Statistics for Spatial Data.

Publisher Summary This chapter reviews the rates at which Coarse Woody Debris (CWD) is added and removed from ecosystems, the biomass found in streams and forests, and many functions that CWD serves. CWD is an important component of temperate stream and forest ecosystems and is added to the ecosystem by numerous mechanisms, including wind, fire, insect attack, pathogens, competition, and geomorphic processes. Many factors control the rate at which CWD decomposes, including temperature, moisture, the internal gas composition of CWD, substrate quality, the size of the CWD, and the types of organisms involved. The mass of CWD in an ecosystem ideally represents the balance between addition and loss. In reality, slow decomposition rates and erratic variations in input of CWD cause the CWD mass to deviate markedly from steady-state projections. Many differences correspond to forest type, with deciduous-dominated systems having generally lower biomass than conifer-dominated systems. Stream size also influences CWD mass in lotic ecosystems, while successional stage dramatically influences CWD mass in boat aquatic and terrestrial settings. This chapter reviews many of these functions and concludes that CWD is an important functional component of stream and forest ecosystems. Better scientific understanding of these functions and the natural factors influencing CWD dynamics should lead to more enlightened management practices.

Ecology of Coarse Woody Debris in Temperate Ecosystems

This article describes ways in which excess nitrogen from fossil fuel combustion may stress the biosphere. Nitrogen emissions can have a direct effect on air quality through both the oxidizing potential of nitrogen oxides and the role these compounds play in the formation of ozone. The complexity of these effects on water quality and on forest nutrition is discussed.

https://harvardforest.fas.harvard.edu/sites/harvardforest.fas.harvard.edu/files/publications/pdfs/Aber_BioScience_1989.pdf

Nitrogen saturation in northern forest ecosystems

Two features characterize all natural communities. First, they are dynamic systems. The densities and age-structures of populations change with time, as do the relative abundances of species; local extinctions are commonplace (37). For many communities, a self-reproducing climax state may only exist as an average condition on a relatively large spatial scale, and even that has yet to be rigorously demonstrated (36). The idea that equilibrium is rarely achieved on the local scale was expressed decades ago by a number of forest ecologists (e.g. 10 1, 168). One might even argue that continued application of the concept of climax to natural systems is simply an exercise in metaphysics (41). While this view may seem extreme, major climatic shifts often recur at time intervals shorter than that required for a community to reach competitive equilibrium or alter the geographical distributions of species (6, 21, 43, 76, 92). Climatic variation of this kind influences ecological patterns over large areas, sometimes encompassing entire continents. Other agents of temporal change in natural communities operate over a wide range of smaller spatial scales (47, 242). Second, natural communities are spatially heterogeneous. This statement is true at any scale of resolution (242), but it is especially apparent on what is commonly referred to as the regional scale. (By region I mean an area that potentially encompasses more than one colonizable patch.) Across any land or seascape, one observes a mosaic of patches identified by spatial discontinuities in the distributions of populations (153, 159, 161, 231, 239, 240). Closer examination often reveals a smaller-scale patchwork of same-aged individuals (e.g. 85-87, 101, 146, 199,204,217-220,235,246). Discrete patch boundaries sometimes reflect species-specific responses to

The Role of Disturbance in Natural Communities

Soil microorganisms as controllers of atmospheric trace gases (H2, CO, CH4, OCS, N2O, and NO).

The study of plant litter decomposition in terrestrial ecosystems commonly employs litter bags to compare the loss of mass among species, among sites, and under various experimental manipulations, or to investigate the process itself. Analysis of the resulting data is quite variable among investigators, and at times inappropriate. Two general analytical approaches to the examination of decomposition data are reviewed. Analysis of variance is useful if the intent is to compare treatment means, but does not directly test hypotheses regarding decomposition rates. If the intent is to determine rate constants, than fitting mathematical models to data is the more appropriate analysis. Single and double exponential models best describe the loss of mass over time with an element of biological realism. See full-text article at JSTOR

/pdf/a-critique-of-the-analytical-methods-used-in-examining-3afnrce5pj.pdf

A Critique of the Analytical Methods Used in Examining Decomposition Data Obtained From Litter Bags

Decay of balsam fir (Abies balsamea) boles was examined in an upper subalpine forest of the White Mountains, New Hampshire, USA. Fifty percent of the initial mass was lost in 23 yr; 90% was lost in 77 yr. High decay rates were attributed to the small diameters of the boles, ample moisture, and a nitrogen-rich environment. Average dead wood mass in this forest was 4.9 kg/M2, representing 25% of the sum of dead wood, live plant biomass, and forest floor organic matter. Changes in density and moisture and in the concentrations and content of various chemical com- ponents of the boles were traced over the decay sequence. Changes in the content of cellulose, lignin, carbon and sodium followed loss of mass during decay. Contents of calcium, magnesium, potassium and phosphorus decreased faster than loss of mass in the early stages of decay. Much of this initial loss was acribed to sloughing of nutrient-rich bark which in these small boles comprised 13% of dry mass. Later in decay, the loss rates of calcium, magnesium and potassium were about the same or slightly less than the loss rate of mass. After a steep initial drop, phosphorus content of the boles remained approximately constant between years 12 and 33. Thereafter the loss rate paralleled loss of mass. Nitrogen content was approximately constant in the first 33 yr after which it declined in parallel with loss of mass.

