This is the third in a series of posts on carbon fixation in Mohave desert plants. In this post we will focus on plants that use CAM carbon fixation which includes cactus, yucca and agave. The most important benefit of CAM to plants is the ability to leave most leaf stomata closed during the day. Plants employing CAM are most common in arid environments, where water comes at a premium. Being able to keep stomata closed during the hottest and driest part of the day reduces the loss of water through evaporation and transpiration, allowing such plants to grow in environments that would otherwise be far too dry. Plants using only C3 carbon fixation, for example, lose 97% of the water they take up through the roots to transpiration – a high cost avoided by plants able to employ CAM. The Mojave Desert is the northernmost “hot desert” in North America and essentially a transition land between the Great Basin and Sonoran. It’s the smallest of the Big Four, covering some 54,000 square miles of southeastern California, southern Nevada, and itty-bitty strips of southwestern Utah and northwestern Arizona. Roughly speaking, the Great Basin Desert yields to the Mojave at the northern range limit of creosote bush, the defining shrub of North America’s hot deserts; its distribution essentially outlines them. You can rightly think of it as the hot-desert equivalent of big sagebrush. But the trademark plant of the Mojave, the one whose geography basically maps out this desert, is the Joshua-Tree. This outsized yucca actually flourishes best on the Mojave margins, reaching peak development on middle slopes of foothills and bajadas. Interestingly, the Joshua-Tree uses C3 carbon fixation while most of the remaining yucca and agave use CAM carbon fixation, along with all of the cactus species.
This post is the second on my series on Mohave desert plants, this time focused on C4 plants, not really as complex as it might sound. The C4 photosynthetic pathway has evolved an estimated 45 times in terrestrial plants (Sage 2004), and is most prominent in grasses, which account for roughly 25% of global terrestrial primary production (Still et al. 2003) and include important crop and weed plants and potential biofuels such as maize, sugarcane, sorghum and switchgrass. The highest rate of photosynthesis is typically observed in C4 plants. The photosynthetic rate in such plants is known to be directly related with the variation of the solar rays in the daytime. Maximum rate of photosynthesis occurs in the red and blue regions of the visible light as seen in the absorption spectra of chlorophyll a and b. These are of economic importance as they have a comparatively higher photosynthetic efficiencies in comparison to other plants. C4 photosynthetic plants outperform C3 plants in hot and arid climates. By concentrating carbon dioxide around Rubisco C4 plants drastically reduce photorespiration. The frequency with which plants evolved C4 photosynthesis independently challenges researchers to unravel the genetic mechanisms underlying this convergent evolutionary switch. The conversion of C3 crops, such as rice, towards C4 photosynthesis is a long‐standing goal. Nevertheless, at the present time, in the age of synthetic biology, this still remains a monumental task, partially because the C4 carbon‐concentrating biochemical cycle spans two cell types and thus requires specialized anatomy.
Desert plants tend to look very different from plants native to other regions. They are often swollen, spiny, and have tiny leaves that are rarely bright green. A desert always has a limitation of water but the temperature may be hot or cold, high altitude and cloudy like parts of Costa Rica or low altitude and windy like the Cape Preserve in South Africa. The strange appearance of these plants is a result of their remarkable adaptations to the challenges of the desert climate. Desert plants have developed three main adaptive strategies with diverse implementations often in different species with convergent evolution to the same form: succulence, drought tolerance and drought avoidance in annual plants. Each of these is a different but effective suite of adaptations for prospering under conditions that would kill plants from other regions. These differences often extend to the cellular level with the development of special structures to store water in leaves and stems, the periodic shedding of leaves, and special adaptations to even the basic photosynthesis process. Chlorophyll (the green pigment in plants) is the only known substance in the universe that can capture volatile light energy and convert it into a stable form usable for biological processes (chemical energy) through the Calvin Cycle and the enzyme RuBisCO. Green plants use blue and red light energy to combine low-energy molecules (carbon dioxide and water) into high-energy molecules (carbohydrates or starch), which they accumulate and store as energy reserves. There are at least three variations of photosynthesis, all of which use the same basic mechanism, C3 carbon fixation used by most plants, C4 carbon fixation used in about 3% of plants and the CAM (crassulacean acid metabolism) carbon fixation pathway that evolved in plants like cactus as an adaptation to arid conditions.
