Project Report No. 62, Site Index Equations for Loblolly and Slash Pine Plantations in East Texas, Update: Fall 1998

This update utilizes height-age pairs measured from 1982 - 1998. As a result, the number of observations available for analysis is 1,814 loblolly and 788 slash. It is anticipated that the equations in this Fall 1998 update may quantify the productivity of East Texas loblolly and slash pine plantations in a more accurate and reliable manner than the seven previous sets of equations

Potential stream density in Mid-Atlantic US watersheds.

Stream network density exerts a strong influence on ecohydrologic processes in watersheds, yet existing stream maps fail to capture most headwater streams and therefore underestimate stream density. Furthermore, discrepancies between mapped and actual stream length vary between watersheds, confounding efforts to understand the impacts of land use on stream ecosystems. Here we report on research that predicts stream presence from coupled field observations of headwater stream channels and terrain variables that were calculated both locally and as an average across the watershed upstream of any location on the landscape. Our approach used maximum entropy modeling (MaxEnt), a robust method commonly implemented to model species distributions that requires information only on the presence of the entity of interest. In validation, the method correctly predicts the presence of 86% of all 10-m stream segments and errors are low (<1%) for catchments larger than 10 ha. We apply this model to the entire Potomac River watershed (37,800 km(2)) and several adjacent watersheds to map stream density and compare our results with the National Hydrography Dataset (NHD). We find that NHD underestimates stream density by up to 250%, with errors being greatest in the densely urbanized cities of Washington, DC and Baltimore, MD and in regions where the NHD has never been updated from its original, coarse-grain mapping. This work is the most ambitious attempt yet to map stream networks over a large region and will have lasting implications for modeling and conservation efforts

Modeled vs. NHD stream density metrics for each HUC12 watershed in the study area.

<p>In (A) modeled stream density is compared to NHD stream density, and in (B) modeled channel head density is compared to NHD channel head density. Although there is a strong correlation, modeled streams exhibit many more small streams per unit area, each with its own channel head.</p

Stream length as a function of the log catchment area for each physiographic province (CP = Coastal plain; PD = Piedmont; BR = Blue ridge; RV = Ridge and valley; and AP = Appalachian plateau).

<p>Stream length as a function of the log catchment area for each physiographic province (CP = Coastal plain; PD = Piedmont; BR = Blue ridge; RV = Ridge and valley; and AP = Appalachian plateau).</p

Local slope vs. Log₁₀(catchment area) for bins of increasing catchment area (black dots) across the entire survey region and for the locations of channel heads (colored dots).

<p>Characteristics of this plot have been discussed previously in the literature [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074819#B21" target="_blank">21</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074819#B53" target="_blank">53</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074819#B64" target="_blank">64</a>], and are covered briefly in the text.</p

Examples showing the density and configuration of the streams mapped in this study (blue; MaxEnt streams, smoothed and connected as in Figure 3B) compared with the NHD streams (black) for (A) an urban area and (B) a rural area.

<p>The background image shows the 2006 NLCD land cover using the standard color scheme: urban (shades of red), forest (green), agriculture (yellow), and water (blue).</p

Stream density maps for HUC12 watersheds in the study region.

<p>(A) NHD stream density was more uniform and lower than (B) the stream density calculated from MaxEnt after smoothing, connecting discontinuous segments, and merging with NHD. (C) The percent change in stream density highlights the effects of urban areas and other areas with poor quality NHD stream maps. (D) Spatial variation in stream density can be explained in part by differences in geology between physiographic provinces.</p

The mean and variance of stream density for HUC12 watersheds by physiographic province (CP = Coastal plain; PD = Piedmont; BR = Blue ridge; RV = Ridge and valley; and AP = Appalachian plateau).

<p>The mean and variance of stream density for HUC12 watersheds by physiographic province (CP = Coastal plain; PD = Piedmont; BR = Blue ridge; RV = Ridge and valley; and AP = Appalachian plateau).</p

False positive and false negative predictions, expressed as a percentage of stream observations in the field survey (10,565), for four stream maps: (A) raw MaxEnt results with the province-specific thresholds applied; (B) MaxEnt results after smoothing and connecting discontinuous stream segments; (C) the results in (B) after merging with NHD maps of streams, and (D) the Tuned Ac stream map, which uses a province-specific critical catchment area to define streams.

<p>Methods for each map are described in detail in the text.</p