Silvicultural treatments enhance growth rates of future crop trees in a tropical dry forest

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.     

Beyond reduced-impact logging: Silvicultural treatments to increase growth rates of tropical trees

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.     

Damage to Brazil nut trees (Bertholletia excelsa) during selective timber harvesting in Northern Bolivia

The success of multiple forest management systems is contingent on a variety of social, economic, biophysical, and institutional factors, including the integration of timber and non-timber forest product (NTFP) extraction and management. Selective logging for timber is increasingly taking place in forests where the collection of Brazil nuts, a high-value Amazonian NTFP, also occurs. We report on logging damage to Brazil nut trees in three certified timber concessions in Northern Bolivia from which timber is harvested using reduced-impact logging (RIL) guidelines and nuts are gathered yearly from the ground by local people. Observed frequencies of logging damage to Brazil nut trees were low, likely mirroring the low intensity of timber harvesting (∼0.5 trees/ha and ∼5 m³/ha) being currently applied across the study area. Of the trees ≥10 cm in diameter at breast height about 0.1 Brazil nut trees and 0.4 timber species per hectare suffered some degree of logging damage. Crown loss was the predominant damage type for Brazil nut trees accounting for 50% of all damage. In spite of the observed low rates of tree damage, we further recommend that RIL guidelines be amended to include the pre-harvest marking of pre-reproductive Brazil nut trees along with the future crop trees of commercial timber species. Further refining directional felling to reduce crown damage to Brazil nut trees would also serve to help maintain nut yields in the long term.     

An alternative water source and combined agronomic practices for cotton irrigation in coastal saline soils

The field experiment for cotton crop (Gossypium hirsutum L.) was conducted at the Zhongjie Farm, Huanghua city of Hebei province in the coastal salinity-affected areas in North China Plain, to determine the effects of an alternative of irrigation water sources/methods and agronomic practices on seedling emergence and yields of cotton, soil water–salt distributions, and soil pH changes during cotton growth stages. The experiment was setup using split-plot design with two water sources as main treatments (well water/desalinized sea-ice water); two irrigation methods (+PAM (Polyacrylamide)/−PAM); and four fertilization modes: check (CK), mineral fertilizer (F), mineral + organic fertilizer (FM), and mineral fertilizer + gypsum (FG). Using desalinized sea-ice water irrigation showed the same effects on top-soil salt leaching and desalinization as using well water did. There was no significant difference in seedling emergence and cotton yields between two irrigation water sources for cotton irrigation. Using PAM-treated irrigation, the 10-cm top-soil salinity significantly decreased to about 2.3–3.9 g kg⁻¹ from 4.6 to 8.6 g kg⁻¹ (PAM untreated). The PAM-treated irrigation increased seedling emergence by about 13, 29 and 36% and yields by about 50, 49, and 70%, with F, FM, and FG, respectively, as compared with CK. PAM-treated irrigation, either using well water or desalinized sea ice, especially in combination with gypsum-fertilization, shows the best practice for both seedling emergence and cotton yields. In conclusion, the desalinized sea-ice water used as an alternative water source, integrated with better agronomic practices of soil water-salt management could be acceptable for cotton irrigation in the coastal saline areas.