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This chapter reviews previously published palaeovegetation and independent palaeoclimatic datasets to determine the responses of Amazonian ecosystems to changes in temperature, precipitation, and atmospheric CO₂ concentrations that occurred since the last glacial maximum (LGM), about 21,000 years ago, and it uses this long-term perspective to predict the likely vegetation responses to future climate change. Amazonia remained predominantly forested at the LGM, although savannas expanded at the margins of the basin. The combination of reduced temperatures, precipitation, and atmospheric CO₂ concentrations resulted in forests structurally and floristically quite different from those of today. Evergreen rainforest distribution increased during the glacial-Holocene transition due to ameliorating climatic and CO₂ conditions. However, reduced precipitation in the early-mid Holocene (about 8000-3600 years ago) period caused widespread, frequent fires in seasonal southern Amazonia, with increased abundance of drought-tolerant dry forest taxa and savanna in ecotonal areas. Rainforests expanded once again in the late Holocene period as a result of increased precipitation. The plant communities that existed during the early-mid Holocene period may constitute the closest analogues to the kinds of vegetation responses expected from similar increases in temperature and aridity posited for the 21st century.

Drought stress in tropical forests can have a major impact on global carbon, water, and energy cycles. This chapter examines drought-induced responses in the processing of carbon and water by intact tropical forest ecosystems over short (physiological) and longer (ecological) timescales. Both levels of understanding should be represented in analyses of climate-forest ecosystem feedback. Although limited spatial information on the diversity of the physical properties of soil constrains estimates of drought vulnerability, tree functional convergence across species based on simple measures such as wood density would simplify how drought responses can be represented and linked to changes in forest composition through mortality indices. While insufficient on their own, satellite-derived measurements of ecosystem properties (e.g. leaf area index) and processes (e.g. mortality and photosynthesis) are expected to provide increasingly detailed information that can be used to test understanding of short- and longer-term responses to drought.

This chapter maps the geographic extent of the ecosystems created by conifers, and coincidentally the areas of dominance of one or more identifying conifer species. The result is a mosaic of “regions.” In all the regions except the Great Lakes, the St. Lawrence, and the Acadian, conifers dominate. The forests of the latter two regions vary between coniferous and mixed (that is, with various broadleafs as well as conifers). The trees that are found at any one site depend mainly on the climate, the terrain and soil, the location from which their ancestors immigrated, and the number of years since the site was last burned. In mountainous country, elevation is another important factor.

This chapter presents an overview of climate changes, and assesses the potential effects on giant kelp and associated organisms. The earth's climate is changing at an unprecedented rate, and many predictions are critical about the consequent changes on ecosystems. In regard to the ocean, the major physical variables of change are likely to be temperature, wave forces, sea level, and pH from increasing atmospheric CO₂. The potential changes to kelp forest ecosystems are far less certain and largely assumed, due not only to the unpredicted and complex ways that climate variables may act on species and their interactions, but also in how they may act in a more direct way on giant kelp itself with its complex requirements and physiological-ecological responses across its life stages.

This chapter examines the effects of excess nitrogen (N) on the herb layer of forests, reviewing recent pertinent literature from both North America and Europe. It shows that excess N has the potential to substantially alter species composition and decrease biodiversity of the herbaceous layer of forests of eastern North America, and does so in ways that are distinctive from other forms of forest disturbance. Numerous studies confirm that increasing N in forests from N limitation to N saturation can not only alter soil N biogeochemistry and deplete nutrient cations, but it can also (1) alter competition to give advantages to fewer nitrophilous species; (2) increase intensity and degree of herbivory; (3) increase frequency of mycorrhizal infection; (4) increase occurrence and severity of fungal pathogens; and (5) enhance species invasions.

This chapter looks at the ecosystem of the forest floor. The forest floor consists chiefly of soil. One of the most distinctive soils is podsol, the typical soil in conifer forests. This soil is easily recognizable if you expose it by digging a hole, or even more easily by seeing it exposed in an eroding stream bank. It has a thin, dark top layer of packed needle-leaf litter gradually decaying into humus (newly decomposed material with organic ingredients only). Immediately below that is a layer, often thick, of almost pure white sand. The soil is cold, acidic, and sometimes wet. The most common flowers on the coniferous forest floor belong to three families: one, of plants that prefer acid soil; a second, of epiparasitic plants; and a third, of ancestors of the epiparasites. The remainder of the chapter discusses the floor of the boreal forest; the value of dead wood and debris; and animals found in the evergreen forest—beavers, birds, and ducks.

The Hubbard Brook Experimental Forest (HBEF) in central New Hampshire, in the heart of the White Mountains, was established in 1955, two decades after Coweeta Hydrologic Laboratory (CHL). However, research objectives at both sites have long been similar, that is, to understand hydrologic and nutrient cycling processes for forest ecosystems, and to determine responses to natural and human disturbances. This chapter summarizes the responses to intensive cuttings on three watersheds at HBEF and compares the results with those from the clearcutting on Watershed 7 (WS 7) at CHL. Despite significant differences in site characteristics between CHL and HBEF, responses to intensive harvests showed several similarities. Among these are that harvested sites regenerated rapidly, with opportunistic and pioneer species dominating regrowth for the first 20+ years after harvest. Water yield also increased during the early years after harvest but declined rapidly with regrowth.

This chapter has three primary objectives. First, it determines via literature review what is known of interaction among forest strata, with a specific focus on overstory-herbaceous layer interactions in eastern deciduous forests. It presents contrasting views of the nature of these interactions, from one that sees a quantifiable linkage among strata to one that sees little true interaction occurring. Second, it develops a mechanistic explanation for patterns of linkage in forest ecosystems, with emphasis on eastern deciduous forests. Finally, it examines data from two different forest types—a central Appalachian hardwood forest and a successional aspen forest of northern lower Michigan—for evidence supporting or refuting this explanation.

This chapter explores the meaning of mourning for the death of others by looking through the lives of Hawaiian crows. Unlike other urban scavenging corvids, Hawaiian crows lived primarily among the trees, as these shelter the bulk of their diet—invertebrates and forest fruits. Also, as the island's largest forest bird with a role as a seed dispenser, Hawaiian crows influence the normal functioning of dry- and wet-forest ecosystems. These birds are considered exceptional because they not only live a meaningful life in the forest, they also possess a high degree of intelligence and a capacity for deeply social and emotional lives. Nonetheless, the key problem causing their extinction is the rapid and ongoing alteration of the environment due to the human settlement that began about 1,500 to 2,000 years ago.