CO2 Impacts Tropical Forest Resistance to Climate Change

by Leta Ames

It is well known that fire can play a crucial role in the reproduction and development of plant populations. The availability of water and CO2 also impact plant growth, especially of larger species. It is believed that the interactions of climate, fire, and CO2 greatly influence the shift between savanna and tropical forest ecosystems and their permanence thereafter. Previous research has relied on data collected from intact tropical forests, but although useful, these data only provide a snapshot of the impact of CO2, fire, and climate on these ecosystems. To gain a better understanding of what factors influence tropical ecosystems Shanahan et al. (2016) used the concentrations of carbon and hydrogen stable isotopes from sedimentary leaf wax n-alkanes (δ13Cwax and δDwax) and the frequency of charcoal layers from sediment obtained from Lake Bosumtwi in Ghana to construct a history of changes in vegetation and hydrology, as well as to estimate the annual fire frequency. Continue reading

Identifying Suitable Trees For Urban Heat Management In Face Of Global Warming

by Deniz Korman

Global ambient temperatures keep rising year by year, and urban areas specifically experience higher temperatures compared to rural areas due to lower vegetation coverage and increased emissions. An effective strategy to counteract this problem is to expand green spaces and improve urban forestry. However, it is important to ensure that the greenery that we integrate into our cities can withstand changing climate conditions as ambient temperatures keep increasing at a rate faster than ever. Lanza and Stone (2016) focus on how global warming has affected the climate conditions around 20 highly populated metropolitan areas in USA, and the impact that this has had on present tree species. Continue reading

Forest Restoration May Only Have Short-term Positive Effects on Ground Water Storage in Semi-arid Aquifers

by Zoe Dilles

The already scarce water resources of the semi-arid western United States will become increasingly precarious with the progression of warming and drying climate change. When compounded with growing demand for water, this issue mandates a balanced management practice incorporating sustainable water budgets and land use. Forest restoration efforts are currently slated for an area of some 600,000 acres of National Forest in north-central Arizona, comprising nearly 1% of the state’s footprint. These treatments, anticipated to last the duration of the coming decade, will consist of selective thinning and burning of high-density conifer forest to mitigate wildfire potential and increase the health of regional forested watersheds. The impact of tree removal on surface water has been the subject of previous study but is rarely quantified in regards to groundwater resources. Especially in such a dry region, the future of water availability lies in the relationship between rainfall and recharge of deep aquifers, reservoirs that are permanently diminished through over-pumping. Continue reading

Community Composition is Different at Forest Edges, but Carbon Storage Remains the Same

by Stephen Johnson

Forest fragmentation is one of the leading ways that humans alter natural habitat. Forests are frequently fragmented as land is cleared piecemeal for the expansion of agriculture, logging, and human settlement. Often, rather than clearing an entire forest, fragments of forest are left embedded in a matrix of agricultural and other habitats. As an increasing percentage of the world’s forests are fragmented, it is crucial to understand how forest fragments function. Fragments are subject to a variety of influences, most notably edge effects. Edge effects occur at the edges of two habitats, and include altered microclimate, reduced biodiversity, and vegetation changes. These edge effects can bring about altered species communities, which in turn could affect the amount of carbon that can be sequestered near forest edges. As forest fragmentation continues, a greater percentage of forest will be exposed to edge effects, potentially inhibiting forests’ ability to act as carbon sinks. To understand these effects, Ziter et al. (2014) examined how tree species composition and carbon storage capacity change with proximity to forest edge in large and small fragments. Using tree measurements and allometric data in the literature, they determined how much carbon was stored, and which species were present. Using linear mixed models and multidimensional scaling, they found that community composition shifts with proximity to the forest edge. Despite this shift, however, carbon storage did not decrease closer to the edge. Continue reading

Drought-Fire Interactions in the Amazonian Rainforest Increase Tree Mortality

by Maithili Joshi

The relationship between fire-induced tree mortality and extreme weather remain poorly understood because it is restricted to post-fire observations of tree mortality. Studies done on the effects of forest fires and biodiversity remain understood on the patch scale, and do not consider the effects of fire on vegetation dynamics and structure. In the southeast Amazon forest, scientists established a large scale, and long term prescribed forest fire experiment in a transitional forest. Primarily, trying to determine if there are weather, and fuel, related thresholds in fire behavior associated with high levels of fire-induced tree mortality across two different fire regimes, and secondarily, what the effects of an intense forest fire are on forest structure, flammability, and aboveground live carbon stock. Continue reading

The Vulnerability of Trees and Biomes of the Rocky Mountains to Climate Change

by Kyle Jensen

As the reality of climate change becomes ever clearer, federal land managers are becoming increasingly concerned with how climate change will affect natural resources and ecosystem services within their jurisdictions. The western US in particular is expected to warm significantly, which will have widespread effects on the distribution of forests and various species; understanding these effects is essential to developing strategies to cope with future changes. Hansen and Phillips (2015) conducted a meta-analysis of five studies assessing the vulnerability of tree species and biome types to projected future climate changes, the results of which are expected to be used by the National Park Service as it initiates climate vulnerability assessments. The studies utilized bioclimate envelope modeling, which showed a severe loss of territory for subalpine systems, especially for the white bark pine (Pinus albicaulis) and Mountain hemlock (Tsuga mertensiana). Continue reading

Carbon Storage Increases Continuously as Trees Grow

by Stephen Johnson

Though it has been assumed that the rate of carbon accumulation declines with the age of an individual tree, little empirical evidence has been produced to support this assumption. Understanding how carbon storage capacity changes throughout the life of the tree is important in modeling carbon dynamics in forests, which can be used to determine how forests will contribute to climate change mitigation plans. Net primary productivity is well known to decline in even-aged forests, as does mass gain per unit leaf area. However, few forests are completely even-aged, and many are subjected to selective logging that removes the largest trees. Proper modeling of the amount of carbon lost through this logging can be used to more accurately price carbon credits for the preservation of natural forests, aiding efforts to keep them intact. In order to determine how carbon storage rates change with tree age, Stephenson et al. (2014) collected data from long-term monitoring plots in tropical and temperate areas across the globe. By measuring the diameter of each tree and using allometric equations, the researchers determined how much carbon was being stored over time. They found that while stand productivity declined with age, individual tree carbon gain rate increased, with no signs of declines at any age. Continue reading