosus and Tabernaemontana spp.) had an extended phase while the third (Teclea nobilis) had a short (≤5 months) fruiting phase. Of the selected species, only Strombosia scheffleri (a sub‐canopy species) and P. excelsa had more than one fruiting episode.     

Effects of Selective Logging on Populations of Two Tropical Understory Herbs in an Amazonian Forest1

This study examined the effects of (1) rime elapsed after logging and (2) logging intensity on the total, juvenile, and adult densities, and on reproduction of Calathea altissima and Ischnosiphon amuma (Matantaceae), two monocot herb species in the understory of Central Amazonian forests. Logging was carried out experimentally at various intensities in eight plots (4 ha each) during 1987 and three plots in 1993. Five plots were left as experimental controls. In 1998, total and adult densities of the two species were greater in the plots logged 11 years before than in controls. For I. arouma, total and adult densities were also higher in the plots logged 5 years before; however, juvenile densities were less affected. The intensity of logging influenced adult density of both species but not total or juvenile densities. Densities of reproductive individuals of both species were higher in the logged areas and increased with logging intensity. The effects of time after logging and logging intensity on reproduction were indirect due to the greater number of adult plants in those areas. The observed effects were probably mediated by changes in canopy cover in logged areas. Greater light intensities in logging gaps, roads, and their margins may lead to increased reproduction, recruitment, growth, and survival, which in turn can lead to increased plant density. These results indicate that logging has long–term effects on understory plant populations.     

Effects of selective logging (50 years ago) on habitat use and ranging behaviour of a forest understorey bird (red-tailed bristlebill, Bleda syndactyla) in Uganda

To understand the effects of selective logging on animals we compared habitat use and ranging behaviour of a common understorey passerine bird, the red‐tailed bristlebill (Bleda syndactyla), in logged and unlogged forest in the Budongo Forest Reserve, Uganda. The secondary forest had been selectively logged about 50 years ago, and differed in vegetation structure from the unlogged, primary forest in particular by having a denser understorey. Home range size of radio‐tagged bristlebills was 10–20% larger (depending on data sample used) in unlogged forest compared with logged forest, but the difference was not significant. Movement rates during 1‐h observation periods were highest in unlogged forest. The bristlebill has been characterized as a bird of dense understorey vegetation, and data from unlogged forest in the present study suggested that areas with dense understorey were used more often than expected. In logged forest, no habitat preferences were found, probably because the forest had a dense understorey throughout. Assuming that smaller home ranges and lower movement rates indicate better habitat, there was no evidence that bristlebills were negatively affected by logging. The preference for dense understorey in unlogged forest suggests that the bristlebill may benefit from selective logging because this leads to an increase in dense understorey.     

Changes in forest land use and management in Sabah, Malaysian Borneo, 1990-2010, with a focus on the Danum Valley region

In an earlier special issue of this journal, Marsh & Greer summarized forest land use in Sabah at that time and gave an introduction to the Danum Valley Conservation Area. Since that assessment, during the period 1990-2010, the forests of Sabah and particularly those of the ca 10 000 km(2) concession managed on behalf of the State by Yayasan Sabah (the Sabah Foundation) have been subject to continual, industrial harvesting, including the premature re-logging of extensive tracts of previously only once-logged forest and large-scale conversion of natural forests to agricultural plantations. Over the same period, however, significant areas of previously unprotected pristine forest have been formally gazetted as conservation areas, while much of the forest to the north, the south and the east of the Danum Valley Conservation Area (the Ulu Segama and Malua Forest Reserves) has been given added protection and new forest restoration initiatives have been launched. This paper analyses these forest-management and land-use changes in Sabah during the period 1990-2010, with a focus on the Yayasan Sabah Forest Management Area. Important new conservation and forest restoration and rehabilitation initiatives within its borders are given particular emphasis.     

