The federally listed endangered red-cockaded woodpecker (RCW hereafter) (Picoides borealis Vieillot) (U. S. Department of Interior, 1985) is endemic to pine forests in the southeastern United States from Virginia to Florida and west to Texas ( Jackson, 1971, Hooper et al., 1980; Lennartz et al., 1983; James, 1995 ). The RCW is a cooperative breeder where young males remain in their natal groups as helpers (Ligon, 1970; U. S. Department of Interior, 1985; Lennartz et al., 1987; Walters et al., 1988; Walters, 1990; Conner and Rudolph, 1995) . Red- cockaded woodpeckers excavate roost and nest cavities into the heartwood of living pines, generally 85 - 350 years old (Conner and Rudolph, 1991) . Upon cavity completion, RCWs excavate shallow holes in the xylem, termed resin wells, and peck them daily to stimulate copious resin flow (Ligon, 1970; Dennis, 1971) , to protect against predators and some nest competitors (Jackson, 1974; Jackson, 1978; Rudolph et al., 1990) . Bark beetles are less successful in invading and killing southern pines with high resin flow (Lorio et al., 1990) .

Artificial cavity construction (Copeyon, 1990; Copeyon et al., 1991; Taylor and Hooper, 1991) is an effective method to induce red-cockaded woodpeckers to occupy previously unoccupied habitat ( Hooper et al., 1990; Watson et al., 1995) . A tree characteristic not directly considered in the tree selection process for artificial cavities is the pine’s resin yielding capabilities. When selecting a potential artificial cavity tree, tree diameter at cavity height (38 cm minimum), trees with larger crowns and stand location is important. Resin yield can be sampled following the methods of Lorio and Sommers (1986) and Lorio (1990) . Resin production from preformed resin ducts is a primary defense against bark beetle attack (Hodges et al., 1979; Paine et al., 1985; Cook and Hain, 1986; Mitchell et al., 1991; Bowman and Huh, 1995; Coulson et al., 1995; Ross et al., 1995; Ross et al., 1997; Conner et al., 1998) . Resin sampling to estimate resin from preformed resin ducts follows the methods of Lorio (1990) for measurement from 0700 - 1000 hrs. Ross et al. (1997) examined resin production in RCW longleaf pine cavity and non-cavity trees on the Angelina National forest. Bowman and Huh (1995) examined resin flow in Florida in two vegetation communities. Losses to hurricanes and bark beetles can cause loss of RCW cavity trees (Hooper et al., 1990; Conner et al., 1991; Conner et al., 1998) , so both methods of evaluation for resin production for potential RCW trees and current resin status of existing cavity can assist in long term management of the species.

The objectives of this project were to evaluate resin production in longleaf pine, Pinus palustris, in red- cockaded woodpecker clusters in the Angelina National Forest, Texas. Comparisons in resin production were made between natural active and inactive, and artificial natural and inactive cavity trees. Similar sizes of longleaf pines were sampled for resin as control trees.

The seasonal pattern of resin production observed coincides with that previously reported (Lorio, 1985; Conner et al., 1991; Ross et al., 1993, 1997) . With the growth-differentiation balance at a low in the winter, there is little oleoresin flow from wounds while photosynthates accumulate in storage. The spring brings the start of new growth but little differentiation occurs because few vertical resin ducts are formed. Resin yield from wounds slowly begins during this time. The formation of summer latewood and the onset of water deficits results in differentiation that yield high resin flow. The shorter day lengths and cooler temperatures in the fall months show a halting of radial growth and a slowing of resin production and yields (Lorio, 1985) . The seasonal dynamics in resin yield supports the statistical design output that there was no difference in the tree types or their interaction with time but that there was a difference in the effect of the season on resin.

With the seasonal differences (Table 4), biologists may track a tree at any time of the year to gauge its resin abilities before the decision is made for selection of potential trees for insert installation. Super rein producers occurred over the five types of sample trees indicating sampling from a homogeneous population. Depending on the limiting environmental factors, growth and differentiation processes become competitive sinks for photosynthates (Lorio, 1985) . Wider spacing of trees can yield larger crowns, and faster growth until senescence is approached with tree age, and increased synthesis and flow of resin that produces conditions that favor the RCW but hinder the southern pine beetle, Dendroctonus frontalis Zimmermann, especially in longleaf pine.

Extreme moisture stress can affect the duration and quantity of resin flow decreasing the host tree defenses against bark beetles and also decreasing the success of the RCW with less resin for protection from predation by rat snakes. Adequate resin flow is affected by moisture stress reducing the flow and duration of resin (Lorio and Hodges, 1977) . Droughts during the two years of this study and may be a contributing reason for less resin in 2000 (Table 4, Table 8 and Table 9).