Sometimes, looking for plants and flowers in winter can be interesting, particularly near a source of fresh water in the desert. In November, I visited Rogers and Blue Point Springs on the north shore of Lake Mead in the Lake Mead National Recreation Area. Rogers Spring and other springs in the “North Shore Complex” comprise one of the terminal discharge areas for the regional carbonate-rock aquifer system of eastern Nevada and western Utah. The source of the water to this spring and other regional carbonate-rock aquifer springs is uncertain. The prevailing theory suggests that much of the recharge water that enters the carbonate-rock aquifer occurs in the high mountain ranges around Ely, Nevada, located 250 miles north of Lake Mead. As this ground water flows south through the carbonate rocks, it encounters several faults along the way, including the Rogers Spring Fault, which has caused the older carbonate rocks (primarily limestone and dolomite) to be displaced against younger evaporite deposits of the Muddy Creek and Horse Spring formations. Here, the lower permeability of these evaporite deposits, along with high subsurface water pressure, forces the ground water in the carbonate rocks to flow upward along the fault and emerge at the surface as Rogers Spring.
The Company’s Garden is the oldest garden in South Africa, a park and heritage site located in central Cape Town. The garden was originally created in the 1650s by the region’s first European settlers and provided fertile ground to grow fresh produce to replenish ships rounding the Cape. It is watered from the Molteno Dam, which uses water from the springs on the lower slopes of Table Mountain. The Dutch East India Company established the garden in Cape Town for the purpose of providing fresh vegetables to the settlement as well as passing ships. Master gardener and free burgher Hendrik Boom prepared the first ground for sowing of seed on the 29th of April 1652. The settlers sowed different kinds of seeds and kept record thereof each day. Through trial and error they managed to compile a calendar which they used for the sowing and harvesting throughout the year. At first they grew salad herbs, peas, large beans, radish, beet, spinach, wheat, cabbage, asparagus and turnips among others. By 1653 the garden allowed the settlers to become self sustainable throughout the year.
The South African Ostrich (Struthio camelus australis), also known as the Black-Necked Ostrich, Cape Ostrich or Southern Ostrich is a subspecies of the common ostrich endemic to Southern Africa. In the 18th century, ostrich feathers were so popular in ladies’ fashion that they disappeared from all of North Africa. If not for ostrich farming, which began in 1838, the world’s largest bird would probably be extinct. Today, ostriches are farmed and hunted for feathers, skin, meat, eggs, and fat — which, in Somalia, is believed to cure AIDS and diabetes. Ostriches were hunted to extinction in the Middle East and might have met the same fate in Africa if not for the evolution of ostrich farms. Ostriches are now farmed commercially in more than 50 countries around the world, including the United States. In Roman times, there was a demand for common ostriches to use in venatio games or cooking. They have been hunted and farmed for their feathers, which at various times have been popular for ornamentation in fashionable clothing (such as hats during the 19th century). Their skins are valued for their leather. In the 18th century they were almost hunted to extinction; farming for feathers began in the 19th century. At the start of the 20th century there were over 700,000 birds in captivity. The market for feathers collapsed after World War I, but commercial farming for feathers and later for skins and meat became widespread during the 1970s. Common ostriches are so adaptable that they can be farmed in climates ranging from South Africa to Alaska.
Cape Point is in the Cape of Good Hope Nature Reserve within Table Mountain National Park, which forms part of the Cape Floral Region, a World Heritage Site. It includes the majestic Table Mountain chain, which stretches from Signal Hill to Cape Point, and the coastlines of the Cape Peninsula. This narrow stretch of land, dotted with beautiful valleys, bays and beaches, contains a mix of extraordinarily diverse and unique fauna and flora. The Cape Peninsula (around 470 sq km) has 2285 flowering plant species. Table Mountain National Park alone has 1470 of these. Mountain fynbos dominates the park. It’s characterised by four main groups: protea shrubs with large leaves (proteoids), fine-leaved shrubs (ericoids), wiry, reed-like plants (restioids) and bulbous herbs (geophytes). Table Mountain National Park includes the Cape of Good Hope and Cape Point. Although the Cape of Good Hope Nature Reserve (or Cape Point as it is colloquially called) occupies only 16% of the area of the Cape Peninsula as given by Adamson & Salter (1950), the flora of Cape Point comprises 41% of the flora of the whole Peninsula. This illustrates the fact that many of the habitats and plant communities of the Peninsula are represented at Cape Point. Cape Point is the windiest place in South Africa and experiences only 2% of all hours in the year with calm conditions. I also want to mention that all of the following photographs were taken in October, in the middle of spring in the Southern Hemisphere.