Coarse woody debris in undisturbed and logged forests in the eastern Brazilian Amazon

Coarse woody debris (CWD) is an important component of the carbon cycle in tropical forests. We measured the volume and density of fallen CWD at two sites, Cauaxi and Tapajós in the Eastern Amazon. At both sites we studied undisturbed forests (UFs) and logged forests 1 year after harvest. Conventional logging (CL) and reduced impact logging (RIL) were used for management on areas where the geometric volumes of logs harvested was about 25–30 m³ ha^?1. Density for five classes of fallen CWD for large material (>10 cm diameter) ranged from 0.71 to 0.28 Mg m^?3 depending upon the degree of decomposition. Density of wood within large fallen logs varied with position relative to the ground and with distance from the center of the log. Densities for materials with diameters from 2 to 5 and 5 to 10 cm were 0.36 and 0.45 Mg m^?3, respectively. The average mass (±SE) of fallen CWD at Cauaxi was 55.2 (4.7), 74.7 (0.6), and 107.8 (10.5) Mg ha^?1 for duplicate UF, RIL, and CL sites, respectively. At Tapajós, the average mass of fallen CWD was 50.7 (1.1) Mg ha^?1 for UF and 76.2 (10.2) Mg ha^?1 for RIL for duplicate sites compared with 282 Mg ha^?1 for live aboveground biomass. Small‐ and medium‐sized material (<10 cm dia.) accounted for 8–18% of the total fallen CWD mass. The large amount of fallen CWD at these UF sites relative to standing aboveground biomass suggests either that the forests have recently been subjected to a pulse of high mortality or that they normally suffer a high mortality rate in the range of 0.03 per year. Accounting for background CWD in UF, CL management produced 2.7 times as much CWD as RIL management. Excess CWD at logging sites would generate a substantial CO₂ emission given the high rates of decay in moist tropical forests.     

Cloud forest dynamics in the Mexican neotropics during the last 1300 years

Key questions for understanding the resilience and variability of Mexican Neotropical cloud forest assemblages in current and future climate change include: How have human disturbances and climate change affected the dynamics of the cloud forest assemblage? What are the predominant processes responsible for its present day composition and distribution? Are the current conservation strategies for the cloud forest in accordance with preserving its natural variability through time? In this study, the temporal dynamics of the cloud forest in west‐central Mexico over the last ～1300 years were reconstructed using palaeoecological techniques. These included analyses of fossil pollen, microfossil charcoal, and sediment geochemistry. Results indicated that a cloud forest assemblage has been the predominant vegetation type in this region over the last ～1300 years. During this time, however, there have been changes in the vegetation with an apparent expansion of cloud forest from ～832 to 620 cal years bp and a decline from 1200 to 832 cal years bp . Climate change (intervals of aridity) and human disturbances through anthropogenic burning appear to have been the main factors influencing the dynamics of this cloud forest. The spatial heterogeneity reported for high‐altitude forests in this region, in concert with high beta diversity, appears to be a manifestation of the high temporal variability in species composition for these forests. Greater turnover in cloud forest taxa occurred during intervals of increased humidity and is probably representative of a higher temporal competition for resources among the cloud forest taxa. The present results support the current protection scheme for cloud forests in west‐central Mexico where areas are kept in exclusion zones to avoid timber extraction, grazing, and agriculture; this will maintain diversity within these forests, even if there are only a few individuals per species, and enable the forests to retain some resilience to current and future climate change.     

Effects of Selection Logging on Birds in Northern Belize1

We compared bird diversity and frequency in selection logged and unlogged forest to determine the effects of recent selection logging on avian biodiversity in a subtropical, moist evergreen forest. We used a combination of mist netting and fixed-radius point counts to assess bird communities in February and March 1993 in northwestern Belize. Vegetation structure and composition was similar in logged and unlogged forest. The 66 most common species occurred with statistically similar frequency in logged and unlogged forest although 13 species were two times more frequent in intact forest. Numbers of total bird species were similar between logging gaps and the logged forest matrix, and between the logged forest matrix and unlogged forests. A comparison of numbers of species in 26 guilds based on migration strategy, diet, foraging substrate, and height strata also showed them to be similar regardless of logging history. Our results differed from previous studies that reported lower bird species richness and abundance of individual species in logged tropical forests than in unlogged forest. The differences might be explained by the lower logging intensity and/or greater levels of natural disturbance in our study area compared to previous studies.     

