<p><em>E. globulus</em> stands displace native plant communities. Plant communities can be severely altered in circumstances where blue gum was planted at high density and growing conditions are favorable. Plant communities in other places can be significantly less impacted.<br /><br />Conditions are most favorable for blue gum growth and regeneration along the coast in northern and central California (Ritter and Yost 2012). Capacity for regeneration is based on environmental conditions; areas with reliable year-round moisture, such as along riparian corridors and along the coast from Monterey Bay north where summer fog drip provides seedlings with some moisture, are most likely to support naturally reproducing eucalyptus populations (Yost 2014). Juvenile foliage is seldom browsed by livestock or wildlife, aiding seedling survival (Skolmen and Ledig 1990).</p>
<p><br /><em>E. globulus</em> stands can form near monocultures in areas where they were planted at high densities (Griffiths &amp; Villablanca 2013). On Angel Island in San Francisco Bay, native trees were only found in eucalyptus plantings where the blue gums had been widely spaced, and these natives were &ldquo;not vigorous&rdquo; (McBride, Sugihara, and Amme 1988).</p>
<p><br />Reports of plant diversity within <em>E. globulus</em> stands vary, reflecting the range of conditions, including original planting density, suitability of the microclimate for eucalyptus growth and regeneration, composition of native seed bank, size of the stand and diversity of the surrounding vegetation. Some studies report depauperate plant communities (Esser 1993, DiTomaso &amp; Healy 2007, Bean &amp; Russo 2014) limited by shading and a thick litter layer, while other studies report some native plant species being supported in the understory (LSA Associates 2009, San Francisco Recreation and Park Department 2006).</p>

<p>See references within text.</p>

<p>No congeners native to the United States; no hybridization between non-native Eucalyptus spp. and native plant species in California.</p>

<p>Baldwin et al. 2012,&nbsp;Calflora 2014</p>

<p>Though not all <em>E. globulus</em> stands are expanding, those in moist coastal habitats often expand at a significant rate. New populations are rare; spread is almost entirely along the periphery of existing stands.</p>
<p>Most naturalized stands of <em>E. globulus</em> are present along the coast in northern and central California (Ritter &amp; Yost 2012). Aerial photographs show a 50-400% increase in eucalyptus stand size between 1930 and 2001 across six sites in coastal California (Van Dyke 2004). On Angel Island, blue gum &ldquo;invaded areas adjacent to all sites where it was originally planted,&rdquo; resulting in an expansion from 24 acres to 86 acres, a 360% expansion, over a century (McBride, Sugihara and Amme 1988). Potential spread rate has been estimated at 10-20 feet per year under favorable conditions (Bean &amp; Russo 2014).</p>
<p><br />Some studies show that this is not the case with all populations. An assessment of changes in cover over a 58-year period at three regional parks in the East Bay hills indicates a decline in eucalyptus cover at all three locations (Russell and McBride 2003), though it is unclear how management activities may have affected stand size in these locations.</p>
<p><br />California State Parks personnel submitted the following recent reports:</p>
<ul>
<li>Tim Hyland (2014) in the Santa Cruz District reports that nine coastal units have E. globulus patches that have moved into riparian, coastal prairie, and coastal scrub habitats. Two units have E. globulus patches that exist in forested settings and show no signs of reproduction.</li>
</ul>
<ul>
<li>Vince Cincero (2014) in the San Luis Obispo Coast District referred to a 1990 report compiled by Susan Bicknell of Humboldt State University on eucalyptus at Montana de Oro State Park in Los Osos. The report describes an original plantation established in 1907/08, with the earliest aerial photos from 1949 showing 7 species of eucalyptus covering 119 acres. Forty years later in 1989, the grove had expanded 52% to 181 acres, of which E. globulus covered 108 acres (the original portion comprising blue gum is unknown).</li>
</ul>
<ul>
<li>Suzanne Goode (2014) in the Angeles District reports that: at Mulholland Highway and Pacific Coast Highway, E. globulus is spreading upslope; at Nicholas Flats Natural Preserve, E. globulus (and possibly other eucalyptus species) are spreading from an original plantation homestead;and at the Will Rogers State Historic Park E. globulus continues to spread from plantings into the hillsides.</li>
</ul>
<ul>
<li>Michelle Forys (2014) in the North Coast Redwoods District reports that the few planted clumps of E. globulus located on district property are actively controlled to stop spread beyond the historical planted area. Additionally, she has observed a planting on the west side of along Highway 101 between Arcata and Eureka spreading across to the east side of the highway.</li>
</ul>

