How do broadleaf trees reproduce

Annual leaf loss may seem like a surprising competitive strategy. Keeping leaves for several years saves a tree the cost of creating them anew every spring. Conifer needles last for several years, with spruce needles living up to a decade and those of Bristlecone pines in California lasting 20, 30, or even as long as 40 years. Holding onto needles during the winter also allows the tree to photosynthesize year round…as long as temperatures are mild enough and days long enough.

In a few very harsh environments, winter needles may not offer that advantage. Deciduous conifers like larches have evolved to occupy those demanding niches.

However, leaves must be tough to survive the winter. They are subject to desiccation drying out when the air is cold and dry, abrasion from snow and ice, and browsing by animals that have fewer food sources in winter that during the growing season.

One way conifers protect their leaves is with a waxy coating, the cuticle, which helps prevent water loss and makes the leaves more durable and less palatable than their undefended counterparts. Growing a cuticle comes at a price, though. It requires an investment of carbon, which the tree must recruit via photosynthesis. Individual trees, and each species as a whole, must find just the right balance between costs like growing a cuticle and benefits like durable leaves that foster survival.

Whereas conifers invest in growing long-lived leaves, deciduous trees put their resources into creating more leaf area. Since they photosynthesize for only a short period, they must catch as much sun as they can during the months when they are in leaf. The leaves of many conifers are known as needles, for their slender form as well as their pointy tips. Other conifers grow scale-like leaves—the Western Red-Cedar Thuja plicata is a local example.

In either case, conifer leaves are compact. The compact form minimizes surface area and so reduces water loss. It also enables the leaf to bury its vascular tissue—through which water moves—in protective photosynthetic tissue. The cells that use sunlight are close to the surface, while the water-bearing cells are deep in the needle, keeping the precious liquid safe from evaporation.

Deciduous trees take a different approach. Rather than try to conserve water, they grow where there is more of it—for instance, along watercourses, in the shade of conifers, or in places with high summer precipitation. Then they spread their leaves wide to catch as much sun as possible. In the course of a growing season, many of those leaves will be torn by the wind, eaten by insects, pecked by birds, and colonized by fungi and bacteria.

The overall leaf area is so much greater, though, that the short-lived leaves are still a good investment. Their photosynthetic capacity—that is, their ability to capture carbon and convert it to nutrients—is greater than that of the longer-lived coniferous leaves.

So, what other mechanisms do conifers use to maintain their competitive edge? Canopy shape and needle arrangement both work in their favor. The classic conical shape intercepts sunlight more efficiently than a rounded canopy. A very broad canopy would also catch a lot of sun, but, in a climate like ours, it would be too susceptible to damage by ice and snow to be efficient.

In the Methow, even deciduous trees tend to be fairly upright in form so that their branches are less likely to catch snow and less likely to break when snow does accumulate. Losing leaves helps protect deciduous trees' branches, too.

Whereas conifers are shaped to shed snow, the upright branches of broadleaved trees would be further compromised if the leaves were present in winter. Conifer needles tend to be clustered on branches, helping light to penetrate the canopy. And, because the needles are small and tend to be relatively widely spaced on the tree, light can also spread more easily once it is within the canopy. Looking at those Ponderosa Pines outside my window, I can see that almost all the needles are being touched by the sun.

In contrast, shade keeps many deciduous leaves from achieving their photosynthetic potential. As noted above, deciduous leaves have greater photosynthetic ability than do coniferous ones.

That is partly because of their greater surface area, and partly because they invest more nitrogen in leaf building to begin with. High-nitrogen leaves photosynthesize more efficiently This is a broad statement based on observed correlations.

One reason for the correlation between foliage nitrogen levels and photosynthetic efficiency may be that photosynthesis requires nitrogen-containing enzymes.

They are also more costly to maintain, being better stocked with proteins and other energy-demanding components. So, it makes sense for the tree to shed them at the start of the cold season and produce new ones in the spring…if there is an adequate supply of nutrients with which to create those new leaves, that is. Where nutrients are in short supply, the evergreen habit may be more efficient. That is at least part of the reason conifers tend to predominate at higher elevations in the Methow.

Explanation: broad leaves have greater surface area so, transpiration takes place effectively and easily. Instead of flat leaves that dazzle us in the fall with their vivid coloring, some trees—the evergreens—have needles instead. On true pine trees, the needles are arranged and attached to the branches in clusters of two red pine group , three yellow pine group , or five white pine group needles per cluster.

Skip to content Natural sciences. What are broadleaf trees used for? Follow the steps carefully for observing leaves and try and identify the trees in your neighbourhood. But first here are a few basic observations to help you identify the different parts of a leaf. Every leaf grows from a bud in the spring. It is formed from a very thin, often green, skin called a blade.

The blade may have one or more leaflets depending on the type of leaf. The leaf may be supported by a small stem called a leafstalk.

When there is no stalk, the leaf is said to be sessile. A network of veins running through the blade is easily seen. You will notice that many trees shed their leaves in the autumn. These leaves are called deciduous leaves. Almost all broadleaf trees have deciduous leaves.

However, some trees retain the dead leaves attached to their branches during winter. These are called marcescent leaves. Oak leaves are often marcescent. In winter, try to find an oak by looking for dead leaves attached to the branches.

When observing leaves, it is preferable to gather twigs, because many characteristics are influenced by the arrangement of the leaves on the twigs. If the blade consists of one leaflet, it is a simple leaf. However, if the blade is made up of several leaflets attached to a leafstalk, the specimen is a compound leaf.

Take a close look at the illustrations to distinguish between a simple leaf and a compound leaf. The arrangement of leaves on twigs is an essential clue to the identification of trees. A number of tree species can be identified using this observation criterion. Leaves may occur in pairs at one position on opposite sides of the stem.

These are called opposite leaves. The red maple has leaves in opposite pairs. Try to find other species with opposite leaves. When leaves occur at different positions on the stem, they are called alternate leaves. Look at a twig from an American elm to see whether the leaves are alternate. If the leaves are arranged in star-like fashion all around the stem at the same position, they are called whorled leaves. However, whorled leaves are found far more frequently on plants than on trees.

The shape, or more precisely, the contour of a leaf is extremely useful for identifying a tree. So make sure you pay special attention to the contours of leaves. The description of the four different types of edges will help you classify leaves according to their contours. Smooth-edge leaves as the name suggests have a smooth contour with no particular projections on the edges.

Willow leaves are a perfect example of a smooth-edge leaf. Lobed leaves have a contour that is divided by empty spaces called a sinuses that separate two lobes.

The sinuses and lobes may be either rounded or pointed. The oak leaf is an example of a lobed leaf. To see the difference between a lobed leaf with rounded sinuses and lobes, and another with pointed sinuses and lobes, compare a bur oak leaf with a red oak leaf. Which of the two has pointed lobes?

Leaves with pointed teeth of the same size are called toothed-edge leaves. Take a look at a Balsam poplar ; it has leaves with toothed edges.

Some leaves have two sizes of teeth on their contour, large teeth which themselves contain smaller pointed teeth. These are called double-toothed leaves. Why not practise by observing a white birch leaf. Veins in leaves are the equivalent of the blood system in the human body. This network of vessels runs through the leaf and supports the blade. Veins can change the direction of the leaf to enhance photosynthesis.

The arrangement of veins is a useful clue to tree identification.