Loss of mass and chemical change in decaying boles of a subalpine balsam fir forest

All trees @>25 cm dbh were censused on a 15—ha tract of 60—yr—old tropical moist forest in 1968 and again in 1978 to determine rates of tree mortality, recruitment, dbh increment, and canopy gap formation Species composition changed very little The pioneer of gap species Cordia alliodora, Luehea seemanii, and Spondias radlkoferi had no recruitment and accounted for most mortality in the larger size classes Ninety percent of all mortality was for stems <10 cm dbh Total tree density decline 11% (from 3112 to 2781 trees/ha), but basal area increased 22% (from 257 to 314 m2/ha) Growth in diameter was highly variable, both among species and among size classes Trees in the 30—50 cm dbh class had a mean dbh increment of 09 cm/yr Gaps occurred over an area equal to 73% of the plot during the 10—yr period, suggesting that about 137 yr would be required for the 15—ha plot to be affected by tree falls

https://www.jstor.org/stable/info/1937816

Tree Growth, Mortality, Recruitment, and Canopy Gap Formation during a 10-year Period in a Tropical Moist Forest

Vegetation structure and dynamics of the upper subalpine or fir zone were studied in the White Mountains of New Hampshire. The fir zone extends from 1220 m, the approximate upper limit of Picea rubens occurrence, to treeline (-41450 m) where it is usually represented by a low krummholz. Live tree density in the part of the zone in which trees are >2 m tall averages 5000 stems/ha. Eighty-four percent of these are Abies balsamea, and most of the rest are Betula papyrifera var. cordifolia. Basal area averages 30 m2/ha; canopy height averages 6.8 m. Stands tend to be dominated by discrete age classes. Tree ages range up to 111 yr (average 55 yr). Fir zone vegetation is subject to a number of processes that lead to a hierarchical set of overlapping patterns. Elevation and wind exposure produce general, or first-order, patterns over the landscape, e.g., canopy height decreases with elevation and exposure. Overlying this general pattern are a series of second-order patterns. Two acute disturbance factors-hurricanes and avalanches-have stamped discrete impressions over the general pattern. Other, more endogenously generated patterns, mark the landscape with more subtle textures. These patterns include fir waves, broken tree gaps, strips, and glades. A conceptualization of vegetation as a hierarchical series of overlapping patterns is an extension of Watt's view of vegetation dynamics and bears important ecological implications.

https://www.jstor.org/stable/pdfplus/1937668.pdf

Vegetational patterns and processes in the balsam fir zone, white mountains,

Vegetation structure and dynamics of the upper subalpine or fir zone were studied in the White Mountains of New Hampshire. The fir zone extends from 1220 m, the approximate upper limit of Picea rubens occurrence, to treeline (°1450 m) where it is usually represented by a low krummholz. Live tree density in the part of the zone in which trees are >2 m tall averages 5000 stems/ha. Eighty—four percent of these are Abies balsamea, and most of the rest are Betula papyrifera var. cordifolia. Basal area averages 30 m2/ha; canopy height averages 6.8 m. Stands tend to be dominated by discrete age classes. Tree ages range up to 111 yr (average 55 yr). Fir zone vegetation is subject to a number of processes that lead to a hierarchical set of overlapping patterns. Elevation and wind exposure produce general, or first—order, patterns over the landscape, e.g., canopy height decreases with elevation and exposure. Overlying this general pattern are a series of second—order patterns. Two acute disturbance factors–hurricanes and avalanches–have stamped discrete impressions over the general pattern. Other, more endogenously generated patterns, marks the landscape with more subtle textures. These patterns include fir waves, broken gaps, strips, and glades. A conceptualization of vegetation as a hierarchical series of overlapping patterns is an extension of Watt's view of vegetation dynamics and bears important ecological implications.

Gerald E. Lang

Papers

A Critique of the Analytical Methods Used in Examining Decomposition Data Obtained From Litter Bags

Loss of mass and chemical change in decaying boles of a subalpine balsam fir forest

Tree Growth, Mortality, Recruitment, and Canopy Gap Formation during a 10-year Period in a Tropical Moist Forest

Vegetational patterns and processes in the balsam fir zone, white mountains,

Vegetational Patterns and Processes in the Balsam Fir Zone, White Mountains New Hampshire