#51 - Jul 2021 - Garden Stuff - © - Sandy Lang - slang@xtra.co.nz
TREE-TIMEJuly: Mid-winter. Too cold for much growth - no growth if average daily temperature dips below 10°C (see #5 TEMPERATURE). Most trees go dormant. Tree (Gk. δένδρον): Shave the rough bark off a tree and you find a soft whitish layer just beneath (the phloem) and just beneath that, the hard wood (the xylem). The phloem tubes carry the sugary sap (food) down from the canopy to the roots, the xylem tubes carry the watery sap (hydration) up from the roots to the canopy. Between phloem and xylem is a very thin cell layer - the cells busy multiplying - the cambium. Time (Gk. χρόνος): Spring to autumn the cambium produces new phloem cells (to the outside) and new xylem cells (to the inside). But the cambium goes to sleep in winter. Then, as the buds swell in spring, they send down a hormone signal to re-awaken the cambium. You see the effects of the seasonal changes in cambium activity in the wood. A darker (winter) layer separates one season’s paler layer of wood from the next. A growth ring. The oldest growth ring in the middle of the tree, the youngest on the outside. δενδροχρονολογία: So... •Count the growth rings and you discover a tree’s age. •Measure ring width and you discover how much a tree grows each year – wide rings (1-2 cm) in NZ pines (mature at 25 yr), narrow rings (1-2 mm) in Norwegian pines (mature at 250 yr) - a cold climate. •Measure the year-by-year variation in ring width and you discover some seasons were better than others. The seasonal weather pattern leaves its ‘signature’ in the ring-width pattern, a narrower ring after a cool, dry season, a wider ring, after a warm, moist one. •Cut down a 200-year-old tree and measure the pattern of wide and narrow rings and you discover how good/bad each season was over the last 200 years – maybe 1876 was cold, dry (narrow) and 1953 was warm, wet (wide). Useful for history, climatology. •Measure the ring-width pattern (signature) in an old table, compare it with your 200-year tree. You discover when your old table was growing. Useful for forensics, archaeology, history. •Measure these patterns in a living kauri and you discover the seasonal patterns over the last 1000 years. •Find a swamp kauri and you have the seasonal patterns over a 1000-year period, 50,000 years ago. Wow...! Google dendrochronology ___________________________________
TREE-TIMEJuly: Mid-winter. Too cold for much growth - no growth if average daily temperature dips below 10°C (see #5 TEMPERATURE). Most trees go dormant. Tree (Gk. δένδρον): Shave the rough bark off a tree and you find a soft whitish layer just beneath (the phloem) and just beneath that, the hard wood (the xylem). The phloem tubes carry the sugary sap (food) down from the canopy to the roots, the xylem tubes carry the watery sap (hydration) up from the roots to the canopy. Between phloem and xylem is a very thin cell layer - the cells busy multiplying - the cambium. Time (Gk. χρόνος): Spring to autumn the cambium produces new phloem cells (to the outside) and new xylem cells (to the inside). But the cambium goes to sleep in winter. Then, as the buds swell in spring, they send down a hormone signal to re-awaken the cambium. You see the effects of the seasonal changes in cambium activity in the wood. A darker (winter) layer separates one season’s paler layer of wood from the next. A growth ring. The oldest growth ring in the middle of the tree, the youngest on the outside. δενδροχρονολογία: So... •Count the growth rings and you discover a tree’s age. •Measure ring width and you discover how much a tree grows each year – wide rings (1-2 cm) in NZ pines (mature at 25 yr), narrow rings (1-2 mm) in Norwegian pines (mature at 250 yr) - a cold climate. •Measure the year-by-year variation in ring width and you discover some seasons were better than others. The seasonal weather pattern leaves its ‘signature’ in the ring-width pattern, a narrower ring after a cool, dry season, a wider ring, after a warm, moist one. •Cut down a 200-year-old tree and measure the pattern of wide and narrow rings and you discover how good/bad each season was over the last 200 years – maybe 1876 was cold, dry (narrow) and 1953 was warm, wet (wide). Useful for history, climatology. •Measure the ring-width pattern (signature) in an old table, compare it with your 200-year tree. You discover when your old table was growing. Useful for forensics, archaeology, history. •Measure these patterns in a living kauri and you discover the seasonal patterns over the last 1000 years. •Find a swamp kauri and you have the seasonal patterns over a 1000-year period, 50,000 years ago. Wow...! Google dendrochronology ___________________________________