John M. Hagan

Forest damage caused by selection logging of mahogany (Swietenia macrophylla) in northern Belize

Abstract We assessed the damage caused by selection logging of mahogany in a tropical forest in northern Belize and compared it with damage reported in other Neotropical logging and disturbance studies. We mapped skid roads and tree felling sites, and assessed soil compaction, loss of canopy cover, damage to saplings and trees, seedling survival and seedling height growth. Logging had been conducted using hand crews with chain saws and cable skidders. Logging directly affected 11.9 ha (12.9%) of the 92.3 ha logging area. Canopy cover decreased the most at logging gaps, and soils were most compacted on skid roads. Soil compaction was much greater on roads where more than one tree had been skidded. For the whole logged area, canopy cover declined 2% and compacted soils covered 3.8% of the area. Seedling height growth was unaffected by soil compaction, but seedling survival was less on compacted sites. About 50% of the trees and about 15% of the saplings were damaged in gaps and along skid roads. However, only 4.8% of the trees and 1.9% of the saplings were damaged for the logged area as a whole. The most common kinds of damage included scraped bark, snapped tops, and run-over stems. Although this logging operation had relatively low impacts compared with other logging operations in the Neotropics, it may not be silviculturally sustainable because its disturbance may be insufficient to promote adequate mahogany regeneration.

A Comparison of Two Bird Survey Techniques Used in a Subtropical Forest

Mist netting and point counting have been used equally in the Neotropics for the purpose of surveying bird communities, although their effectiveness is poorly known. We compared mist netting and point counting data collected from the same survey points in a mature subtropical forest in Belize to assess their descriptions of a bird community within a small region and across many survey points. We surveyed each point for three consecutive days using one technique and then for three additional days using the other technique. Mist netting and point counting detected only 25% and 60%, respectively of all forest species. The species lists from mist netting and point counting had similar proportions of species in groupings based on families, abundance, and migratory status, and in diet, habitat use, and foraging substrate guilds. Species lists from mist netting had a greater proportion of understory and small species than the species list from point counting. Species lists from mist netting and point counting had smaller proportions of large-bodied and rare species than a local checklist. Point counting detected more species per point with greater time efficiency and more species per point in 25 of 28 guilds than did mist netting. Point counting detected three common species less frequently than mist netting, whereas mist netting detected 38 common species less frequently than point counting. Point counting detected understory species as frequently as mist netting did at individual points. The two methods had > 50% agreement on the presence of only four species at individual points. Both techniques detected different sets of common species with similar frequency, although point counting detected many more uncommon species. Although using both techniques was more effective than using either alone, point counting alone was significantly more efficient for conducting bird surveys.

Carbon Accounting for Woody Biomass from Massachusetts (USA) Managed Forests: A Framework for Determining the Temporal Impacts of Wood Biomass Energy on Atmospheric Greenhouse Gas Levels

Policies based on assumed carbon neutrality fail to address the timing and magnitude of the net greenhouse gas (GHG) changes from using wood for energy. We present a “debt-then-dividend” framework for evaluating the temporal GHG impacts of burning wood for energy. We also present a case study conducted in Massachusetts, USA to demonstrate the framework. Four key inputs are required to calculate the specific shape of the debt-then-dividend curve for a given region or individual biomass facility. First, the biomass feedstock source: the GHG implications of feedstocks differ depending on what would have happened to the material in the absence of biomass energy generation. Second, the form of energy generated: energy technologies have different generation efficiencies and thus different life cycle GHG emissions profiles. Third, the fossil fuel displaced: coal, oil, and natural gas each have different emissions per unit of energy produced. Fourth, the management of the forest: forest management decisions affect recovery rates of carbon from the atmosphere. This framework has broad application for informing the development of renewable energy and climate policies. Most importantly, this debt-then-dividend framework explicitly recognizes that GHG benefits of wood biomass energy will be specific to the forest and technology context of the region or biomass energy projects.

The effectiveness of different buffer widths for protecting water quality and macroinvertebrate and periphyton assemblages of headwater streams in Maine, USA

We evaluated the effect of timber harvesting on water quality and macroinvertebrate and periphyton assemb- lages in first-order streams in Maine, USA. Fifteen streams were assigned to one of five treatments: clearcutting without a stream buffer, clearcutting with 11 m buffers, clearcutting with 23 m buffers, partial harvesting with no designated buffer, and unharvested controls. Harvest blocks on both sides of the stream were 6 ha and partial harvesting within buffers was allowed. Specific conductivity, pH, dissolved oxygen, turbidity, and soluble reactive phosphorus did not change signifi- cantly for 3 years after harvesting in all treatments. Unbuffered streams had significantly elevated concentrations of chlorophyll a as well as increased abundance of algal feeding organisms (Diperta Cricotopus and Diptera Psectrocladius). Streams with 11 m buffers had substantial (10-fold) but nonsignificant increases in chlorophyll a. No other significant changes were detected in other treatment groups. In all treatment groups, the dominant taxa (periphyton Achnanthes minu- tissimum and macroinvertebrate Chironomidae) are adapted to disturbed environments. We attribute the limited harvest-in- duced changes to lack of soil disturbance within 8 m of the stream, the small (£40%) proportion of watersheds harvested, and the resilient nature of aquatic organisms. However, small-scale changes may not be detected due to the small sample size, an inherent limitation of field-based studies.