Short‐Term Responses of Birds to Forest Gaps and Understory: An Assessment of Reduced‐Impact Logging in a Lowland Amazon Forest1

We studied physiognomy‐specific (i.e., gaps vs. understory) responses of birds to low harvest (18.7 m³/ha), reduced‐impact logging by comparing 3500 mist net captures in control and cut blocks of an Amazonian terra firme forest in Brazil at 20–42 mo postharvest. Species richness did not differ significantly between control (92 species) and cut (85) forest based on rarefaction to 1200 captures. Fifty‐six percent of all species were shared between control and cut forest, compared to the 64 percent shared between control blocks. Higher captures of nectarivores and frugivores in cut forest likely occurred as a consequence of postharvest resource blooms. Higher captures of some insectivores in cut as compared to control forest were unexpected, attributable to increased wandering or shifts from association with midstory to understory as a consequence of habitat alteration. Logging influenced capture rates for 21 species, either consistently, or via positive interaction with physiognomy or time (13 species higher in cut forest and 8 species higher in control forest). Cut understory sites had lower diversity (H′) and scaled dominance than understory and gap sites in control forest. Temporal changes in captures may have resulted from successional dynamics in cut forest: two guilds and three species increased in abundance. Increases in abundances of guilds and particular species were more prevalent in control than in cut forest, suggesting that logging displaced birds to control forest. In general, the effects of logging were relatively minor; low harvest rates and reduced‐impact methods may help to retain aspects of avian biodiversity in Amazon forest understories.     

The effects of disturbance on forest butterflies using two methods of sampling in Trinidad

The butterfly assemblages of pairs of forest habitats, differing in disturbance level, within the Victoria Mayaro reserve of South-East Trinidad, are described using walk-and-count transects and canopy and understorey fruit traps. The concurrent use of these two butterfly censusing techniques, revealed major but conflicting differences in species accumulation rates under different disturbance conditions. The disturbed evergreen habitat had the significantly highest accumulation rate from walk-and-count data but the significantly lowest from fruit trap data. This reflects the specificity of much of the fruit-feeding guild for closed canopy forest. Disturbed habitats were found to lack a distinct canopy fauna. These results are discussed in light of the intermediate disturbance hypothesis. Within a region of forest, butterflies were found to be more characteristic of a disturbance level than of a particular forest type, lending weight to the belief that butterfly faunas can be used as bioindicators of forest disturbance. Several restricted geographic range species were not adversely affected by forest disturbance, at these levels of disturbance. The butterfly censuses in this study suggest that the optimal strategy for safeguarding butterfly species richness under natural forest management regimes would be to maintain a mosaic of habitats that included areas of undisturbed primary forest and a network of other forest patches, that varied in management regime and level of disturbance.     

Macroinvertebrate community response to natural and forest harvest gradients in western Oregon headwater streams

