<div dir="ltr"><b>Hypothesis 6</b>. Increased frequency of intense hurricanes could result in higher-elevation streams shifting<br>from consumer-controlled to producer-controlled ecosystems, due to the increase in stream nutrient<br>concentrations, litter inputs, and light inputs that re-configure terrestrial-aquatic linkages in these<br>headwater streams and riparian forests. (Pringle, Covich, Crowl, McDowell, Ortiz, Ramirez)<br><br><b>Background</b> – Twenty years of research on stream chemistry and biology shows that there is a strong<br>response to hurricanes, which alter the riparian forest-stream connections, increase some nutrients, and<br>change food web dynamics for months to years (Brokaw et al. 2012, Crowl et al. 2012, McDowell et al.<br>2013). After hurricanes, nitrate concentrations remain elevated for 18 months or more (McDowell et al.<br>2013), large litter inputs enter the stream but are rapidly decomposed (Crowl et al. 2001, Beard et al.<br>2005), and light levels increase because of increased canopy openness. In many ways, the Luquillo<br>Mountain streams have been very resilient in response to the past two major hurricanes.<br>23<br>Increased frequency of intense storms is likely to have profound effects on stream communities, bidirectional<br>subsidy exchanges, and biogeochemistry. Shifts in riparian vegetation toward more shade<br>intolerant trees will alter both the transient light regime (more frequent periods of high light due to<br>repeated hurricane disturbance) as well as the baseline light regime (lower LAI with more drought-tolerant<br>species), and the quality, quantity, and timing of leaf-litter inputs. We will focus on species that are most<br>likely to enter or leave the riparian forest community (Hypothesis 4) and their effects on subsidy<br>dynamics. Following Hurricane Hugo, we observed a 1 kg/m2 input of detrital material across the forest<br>including the streams (Lodge et al. 1991). We experimentally demonstrated that this input resulted in an<br>increase in dissolved C, N, and particulate C production and export (Crowl et al. 2001).<br>In the longer term, we expect that our relatively unproductive communities, limited by light and predation,<br>will switch from being consumer controlled to being producer controlled, resulting in increased microbial,<br>algal, insect and decapod and fish densities, total biomass and secondary production, as a consequence<br>of increased nutrients, allochthonous inputs, and light. In addition, the increased inputs of coarse woody<br>debris and palm fronds will result in a significant increase in debris dams, leaf-litter storage, and habitat<br>heterogeneity. This increased habitat complexity will most likely result in more spatial refugia for prey<br>species and decreased predation by larger consumers (Macrobrachium spp) resulting in a decrease in<br>top-down control on insects and smaller shrimp species. Taken in aggregate, we hypothesize that the<br>increased frequency of severe storms in the LEF will fundamentally alter the stream ecosystems,<br>resulting in increased primary productivity, standing stock biomass, and tighter nutrient cycling during<br>extended periods between less-frequent, high-discharge events.<br><br><b>Work plan</b> – We will enhance our existing stream monitoring to include monthly litter inputs, light and<br>light gap measurements and microbial responses. In addition, nutrients, algal standing crop as well as<br>insect, decapod, and fish densities and biomass will be sampled twice a year in six headwater streams<br>(four of which are currently sampled as LTER focal streams; two additional higher-elevation streams).<br>Sampling periods will include during the driest time of the year (Feb-March) and the period of the most<br>severe storms (late September) to capture the effects of dry periods on stream biota. Sampling methods<br>will follow protocols from our long term measurements (Section 3.1) and already established within the<br>LUQ framework. Light gaps, coarse woody debris, and leaf-litter inputs will be mapped and quantified in<br>replicate 100 m reaches in the study streams.<br>We will simulate hurricane impacts on the riparian vegetation using the SORTIE and Demographics<br>models already parameterized for the LEF. Simulations will be used to model both short-term (annual) as<br>well as long-term (decadal) impacts on riparian canopy composition and structure. These simulation<br>results will guide future experimental manipulations of riparian canopy cover and increased light on the<br>stream ecosystem components. Our future goals (LUQ VI) are to conduct a canopy trimming experiment<br>for streams using a similar design as the CTE. We will explore the separate and combined drought<br>(stream-water diversion, SDE) and hurricane disturbance through direct manipulations and modeling.<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Feb 15, 2017 at 8:38 AM, Maria Uriarte <span dir="ltr"><<a href="mailto:mu2126@columbia.edu" target="_blank">mu2126@columbia.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto"><div>Hi Sarah </div><div id="m_-1726642121269328012AppleMailSignature"><br></div><div id="m_-1726642121269328012AppleMailSignature">Can u pls send us hypothesis 6?</div><div id="m_-1726642121269328012AppleMailSignature"><br></div><div id="m_-1726642121269328012AppleMailSignature">Thanks Maria <br><br>Sent from my iPhone</div><div><div class="h5"><div><br>On Feb 15, 2017, at 6:40 AM, Sarah Stankavich <<a href="mailto:sarahstankavich@gmail.com" target="_blank">sarahstankavich@gmail.com</a>> wrote:<br><br></div><blockquote type="cite"><div><div dir="ltr">Hi all - The monthly meeting today at 2 pm EST, 3 pm AST will focus on hypothesis 6. 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</div><div><br>-- <br><div class="m_-1726642121269328012gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div>Sarah Stankavich<br>LUQ-LTER Coordinator<br></div>El Verde Field Station, Puerto Rico<br></div><div><a href="tel:(787)%20764-0000" value="+17877640000" target="_blank">787-764-0000 ext. 83466</a> (office)<br></div><div><a href="tel:(787)%20222-7756" value="+17872227756" target="_blank">787-222-7756</a> (cell)<br></div></div></div></div></div></div></div></div></div></div>
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</div></blockquote></div></div><blockquote type="cite"><div><span>______________________________<wbr>_________________</span><br><span>Long Term Ecological Research Network</span><br><span>luq mailing list</span><br><span><a href="mailto:luq@lternet.edu" target="_blank">luq@lternet.edu</a></span><br></div></blockquote></div></blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div>Sarah Stankavich<br>LUQ-LTER Coordinator<br></div>El Verde Field Station, Puerto Rico<br></div><div>787-764-0000 ext. 83466 (office)<br></div><div>787-222-7756 (cell)<br></div></div></div></div></div></div></div></div></div></div>
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