In 1976 spring prescribed burning was conducted in open-canopy limber pine stands in the Little Belt Mountains of central Montana at about 5,500 feet (1,675 m) [55]. Further general site descriptions appear in Keown 1982 [56]. Air temperatures ranged from 55 to 65 degrees Fahrenheit (13-18
oC). Relative humidity was 20% to 40%, and winds were calm to 25
miles per hour (40 km/h). Fuel moisture was 7%. The management objective was to improve understory browse and forage.
Limber pine mortality at postfire year 1 was 20% in grassy stands and as high as 80% in shrubby
stands [55].
The Research Project Summary Response of vegetation to prescribed burning in a Jeffrey pine-California
black oak woodland and a deergrass meadow at Cuyamaca State Park, California, provides information on prescribed
fire and postfire responses of many plant community species including limber pine.
Clark's nutcrackers have co-adapted an important mutualism with limber pine
and are the primary harvester and disperser of its seeds. Limber pine regeneration
on burns is largely from germinants of Clark's nutcrackers seed caches [63,64,66,110,125].
The birds begin harvesting seeds in late August, while the cones are still green and slightly closed. They remove the cones by pecking them loose,
fly them to perches, and peck between the scales to remove the seeds. As cones begin to open on the trees in September, Clark's nutcrackers remove exposed seeds.
An individual bird can store as many as 125 seeds in its sublingual pouch, then
flies to a cache area and deposits numerous caches from its pouchful of seeds. In a burned-over area in northern Utah,
Clark's nutcrackers cached an estimated 12,140 seeds per acre (30,000/ha) in 1 year [62,101,112].
Mating system: Limber pine seed dispersal by corvids leads to a genetic population structure different from that of wind-dispersed conifers with respect to patterns of gene flow and genetic relationships among neighboring trees. The seed caching
by birds influences the distribution, population age structure, and spacing of limber pine. Clusters of seedlings germinating from a single cache may generate
multi-stemmed growth forms that contain 2 or more distinct genotypes. A consequence of this growth form is
a tendency toward clumped stand structure. Because seeds within an individual
cache were often collected from a single parent tree, trees within clumps may be
more closely related compared to trees from neighboring clumps [64,110,113],
although multi-stemmed growth is most often a result of apical meristem damage
that results in several leaders on an individual tree [123]. Tomback and Linhart
[112] found that on 361 limber pine sites in Colorado, 30% showed clumping.
Several genetic studies have shown that from 0 to 82% of individuals
within limber pine clumps are closely related [101,117,123]. On the Pawnee
National Grassland, clump members were related, on average, as nearly half-sibs.
Genetic consequences of this kinship include possible inbreeding. On the plus
side, closely related trees within clumps often form roots grafts, which may
increase survivorship and fitness of the entire clump [123].
Pollen phenology also influences gene flow. In Colorado, most sites that differ in elevation by more than 1,300 feet (400 m) in elevation do not have overlapping pollination periods, restricting
pollination between populations that are widely separated by elevation; however,
pollen transfer between intermediate populations and a high level of gene flow via
bird-dispersed seeds appear to maintain interpopulation gene flow [97].