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Integrating remote sensing into assessments of carbon stocks and fluxes has advanced our understanding of how global change affects landscapes and our capacity to support decision making about forest management. However, there remains a lack of detailed and actionable analyses conducted across widely ranging environmental conditions that are appropriate for tactical planning. We used airborne laser scanning data and multi-source satellite imagery to estimate forest aboveground carbon density and gross primary production, and to map forest cover across the main Hawaiian Islands. We used these measures to develop the Carbon Sequestration Potential Index (CSPI), which identifies where the potential for carbon sequestration following afforestation would be highest within a complex landscape of 304 management units. Variation in CSPI was high across islands and between ecosystems, with low values for cool, dry and largely intact forest systems and high values for warm, wet and largely non-forested systems. The CSPI provided a rapid, spatially-explicit and actionable assessment of Hawaiian forest reserves, which can help stewardship agencies contribute to state carbon neutrality goals through climate-smart and science-driven prescriptions that encompass conservation to restoration.

Non-native species invasions, growing human populations, and climate change are central ecological concerns in tropical island communities. The combination of these threats have led to losses of native biota, altered hydrological and ecosystem processes, and reduced ecosystem services. These threats pose complex problems to often underfunded management entities. We developed a watershed decision support tool (WDST) for the windward coast of Hawai‘i Island aimed at prioritizing catchments for invasive species removal and native forest protection from non-native species invasions. Using the Ecosystem Management Decision Support (EMDS) system, we integrated spatial data from four sources: (i) native and invasive species coverage; (ii) modeled water yield; (iii) treatment cost and efficacy; and (iv) native species conservation value. We used a distributed hydrology model (DHSVM) to estimate catchment-level (∼90 ha) water yield under six climate and non-native species invasion scenarios to identify where (1) invasive species removal and (2) protection from invasion would have the greatest benefit to increasing or maintaining native biodiversity and hydrologic functioning. The hydrology model predicted a 30% decline (386 Gl yr−1) in total water yield under a drier future climate (20% reduction in rainfall), with an additional 2% reduction when catchments were fully invaded by non-native species. Increased temperatures had a small compensatory effect on water yield. The WDST identified 6.3% of the study area as high priority for invasive species removal, based on characteristics of large hydrological response to the removal treatment (concentrated in high rainfall areas), high quality road or trail access, and high conservation value. High protection priority from invasive species (5.9% by area) occurred in higher elevation catchments, near the upper range of strawberry guava (the main invasive species), where water yield was most sensitive to invasion. Climate change scenarios had little influence on the spatial distribution of priority scores despite large changes in overall water yield. In contrast, priority scores were sensitive to very high variation in treatment costs, which were influenced largely by travel times to catchments via road and trail networks. This last finding suggests that future management feasibility will hinge on improvements to road and trail networks, or development of alternative management strategies that reduce travel costs and time.

Nearshore ecosystems (e.g., mangrove forests, sea grass beds, coral reefs) are some of the most biologically diverse and ecologically productive on Earth, while providing essential goods and services to human communities. Because these ecosystems are subject to threats from both land and sea, their conservation and management requires a ridge to reef approach. Here, we developed a watershed decision support tool (DST) for Babeldaob Island, Republic of Palau, aimed at prioritizing catchments for reforestation of fire degraded savanna or protection of native forest against conversion to savanna. We use a distributed hydrology model to estimate catchment-level sedimentation and water yield for three vegetation scenarios: (1) current vegetation; (2) a hypothetical fully-forested Babeldaob Island; and (3) a hypothetical Babeldaob Island that has been fully converted to savanna. Using the DST, we integrated model results with geospatial information on treatment cost, efficacy, and conservation value to identify where reforestation and forest protection investments would provide the greatest benefits to coral reef health. Modeled sediment yields were lowest for catchments with > 80% tropical forest cover and highest for those with

