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Abstract: Logging is an integral component of most conceptual models that relate human land-use and climate change to tropical deforestation via positive-feedbacks involving fire. Given that grass invasions can substantially alter fire regimes, we studied grass distributions in a tropical dry forest 1–5yr after selective logging, and experimentally tested the effect of forest fire on populations of invasive grasses. In unlogged forests and in microhabitats created by selective logging we found a total of four alien and 16 native grass species. Grasses covered 2% of unlogged and 4% of logged forest, with grass cover in logged forest concentrated in areas directly disturbed by logging; log landings and roads had relatively greater grass cover (37% and 17%, respectively) than did skid trails (10%) and felling gaps (8%). Total grass cover and grass species richness increased with canopy openness and were greatest in sites most severely disturbed by logging. The grass flora of these disturbed areas was composed mostly of native ruderal species (e.g., Digitaria insularis, Leptochloa virgata), a native bamboo (Guadua paniculata), and Urochloa (Panicum) maxima, a caespitose C4 pasture grass introduced from Africa. Urochloa maxima formed monodominant stands (up to 91% cover and 2–3m tall) and grew on 69% of log landings and 38% of roads. To better understand the potentially synergistic effects of logging and fire on the early stages of grass invasion, we tested the effect of a 12-ha experimental fire on U. maxima populations in a selectively logged forest. Three years after the fire, the area covered by alien grass in burned forest increased fourfold from 400m2 (pre-fire) to 1660m2; over the same period in a logged but unburned (control) area, U. maxima cover decreased from 398m2 to 276m2. Increased canopy openness due to fire-induced tree mortality corresponded with the greater magnitude of grass invasion following fire. Selective logging of this dry forest on the southern edge of the Amazon Basin promotes alien grass invasion; when coupled with fire, the rate of invasion substantially increased. Recognition of the grass-promoting potential of selective logging is important for understanding the possible fates of tropical forests in fire-prone regions. [Copyright &y& Elsevier]

Abstract: Silvicultural treatments are often needed in selectively logged tropical forest to enhance the growth rates of many commercial tree species and, consequently, for recovering a larger proportion of the initial volume harvested over the next cutting cycle. The available data in the literature suggest, however, that the effect of silvicultural treatments on tree growth is smaller in dry forests than in humid forest tree species. In this study, we analyze the effect of logging and application of additional silvicultural treatments (liana cutting and girdling of competing trees) on the growth rates of future crop trees (FCTs; i.e., trees of current and potentially commercial timber species with adequate form and apparent growth potential). The study was carried out in a tropical dry forest in Bolivia where a set of 21.25-ha plots were monitored for 4 years post-logging. Plots received one of four treatments that varied in intensity of both logging and silvicultural treatments as follows: normal (reduced-impact) logging; normal logging and low-intensity silviculture; increased logging intensity and high-intensity silviculture; and, unlogged controls. The silvicultural treatments applied to FCTs involved liberation from lianas and overtopping trees. Results showed that rates of FCT stem diameter growth increased with light availability, logging intensity, and intensity of silvicultural treatments, and decrease with liana infestation degree. Growth rate increment was larger in the light and intensive silvicultural treatment (22–27%). Long-lived pioneer species showed the strongest response to intensive silviculture (50% increase) followed by total shade-tolerant species (24%) and partial shade-tolerant species (10%). While reduced-impact logging is often not sufficient to guarantee the sustainability of timber yields, application of silvicultural treatments that substantially enhanced the growth rates of FCTs will help move the management of these forests closer to the goal of sustained yield. [Copyright &y& Elsevier]

Abstract: Use of reduced-impact logging (RIL) techniques has repeatedly been shown to reduce damage caused by logging. Unfortunately, these techniques do not necessarily ameliorate the low growth rates of many commercial species or otherwise assure recovery of the initial volume harvested during the next cutting cycle. In this study, we analyze the effect of logging and application of additional silvicultural treatments (liana cutting and girdling of competing trees) on the growth rates on trees in general and on of future crop trees (FCTs) of 24 commercial timber species. The study was carried out in a moist tropical forest in Bolivia, where we monitored twelve 27-ha plots for 4 years. Plots received one of four treatments in which logging intensity and silvicultural treatments were varied: control (no logging); normal (reduced-impact) logging; normal logging and low-intensity silviculture; and, increased logging intensity and high-intensity silviculture. Tree growth rates increased with intensity of logging and silvicultural treatments. The growth rates of FCTs of commercial species were 50–60% higher in plots that received silvicultural treatments than in the normal logging and control plots. Responses to silvicultural treatments varied among functional groups. The largest increase in growth rates was observed in FCTs belonging to the partially shade-tolerant and the shade-tolerant groups. These results indicate that silvicultural treatments, in addition to the use of RIL techniques, are more likely to result in a higher percentage of timber volume being recovered after the first cutting cycle than RIL alone. [Copyright &y& Elsevier]

Tree regeneration was compared in burned and unburned portions of a tropical dry forest (1110 mm ppt/year) and a tropical humid forest (1542 mm ppt/year) in southeastern Bolivia. Both forests burned 5 years prior to our study, and both forests were also lightly selectively logged (intensity<1 m3/ha)—the dry forest during the 1970 and 1980s and the humid forest just prior to the wildfire. The objective of this study was to compare abundance, size, and mode (seedling or resprout) of tree regeneration in burned and unburned areas of these forests, focusing on the most common canopy tree species and the commercial timber species at each site. Regeneration of 13 species of trees was quantified in the humid forest and 12 species in the dry forest. Tree regeneration <5 cm basal diameter but >20 cm tall was more abundant in the dry forest (x¯=1807 stems/ha) than in the wet forest (x=490 stems/ha). In both forests, resprouts were generally larger but less abundant than seedlings. In the dry forest, regeneration of the following commercial tree species was significantly more abundant in the burned areas: Cedrela fissilis, Anadenanthera colubrina, Astronium urundueva, and Centrolobium microchaete. However, Acosmium cardenasii, a canopy tree species not marketed for timber in Bolivia, represented the majority of regeneration (63%) in the dry forest and was equally abundant in burned and unburned areas (∼1100 stems/ha). In the humid forest, only one timber species, Aspidosperma rigidum, was more abundant in burned than unburned areas (51 vs. 0 stems/ha, respectively). Another timber species that is rarely harvested in the region, Pseudolmedia laevis, was significantly less abundant in the burned than unburned area (22 vs. 173 stems/ha, respectively). The results of this study suggest that controlled burning could increase the abundance of timber tree regeneration at the dry forest site and to a lesser extent at the humid forest site. No data were collected to assess the likelihood that this increased density of regeneration will result in increased harvestable timber. However, local forest management institutions do not presently appear capable or motivated to conduct fire management—whether for enhancing timber regeneration or for limiting the damage caused by accidental wildfires. [Copyright &y& Elsevier]