1. To examine the effects of forest harvest practices on headwater stream macroinvertebrates, we compiled a 167 site database with macroinvertebrate, fish, physical habitat and catchment land cover data from the three forested ecoregions in western Oregon. For our analysis, headwater streams were defined by catchment areas <10 km² and perennial water during summer low flows. Almost all sites in the database were selected using a randomised survey design, constituting a representative sample of headwater streams in these ecoregions. 2. Macroinvertebrate taxonomic and functional feeding group composition were very similar among the three ecoregions in the study area (Coast Range, Cascades and Klamath Mountains). On average, 55% of the individuals at each site were in the orders Ephemeroptera, Plecoptera or Trichoptera. Dipteran taxa (mostly chironomids) accounted for another 34%. At almost all sites, non‐insects made up <10% of the macroinvertebrate assemblage. Almost half (49%) of the assemblages were collectors; remaining individuals were about evenly divided among scrapers, shredders and predators. 3. There were 189 different macroinvertebrate taxa at the 167 sites with richness at individual sites ranging from 7 to 71 taxa. Ordination by non‐metric multidimensional scaling revealed a strong association between % Ephemeroptera, especially Baetis, and site scores along the first axis. This axis was also strongly related to % coarse substratum and fast water habitat. The second axis was strongly related to % intolerant individuals, site slope and altitude. No strong relationships were evident between any ordination axis and either logging activity, presence/absence of fish, catchment size or ecoregion. 4. Based on macroinvertebrate index of biotic integrity (IBI) scores, 62% of the sites had no impairment, 31% of the sites had slight impairment and only 6% of the sites had moderate or severe impairment. IBI scores were not strongly related to forest harvest history. All four severely impaired sites and five of the seven sites with moderate impairment were lower altitude, shallower slope stream reaches located in the Coast Range with evidence of agricultural activity in their catchment or riparian zone. % sand + fine substratum was the environmental variable most strongly related to macroinvertebrate IBI.     

Impacts of selective logging on inbreeding and gene flow in two Amazonian timber species with contrasting ecological and reproductive characteristics

Selective logging in Brazil allows for the removal of up to 90% of trees above 50 cm diameter of a given timber species, independent of a species’ life history characteristics or how quickly it will recover. The genetic and demographic effects of selective logging on two Amazonian timber species (Dipteryx odorata Leguminosae, Jacaranda copaia Bignoniaceae) with contrasting ecological and reproductive characteristics were assessed in the same forest. Genetic diversity and gene flow were characterized by genotyping adults and seed sampled before and after logging, using hypervariable microsatellite markers. Overall, there were no short‐term genetic impacts on the J. copaia population, with commercial application of current Brazilian forest management regulations. In contrast, for D. Odorata, selective logging showed a range of genetic impacts, with a 10% loss of alleles, and reductions in siring by pollen from trees within the 546‐ha study area (23–11%) and in the number of pollen donors per progeny array (2.8–1.6), illustrating the importance of the surrounding landscape. Asynchrony in flowering between D. odorata trees led to trees with no breeding partners, which could limit the species reproduction and regeneration under current regulations. The results are summarized with other published studies from the same site and the implications for forest management discussed. The different types and levels of impacts associated with each species support the idea that ecological and genetic information by species, ecological guild or reproductive group is essential in helping to derive sustainable logging guidelines for tropical forests.     

Long-Term Impacts of Fuelwood Extraction on a Tropical Montane Cloud Forest

Fuelwood extracted from natural forests serves as a principal energy source in rural regions of many tropical countries. Although fuelwood extraction (even low intensities) might strongly impact the structure and species composition of natural forests, long-term studies remain scarce. Here, we estimate the potential long-term impacts (over several hundred years) of such repeated harvesting of single trees on tropical montane cloud forest in central Veracruz, Mexico, by applying a process-based forest growth model. We simulate a wide range of possible harvesting scenarios differing in wood volume harvested and preferred tree species and sizes, and use a set of indicators to compare their impacts on forest size structure and community composition. Results showed that the overall impact on forest structure and community composition increased linearly with the amount of harvested wood volume. Even at low levels of harvesting, forest size structure became more homogeneous in the long term because large old trees disappeared from the forest, but these changes might take decades or even centuries. Although recruitment of harvested species benefited from harvesting, species composition shifted to tree species that are not used for fuelwood. Our results demonstrate that fuelwood extraction can have marked long-term impacts on tropical montane cloud forests. The results also offer the possibility to support the design of management strategies for the natural species-rich forests that achieve a balance between economic needs and ecological goals of the stakeholders. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.