Amateur Naturalist: October, The Artistic Month

By BOB DRYJA
Los Alamos

October is a good time for uplifting walks, knowing that the winter months are not too far away.  A physically uplifting as well as an emotional walk is possible by hiking up one of the slopes of the nearby Jemez Mountains. The slopes set the stage for what can be seen.

The Pajarito Mountain provides a good setting. Its peak is at 10,400 feet. Its eastern slope drops to about 7,400 where it begins to level out on a mesa top. This is a vertical drop of 3,000 feet over a horizontal distance of four miles. There is another 500 foot drop over another five miles to the eastern end of mesa top. The combined drop therefore is 3,500 feet over nine miles. Hiking trails make it possible to explore this slope. Changes in plant life can be seen along the way. The views are breathtaking as part of the final assent to the peak. The gain in elevation also may take one’s breath away.

All forms of plant life have green leaves at the start of October. These change as the month progresses.  The leaves of gambel oak trees turn brown and wither. However the leaves remain attached to their branches. The leaves of aspen trees in contrast turn brilliant yellow and then fall away. There are a few days just before the aspen leaves fall that slopes are painted brown or yellow. Aspen or gambel oak dominate sections of a slope, forming fields with one color. An artistic painting is created by the yellow, brown and green colors of October spread across the mountain side.

The physical steepness and direction faced by a slope influences what kind of plant may come to dominate it. An eastward facing slope receives more sunlight. A steeper slope tends to have more of its top soil washed away. The elevation of a slope also is a factor. Higher elevations have cooler air and winter temperatures arrive sooner. Aspen are adapted to growing at higher elevations on steeper slopes compared to gambel oak.

Picture 1 below shows the breathtaking artistry that results from these ecologic factors.

Aspen trees create impressive pathways in the mountain high country. Photo by Bob Dryja

Aspen may appear to be individual plants growing next one another. However a group actually may be a single plant that repeatedly grows stems upward from its roots spreading horizontally.

Picture 2 below is an example.

The field of yellow aspen is just a few trees that have grown many stems from their roots. Gambel oak tree with their brown leaves surround the aspen. Photo by Bob Dryja

A spreading point of yellow extends down the slope for hundreds of feet. It represents a single or a few plants. Circular patches of yellow can be seen to either side of the spreading point. These represent separate plants.

Forest fires can have a major impact on which species of plant may dominate an area.  A forest fire may burn away a forest of ponderosa trees. These may have taken two or three centuries to become the dominant trees. Faster growing aspen start as the new dominant tree in a recently burnt area. Ponderosa may replace them in later decades.

Picture 3 below shows a recently burnt slope with aspen as the newly emerging dominant plant species.

Aspen in their autumn yellow stand out in an area previously covered by ponderosa trees prior to a forest fire. Photo by Bob Dryja

The October yellow leaves make the aspen stand out in the upper half of the picture. The lower half of the picture shows ponderosa still dominating an area that had not been burnt by the forest fire.

Picture 4 below shows the impact of all of the factors presented in the preceding pictures.               

Grassland dominates at the highest elevation of the mountain slope while aspen dominates mid-elevations. Gambel oak is growing at the lower elevation on a steeper, rockier slope that is part of the canyon. Photo by Bob Dryja                                                                                                                                                                                                                                                                                                                            Grassland typically dominates at the top of the mountain with its lower temperatures. Ponderosa also grows at this high elevation but is spread out. A forest fire passed over this mountain in 2000 but burnt at a low intensity in the grassland. The ponderosa had their lower branches burnt but not killed outright. The forest fire then became a high intensity burn at lower elevations, killing the ponderosa. Aspen now is the dominant tree, replacing the grasslands and ponderosa. The few remaining ponderosa may provide the seed for a replacement forest. The slope then becomes steeper as it becomes part of canyon. Less water remains in this area since it can flow more quickly down the slope. It also can evaporate in the more direct sunlight coming from the east. Disbursed gambel oak trees now grow down the rocky slope. 
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