I thought that I would write an introductory post on the geography and history of the Cape Peninsula, mainly because while everyone has heard of Cape Town and the Cape of Good Hope, knowledge usually ends at recognition. The Cape Peninsula (Kaapse Skiereiland) is a rocky and hilly peninsula that juts out into the Atlantic Ocean at the south-western extremity of the African continent. At the southern end of the peninsula are Cape Point and the Cape of Good Hope. On the northern end is Table Mountain, overlooking Cape Town, South Africa. The peninsula is 32 miles (52 km) long from Mouille point in the north to Cape Point in the south. The Peninsula has been an island on and off for the past 5 million years, as sea levels fell and rose with the ice age and interglacial global warming cycles of, particularly, the Pleistocene. The last time that the Peninsula was an island was about 1.5 million years ago. Soon afterwards it was joined to the mainland by the emergence from the sea of the sandy area now known as the Cape Flats. The towns and villages of the Cape Peninsula and Cape Flats now form part of the City of Cape Town Metropolitan Municipality. One of the many reasons that travelers choose to visit Cape Town is its abundance of scenic beauty and natural attractions. The city itself is situated between the Atlantic Ocean and Table Mountain, one of the world’s Seven Wonders of Nature. Table Mountain’s iconic plateau forms the dramatic backdrop of the city and is a must-see for visitors. On the peninsula, there are beaches, penguins, seals, ostriches and lots of hiking trails with beautiful scenery. For me, the famous fynbos with it’s many plants and flowers were a major draw along with the history and all of the above.
The Boulders Beach African Penguin Colony was established in 1982 by a breeding pair of penguins who settled near Capetown, South Africa after fleeing when a larger colony was devastated. Today there are currently 28 African penguin colonies, only four of these occurring on the African mainland. These colonies run along the coast, from Algoa Bay in South Africa to Namibia’s Penguin Islands. Despite the huge distances between these colonies, it is not uncommon for young penguins to visit, and occasionally resettle, at a different colony from which they hatched. African penguins are clearly resilient animals. They have evolved the behavioral mechanisms to move their entire population to deal with changes in the abundance of food. Despite their wide range and versatile juveniles, African penguin numbers are declining fast – so fast that it is believed they will be extinct within 10 years. Today there are fewer than 21 000 pairs of African penguins left in the wild – 100 years ago there were single colonies that had over a million, like Yzerfontein’s Dassen Island. Dassen Island is, unfortunately, not a unique case. The total breeding population across both South Africa and Namibia fell to a historic low of about 20,850 pairs in 2019. Quite simply, our common seafoods – sardines, anchovies and pilchards – are the products directly linked to the decline in penguin numbers. You may have been unaware, but sardines/pilchards have recently been added to the WWF SASSI Orange List – a seafood you should avoid. These ratings do not only mean that the fish itself is at risk, but also that the practices used to catch it are harmful to other species. I would go a step further in saying seafood of any kind should only be consumed if it is sustainably farmed. Bottom trawling destroys far more ocean habitat than any other fishing practice. In this common fishing method, large weighted nets are dragged across the ocean floor, clear-cutting a swath of habitat in their wake. Some of these scars will take centuries to heal, if ever.
When I visited Africa three years ago, I spent some time in Cape Town and had an opportunity to visit the Cape of Good Hope. About 12 miles south of Cape Town is the little settlement of Hout Bay, famous for a colony of seals on a rocky outpost just outside the harbor. Tiny Duiker Island—also known as “Seal Island” for its large population of Cape fur seals—sits just off the South African coast at Hout Bay, near Cape Town. It measures just 253 feet by 312 feet (77 meters by 95 meters) and is a seabird sanctuary in addition to sheltering thousands of Cape Fur seals. The island is renowned for its marine wildlife, including the Cape fur seals and marine bird species such as the common cormorants and kelp gulls. They have tourist boats going out to the island frequently from Mariner’s Wharf and the whole experience takes about an hour. It is one of the more interesting sights on the way to Cape Hope.