<p>See references within text.</p>
<p>&nbsp;</p>

<p style="margin: 0in; margin-bottom: .0001pt;"><strong><span style="font-size: 8.5pt; font-family: Verdana, sans-serif;">1. Reaches reproductive maturity in 2 years or less: No</span></strong></p>
<p style="margin: 0in 0in 0.0001pt;"><span style="font-size: 8.5pt; font-family: Verdana, sans-serif;">Most sources estimate trees usually begin to produce seeds at 4 to 5 years and yield heavy seed crops in most locations at 3- to 5-year intervals (Skolmen &amp; Ledig 1990, HEAR 2007). Metcalf (1924) stated that flowers and fruits could be found on sprouts only two or three years old, although not in great quantities.</span></p>
<p style="margin: 0in 0in 0.0001pt;"><strong><span style="font-size: 8.5pt; font-family: Verdana, sans-serif;">2. Dense infestations produce &gt;1,000 viable seed per square meter: Unknown<span class="apple-converted-space">&nbsp;</span></span></strong></p>
<p style="margin: 0in 0in 0.0001pt;"><span style="font-size: 8.5pt; font-family: Verdana, sans-serif;"> Sources indicate prolific seed production, but viable seeds produced per square meter are not given. There are 18 to 320 seeds per gram (500 to 9,100/oz) of seeds and chaff, or about 460 clean seeds per gram (13,000/oz) (Skolmen &amp; Ledig 1990). Germination rates are typically very low: a 1% germination rate is good, given the more usual 0.1% germination success rate (Bean &amp; Russo 2014). This does not indicate the amount of viable seed, as germination can be limited by other factors as well (e.g., allelopathy, thick litter layer, moisture, etc).<br /> <strong>3. Populations of this species produce seeds every year: unknown, assume no</strong><br /> Skolmen &amp; Ledig (1990) indicate that E. globulus yields heavy seed crops in most locations at 3- to 5-year intervals. This does not indicate whether seed is produced every year and only heavily at several year intervals, or whether seed is produced only at 3- to 5-year intervals.<br /> <strong>4. Seed production sustained over 3 or more months within a population annually: Yes<span class="apple-converted-space">&nbsp;</span><br /> </strong>Blue gum eucalyptus in California flowers from November to April during the wet season. The fruit (a distinctive top-shaped woody capsule 15 mm long and 2 cm in diameter) ripens in October to March, about 11 months after flowering (Skolmen &amp; Ledig 1990).<br /> <strong>5. Seeds remain viable in soil for three or more years: No<span class="apple-converted-space">&nbsp;</span><br /> </strong>Germination occurs readily (within 26 days) after seeds are released if conditions are suitable (Skolmen &amp; Ledig 1990). When stored, seeds can remain viable for several years, but in field conditions, viable seed banks are not expected to be maintained beyond a year (Rejmanek &amp; Richardson 2011).<br /> <strong>6. Viable seed produced with both self-pollination and cross-pollination: No<span class="apple-converted-space">&nbsp;</span><br /> </strong>When the cap covering the reproductive organs (the operculum) is shed, the anthers have mature pollen, but the stigma does not become receptive until some days later. This sequence impedes self-pollination of an individual flower. Flowers are pollinated by insects, hummingbirds, and other pollen and nectar feeders. There is no evidence that wind plays anything but a minor role in eucalypt pollination. The flowers of eucalypts are not highly specialized for insect pollination (HEAR 2007).<br /> <strong>7. Has quickly spreading vegetative structures (rhizomes, roots, etc.) that may root at nodes:&nbsp;No<br /> </strong>Blue gum eucalyptus can sprout from the bole, from stumps of all sizes and ages, from the lignotuber, and from the roots. The lignotuber can live for many years in the soil after stems die back (Esser 1993). This contributes to re-growth, but not spatial spread of the plant. One professional land manager reports that stand spread may arise from root sprouts in addition to seed sprouts (Heath 2014), but this has not been confirmed.<br /> <strong>8. Fragments easily and fragments can become established elsewhere: No<br /> </strong>No evidence found.<br /> <strong>9. Resprouts readily when cut, grazed, or burned: Yes<span class="apple-converted-space">&nbsp;</span><br /> </strong>Blue gum coppices readily from stumps of all sizes and ages when the tree is damaged. If the tree is cut down, lignotubers become active and each bud produce a shoot bearing foliage. Such shoots are commonly known as "sucker growth" or coppice shoots, and a large number are usually formed. E. globulus resprouts after being burned (Skolmen &amp; Ledig 1990, Bean &amp; Russo 2014).</span></p>

<p>See references in text.</p>

<p>In general, E. globulus seed is not easily dispersed over large distances (Skolmen &amp; Ledig 1990, HEAR 2007, Rejmanek &amp; Richardson 2011). E. globulus seeds are distributed by wind and gravity; calculated dispersal distance from a 40 m (131 ft) height, with winds of 10 km/hr (6 mi/hr), was only 20 m (66 ft) (Skolmen &amp; Ledig 1990). Some seed may be moved by such agents as flood, erosion and birds, but usually seed is dropped within 100 feet of the parent tree (Bean &amp; Russo 2014).</p>

<p>See references in text.</p>

See Worksheet C. 5-20% is the highest portion of occurrences invaded in any of the invaded ecotypes.

Observational