The storage and flow of carbon (C) into and out of forests can differ under the influence of dominant tree species because of species-based variation in C production, decomposition, retention, and harvest-based export. Following abandonment of agricultural activities in the first half of the 20th century, many landscapes of the Great Lakes region (USA) were planted to red pine (Pinus resinosa) or naturally regenerated to northern hardwood species including sugar maple (Acer saccharum), red oak (Quercus rubra) and red maple (Acer rubrum). We located eight pairs of adjacent, similarly aged (∼60 yr) stands of planted red pine and naturally regenerated hardwood forests on previous agricultural fields. We found that the hardwood forests stored more C than pine stands (255 vs. 201 Mg C ha−1), with both storing substantially more than an adjacent area maintained as pasture (107 Mg C ha−1). The greater accumulation of C in the hardwood stands occurred mostly in living biomass. No significant differences for soil C (to 1 m depth) were found between forest types, despite significantly higher belowground inputs and aboveground litterfall in hardwood stands. Notably, both forest types had about 18% more soil C than the pasture, with O horizon C accounting for about one-third of the increase under trees. Forest type had no significant effect on estimated amount of exported C despite fairly large differences in projected end uses (solid wood products, land-fills, bioenergy). Using adjacent pasture as our baseline condition, we combined estimated on-site accumulation rates with estimates of exported C, and found that average total C sequestration rates were higher for hardwood (2.9 Mg C ha−1 yr−1) than red pine plots (2.3 Mg C ha−1 yr−1). The modeled potential contribution of exported C to these sequestration rate estimates did not differ between species, but the fate of modeled post-harvest off-site C may exert a large influence on sequestration rate estimates depending on actual displacement actions, including product longevity. These results show that tree species selection has the potential to impact C sequestration rates but effects vary by ecosystem component and could not be predicted from previous species effects studies.

Coarse woody debris (CWD; defined here as fallen and standing dead trees and tree ferns) is a critical structural and functional component of forest ecosystems that typically comprises a large proportion of total aboveground carbon (C) storage. However, CWD estimates for the tropics are uncommon, and little is known about how C storage in CWD will respond to climate change. Given the predominant role that tropical forests play in global C cycling, this information gap compromises efforts to forecast climate change impacts on terrestrial C balance. The primary objectives of this study were to: (i) quantify CWD C storage in a tropical montane wet forest; and (ii) determine if CWD C storage varies with mean annual temperature (MAT). Coarse woody debris C was quantified with line-intercept sampling techniques in nine permanent plots located across a highly constrained 5.2 degree C MAT gradient spanning 800 m elevation on the eastern slope of Mauna Kea Volcano, Island of Hawaii. Forests across this tropical montane MAT gradient contained large quantities of CWD C (44.3 ± 11.2 Mg ha-1; Mean ± 1 SE), which accounted for an estimated 17% of total aboveground C storage. Across the entire gradient, CWD C was found primarily as: moderately decayed CWD (Decay Class 2); tree CWD; fallen CWD; and small diameter CWD (2–10 cm). Tree ferns accounted for an average of ∼20% of total CWD C, but are rarely included in tropical CWD estimates. Overall, total CWD C ranged from 12.2 to 104.6 Mg ha-1 across the MAT gradient, and decreased with increasing MAT. The negative relationship between CWD and MAT was driven by large accumulations of standing tree CWD at cooler MATs, as fallen CWD did not vary with MAT. The results presented here are in line with limited evidence from tropical studies showing that CWD can make up a large fraction of total aboveground C storage. In addition, these data suggest that CWD could become a net C source to the atmosphere in tropical forests with future warming. A decrease in tropical montane CWD C storage would have important implications for global C dynamics and atmospheric CO2 levels.

Timber harvesting, with and without prescribed slash fire, and wild fire are common disturbances in pine forests of western North America. These disturbances can alter soil nitrogen (N) pools and N supply to colonizing vegetation, but their influence remains poorly understood for many forests. We investigated the effects of clear cut harvesting and fire on KCl extractable N pools, net N mineralization rates, phosphorus (P) fractions, seedling N uptake, and seedling growth in mineral soils sampled from a lodgepole pine forest in southern Wyoming. At a site where wild fire burned through a harvested stand of lodgepole pine and the adjacent intact forest, we analyzed mineral soils from the following four treatments: unburned clear cut, burnt clear cut, unburned forest, and burnt forest. Soils from unburned and burnt clear cut treatments had higher concentrations of KCl extractable N and higher net N mineralization rates, and produced larger pine seedlings in bioassays than soils from unburned and burnt intact forest treatments. Further, while seedlings grown in soils from the unburned and burnt forest treatments responded strongly to N fertilization, seedlings grown in clear-cut soils did not respond to fertilization. Taken together, these results suggest that harvesting had increased soil N supply. In comparing clear cut treatments, soils from the unburned clear cut had smaller extractable N and P pools, and lower net N mineralization rates, but produced larger pine seedlings than soils from the burnt clear cut.