Each tree type showed no significant statistical variance in resin flow compared to other tree types even during periods of increased resin yield. Trees selected for artificial cavity installation for use by the RCW should have a minimum threshold for resin production if these cavities are to be protected from rat snakes by an adequate rein barrier. The AI category had the lowest mean (Table 1, Table 8 and Table 9) for most sampling periods, lower than the C category. Conversely, the AA, artificial active trees had the highest mean (Table 1, Table 8 and Table 9) and produce more resin in the upper percentiles (Table 2 and Table 3). The active categories (NA, AA) separate from the inactive categories in the second year’s spring resin yields (Table 5) with the actives holding the minimum 11 ml amount, the highest mean in the peak resin yielding month (Table 1). Since the AA tree type mean was higher that the NA, it can be assumed that some trees chosen were very high resin producers, beneficial to the red-cockaded woodpecker. Increased observations are needed to see if high resin yields can negatively affect the RCW. The NI had a higher mean that the AI (Table 1, Table 8 and Table 9) indicating inactive natural trees can potentially produce more resin that an inactive artificial tree. In the AI category, there was one tree above the 90^th percentile, but 46 % were in the 25^th percentile or below (Table 3).

There were droughts during the two years the study took place. The cumulative effect of two years of moisture stress related to drought may be the cause of the second year of resin measurement (Table 8 and Table 9). The same increasing trend of resin production exists from late spring to late summer during 2000, but the extent of the increase in 2000 does not reach the peaks observed in 1999 (Table 4). The start of the year 2000 resin production was higher than that of 1999. The overall trend of resin production needs to be sampled over a longer period of time to determine resin amounts over time. With guidance from this study and Ross et al. (1997) in the same area, sampling can indicate the best resin producing longleaf pine to select for artificial cavity insertion. Strom et al. (2002) investigating loblolly pine, (Pinus taeda), promoted identifying, producing and planting high resin yielding loblolly pine as a silvicultural approach to reduce damage from the southern pine beetle.

Although longleaf pine is not the primary host of the southern pine beetle, the amount and seasonal production of resin is a deterrent against the bark beetle. Reduced resin production in RCW cavity trees may make them vulnerable to bark beetle attack (Conner et al., 2001) . The presence of resin volatiles around active cavity trees may be a factor in bark beetle induced morality in active cavity trees (Conner and Rudolph, 1991; Conner et al., 1995; Hain et al., 2011) . Active RCW cavity trees were more susceptible to bark beetle induced mortality than inactive cavity trees in loblolly, shortleaf (Pinus echinata) and longleaf pine ( Conner and Rudolph, 1991; Conner and Rudolph, 1995; Conner et al., 1998; Hain et al., 2011 ). RCW breeding males selected nest cavities in trees that were heavier resin producers than cavity trees used for roosting by other group members (Conner et al., 1998) . Newer cavity trees were selected for the nest cavity in longleaf pine, but the RCW did not switch to the newest artificial cavity indicating sufficient resin was available (Conner et al., 1998) . Results of our study can provide times to sample and indications of higher producing resin trees. Thresholds of resin production (Table 3) indicate higher producing trees are available. For example, if 22 ml of resin in 24 hrs in deeded adequate, then this indicates the top 25 percent of the measured trees would be potential candidates for RCW cavities. Mean resin production is this study was 16.4 ml in August 1999 and 13.3 ml in September 2000 (Table 4) and can be used as a guideline for artificial cavities. The months of July, August and September are used as reference months as they are typically the peak resin yielding months (Lorio, 1985; Bowman and Huh, 1995; Ross et al., 1997) . Bowman and Huh (1995) found RCWs excavate cavities in pines with maximum crown-bole ratios. Use of the regression models gives guidance to resin production (Table 5 and Table 6) over time and these can be used depending on resin measurements. RCW management is aimed at mimicking natural processes that shape the habitat for the bird.

Although no significant differences in resin yield were detected among cavity tree types, some pines produced more resin and were termed super producers. Pines chosen for cavity insert installation should be those pines that produce yields above the overall mean, but closer to the optimum mean of the AA and NA categories (Table 1). Any resin production by a pine that is closer to 11 ml in the optimum resin producing months of July, August and September would have less chance for placing the RCW at risk for snake predation, or the host tree for bark beetle attack. It is not known if the RCW chooses super resin producers for nesting or roosting as super resin producers were found in each cavity tree type indicating not all super resin producers were colonized by RCW.

Mean resin production in this study was 16.34 ml (standard deviation of 9.53) in August 1999, and 13.33 ml (standard deviation of 4.99) in September 2000. These mean values could be used as a guideline to select the appropriate artificial cavity tree in the southern Angelina National Forest. The mean, however, will fluctuate according to moisture stress. The months of July, August and September can be used as reference months for cavity selection based on resin production. Regression equations were developed to predict resin production later in the season from early season sampling.

This project was supported by a grant from the USDA Forest Service, Southern Research Station, Nacogdoches, Texas, and McIntire Stennis funding from the Arthur Temple College of Forestry and Agriculture, Stephen F. Austin State University, Nacogdoches, Texas. Thanks are extended to Allen Smith, Carey Russell, Scott Ford, Kenny Murphy, Heather Osborne, Reagan Stephens and Scott Assenheimer for field assistance. Dr. Greg Miller, Stephen F. Austin State University, assisted with statistical analysis.